Making your XJ happier vs. being a sucker for advertisement.

[Jeepsqueak]

Hello everybody. I was hoping to get the opinions of as many people as possible on reasonable (and hopefully cost-effective) methodologies for improving and maintaining the performance of your XJ. I've been inspired by the ridiculous amount of advertising suggesting that you could (if you add it all up with a calculator) double your MPG and add fifty ponies with a slew of products costing thousands of dollars. It strikes me as bullshit, and the mechanically inclined I know are generally a skeptical bunch when it comes to most of these products. Still, I'm not sure what to think about a lot of this. I definitely don't have a lot of mechanical knowledge, but I'm pretty sensible. I'm hoping to see what others have come across in their quest for answers. Here are a few in particular I was wondering about.

Fuel additives. I've heard from a few that certain fuel additives serve to keep things clean and will sometimes improve your fuel economy. I know there are dozens of these products, some claiming to be safe for your catalytic converters and O2 sensors and some not saying much at all. I've used fuel additives in other vehicles at times, and I have noticed, especially during highway driving, that the gas indeed seems to last a bit longer. Similar experiences? Arguments against?

Aftermarket or late-model XJ exhaust header. I'm not sure exactly what the issue was engineering-wise, but I've heard a lot of talk about how the pre-99 (I believe) XJ's came with a header which eventually would succumb to the pressure (particularly with the 4.0 HO?) and crack. Some have suggested that replacing it with a later-model XJ or Borla header will prevent the issue from occuring and improve the efficiency of the engine. What's everybody think? This seems credible to me at least from the standpoint of not having to deal with that specific problem every couple of years.

Less restrictive exhaust systems. I've heard what sound like strong arguments from both sides of the issue on this, but I'd still like to solicit people's experiences on the matter to learn more. Strong arguments for stock mufflers?

"Performance" distributor caps/rotors/plugs. It seems a lot of experienced wrenchers feel that the stock plugs are the best to use for a number of reasons, and that expensive "upgrade" plugs (like Bosch Platinums) are basically a waste of time. I haven't heard a lot of talk about after-market distributor caps, etc, yet. I understand a lot of people do homebrewed electrical mods, like widening the gauge of the battery terminal wire. I would love to hear from anybody who was into this sort of stuff.

Computer modification chips (e.g., Jet Phase I module). It seems to me that these devices mainly reconfigure the range in which the engine is performing at it's optimum. I'm not sure if they actually provide overall gains, or just basically shift around the bands in which the power is being delivered. Testimonials or tech stuff?

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare? Rebuild your engine? ;)

And basically, anything anybody wants to suggest or talk about on the matter of maintaining and caring for their XJ's engine. I'm sure many of these matters will vary depending on the engine you've got. I've read a lot of what's been posted here in the past on some of these matters -- a lot of very intelligent posters. I don't mean to stir the pot again, but I figured you can always opt out if you're tired of talking about it. ;)

Thanks in advance for your thoughts!

[Wayne Sihler]

I,ll bite--
fuel additives-Chevron Techrolen(sp)seems to be the best for cleaning the injectors,a little Dry Gas to remove moisture can,t hurt
Headers- Yes the stock header will eventually crack,Borla and Banks would appear to have the least problems
Exhaust-Reducing back pressure will help.A K&N air filter to help it breath better.
Cap,Wires ,ect-stock works fine
Jet Chip-IMHO not worth the gain in the RPM range most of us run
Synthetics-Yes reducing friction loss is a good thing
These are my thoughts on the matter--good or bad
YMMV
Wayne

[90NHXJ]

I can tell you now that vehicle manufacturers are under increased pressure to make vehicles more environmentally friendly. A lot of money is spent on researching and producing a vehicle that is balanced between power, fuel economy, low emissions, and attractive to the wallet. With that in mind there are few aftermarket items out there that will boost the performance of all but the wallet. The fuel additives may work some by keeping your injectors and valves clean. Performance chips will increase your horsepower but will do little to improve mileage. High flow exhaust may help with the horsepower but not usually cost effective for the manufacturer. High flow air filters are good too, again, not too cost effective for the manufacturer. Oil additives or synthetics are nice, and tend to be super slippery. Good for broken in younger engines but probably does little for performance. General rule of thumb is that there's probably a tradeoff somewhere, ie. increased HP = lower mileage (not in all cases)

[CaptTrev]

Fuel additives. I use Chevron with Techron at every oil change interval. I HAVE used dry gas onceor twice.....but I usually try to keep my tank close to full during the winter, as to help keep condensation from forming in the tank

Aftermarket or late-model XJ exhaust header. I believe (mostly from what I have read on NAXJA over the years) that the Borla header is really the best replacement for durability, power and overall quality/fit


Less restrictive exhaust systems. Depending on the year XJ, the stock exhaust isnt too bad, it gets better with the later yar models. (Much of the later year XJs share cat's with the 4.7 v8 grand cherokess)
I'm currently running a 96 XJ 4.0 HO, with a hi-flow stainless cat (my OEM one went bad) and a stainless steel Borla cat back system.
Many Xj'ers successfull upgrade their exhaust systems simply with a flowmaster type muffler and call it quits with that.
As far as the K&N filters go........well, i suggest you do a search and read everything for yourself.
Heres a quick overvew of the debate:
PRO K&N: increased airflow, increased performance (BEST with a aftermarket exhaust), better engine sound
CON K&N: poor filtration, some tests show it allows more dust/debris into the engine=increased engine wear
so its really "short term" performance VS. long term reliability
so, what do i run? a K&N cone style filter (its actually an S&B filter) off of a rustys air tube.


"Performance" distributor caps/rotors/plugs.
My advice for this would be (also what i run) a good cap & rotor (brass, not aluminum contacts) good 8mm wires and good champion plugs gapped correctly.
Many promote the Mopar "performance wires" available at the stealership for what i seem to remember being a reasonable price.
Many have complained that the 4.0 does NOT like bosch platinum +4 plugs. I have run them with no problems (got them before everybody started complaining about them).
Basically electricity can only flow between 2 points of least resistance, so really only 1 out of 4 tips will be used to fire. However, if that 1 tip becomes fouled up, i suppose it would then choose on of the remaining 3 tips. The platinum tip also has a longer (argueable) service life=less changing.


Computer modification chips (e.g., Jet Phase I module).
Never used any, so i'll refrain from comment. do a search though. . .

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare? Rebuild your engine? ;)
I have used Mobil 1 10W-30 synthetic for the last 6 years, and I swear by it.
Just get a good filter (NOT FRAM). I use synthetic gear oil in the diffs too. Stay away from synthetic ATF.
DO A SEARCH ON HERE CONCERNING ALL OF THESE TOPICS. THEY ARE ALL WELL COVERED!!!
NAXJA is a tremendous asset. use it! ;)

CaptTrev

[5-90]

OK - I'll weigh in...

Hello everybody. I was hoping to get the opinions of as many people as possible on reasonable (and hopefully cost-effective) methodologies for improving and maintaining the performance of your XJ. I've been inspired by the ridiculous amount of advertising suggesting that you could (if you add it all up with a calculator) double your MPG and add fifty ponies with a slew of products costing thousands of dollars. It strikes me as bullshit, and the mechanically inclined I know are generally a skeptical bunch when it comes to most of these products. Still, I'm not sure what to think about a lot of this. I definitely don't have a lot of mechanical knowledge, but I'm pretty sensible. I'm hoping to see what others have come across in their quest for answers. Here are a few in particular I was wondering about.

Fuel additives. I've heard from a few that certain fuel additives serve to keep things clean and will sometimes improve your fuel economy. I know there are dozens of these products, some claiming to be safe for your catalytic converters and O2 sensors and some not saying much at all. I've used fuel additives in other vehicles at times, and I have noticed, especially during highway driving, that the gas indeed seems to last a bit longer. Similar experiences? Arguments against?

Frankly, I don't care for fuel additives at all. The only thing I might want my fuel diluted with would be another fuel - like ethanol/ethyl alcohol, or something similar. All these additives are more like trying to burn wet wood to me - you can, but it don't work well...

Aftermarket or late-model XJ exhaust header. I'm not sure exactly what the issue was engineering-wise, but I've heard a lot of talk about how the pre-99 (I believe) XJ's came with a header which eventually would succumb to the pressure (particularly with the 4.0 HO?) and crack. Some have suggested that replacing it with a later-model XJ or Borla header will prevent the issue from occuring and improve the efficiency of the engine. What's everybody think? This seems credible to me at least from the standpoint of not having to deal with that specific problem every couple of years.

I'd have to check the figures, but I seem to recall that the XJ exhaust plumbing is close to the optimal size. Too big, and the gasses flow out too fast, cool off, and reduce scavenging. Too small, and the gasses don't have enough room to flow, backpressure is induced, and scavenging is reduced. That's the same sort of thing that drives aftermarket muffler design - finding a happy medium between the Maxim Silencer (to comply with noise laws) and the straight pipe (to give the most power.) Make sense so far?

Less restrictive exhaust systems. I've heard what sound like strong arguments from both sides of the issue on this, but I'd still like to solicit people's experiences on the matter to learn more. Strong arguments for stock mufflers?

See my comments on headers - the two issues are related. "Less exhaust restriction" is usually an argument for "broomsticking" the cat - and a properly tuned engine can tolerate the deletion of the catalytic converter (and the EGR, while we're at it) and run better due to the removal of the restriction. The catalytic converter is present to compleat the combustion process that suffers in the combustion chamber - mostly because of the various impurities in modern fuels and the presence of the EGR system. Improving engine cooling efficiency will allow a mixture less rich than currently allowed for (rich mixtures run cooler,) which will obviate the need for the EGR system, and contribute to the deletion of the catalytic converter.

"Performance" distributor caps/rotors/plugs. It seems a lot of experienced wrenchers feel that the stock plugs are the best to use for a number of reasons, and that expensive "upgrade" plugs (like Bosch Platinums) are basically a waste of time. I haven't heard a lot of talk about after-market distributor caps, etc, yet. I understand a lot of people do homebrewed electrical mods, like widening the gauge of the battery terminal wire. I would love to hear from anybody who was into this sort of stuff.

Go with ignition parts that have brass terminals instead of aluminum, and I do like spark plugs with platinum centre electrodes. I have noted that Pt plugs do a better job of self-cleaning, and seem more resistant to HV erosion than the copper plugs. Also, a "better-than-OEM" wire (I like Accel, Mallory, or MSD) for the HV leads will make an improvement. If you're spending more than $2 per plug, you're getting boned over.

For general electrical work, increasing wire gages can help. The best you can do (for starters) is to ground the generator case, improve the engine/chassis ground, and use larger grounds from the engine and chassis to the body. Ground each separately, and tie the two together. Power is like water - it's limited by the greatest restriction. In factory wiring, that's usually the ground. Make sure you ground to clean metal, assemble, and then coat the connexion. Also, get rid of those damn lead battery clamps and go to brass - that's usually the second restriction. Going to a larger battery cable helps if you plan on adding electrics later.

While you're at it, make sure your ignition component grounds are solid as well - losses here are losses EVERYWHERE.

Computer modification chips (e.g., Jet Phase I module). It seems to me that these devices mainly reconfigure the range in which the engine is performing at it's optimum. I'm not sure if they actually provide overall gains, or just basically shift around the bands in which the power is being delivered. Testimonials or tech stuff?

No amount of electronic tuning can change the "native" power band of the engine - and that is determined by hard parts. Camshaft, intake manifold, head porting, and exhaust manifold are the key elements here (I'd have to dig up the math involved...) I'd sooner change hard parts than software - you just can't argue with physics...

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare? Rebuild your engine? ;)

Synthetic oil as a power increaser had some validity - simply be reducing the parasitic drag from friction inside the running gear. Choices will also be key - the average automatic transmission can require 15-30 horsepower to operate, while a manual might need only 2-5. Horsepower used before it gets to the wheels is horsepower that doesn't make it to the ground! That's another reason that "underdrive" pullys are so popular - that's less power used to turn pumps and generators. Choose these carefully...

And basically, anything anybody wants to suggest or talk about on the matter of maintaining and caring for their XJ's engine. I'm sure many of these matters will vary depending on the engine you've got. I've read a lot of what's been posted here in the past on some of these matters -- a lot of very intelligent posters. I don't mean to stir the pot again, but I figured you can always opt out if you're tired of talking about it. ;)

Thanks in advance for your thoughts!

I have to admit, I'll be interested in seeing what comes up here myself. Perhaps Ed Stevens or Eagle might care to chime in here?

5-90

[Boatwrench]

Can only accruartely comment on what I've have used, but these opinions will be like .....everyone will have one and they'll all be different.

Fuel Additives: I use during the winter for condensation removal. When filling up I do notice I get better MPG with Chevron and Union 76 than I do with Shell, so there may be something to that Techron claim. Also I belive Shell hasn't phased out MTBE yet.

Headers & modified exhaust: Although haven't used on my XJ, had bad experiences with them in the early 80s on my CJ and K20 so won't touch the things. Stock all the way.

K&N airfilter: I removed my K&N after Moab and replaced with a paper element for the ride home. Still have the paper one in the XJK as I haven't bothered to clean the K&N. Well now two engine oil changes later I noticed the oil stays cleaner longer, doesn't turn black as quick....hmmmmm....will probably keep the paper one, and it's a Fram.

Synthetics: I switched to synthetic as soon as I got the XJ (24K miles)everything but the AW4 tranny. Would not have it any other way, it reduces parasitic friction and prevents dry bearing wipe on start up after the vehicle has sit for months (like mine sometimes does). I use a K&N oil filter, however I have no qualms about using Fram. Fram has been on my 137K mile 1990 454 cu.in. Suburban since the first oil change and experienced no problems (just jinxed myself). I typically drive from San Francisco to Phoenix 3-4x per year in either the burb, XJ or Mazda without oil breakdown.

Didn't ask about grease, but I use the red stuff.

Tom

[Pale Horse]

Yeah, it seems alot of us, are all pointing to the same simple goodies for extra HP and a few extra miles from every tank. I myself have added Rusty's exhaust (cat back), a K/N filter (modified the stock air box to flow better..can you say hole saw ?), and put Amsoil synthetic in the t-case, gear box, engine, and both pumkins. I occasionally (every 10k or so) add Chemtool b-12 to the gas tank. I noticed much better performance from my XJ over time, and I'm getting unheard of highway mileage...25 mpg cruising at 70 (unloaded), although my city mpg isn't that spectacular, it did improve a bit. To keep my XJ as reliable as possible, I've strayed away from "chips", headers, and fancy doulble-platinum-fifteen-electrode-gold-covered-spark plugs and fancy wires. :puke: Keep it simple, save a few bucks, and still wheel with the best of them! :peace:

[wascobi]

after going through a few brands of plugs I can say my jeep starts and runs best with champion heavy duty truck plugs :peace:

[ThePhantum]

Well, I can only speak from my own personal experiance on this...and in relation to the 4.0 I6, so here goes:

Fuel additives.
I run Techron at every oil change. The XJ runs as good as it did the day I drove it off the lot in '97. I have heard of people running "cheaper" aditives and experiencing O2 and cat problems...but that's hearsay.

Aftermarket or late-model XJ exhaust header.
Less restrictive exhaust systems.
Both of these are related. An internal combustion engine is, at it's core, an air pump. The less restrictive the exhaust and intake the more air the engine can pump. Having said that, the engine does need a certain amount of backpressure to operate correctly. IMO, header and a cat back (2.5"). You could also replace the Cat with a hi flow model. Performance gains? It will seem a little smoother as you run up the gears at throttle...you might get 1 more MPG out of it and maybe a little more low end torque...but that's about it. I'm persoanlly doing it for the "glug, glug" Flowmaster sound more than anything else... :guitar:

"Performance" distributor caps/rotors/plugs.
Go OEM. You won't see any gains. Like someone posted before...Champion truck plugs rock!

Computer modification chips (e.g., Jet Phase I module).
They will give you a bit more HP. But IMO for the money you'll spend on a chip...save it for other mods.

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare? Rebuild your engine?
Synthetics all the way. I run 'em everywhere. I don't do trick shift in the tranny though. That stuff is for performance transmissions...stick with the OEM spec and go synthetic. I also run a Mobil M301 oil filter. It's bigger than the stock filter, flows the same and holds a bit more oil.

As far as getting the most out of the engine? There are three keys:
Maintenence...maintenence and maintenence. Keep all the fluids (oil, tranny, diff, coolant, etc.) changed on schedule, keep it tuned up and keep the air filter clean....it'll run forever.

Rock On!

Steve

[8Mud]

I recently aquired a a new to me 88 XJ. The more of the after market stuff, I take off and replace with OEM stuff (or stuff close to OEM spec.) the better it runs.
Some of the more noticeable improvements, where getting shut of the Bosch plugs and going back to Champions. Cleaning and repairing the grounds. Replacing the solid core plug wires with resistor wires. Replaceing the near open exhaust, with a little more restictive muffler. Inspecting and cleaning all cable connectors and vacume lines. The last guy who owned it, liked to do his own work, but he wasn´t very good at it.
I did change the motor over to synthetic oil (10-50), the oil pressure was a touch low, now it sits just where it´s supposed to.
Took the ATF out of the AW4 and replaced it with Dexron, really helped the shifts.
An occasional load of a gas additive, injector cleaner and gas drier, seems to help some (Use Liquid Moly brand/on sale).
Seems the closer I get to stock spec. the fewer misses, stumbles and quirks I have to deal with.
The only real mods I´ve done to it, is a dual diaphram brake booster, a long leaf in the rear spring pack and 30 X 9.50 Kumho mud tires.
If I felt the need to upgrade the iginition system (more spark), I´d probably research a kit with a larger diameter distributor cap. With higher voltages, cross fire, could be a problem.
This summer, I´m probably going to buy some shrink tubing (and silicon), bypass (cut, splice, solder and water proof) as many of the connectors in the motor compartment as possible (I´ve got an extra wiring harness, if I need it). Probably add a few more ground wires (I´ve added a couple/it hepls). Put die electric grease on eveything else. Moisture in the wrong places, is often a cause of trouble (happens when I was the mud off :idea: ).

[pancake]

Fuel additives:
Perhaps fuel injector cleaner (only if done on regular basis) would be helpful, but could cause deposits to break loose from fuel filter and get into injectors.

Aftermarket or late-model XJ exhaust header:
No comment...I'm running OEM header. If it cracks, I'll probably go with Borla.

"Performance" distributor caps/rotors/plugs:
Champion copper plugs ONLY!

Computer modification chips (e.g., Jet Phase I module):
Waste...

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare?
Conventional oil has many times the anti-friction properties NEEDED for the engine to run safely and at optimum power. Synthetic is nice for not foaming as easily if you are racing, and for flowing better at low temps. It also can go longer before being changed...that's what they SAY. However, oil does a LOT to clean the engine, and synthetic gets dirty too. IMO 9,000 miles for each oil change is asking too much.

[pancake]

Valvoline for EVERYTHING!!! Been using it for years, it's in my motorcycle also. Nothing I ever tried was better.

[Ronbo]

Fuel additives.
Regular gas only. Remove and clean the TB with throttle body cleaner(spray) every few thousand miles.

Aftermarket or late-model XJ exhaust header.
My factory exhaust manifold is perfect after 6 years and 110K miles.

Less restrictive exhaust systems.
Slight increase in mileage/sound, no real HP gains.

"Performance" distributor caps/rotors/plugs.
I use the Mopar cap/rotor/wires. Nothing fancy. I've tried fancy, never experienced a difference.

Computer modification chips (e.g., Jet Phase I module).
None. Every first hand experience with a stock 4.0 indicates the stock PCM does the best, or is not beat by the aftermarket addition.

Synthetic oils (gearbox, diff., engine)? B&M Trick Shift? Rabbit's foot strapped to the spare? Rebuild your engine? ;)
I personally use Mobil 1 in the engine. Although I've tried fancy synth in the axles and transfercase: no real noticeable difference. I used the top-o-line Amsoil in the AX15, there was no benefit/change at all, over the OEM fluid with 100k+ miles on it. (No water intrusion out here in the desert!)

These are just my experiences, not recommendations.

[woody431]

So you guys reall recommend the Champion plugs? Should I go with copper, and what's a good plug wire?

I have a load of 4 gauge wire, what are some good places to replace the grounds?
Thanks

[pancake]

So you guys reall recommend the Champion plugs? Should I go with copper, and what's a good plug wire?

I have a load of 4 gauge wire, what are some good places to replace the grounds?
Thanks

OEM plug wires

[woody431]

Alright cool, I'll try that out. Thanks!

[89 XJer]

8MUD, will the 10w-50 work better for a higher mile engine? My 89 has 166,000 on it and i just run the 10W-30. Is there less chance to experience leaks from the syn if it is thicker

[2offroad]

if you really want a Jet chip i'll sell you mine for $100 most of the improvments are at high RPMs, i have Proformance Distribtors Firepower kit i like it, but it is alot of money.

[8Mud]

My new to me 88 with a 100,000 miles, has a bunch of seeps, but no real leaks. I used the 10-50 synthetic, because I had it on the shelf and planned to change again soon. The last owner neglected (It appears) normal maintenance, but did have a thing about perofrmance add on´s (that mostly didin´t work well).
I kind of held my breath for the first few months, after changing to synthetic (though one, years old, oil change tag, did say,a synthetic blend oil was used at some time). No new oil leaks, some of the seeps actually slowed some (though this could be, because I cleaned the crankcase vent system tubes). The 10-50 synthetic oil raised the oil pressure a bit, cranks OK in really cold weather and the motor seems to run a little quieter. Snythetic seems to have a more constant viscosity in cold or warm weather, doesn´t seriously thicken in very cold weather and /or seriously thin when hot.
I usually buy my Jeeps new and keep them forever, this is only the second used Jeep, I´ve purchased, time will tell how the sythetic works in an old motor. I´ve been running synthetic in my motors since the early 80´s, I´ve taken a few apart after 150,000 miles or so for gaskets and such, wear was minimal, very little ridge on the piston walls, a really clean looking motor internally and a clear durable cylinder wall glaze, that seems to be much more durable than normal oils.

[8Mud]

Grounds. I cleaned and tightened what I had, really a noticiable imrovement in idle, shifts and horses. The ground by the firewall on the drivers side in the early (Renix) XJ, seemed to be the more important. A scraped away the paint and used a cone star washer, to get a really good ground. Could feel the difference in the seat of my pants, horse power gain, like what is advertised for a fancy header (like 15%).
I added one between the battery and the front clip, headlights were noticeably brighter.
I´m gonna check the ground behind the winshield washer bottle next. And add one to the alternator straight to the battery and maybe add one to the tranny (tranny to frame). Probably add one to the TPS. Why not, after my experience witht the firewall ground; I´ve turned into a believer. May even add some grounds to the doors, may improve window and door lock function, sure can´t hurt much.
Have noticed when the undercarriage is wet, the motor seems to run better, might be a sign of insufficient ground or maybe just a Quirk of my XJ.

[CaptTrev]

or maybe just a Quirk of my XJ.

a quirk in an XJ??


noooooooooooo..............

:laugh3:

CaptTrev

[XJFREK]

My 2 cents-I bought my 94 used in 98 with about 51,000 mi. Lost a rod bearing at 83,000 mi and got a re-man Marshall engine, just turned 101,000 with no probs from it yet. Just some additional info for additional consideration.
Fuel additives: I started using the valvoline fuel treatment last fall as recommend. Every oil change for the injector cleaner, twice a year for the whole system treatment. Too soon to tell any real difference yet, but no ill effects either.
Aftermarket Header: After losing and replacing my engine, about 5 months later my exhaust manifold cracked and began leaking badly. Faced with a $300 welding repair I instead purchased the cheapest header I could from Summit and had a local shop install it. Worked great for about 2 months before the cheap gasked blew out. Since the labor cost would be far more than that header was worth I then went to 4 wheel parts and had them install a stainless Gibson header. Cost was almost equal to the dealership replacing the factory manifold but it's been holding for almost a year now without problems.
Less Restrictive Exhaust: I had a 3 chamber flowmaster with rusty's pipe on after my stock cat when I got my new header. No noticable increase in performance with the stock cat and downpipe. After my Cat went south I had a performance shop fab a new 2.5 in downpipe and install a new high flo cat. I immediately noticed an increase in accleration, so the change to 2.5 in pipe throughout was worth it in my opinion.
High performance cap/rotor/plug/wires: I originally changed my stock setup to Jacobs wires and overgapped the plugs a little. Noticed an improvement in off the line performance but it diminished over time and my idle immediately after starting became rough. Went away after changing plugs but returned eventually. Changed to Magnecor wires and Bosch +2 plugs and the rough idle never returned, although performance was somewhat diminished. Still better than stock though. Overgapping didin't seem to agree with regular plugs, but in the short term was fun to drive. I am running a Napa cap&rotor, and a coil from them as well. Have heard that the stock coil is hi-performance, don't know but noticed no difference with the aftermarket items.
Computer Mods: I have the Jet stage 1 chip, all I noticed was that it delayed the shift points some, like holding a manual transmission a little longer before shifting. This helps accleration and towing some, but not sure if it was worth the money.
Synthetics and Good Mojo: I started running valvoline synthetic oil after purchasing my xj, and about 30,000 mi later I lost a rod bearing. After running regular oil in my re-man engine for the break-in I now run Wal-Mart 10w-30 syn. Figure it's better than regular but not willing to spend the $$ on name brand anymore. No issues yet. I also run a foam element intake, ran the K&N stock replacement for awhile but got a great performance boost with the new intake, header, and 2.5in exhaust and hi-flo cat. I also have the 3-core GDI radiator, and a flex-a-lite fan in place of my stock clutch fan. If I had it to do over, I'd keep the stock fan and get the modine radiator. The foam intake is probably not as good at filtering as a paper filter, but the performance is good enough that I'm keeping it for the moment. I get my chassis lubed twice a year and the coolant flushed every 18 months or so. Same with the tranny, about 18 months. Diff lube changed every couple years, I don't do alot of water fording or extreme off-roading, this is my daily driver so I can't afford to beat it too hard. Hope this epic posting helps you make a informed choice. Good luck with your project and be sure to report your experiences so we can all get your opinion on whatever you do.

[egon]

Might as well throw in my experience thus far.

What I have: 96 XJ, 108K miles, AW4, 242, 30/44 (3.55), 31"s.

I've used both Chevron Techron and Marval Mystery Oil added to my gas, both have worked very good in other vehicles, but I never saw any noticable improvements. As for cleaning out the top of the engine, I use GM Top Engine Cleaner. That gave me a slight MPG improvement. Depending on how dirty your combustion chamber and valves are will dictate how much difference you'll see.

Fluids: Mobil 1 10-30 and a Mobil 1 301 filter, switched to synthetic at 60K. Amsoil ATF in the AW4 and the 242, yes I run synthetic ATF in my AW4, since 60K miles. The diffs get Amsoil 75w90. Grease: Mobil 1 or Valvoline SynPower; Brake fluid: Valvoline SynPower; Power steering: Valvoline SynPower.

Stock air box with a Wix filter. I had a K&N for awhile. Yes there is slightly better throttle response and a cool sound when you give in the boot, but I'm looking at longevity. A Flowmaster will give you a little more throttle response too, I have a Series 40.

Ignition: Bosch Platinum (not the plus series), Accel cap, rotor, and wires. Noticed a big difference when I switched from OE copper plugs and OE wires. Smoother idle and smoother at the high RPMs.

What does all this add up to? My XJ gets the same gas milage and is just as quick as a friends 96 XJ that is stock. I do most of the maintainence of his XJ so I know its in good running order.

--Matt

[LBEXJ]

I currently have two vehicles ... a '94 XJ and a '94 Eagle Vision. I use 5W-30W Valvoline oil substituting in a quart of Slick 50 at oil changes every 5000 miles. I'm not sure the Slick 50 helps, but I'm using it to (hopefully) take advantage of the "improved" residual lubrication (the cars "sits" for long periods of time). I've got 240,000 miles on the Jeep and 175,000 miles on the Eagle and they both start well and run very smooth.

I use standard ignition components, filters, and lubes ... always have and see no reason to change at this point. Every vehicle I've ever owned died from rust ... guess I should pay more attention to sheet metal protection ... but then I kept the last two vehicles, prior to these, over ten years.

I have always been told the key is regular maintenance. It works for me ...

Les

[XJ Saga]

My experience:

Fuel additives: Chevron techron Fuel System cleaner works very well for me. I use it about 3 times annually.

Exhaust: I've got a 50 series delta flow, Carsound hiflow, and a Banks header and I've got loads of power across the entire rpm band and no perceiveable loss of torque down low.

Ignition: I've got the Coil On Plug ignition (2001) along with Champion Truck plugs and I could not improve upon that no matter how much I spent. (coil on plug fires twice vice a standard distributor set-up during one intake/exhaust stroke)

Chips/Modules: I love my Jet Stage II, the stage II as been dynoed at 8-10hp gain on a Jeep 4.0L and that is exactly what I feel sotp. Some dont care for Jet but I do. (note: for the chip to work as advertised you have to have everything else in the exhaust/intake stream to flow very well or it will not work correctly.)

Synthetics: I swear by Mobil 1. I've got it running in my Diffs/Transfer case/Tranny/Engine and along with the oversized Mobil 1 filter (M1-301) I could'nt ask for better mileage or protection.

HTH party1:

[xp153]

I went with the k&n air filter and the flowmaster exhaust on my 1990 laredo and have been happy with the results. you can definatly notice an increase in available power. jumping on a freeway where you need it is the most noticeable. worth it? YES.
the noise level is also increased and can be aggravating as you can tell that you are setting off other peoples car alarms, but they are probaly set to sensitive anyway.

[rumblebelly]

I'm curioius about plugs too. A mechanic told me that using platinum plugs is asking for trouble because the system wasn't designed for them. He said platinum plugs could create problems with my ignition system down the road.

The best thing I've ever done for my jeep was put synthetic oil in my manual tranny. When it was cold that sucker would get so stiff. Putting synthetic oil in solved that problem, shifts just as smoothly at 0 deg F as it does at 100 deg F.

[RichP]

The single biggest thing you can do is regular maintenance. My 98XJ has over 194,000mi on it. Lubricants I run Mobil-1 10w30 in the engine, Mobil-1 in the Transfer case, Mobil-1 in the 5 speed and Mobil-1 in the diffs. At regular intervals I dump a large bottle of Chevron Techron in the tank and on a yearly basis I borrow my neighbors 3M Injector cleaner kit, go buy a fuel/cleaner refill and hook that up to clean them. Filters I use Mobil, K&N for the oil and Mopar & K&N for the air, when the K&N gets pulled for cleaning I put a Mopar paper filter in and run that till the next change and the K&N goes back in after cleaning.Tune up Plugs, cap, rotor, wires I use Mopar OEM and I buy them from the dealer, the Champion plugs from the parts stores are different then the ones the dealers carry. Jet chip, No thanks. Exhaust system is still original, maybe when it goes I'll 'upgrade'.
I need to do my O2 sensors, they are still original, ordered a bunch of parts the other day and will be taking a free weekend to do the cooling system hoses, cap, tstat, flywheel clutch and maybe the raditor.
Keeping it up to snuff is the single biggest thing you can do, no amount of bolt on muscle parts are going to compensate for dirty injectors, a filthy throttle body and low tire air pressure.

[BrettM]

can someone elaborate on being against synthetic in the AW4? I just swapped one in (replacing the Peugoet) and I was under the impression that Mobile 1 synthetic was the lube of choice, so that's what i filled it with. what's wrong with synthetic, and should i change it now, or just wait until next time it needs to be changed?

[4WDXPRT]

If you remember only one thing..."There is no substitute for cubic inches." With that said I've owned four XJs currently two 89s and the best of all years a 1999 and I find the above statement to hold true time and time again.

Until you stroke the 4.0 out to 4.7 Liters you will never see a noticable increase in power for the money you've spent. You can SuperCharge it and add 50+ horsepower but that cost $3000...so for that I'd start looking into the following.

The other option is to throw a Vortec Chevy engine LS1, LT1, 5.3L-6.0L out of a Silverado, etc but again this holds true to the cubic inches quote.

I wathced a Hot Rod TV spot once where they changed pulleys to fuel injectors on a LT1 V8 Camero and maybe got about 15hp out of over $1000 in upgrades that were quite extensive and time consuming. A RamJet 502 would be a better way to cure the extra powerbug IMHO.

Just my 2 cents.

[JeepinAudiophile]

[QUOTE=4WDXPRT]Until you stroke the 4.0 out to 4.7 Liters you will never see a noticable increase in power for the money you've spent. You can SuperCharge it and add 50+ horsepower but that cost $3000...so for that I'd start looking into the following.

QUOTE]

avenger supercharger-$3995 104 HP Gain- brings STOCK engine to 294 HP.
4.6L stroker, $4695, 260 HP
4.7L, $4695- 275 HP
4.8L, $4895-290 HP
(Jakes Racing Engines)

that being said, when i can afford it, i'm going to supercharge a 4.6

[tugalo]

changing the primary wiring to a larger size and adding an extra ground wire sure helped my 90 xj.
The lights were brighter, and the powered accessories ran much better, not to mention that my alternator gauge show a much higher rate of charge.