many problems...what is this?

I can call him up and find that out tomorrow, and yes I do have a cat, no its not clogged (if you were thinking along those lines..)... i have the factory one on right now but I also have a high flow one that this problem occurs with as well, I also have run it with bypassing the cat, and with downpipe only....same deal in all situations.
 
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well guess what...the problem has been solved!!... it seems as though it was all sorts of things working together as one...or perhaps certain things caused others to fail? not sure...but ill recap as to what I found. So a week after installing the header..and a couple of days after installing the new cat, the problem started..first thing I did was remove the cat and drove without one. same problem, even when i put the old one back on. i found a shorted out o2 sensor and one with a lot of carbon on it...so I replaced those... didn't fix it. during the diagnose I found a broken vacuum hose, so I replaced that, then while testing fuel pressure... I found that i had a significant loss of pressure during the leak down test (at the fuel rail test port) but it was perfectly fine when i hooked the gauge up before the fuel rail (and snipped off the quick connect by this point out of frustration) ..which seemed odd because i thought that reading without clamping or anything should give the same as the test port. so i hooked up my new fuel injector hose (minus the quick connect) tested at the port again and it was perfectly fine....strange because there was no fuel leak however that IS where I was loosing pressure. at this point it just didn't make sense...and it occurred to me that after taking on and off the exhaust so many times i could've done some damage to the old stock cat...so i took it off, set it aside, inspected the new one and found it also had some insulation or something stuffed up against the screen so i cleared that out as well, put it on, with the rest of the exhaust...and sure enough it runs better than it ever has!...the only explanation i can think of was that both of the messed up cats had been throwing the o2 sensor off..and causing the backfires...which then may have spiked the pressure in the crappy brittle hose, breaking that...and who even knows about that quick connect... lol this sound about right to you guys? it was a weird situation and was driving me nuts...I'm just glad its over (for now...) and thanks a lot for all your help...definitely needed a push in the right direction with some encouragement.... on the plus side i learned a hell of a lot about how the engine works during all this...
biggrin.gif
so i cant be happier!...now i just need to find something else to break
 
Thanks for the update. Glad to hear things are back to normal.
 
weeeell. i was right, i hadnt seen the last of this problem. :S it all started up again last week and im ready to pack the thing with c4 and light er up. so i guesss im crawling back for some more advice? for those of you too lazy to go back and read whats going on here ill summarize:

basically im getting intake backfires and stumbling/cutting out around 40-60 degrees during warm-up, but once it happens its pretty well perfectly fine for the rest of the drive. if i ride the clutch and stomp on the gas when it starts happening for a couple of seconds i can skip right by it usually. the only other time there seems to be an effect is while its idling, if you give it some gas and let it idle again itll start stumbling and cutting out.

so far what ive done is replace the o2 sensors, fixed a vacuum line that was cracked, found i was loosing fuel pressure during a leakdown test and discovered it was the quick connect before the fuel rail so i fixed that, also have driven it without the cat to see if it was clogged and still got the same problem. and i have reset the computer a couple of times now. the CPS was also replaced about a year ago so that shouldnt be the problem here. i have a 98 so the map sensor is built into the intake manifold and the TPS is not adjustable..so those two are unlikely as well. this all came up about a week or 2 after i installed a new header. the only engine mods i have done are the intake, header, and exhaust system (not including the down pipe) any suggestions?
 
You have a temp sensor for the gauge or idiot light, and one for the engine. Here's my thought they are thermistor's as temp raises they increase/decrease in resistance. They tell the computer when to run using the O2 sensors and when to run open loop mode(cold), thus adjusting air fuel ratio. I'd try and change the one for the ECM. It could have a heat related short in it. Just a shot in the dark and like $12 part. P.S. I'd break it loose when the engine is warm then drain the coolant down some ,then remove it. It will help so you don't snap it off.
 
hmmm sounds like a possibilty. ill look into it and give it a shot, might as well if its something around $12.

on a side note the CEL is back on and throwing o2 sensor codes... ones that are slightly different than the ones we pulled last time :S

another thing is that the ass end of my muffler (flowmaster 40) took a weird hit after sliding backwards and catching on a rock and took a dent on the vertical face beside the output pipe... this happened around the same time as the install, any possible chance that it could be swirling the exhaust back and throwing off the o2 sensor somehow? far fetched I guess but im running out of ideas...
 
Rokee44 said:
oh is it? I thought the map sensor was either on the drivers side firewall or throttle body?..maybe im just mixing it up with the older models again...
Click to expand...

96 or 97+ puts the MAP sensor directly on the throttle body.

Prior to that it was on the driver's side top of the firewall.
 
Rokee44 said:
hmmm sounds like a possibilty. ill look into it and give it a shot, might as well if its something around $12.

on a side note the CEL is back on and throwing o2 sensor codes... ones that are slightly different than the ones we pulled last time :S

another thing is that the ass end of my muffler (flowmaster 40) took a weird hit after sliding backwards and catching on a rock and took a dent on the vertical face beside the output pipe... this happened around the same time as the install, any possible chance that it could be swirling the exhaust back and throwing off the o2 sensor somehow? far fetched I guess but im running out of ideas...
Click to expand...

And the code(s) are??????

Sounds like something still going on in the exhaust and O2 sensor(s) area.

You could also have an injector acting up.

I would check everything you previously fixed to see it unfixed itself, and everything you upgraded.
 
A couple of us around here have had something similar, and it was a crack in the header. The extra heat under the hood causes vapor lock when you are idling, or when you shut it off and try to start it back up. If you have exhaust escaping out a crack you will show a lean code, and the fuel system will try to adjust. This will also have an effect on your gas mileage as well.
 
Hey rokee, Ive also got a 98 having the same issue. It is perfectly predictable as to when it happens just like yours. It runs fine after a cold start for 10-15 seconds or so then starts acting up. Ive found that when it starts sputtering and backfiring I can slightly let off the gas and go again and it will be fine for a few seconds, then starts sputtering again. I repeat this about 4 or 5 times, then its good to go. After its warm I have no issues whatsoever. If I turn it off and it sits for about 15-20 minutes, it will sputter again the same way when I start it back up. Are my symptoms the same as yours? We'll have to tag team this one if so. I havent been able to pinpoint my issue either. Im about to finish up school for the semester and Ill start trying to diagnose this pesky issue and let you know what I find.
 
yup sounds like you have the same issue as i have. have you done any upgrades to the engine out of interest?... i have literally diagnosed everything lol at least twice. next thing i will do is check the TPS, IAC, and MAP sensors, as suggested to me by someone on SOXJA. i had left them out of my diagnose until now because none of them are adjustable on 98's so it would be a strange coincidence if one of them messed up. if they all check out. and if they check out the last thing ill do is check the fuel injectors for functionality, and if they are fine then im ripping the header off, get a better gasket and do the install again.
 
I have put on the apn header but only used the gasket that came with it. That an a custom downpipe are the only mods I have done.

I had similar symptoms when my TPS went out, namely the stuttering and backfiring, but it was only at one point on the throttle and didnt go away with the warmup period. Im hoping that I dont have a vacuum leak due to a crappy gasket. I really dont want to tear that thing apart again, but I will If I have to. Have you made any headway yet? As of right now, the stutter has just become second nature and something I just plan on. Im just waiting for it to crap out completely and leave me stranded at some point. That wouldnt make my day. Its about ready for a rebuild though so maybe that will be the extra nudge I need.
 
hi all, i'm a rookie to jeeps and have a 99' 4L. I HAVE the same symptoms as what i'm reading here. Thank you to everyone that has tried to help, b/c all of this has helped me understand how to better deal with my situation. I'm in school and live 4 hours away from my garage so it's nearly impossible for me to get to wrenching, so my stupid butt takes my XJ to two dealerships and what do you know they cash in on my wallet and I still have a gas guzzling Jeep. I'm in the process of going through the checklist ya'll have made and hopefully if I find anything that helps I will inform asap...The only question I have is, What is adjustable on my 99' that is not on your 98'? And will it help if I get anything adjusted?
 
That is why we call them stealerships, not dealerships!

Not much of anything is adjustable on a 99. Symptoms usually vary a little. Best to post your exact symptoms. Have you had it scanned for computer error codes, if not run it by some place like autozone, they od it for free. Could be anything from a dying battery, poor electrical contacts, to a dying O2 sensor. Check the easy stuff first, like the battery, battery posts, connectors, vacuum lines (look loose ones) loose or disconected sensors connectors.....and keep reading. Also, get an FSM and or Haynes manual and use the troubleshooting guides there as well as here.

jsu7970m said:
hi all, i'm a rookie to jeeps and have a 99' 4L. I HAVE the same symptoms as what i'm reading here. Thank you to everyone that has tried to help, b/c all of this has helped me understand how to better deal with my situation. I'm in school and live 4 hours away from my garage so it's nearly impossible for me to get to wrenching, so my stupid butt takes my XJ to two dealerships and what do you know they cash in on my wallet and I still have a gas guzzling Jeep. I'm in the process of going through the checklist ya'll have made and hopefully if I find anything that helps I will inform asap...The only question I have is, What is adjustable on my 99' that is not on your 98'? And will it help if I get anything adjusted?
Click to expand...
 
Thank you EcoMike for the tip, I went to go buy a shop manual today and the parts store was out. I've checked and replaced two new sets of O2 sensors and checked everything you suggested...I found a repair shop that seems to be honest and does good work fast. I'm having my XJ looked at mon. morning and having the fuel filter replaced and probably the MAPS sensor. After all the reading i've been doing I thought this would be the cheapest place to start since I've already spent around a grand and haven't got anywhere. I'll let you know how it runs after I pick it up. Again thank you for replying to my post.
 
jsu7970m,

Sounds like you about to waist more time and money. MAP sensor almost never goes bad. Spend your time and money on some gauges like a multimeter (volt - ohm meter), fuel pressure gauge, vacuum gauge, and get an FSM. Take it to an Autozone and get the free OBD-II scan for error codes. Check the engine vacuum at various rpms, fuel pressure, and check the senosrs like the TPS, MAP, CTS, MAT (or IAT), using the ohms and volts scales (see the FSM or look at the old 87-90 Renix threads on sensor testing, as the newer jeeps still use the same basic sensors and test values), check for shorting sensor wires like O2 sensor wires near the exhaust manifold, , loose connections, check the battery cables, posts and voltages. I have seen more engine problems be nothing more than a poor battery connection because prior mecahnics failed to retighten the battery clamps after completeing service work than you can imagine.

Get some hard test data before waisting money on parts. You have better odds of winning in Lost Wages Nevada than you do of fixing a jeep by throwing parts at it!
 
OK, so I just got my XJ back and it runs like a top. I could kick my self for over looking what was wrong. It was a pair of wires from the O2 sensors to the circuit board that were close to the exhaust manifold. The sheath was melted and the wires were touching and shorted out...so what I'm guessing was it was sending a bad signal to the ECU. So HOPEFULLY I won't have to worrie about this particular problem anymore. Oh and by the way I checked fuel pressure, it was fine as well as all of my connections. Thank you everyone for posting all of your helpful tips. I am relieved that I can move on to spending money on a lift, wheels and tires now instead of that other stuff. Thank you again!
 
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