Poor Dad needs help!!!

[propaneman]

I am looking for any assistance in regards to my son's 2002 Liberty 3.7 The jeep is running rough, stuttering and bucking, smells like gas, etc. I plugged it in and got a misfire on Cyl 3 so I went to the store and purchased 6 new Coils and 6 plugs and replaced them. Still got the code - removed the fuel injection rail and with the injectors unplugged but still hooked to the rail, I powered each one to make sure they sprayed gas. I am unsure where to look next - wiring harness? PCM? Bad coil out of the box? Maybe a sensor? I can't find a complete wiring harness to just replace it all for the coils and injectors thinking maybe there is a spot rubbed through I can't see or the PCM is messed up? Changed coils around, still getting the same code and it runs and is still being driven but not well. Help!

 

[MarkA67]

crank sensor? Throttle position sensor?

 

[propaneman]

I was going to try those as well but didn't want to just throw parts and money at it

 

[LibertyTC]

Fuel pressure guage test in psi is?
Do we have a bad valve or seat?
Compression and leak down test?

 

[propaneman]

I will have to buy some tools to do those tests and watch a few videos. I'm more of a parts changer

 

[John P.]

Hi, I’m new to the forum but have been researching the Liberty extensively since I purchased one. With all the reading up I’ve done if I had this issue I would pop off the valve cover on the side that is misfiring since coil and plugs didn’t fix it. A compression test would also be in order too. Once you have the valve cover off you may find the rocker to that cylinder just laying in there. If everything looks normal and the compression test comes out good I would test the engine pcm. I have read several instances where the engine computer fails and shorts a single or more coil packs to ground preventing them from firing. If that’s the case there’s a company that can fix them for around 130 bucks.

 

[propaneman]

Do you have a link to the place that repairs the PCM? I just tried to locate a replacement wiring harness as well but apparently its "Discontinued" and I can not seem to find one anywhere. OEM part number 56044100AO

 

[John P.]

If you google S.I.A Electronics Inc. 730 N. Minnie St. Tilden, IL they will pop up.

 

[LibertyTC]

Why do you think it is a bad PCM they rarely fail and may have a P0601 code - bad Power Control Module (PCM)

 

[propaneman]

I was hoping to find the wiring harness first to just start working backwards towards the PCM. I was hoping to not have to make a new harness myself with new connectors for the coils and injectors.

 

[LibertyTC]

What about finding a harness then at a local scrap yard?

 

[John P.]

That’s where I would go, anyway not trying to lead him astray with extra crap. I wouldn’t look to the PCM until I exhausted all other options.

 

[propaneman]

What about finding a harness then at a local scrap yard?

The local yards don't seem to have much so I will have to expand my search a little bit further

 

[JasonJ]

The local yards don't seem to have much so I will have to expand my search a little bit further

I get that you're more of a parts changer than a diagnostician... but you are going to spend more than the Jeep is worth replacing parts and possibly still never fix this going how you're doing this now.

Given you've checked for injector operation, replaced all plugs and coils and yet still have the same problem on the same cylinder, you need to do a compression test before you do anything else short of cracking open a beer for a break.

You probably have a failed lifter.. this will cause a dead miss on that cylinder and no amount of changing electrical parts is ever going to fix that.

Cylinder 3 is drivers side middle... that's the easy side to work on. Perhaps pull off the valve cover and inspect intake and exhaust lifters and camshaft lobes. A compression test will reveal issues here without doing anything more than pulling the plug. Then you can all stop and assess from there.