Jeep 5.2L V8 problems

[getlost4x4]

I just bought my 1994 GC 5.2 V8 about 2 months ago. It has 132K on it.

It was running great up until last week.

I bought it for around $600. I knew it had some issues.

So far I have replaced:

Radiator and all the cooling hose
Recharged the AC
New plugs
New air and fuel filter
New thermostat
New valve cover gaskets
New battery
New oil and filter
New battery terminals
New rebuilt tranny 4000 miles ago

It suddenly started running really rough. I just pulled the catalytic converter and muffler last night because the cat.was broken and the muffler was rusted out from the inside.

The engine is still screwed up. It back firing. The only way I can get it to run is by pressing the gas pedal to the floor.

What should be my next step? I'm thinking about new wires and cap and rotor.

Do you think it could be a fuel pump or ECM?

Thanks

[it usually runs fine]

I have 5 ideas.

[PilotAustin]

1 New engine.
2 New Engine
3 NEW engine
4 New ENGIne
5 Check Fuel pressure??

[IndyZJ]

CEL? Was this before or after you cut off the exhaust? Have you installed a new cat?

I'd start with the usual basic tune-up and cleaning the IAC/ throttle body since it probably needs it anyway and that seems to solve most rough-running 5.2 issues (assuming no CEL). If it's really backfiring, there's a timing issue.

[getlost4x4]

i did read about the IAC last night searching on another forum. i'll try taking that out and cleaning it up or just buy a new one.

i have not had any CEL lights on with the vehicle. i have not installed another cat. for now its just getting a test pipe until i get it running right again.

this is not a mechanical problem. it must be either vacuum related or ignition related.

[JordanA]

Verified spark at the cylinders? Like stated above, the IAC is a common issue and it can result in similar running conditions, although I admit I've never experienced a backfire on either of our 5.2's.

[rccolacc]

I put my money on the fuel pressure regulator. Hopefully your rail is better than mine and has a pressure port on it so it is easy to check. I think the regulator is part of the fuel pump though, so if it's bad it might be a bear to replace.
-RC

[getlost4x4]

it has a full tank of gas. i'm hoping its not the fuel pump

[getlost4x4]

alright. i spent some time looking under the hood.

the only thing i can see so far is the PVC hose is split. i'll replace that and the PCV.

all the other connections are hooked up. non of the vacuum lines are damaged.

i'll pick up a basic ignition tune up on Monday, including new wires, cap and rotor.

[OverlandXJ]

Figting that dist cap in the V8's is alot of fun.. be carefullof the oilo sending unit just to the left of it. They can be brittle and snap.

I'd throw aq CPS sensor at it first since it's a sudden occurance not typical of tune items.

Did you hose down the engine compartment? TPS dont like water.

[getlost4x4]

i pressure washed it about 2 weeks ago. it was a little dirty with 16 years of grime.

[getlost4x4]

i just the key thing to get the codes.

i got a 55

i looked in my manual and it doesn't have any info for a 1994 GC 5.2L

[Newell1225]

55 means end of codes.. or in your case.. no codes.. that split PCV hose wil cause a higher than normal idle.. idk about rough, but def higher..

[Doctor W]

55 means end of codes.. or in your case.. no codes.. that split PCV hose wil cause a higher than normal idle.. idk about rough, but def higher..

Depends on how bad it's split.......it CAN cause the symtoms you describe if it's a big enough vacuum leak so that it'll only run with throttle wide open/max fuel going in to be able to run with all that extra air leaking in.

A code 55 means end of code reading/no codes in your case.... that's a good thing, it means none of the code type faults are happening with your car so it could be the slit PCV hose.

[IndyZJ]

So is it actually backfiring? Or is it just running rough and not idling? Pulling the PCV line off only makes it idle really high in my experience - the line being cracked could not be any worse than that.

Did this happen after you pressure washed it? If it started right after, My money is on the ignition system. When you're replacing the cap, rotor, and wires, check the coil, too. If it's needed that kind of work, I doubt it got a 100k mile tuneup. The parts are cheap enough to go ahead and replace and can make a huge difference. Go ahead and clean out the throttle body and IAC. I haven't come across a 5.2 that didn't need it at some point.

[getlost4x4]

where is the idle air control valve? got a picture at all.

i pressure washed the engine about 2 weeks ago when i replaced the radiator and hoses. it didn't start running like this until this last week.

i need this thing running really soon.

thanks

[IndyZJ]

Google is your friend. "5.2 idle air control"

It's in the throttle body. I don't even take it out to clean it - I open the butterflies, put either a very long screwdriver or extension in there to keep them open, and go to town with some carb/ throttle body cleaner. If it's looking particularly nasty, I'll use Seafoam and an old tooth brush. I clean the throttle body out once a year because the manifold gasket is bad and it gets pretty nasty in there. I'll also disconnect the battery while doing this to let the computer reset, as it sometimes still won't idle after just cleaning the IAC. I've never had that combination not work, but I have a relatively new ignition system (cap, rotor, wires, plugs, and coil), too.

Is it backfiring or not? What are the exact symptoms?

[getlost4x4]

alright found some pictures. tomorrow i'll check it out and clean it up.

the jeep used to have a K&N filter at one time. there is a sticker on the air box. i'll bet its completely crusty with dirt in the intake.

[IndyZJ]

Fail


Does that look like the 5.2 in your Jeep?

http://www.autozone.com/autozone/rep...00c15280070d5c

[getlost4x4]

i have the right picture in there. i don't know what you are talking about.

Fail


Does that look like the 5.2 in your Jeep?

http://www.autozone.com/autozone/rep...00c15280070d5c

[nateman54]

What plugs are you running? Don't run champion. I had a very similar problem after a tune-up. Also change the plug wire positioning per TSB. That fix my problem.

[dp96zj]

What plugs are you running? Don't run champion. I had a very similar problem after a tune-up. Also change the plug wire positioning per TSB. That fix my problem.

I've had no problem with champion plugs over the past 4+ years....

[getlost4x4]

alright. that sucker was dirty.

i removed the throttle body and cleaned everything except the MAF sensor with B12 chemtool. put on a new gasket and replaced a few rubber vacuum lines. it fired right up. i also found one of my spark plug wires was not fully seated on a spark plug (reason for the miss).

it fired right up.

thanks for the help

[IndyZJ]

Damnit - I knew I should have quoted the 4.0 pic

Glad that did it. If there was oil in the bottom of your intake, you'll want to plan on replacing the manifold gasket before too long. Mine has been bad for a while, but I just haven't gotten around to it. It's another virtually guaranteed 5.2 issue.

[getlost4x4]

i just finished putting the exhaust together.

its still running a little rough. tomorrow i get all the ignition parts and hopefully that will get it running like it should again.

then i need a transfer case, lift kit, tires, bumper, and a winch. and a 45 cal. 1911 pistol.