bellyeyes

I hope someone can help!!!! Here goes, early 99' Jeep XJ, idles perfect, but once I give it the gas, especially after cold start-up she likes to buck, stutter, spit etc, but never backfires.... If I let off the gas, perfect idle, but back in the gas it does the same thing. Seems to somewhat clear up after warm-up but will still partial engine stall, stutter, whatever you want to call it when giving it steady gas pedal. I have replaced the TPS, MAP, exhaust/intake gasket, Intake Temp Sensor and cleaned the IAC. When replacing the exhaust/intake gasket I did notice a hairline crack on the header, but I don't see this causing the issue. New one coming next week. I do have a slight whistle when giving gas under load (vacuum leak?) but cannot reproduce sound when in park/neutral and revving the engine. Tried the starter fluid test with zero result. I did swap the fuel rail with my 2000 2wd and noticed that when taking off the old 99 rail, the pressure in the release nipple seemed higher than the one off the 2000 (when on the 99)... So, maybe the issue lies in the fuel rail? ANY HELP WOULD BE GREAT... Thanks guys.......

Mendax13

is it a normal idle? not high or low?
Does it sputter and such under throttle in gear and idle or just drive?

I'm wondering if you have a fuel delivery issue.. could hook up a fuel pressure gauge to see if you get abnormal readings.

bellyeyes

idles fine right at 800 rpms.... I did notice slightly high idle at startup, 1200rpm for a few seconds then back down to a steady 800 afterwards..... only stutters in drive and rolling.... haven't tried in drive and holding the brakes......

antipode

A clogged cat fits the description. No guarantees on that being your problem, but it's something to consider.

Mendax13

that's a good idea too.

bellyeyes

Yea thats something else I was thinking....... I'll test the fuel rail pressure and see what happens there first.... Just seems like its a fuel delivery issue.... Seems like it started once I swapped out the fuel rail.......

bellyeyes

do you guys run a catless exhaust?

Mendax13

i dont but im about to swap mine after i destroyed it.

bellyeyes

I was curious cause I was thinking about doing away with the cat to run a stage 2 JET chip...... Didn't know what the downsides of running catless especially on a daily driver.....

bellyeyes

I also read that I could remove an O2 sensor and try to see if it runs better? ever heard of this tactic?

dmill89

Aside from the fact that it is a violation of federal law to run a cat-less exhaust if the vehicle came with a cat from the factory you won't gain anything performance wise on an OBDII (96+) system (and may actually hurt performance slightly) and will probably get a constant "check-engine-light".

Many shops will also either refuse to work on your vehicle or require that they re-install a cat (and charge you for this) before performing any other work on your vehicle. Again removing a cat is illegal and shops can be fined in many circumstances if they knowingly perform work (especially exhaust work) on a vehicle with an illegal exhaust and let the vehicle leave the shop without a cat installed (aside from a vehicle not registered for road use that enters and leaves the shop on a trailer/tow truck, of course).

bellyeyes

understood dmill89 just asking thats all......... do you know if the removing an O2 sensor test will work with checking a clogged cat? I do notice that it seems somewhat underpowered when going up hills at highway speed, likes to kick in/out of overdrive.....

dmill89

If it is clogged removing an O2 sensor probably won't help since the back-pressure and exhaust restriction caused by the clogged cat usually causes the issues. The best way to test is to pull the cat and run a "test-pipe" (just a length of pipe to fill the gap in its place, temporarily of course) and depending on the results either re-install the existing cat (if no change occurs) and look elseware, or replace the cat (if the issue goes away with the "test-pipe" installed) .

DieselDaze

I'm not ashamed to say I'm catless whether its a crime or not, I bought the vehicle that way... I do however intend to install a hiflow when I can as I'm getting really tired of the 'check engine' light always being on...

sounds good though

if it was the cat I think your temp would be affected as well at idle??

Turbo X_J

Save your money. Check fuel pressure, compression test won't hurt anything either.