Yup, my Grand Cherokee is backfiring. But only after it is warmed up and I have to be driving down the road. Doesn't do it while idling, parked, at stop signs/lights or accelerating. It does do it while driving part throttle or decelerating.
New plugs/wires, had my mech deck for vacuum leaks, still backfires.
Sometimes it is just a pop or two but other times it sounds like the 4th of July.
I "picked the brains" of a Chrysler/Jeep/Dodge service rep and mechanic and the consensus is that it is either an MDS issue, timing issue or some combo of both.
I've ordered a software package that will log various parameters to show me what's going on with the timing. But until that gets here I'm open to suggestions on how to determine if the MDS is the issue.
As far as I know there is no way to mechanically disable it. Am I wrong on that? If so, how would I do it?
The mechanic said that using the select shift or going to tow mode only disables MDS electrically. So if there is something going on with it then it will still happen.
The Jeep starts, idles, accelerates, etc. just like it should with no hesitations, hiccups, burps, or anything strange. Just backfires.

 

dedgar,

Have you considered allowing your Jeep dealer to inspect further and determine the nature of the issue?
Your Grand Cherokee could be equipped with a monitoring device in order to capture real time faults.
That data would be analyzed by the technicians and a solution would be outlined.
All the best!

 

It could very well be an MDS issue. If it sets a specific misfire code for a cylinder, it may be easier to find it.


If you have any MDS work done, do ALL of the lifter and ALL of the solenoids and also the short harness that attaches to the solenoids.


Get a real diagnosis done first before you have a detonation and damage your engine.

 

I thought I had put this in the first post but it looks like I forgot it> no codes of any kind.
I want to narrow this down as much as possible before I take it to the dealer. Their time is $$$$$$$$$.
And I have $.

 

My dealer doesn't have that. I'd have to drive a tech around while he does live scans. And of course I would have to pay for his time.
Another reason to try to do as much as I can prior to giving it to the dealer.

 

dedgar,

I understand.
Hopefully the issue becomes apparent and you can get it resolved.

 

A crank sensor could do this.


Any PCM codes at all?

 

That was my first thought also, but a faulty crank sensor should throw a code...

 

If they short, it sometimes kills the memory and the code's not there. For his wallet's sake, I hope the code went stored.

 

Installed ScanTool OBDLink SX USB on my laptop and took the WK for a drive yesterday. Got it warmed up nicely and then started the software.
After running down the road for a few miles I stopped and took a look at the laptop.
It is showing 2 codes: P0153 and P0404
P0153- 2/1 Sensor Slow Response - Oxygen sensor response slower than minimum required switching frequency.
P0404 - EGR Position Sensor Rationality - EGR position sensor signal does not correlate to EGR duty cycle.
Why these are not showing in the PCM and no check engine light is making me wonder about the PCM.
I already have O2 sensors on hand and will be changing them today on a friends lift. I replaced the EGR yesterday after I got home and let it cool down.
Next problem (?), why didn't those codes trip the check engine light and set a code in the Jeep's computer?