Deanwjgrandcherokee

Hi all...I am wondering whether anyone has come across this one before. I am down under and have a 2002 JGC Overland 4.7 HO.
About 3,000 k's ago as I was driving the engine just suddenly lost power and the car slowed to a walk, When I tried to accelerate the engine would miss, backfire through both the exhaust and intake and barely rev. I wasn't far from home and managed to crawled it home.

After a couple of hours I went back out, disconnected the battery and crossed the positive to the negative to drain any power in the modules. I restarted the Jeep, drove around the block and it has been fine for the last couple of months.

The symptoms to me were much like fuel starvation...backfires through intake and exhaust, wouldn't rev, stumbling on idle and even near stalling. But being I had recently put a new fuel pump unit into the tank and replaced the inline filter as it was not holding fuel pressure and was hard to start...been good ever since.

It did the same yesterday. I crawled it around a corner and turned the engine off. Being I had experienced this as above, I did the key dance and no codes at all. I restarted and it drove fine for around 7 or 8 k's then just before I got home it did it again. I did the battery thing, drove it around the block it ran fine.

This morning I drove down the road a few k's and it was ok...heading home it did it again, managed to get it home again. I put my OBD reader on it and it tells me no codes.

I replaced the TPS 20,000 k's ago as the idle was fluctuating which fixed that problem and it has been good since. I have not replaced the IAC valve as it idles fine and I can't see that being related to acceleration issues...correct me if I am wrong. I replaced the MAP sensor a few days after the last drama thinking it might be that...it seems not.

I have just ordered the two CO2 sensors for the exhaust after the cats thinking it may be a bad sensor telling the PCM that it is over fueling and may be cutting back on fuel...

The engine has only done 140,000 kms, around 87,000 miles. Does anybody have any ideas?
Cheers

Deanwjgrandcherokee

I have been thinking...I replaced the in tank fuel pump module only 5 months ago with an aftermarket unit. Previously the fuel system wasn't holding pressure and it would take long cranks to start and then it would stumble until it got pressure up, often triggering the check engine light with a cylinder misfire.

When I turn the ignition on since I can hear the pump pressurize the fuel system and it starts fine. I have read in some threads where a new fuel pump has failed in a short time...5 months and 5,000 k's is a very short time! But after market stuff can be a bit hit and miss I am led to believe. It is a lot cheaper than genuine but often for a reason.

What i am thinking as the stumbling and backfiring does sound suspiciously like a lean engine...could the fuel pump be spasmodically failing and losing fuel line pressure? If I turn the engine off it starts just fine again as the fuel pressure would possibly have built up on the restart...then yesterday the engine it was sputtering and failing over and over.

I may have answered my own question, but has anybody experienced similar?

Thanks

Deanwjgrandcherokee

OK...it was the fuel pump module. Though I replaced the fuel pump a few thousand k's ago it decided to work intermittently. Would be fine for a while then falter. It just cost me a fortune as I took it to a dealer to put it on their machine. They found nothing that i didn't already know, the battery died while they had it and they put in a new fuel pump module...at Jeep prices!