I have a 2013 Grand Cherokee MDS 5.7 Hemi v8. Started acting up in July 2022 on a long trip home from JAX to ATL. Felt like a cat was trapped in the wheel well at cruising speed …. Misfires (only on Cyl 6) have been increasing since then. I drove on 30-60% misfire rate (calculated using my odb stats) for short distances and to get repair estimates. I have managing catalyst temp while driving (avg 1400-1600), lots of coasting and slow driving keeps it below 1600. Passed emissions in Oct 5 min after drive cycle completion! Then CEL came back on 2 blocks from the emissions shop! Wow, miracles do happen!
Initial diag: Bad lifter on #6, likely needs a cam as well (based on lifter movement and misfire on #6), three dealers and two mom and pop mechanics all have the same diag, but none of them want to repair it at 170,000 miles. All said need a deep dive into the upper to do a proper diag and est. 2022 cost $210, a few dozen phone calls, and lots of great dinner dates in front of youtube with the SO (she loves the tech too!).
Jan 2023: Got the car back from the dealer deep dive ($550) and now at 100% misfires on cyl 6 and fuel injector fault on #6. The dealer ran a new wire from #6 coil to the computer box, not sure why, wants to do more diag but warned more cost to do it. Not doing it.
Diag from the dealer deep dive: Likely worn cam on #6, no metal detected in oil control valve, needs lifters and maybe more in the upper. #6 has a hot spot and walls are scored, but it holds compression and passes leak down. Recommended new engine, $12k installed, sub-par warranty. Mom and pop shop nearby will do it for $9k good warranty, both are 3rd party refurb long block.
Feb 2023: I have disconnected the # coil and fuel injector, so now a V7. It runs well, has power, and only shakes at idle (600-900 rpm) and when loaded (hill climbing). Cat temp averages 1200-1400 deg. Emissions due in Nov. The car itself and everything else is in excellent shape. I have added about 1500 miles since July 2022. I call her “thumper” and use manual shifting to keep rpms at 1500ish.
I plan to run normal driving now and replace the engine this summer, if $10k repair will get me 30k miles on the car, I will be thrilled.
Questions for the group:
My idle is at 600-800 rpm, shakes enough to mix a martini. If I throttle to 1200-1500 it smooths considerably. I am not sure how to up the idle, or the consequence, suggestions?
Do I really need a lower if #6 holds compression and leak down, but has scoring and hot spot? Is it really a high risk on #6 going south if I just do the lifters on one side? What have you seen? $3-4k for only the upper lifter/cam and I am back on the road. Thoughts?
I just wonder if it would be beneficial to disable what would be the “companion” to the dead slug in an effort balance it out better. Yes, down another cylinder but not shaking itself to death either…
Has the OP considered what the ongoing misfires have done to his catalytic converter?
IMHO, repairing/replacing the engine sooner than this summer would be cheaper in the long run.
It is also necessary to remove the cylinder heads to replace the lifters. That’s why so many shops want to remove the engine assy instead of repairing in car.
I was recently talking to a buddy who sold a Hemi truck running on 7 cylinders. It was something with the lifters or cam so maybe the same exact issue. His had like 200,000 miles or so. With used car prices high, someone made him an offer he couldn’t refuse for a broken truck and he took it.
At the least, remove the electrical connector for the fuel injector so it won’t spew fuel into a non-firing cylinder. The suggestion to pull another injector to balance the problem out might help but will put you down another cylinder on power of course. This is how GM does their cylinder deactivation to save fuel. See the firing order and how they do it because they take two cylinders out at a time to keep things balanced. If the firing order is the same as GM, just pull that connector to the opposing cylinder. I also think GM keeps valves closed on deactivated cylinders which you won’t really be able to do. This creates a cushion of compressed air in the cylinder and reduces losses through the valves/valvetrain.
The cylinder has likely suffered washdown from raw fuel diluting the oil. The catalytic converter may or may not be toast but keeping that unburned fuel out of the engine will definitely help with that. Without the engine running right, you will probably have all kinds of codes that might or might not be related to a different problem.
I assume the check engine light was likely FLASHING due to this problem. That isn’t as bad as having a low oil or overheating indicator but a sign something is malfunctioning in a serious way that could damage the engine, converter, or other. A solid light means there is a problem but not one that could potentially destroy the engine rather quickly.
I understand the cat damage risk. One of many considerations. I have read a lot about this one. Although not definitive, the consensus was below 1600 deg should be considered normal one the “newer” cars. Yea, I call 2013 newer. My monitoring via obd while driving was well below that 95%. A few spikes here and there. How do you test for a bad cat?
Cwatkin, I appreciate the feedback.
I had not really considered the washdown factor. Maybe I will do an oil change now that excess fuel is mitigated? I will be testing the v6 approach asap. obd codes lit up like a Christmas tree when I pulled fuel and spark from #6. Using an old Android with CarScannerPro and a VEEPEAK adapter for $30. I created a custom dashboard … seems to work well for monitoring the cat temp.
GM used to build V6 engines that were created by chopping 2 cylinders off a V8. A Chevy and a Buick.
FWIW, I owned (built and raced) one of those engines in the early 80s. It was lumpy at idle. Smoother at speed, but still lumpy. They built them for 2-3 years like that and fixed it with an offset crank in 1977 or 78. Better but still a little lumpy. They made it very smooth in the 90s with a balance shaft.
Thanks Tester,
I had seen that one before, great writeup. Some great stories in the comments too. My favorite is “going back to a chevy”. I got 270k on my 02 Tahoe! A bit pricey today.
I just watched a video the other day on facebook that showed a Landrover/Jaguar engine that was like that. Admittedly, I have no idea if it is true on not- no personal experience here.
Looks simple enough. Thanks!