Zeustopher

I'm new to this forum and I'm not exactly sure where to post and I am under a big time crunch. I own an '87 Jeep Cherokee Limited. I just recently had it given to me because I really needed a vehicle. It needed exhaust work so I did that fairly easy.

Now to the Actual problem. It won't pass emission tests. It is running really rough, especially down in the lower RPMs. It is also backfiring (I can hear the pops in the exhaust) at those lower RPMs (Obviously why it won't pass emission tests).

The worst section is between 1000 and 2000 RPMs, especially bad at right around 1750 RPMs. I thought timing but in the engine bay it says that timing is not adjustable.

I need suggestions on what to look at and what to check so that I can start to fix this problem and I need them FAST. I have a 14 day temporary registration for it and it is already 3 months past due so a ticket will surely come if I can't fix it.

Thanks for all the help in advance!

Zeustopher

PS - How can I find out if my vehicle is XJ, WJ, etc?

00xj-classic

your jeep is a xj.. and i am going to guess u have a cracked exhaust manifold.. Is the engine loud on a cold start??? you could be throwing off a 02 sensor beacause of the cracked manifold.. just my thoughts,glen...

Zeustopher

Thanks for the VERY quick reply! I'll check out the manifold. It does seem slightly louder on cold starts but not a whole lot really. Why would this cause the backfiring though? Could this all be caused by a bad O2 sensor? Is there a way to test an O2 Sensor?

Also thanks. Now I know I have an XJ.

je4reyk

Yours is an xj ,I would start with the basics compression test,that way you can inspect the plugs. Then check vacuume hoses,plug wires and firing order,then move on to the sensors and wiring.

Zeustopher

Thanks for the suggestions. Keep them coming!

While searching I am reading something about an IAS. What is this, where is it located, and could this be part of the problem also?

How do you do a compression test?

00xj-classic

haha yea you have a xj now!!! The backfiring is probally a differnt issue, I think..? A cracked manifold will cause a major power loss and rough idle and or rough running in general..With my old 99 that jeeps manifold was almost in 2 peices and still drove good, no backfiring.. try some fuel injector cleaner in your gas and see if that helps.. you could have some junk in your gas.. If the manilfold is cracked it SHOULD be visible looking down thru the intake manifold area.. Let me know whats going on Ill try to help as much as i can, glen..

RevZeroX

map sensor? just a though on something to check

Zeustopher

I have put the cleaner in the tank and I am running that through (Just filled up last night so haven't used a whole lot yet).

Thanks for all the suggestions! I really really appreciate it!

je4reyk

A compression test is were you take all the spark plugs out and put the tester to each spark plug hole while the motor is being cranked over. It is a good test to start with becouse,it is easy, cheap and if you have burnt valves or bad rings you could spend alot of time and money trying to find what is wrong without it,this way atlest you know your engine is solid

00xj-classic

He dosnt have the symtoms of low compression, deffeintly a good start thou. When is it backfireing??? when shifting or through out the rpms??? do you have a regular idle?? 600-700rpms??? dose the jeep surge at idle?? Are your rpms low when going into overdrive?? letme know what your problems are and be a little more specific, glen..

Zeustopher

Alright, I'll try to explain the systems as best I can. It starts up fine. It Idles like it should with no real fluctuation. It Idles right around 650-700 and sometimes slightly higher, maybe at 750.

It begins back firing once I step on the gas and the RPMs get about 1000 and then worsen at about 1500 and it is the worst at about 1750 then it sort of backs off at about 2250 and doesn't seem to backfire at all.

This is the same symptoms whether it is in overdrive or whether it is parked and sitting still. I haven't tried driving in a lower gear so the RPMs are constantly higher to see if the backfiring is occuring up there but it doesn't seem like it is because when I accelerate, it sputters and backfires up until 2250 then it runs like normal.

Also I noticed that if I romp on the pedal really hard and give it a ton of gas it sputters less. Where I notice the problem most is at cruising speeds when RPM is at around 1750.

Hope this gives a little more detailed answer of when I am getting the sputtering and the backfiring.

Thanks everyone for all of your help so far! I am going to call a few people I know to find that compression tool. It can't hurt to test it and also to check out the spark plugs.

(Crosses fingers it is something small like a little piece of junk thats passing (like a kidney stone) or something like a wrong gap on an old spark plug....)

**Oh, just thought of this- I know on some cars there is a way to jump 2 connections on the computer connector to see if there are any "codes" being shown of things going wrong. Is there a way to do this on the jeep? Is this worth a shot? **

Brett

along with the injector cleaner it wouldnt hurt to try and clean up the throttle body a lil bit make sure you got a clean air filter ect... speaking of your air filter hows it looking? any oil buildin up on the back side? (the side that goes towards the engine or is facing up when the filter is in place)you may have a bad pcv valve which is really common

je4reyk

Yea it could be even bad plugs,my dad put a new set in his toy it ran worse than the 20 year old ones he took out!

Zeustopher

I'm planning on spending the morning tomorrow checking out a few of the things that you guys have suggested.

I took it out for a Drive to verify all the things I said earlier. It idles fine. At around 1000 rpm it begins to backfire slightly. Once you get up to 1500 it does it more. Then once you get it to 1750 it backfires and sputters ALOT. A few times I had it doing it and it almost sounded like a bag of popcorn in the microwave! Then at around 2250 it just seems to stop backfiring. It seems to be the worst at about 35mph because it is holding steady at about 1750 rpm at that speed. Just to see, I drove faster on it (around 50mph) in 3rd gear to see and when I was holding a steady speed it was backfiring no matter what RPM it was at, but it still seems the worst at right around 1750 rpm.

Thanks again to everyone for your suggestions!

captainwoot

Do you have any history? maybe a basic tune-up plugs, wires cap and rotor, doesn't sound like it should be anything serious....
Good luck!