Performance Injector Size for 98

[CartsXJ]

Ok first here are the stats, 98 4.0L, ~165K, rustys intake, 60mm bored throttle body (soon to be 62mm), 99+ WJ intake manifold, pace setter header, stock CAT, Super 40, rusty's 2.5" tail pipe. I know I am running it lean, can just tell by pulling the plugs and they look white. I think I have my fuel, up to the rail, figured out, new pump/filter/regulator going in soon, but what about injectors???

From what I've read the 98 has 24lb at 49psi injectors, so going to ford 24's would be a waste, right? Should I start looking at an adjustable MAP sensor? DO they work on the 97-98's, I know the OBDII computers have a mind of there own and will compensate any changes to go back to stockish settings.

 

[CartsXJ]

so am I even remotely close to thinking along the right lines? Any help would be great.

 

[lilredwagn]

I think the PCM cycles the pulsewidth as necessary, so going to larger injectors only increases your available overhead and also affects WOT. Which should mean that you just need an adjustable MAP.

I didn't know this when I went ahead with the following injectors - but if you do look for new ones, these should be almost ideal. Been running them for a year now - I'll pull a plug tonight or tomorrow and take a pic for you ... Last I checked, however, they looked a touch on the lean side: white insulator, grey electrode, and very clean overall.

http://www.naxja.org/forum/showpost.php?p=564697&postcount=9

 

[CartsXJ]

I just found that an adjustable MAP sensor is only good from 80% throttle to WOT, since I spend most of my time around 1800-3500 rpm's that doesn't get me anywhere, or does it and I am missing something.

 

[Beej]

I could be wrong, but I thought the adjustable MAP sensor mod wasn't possible on 96 and newer 4.0's due to changes in the electronics?

:dunno:

 

[CartsXJ]

thats what I thought......I am still looking for info. I have yet to find any real electronic mods for the 97+ XJ's..........I hate being the first one.........

 

[Beej]

I was under the impression that the computer automatically adjusted for such changes to a point in the newer 4.0's. I can't find anything to back it up, but I thought the stock injectors were good up to about 240bhp?

Somebody's gotta know for sure, anyone?

 

[CartsXJ]

I would definately be nice to know

 

[Dr. Dyno]

Stock '98 injectors are rated at 23.3lb/hr at 49psi, and are therefore large enough to cater for all the external bolt-on performance mods that you could add as well as a ported head. They should indeed be good for up to 240hp.

 

[CartsXJ]

Thanks Dr. Dyno, I had a feeling that I was right about the injector size. I just checked all my manifold bolts, a few were loose, then I went to the local parts place and picked up some muffler cement and coasted all the compresion fittings, quited done the whole system. Maybe I just had an exhaust leak causing all the issues I am seeing. Only time will tell.

 

[cherokee4.0]

My adjustable MAP works great on my 98 4.0 auto. There's gains at every rpm and I have all the bolt-ons.

Get your 12-volt source from your cigarette lighter and tie-into the (1 of 3) wire (orange)nearest the passenger side.

Do NOT use any other chips or cpu mods with this.

Spend $17 at Radio Shack and have at it.

 

[CartsXJ]

My adjustable MAP works great on my 98 4.0 auto. There's gains at every rpm and I have all the bolt-ons.

Get your 12-volt source from your cigarette lighter and tie-into the (1 of 3) wire (orange)nearest the passenger side.

Do NOT use any other chips or cpu mods with this.

Spend $17 at Radio Shack and have at it.

Who adjustable MAP sensor diagram did you follow and if you mind me asking what voltage setting are you running?

 

[cherokee4.0]

Here's what I followed:

http://www.jeepbarracks.com/modules.php?name=News&file=article&sid=18

I cannot say exactly the output voltage of my unit. My gauge sucks. Its graduations are way too small. All I can tell is its more than stock and less than 6 volts. Besides, what I'm running may not determine what is best for your rig.

This is why you get you source from the cigarette lighter (power ONLY with ignition on) AND you just rest the unit next to your stick shift so you can make adjustments while driving.

I also needed to cool the motor a bit so I did the $2 "ghetto" hood lift. The richer motor does NOT like all the heat from under hood.

 

[CartsXJ]

thanks, so you can adjust yours from inside the passenger while driving?

 

[Beej]

Here's what I followed:

http://www.jeepbarracks.com/modules.php?name=News&file=article&sid=18

I cannot say exactly the output voltage of my unit. My gauge sucks. Its graduations are way too small. All I can tell is its more than stock and less than 6 volts. Besides, what I'm running may not determine what is best for your rig.

This is why you get you source from the cigarette lighter (power ONLY with ignition on) AND you just rest the unit next to your stick shift so you can make adjustments while driving.

I also needed to cool the motor a bit so I did the $2 "ghetto" hood lift. The richer motor does NOT like all the heat from under hood.

If you could bring yourself to do a writeup on this mod, I'm sure it would be greatly appreciated by myself and others who have 97 and newer XJ's.

The existing writeups (Young's, Ansell's, Dyno's & GoJeep's) do not appear to apply to 97 and later Jeeps, due to changes in electrical system and layout, so a current writeup that works for newer Jeeps is needed and would be welcome addition to this site...

:wave:

 

[CW]

An adjustable MAP will only affect from about 80% throttle and up, that is really were a lean condition show up. I am not sure an adjustable MAP will have any affect on an obd II system. I don't think you guys with bolt ons should be having issues with fuel on an OBD II rig. Unless you are getting detonation you are fine, running pig rich doesn't help performance at all. Unless you add displacement late model ecm's should be able to handle everything fine. You can do a cam swap for nearly the price of bigger injectors and that will make a performance difference, you won't feel any differnce with a slightly richer engine unless you are having detonation problems now.

 

[lilredwagn]

I didn't know this when I went ahead with the following injectors - but if you do look for new ones, these should be almost ideal. Been running them for a year now - I'll pull a plug tonight or tomorrow and take a pic for you ... Last I checked, however, they looked a touch on the lean side: white insulator, grey electrode, and very clean overall.

http://www.naxja.org/forum/showpost.php?p=564697&postcount=9

Gonna be nice and you can click the thumbnails for full size. I pulled them and replaced them with copper NGK's, but damn if it doesn't look like they would have lasted another 30k without any maintainance. Definitely gonna keep these around for spares.

 

[CartsXJ]

Well if the 96-98 injection system can handle up too 240hp, then I might as well stick with stock style injectors. I just ordered a set of injectors from T&T performance for $159, I have a feeling that my are on their way out, if not number 6 is about ready too. I'll tell you all how it goes when they get here.

Every other place I've checked around lists the same injector part number for 96-2001, but since 99-01 have a lower rating, I didn't want to replace just that one with a lower for ~$75 a piece. Where I can get the whole set new for $159