'05 Grand Cherokee 5.7L hemi backfores (Page 1/1)
n7vrz JUN 16, 04:46 PM
My Jeep Grand Cherokee Limited w/5.7 Hemi engine backfires. The popping sounds are loud enough to be heard but not a BANG!!!! Sometimes it is just a soft pop or two but can also sometimes sound like a 4th of July fireworks show.
It only happens when driving after the engine and cats are warmed up. But not while accelerating. Happens more often during a decel but will also happen at steady state driving.
My mechanic and I went for a drive so he could hear it. He agrees it is coming from the exhaust and not something banging around.
Just rev--ing the engine to hwy rpm's while parked gets no popping. In gear to simulate driving load with foot on the brake gets nothing. The mechanic put it on his lift, in gear and at hwy rpm's and again, nothing. Drive it down the road and it pops.
New plugs, wires, cats. Had some head work done a month ago but it was popping before that too. I mention the head work so gasket leaks are an unlikely thing.
No check engine light, no codes stored either.
I have new O2 sensors on the way. When they are installed I'm going to put the ECM into learn mode and go for a drive.
I doubt that will do anything but hope that it will. I'm getting desperate.
Run this by your mechanic friends and see what they think. I'll take all suggestions under consideration.
I don't want to just throw parts at it but I'm getting to that point.

EDIT: For those that don't know, this engine has the MDS (Multiple Displacement System). So 4 of the cylinders shutdown during cruise. When they shutdown the valves don't cycle and the injectors don't fire.

[This message has been edited by n7vrz (edited 06-16-2015).]

GreenPlatypus JUL 05, 06:17 PM
How long has it been doing it, since before you've had it or has it recently appeared? Honestly run it through a dealer, there is a huge number of software updates on the Hemi's it is ridiculous. Also, while I am thinking, it could just be "normal" for the truck. My Mini Cooper and couple of my other cars do this on deceleration/overrun; my old super charged Range Rover did it as well. The un-burned fuel igniting in the catalytic converter giving it a popping/backfire sound, not really good for the exhaust. In the case of my Mini, it actually has programming in the ECM to do it. I've driven a few Jeep SRT8's that do this as well. Gets annoying after awhile...

carnut122 JUL 07, 02:46 PM
If it has an air pump(which I doubt), it could be the anti-backfire valve. If not, it could be an exhaust leak.