Overheating/Tuning HELP! . . . PLEASE!

I own a 1998 XJ (4 Door Classic), 4.0L (150,000 miles) and Im looking for some help in diagnosing an overheating question as well as a performance upgrade question... I have spent the last couple days searching/reading other threads and its helped but my questions are fairly specific so maybe someone out there has some good answers....

First of all, about a year ago i posted a thread regarding an overheating problem i had...

http://www.naxja.org/forum/showthread.php?t=925841&highlight=Rust+colored+engine+coolant

The suggestions made were to replace the thermostat with a OEM 195 degree, replace the radiator with a 3 core design, add a OEM 16psi radiator cap, flush the engine and replace with 50/50 mixture, clean out the overflow/reserve tank and replace the lower radiator hose.

I did all this and more, i got the OEM thermostat, a new 3 row all brass/copper radiator (radiatorbarn.com), added the OEM 16psi cap, flushed the engine, replaced every single radiator (lower w/spring) and heater hose, thoroughly cleaned the reserve tank, and added a bottle of Water Wetter to the coolant.

After all the extensive fixes, I was driving west out of Denver up I70 and after about two miles of pulling the steep grade (as any of you know who live in colorado) we just barely made it past the Evergreen exit. Up to the that point the Jeep was barely going 40 mph and seemed to be struggling just to do that, then all of a sudden the transmission jumped from 3rd gear all the way down to 1st, then back to 3rd, then back to 1st, then finally back to 3rd, were by that time the engine temp was through the roof! we pulled over and spent an hour waiting for the temp to return to 210 degrees.

After some major discussion with friends and mechanics here are the theory's i have so far is to the overheating and crazy shifting errors and total lack of power.

1. My current exhaust systems is the original (150K) with a bad cat converter (which rattles constantly) and bent muffler. One theory is that on hard acceleration on a steep grade all of the broken pieces inside the cat are being pushed back and plugging the exhaust, causing too much back pressure and a lack of power.

2. That the current/original fuel injectors (150k) are either failing or the truck is running to lean. We pulled the spark plugs and noticed a consisted white coating on all of them.

The only major engine mods that i have currently are a cold air intake, and and a performance ignition. The exhaust is in need of a couple overhaul including a header, down pipe, cat, muffler, everything. and i have given some thought to a throttle body and the relatively new Unichip.

Anyone have any thoughts to this.... possible bigger fuel injectors or exhaust... please help!

If the cat is bad remove it. Put in a new cat or a test pipe. The excessive back pressure can of course cause the bucking and issue. this being due to fuell air mixture demands by the engine and attempted reugaltioons of the computer. Are you getting any codes being thrown? Is the check engine lighjt on or burned out?


:dunno:

The check engine light did come on, but i didn't have it checked to see the exact code... but on a similar note.... about a two weeks before the trip up I70, the temperature here in denver was over 100 for nearly 3 days. I drove to the liquor store, got my beer, came back out and started the jeep, and it seemed like it was running on two cylinders! the engine seemed flooded. after about a 1/4 mile the engine was back to normal, but i had a check engine light.... I took it down to my local shop and the diagnostic computer showed a miss-fire in cylinder 5.... ever since that hot day, I have not a similar problem. The bucking up I70 seemed to be a different problem to layman like me.

This "test pipe" you describe, where do you find it and how does it work.

Any thoughts in regards to the fuel injectors.... should they be replace, if so, with what.... OEM or an upgraded style, like the ford ones I have read about. Keeping in mind that I will be installing a throttle body and most likely a Unichip on top of the exhaust system which seems to be the number one priority.

May sound dumb, but have you tested your fuel pump? Pressure was low on a friends jeep, did same thing.. IE over heat, missed and sputter..HTH

how does one go about testing a fuel pump?

Too answer both questions mine and other posting.

Alot of the auto parts stores will let you rent or borrow a fuel pressure gauge. i know for sure Autozone will. then plug it onto the end of your fuel rail and test.

second, test pipe you have to have made or build your self.

Good luck I would have the check codes pulled and see what they say. I bet one of your O2 sensors is fried or both. Hal :conceited

Anyone have any thoughts to the fuel injectors.... should I consider ford 24lb injectors if im installing all of the exhaust, throttle body and chip.... is the 24lb injector the proper style for my engine (1998 4.0L)?

Are you running a trany cooler? Remember that the trany fluid runs through the radiator. It could be the trany overheating.

Yes i have a factory tranny cooler.... (i think)

My jeep came with the "up country" suspension package which included a factory tranny cooler.

Is it the small radiator looking thing sitting right behind the grill in front of the radiator? If so then yes I do

Never had any problems before in regards to the tranny shifting... and the fluid is always topped off and looks clean.

milehilonewolf said:

Anyone have any thoughts to the fuel injectors.... should I consider ford 24lb injectors if im installing all of the exhaust, throttle body and chip.... is the 24lb injector the proper style for my engine (1998 4.0L)?

Click to expand...

No, fix your problem first before adding hopped up parts. The exhaust, chip and throttle body do not require a different injector. You said your cat was rattling, if so you need to replace it. I would replace the o2 sensors while your at it too.

I have been private messaging "Dr. Dyno" regarding this issue as well and I think he, I and everyone else who has posted has come to the same conclusion....

Replace the Catalytic Converter!!!!

As you all have all eluded, the engine seems to be running lean and that I should replace the injectors, but use only the "stock" injectors which on a '98 XJ flow 23.3lb/hr at 49psi so even with those I can add all the available external bolt-on performance mods (not including forced induction of course) without maxing out the injectors.

So for now I will be proceeding with a full exhaust overhaul and replacing the fuel injectors with stock replacements.

As to the fuel injectors, anyone know of a good place to buy them at a relatively cheap price, without sacrificing quality?

Why not fix what's broken first?

I believe I already stated thats what I will be doing.... fixing what's broken.

I stated earlier that the ENTIRE exhaust is shot.... there is two cracks in the exhaust manifold, the cat busted, and the muffler is badly bent... I suppose i could just fix the cat, but in my opinion, why not fix the entire system at the same time?

Also, we have concluded that based on miss-fires in cylinder 5, white buildup on the spark plugs and overheating issues, that the injectors are most likely in need of replacement...

So, in the next couple weeks i will be proceeding with the fixes and I will be sure to post my results back on this thread.....

Napa part #272310 is a heavy duty fan clutch out of a 1998 grand cherokee with the 4.0 (NOT the max duty cooling) This is a direct bolt in upgrade that will give you much better air flow from the clutch fan, and much better heat transfer.

thanks for the tip: xj88superjeep

Would you recommend I put this fan clutch (Napa part #272310) in at the same time I do the other upgrades?

Also what do you mean by "(NOT the max duty cooling)"?

milehilonewolf said:

I believe I already stated thats what I will be doing.... fixing what's broken.

I stated earlier that the ENTIRE exhaust is shot.... there is two cracks in the exhaust manifold, the cat busted, and the muffler is badly bent... I suppose i could just fix the cat, but in my opinion, why not fix the entire system at the same time?

Also, we have concluded that based on miss-fires in cylinder 5, white buildup on the spark plugs and overheating issues, that the injectors are most likely in need of replacement...

So, in the next couple weeks i will be proceeding with the fixes and I will be sure to post my results back on this thread.....

Click to expand...

You mentioned the cat rattling, and the muffler being bent, and then said we were all alluding to bad injectors causing a lean condition, which no one but you suggested. If you've got bad sensors, serious exhaust leaks or blockages, you'll have all sorts of issues. I do not understand the preoccupation with replacing the injectors until you've fixed the shit you already know is broken.

I've been down the "throw money at it on a hunch until it runs right" path myself, which is why I'm suggesting you stop that.

I apologize for the miss-print on my behalf, the main reason the injectors keep coming up, from me, is that i have had a bunch of private messages from another forum user "Dr. Dyno" regarding the fact that i had a check engine light thrown, then had it diagnosed as a miss fire in cylinder 5, then it was suggested that i check the spark plugs to see if there was a white buildup, which there was (a considerable amount), so after these symptoms, the thought that on top of a bad cat and exhaust system, there might be a simultaneous problem going with one or all of the injectors.

Trust me when I say this: I hate throwing money away.... i haven't spent a dime yet, hence my post on this forum.... I would rather ask a multitude of questions and possibilities to gather as much information as I could to best decide my course of action.

Don't get mad... be happy.... the reason this forum is so successful is because of people like you and me.... solutions to problems are best left to multiple minds instead not just one..

cut the cat off, test drive. if ok? stop. replace cat if no...
how are wires and cap and rotor(if u dont know age)replace, test drive.if ok, stopif no...
replace o2 sensors. test drive if ok stop. i think you see where im going here
does the elec fan work? blah ,blah blah good luck

milehilonewolf said:

I apologize for the miss-print on my behalf, the main reason the injectors keep coming up, from me, is that i have had a bunch of private messages from another forum user "Dr. Dyno" regarding the fact that i had a check engine light thrown, then had it diagnosed as a miss fire in cylinder 5, then it was suggested that i check the spark plugs to see if there was a white buildup, which there was (a considerable amount), so after these symptoms, the thought that on top of a bad cat and exhaust system, there might be a simultaneous problem going with one or all of the injectors.

Click to expand...

For some reason, I read "white film on the spark plugs" as "on the injectors". Been a long second Monday, sorry. Have you run Mystery Oil, Seafoam, or cleaner of some sort through them? That's become a monthly thing with me.

What's the PN on the injectors? I've got a spare set from my mani donor, but it's a late 99, and I believe it has different injectors than yours, although I'm not 100% certain. They are definitely different than on my 97, so I'm guessing they wouldn't be of any use to you either.

Inconsistent issues are the worst, especially when the vehicle is your DD, and may spontaneously combust or die.