Hi
2007 jeep liberty sport v6 3.7L 4x4 automatic
I'm chasing down a difficult P0300 code with CEL flashing but it only happens when coasting downhill over 50+ mph. I've checked and tested and replaced dozens of things in the process. I also am now getting random long recently might be related starts. P0300 just started happening on way home on long trip.
Freeze frame data , nothing looks odd other then 400rpm which is probably normal in that situation
Idle isn't as smooth as it should but not that bad, usually within hovers at 600rpm +- 30
Misfire counts
I notice a pattern where misfires are spread across all cylinders but bank 1 cylinders 1,3,5 are the worst, sometimes 2-10x worse on that side. And #6 cylinder always has least amount of misfires maybe a handful where #1, 5 can have 100+
AFter fuel pump change, the misfire count pattern is different now it seems more even across banks and cylinders???
Tested and replaced
Fuel system
Weak choppy waveform fuel pump replaced that had poor leakdown results. Now Fuel pressure is 59psi running. Leakdown holds indefinitely at 55psi now w new pump without dropping. Tank is clean, condition of canister unknown. Evap Purge valve was swapped no change in issue
** today test drive after replacing pump the problem returned downhill but I tried reproducing it again like 6 times and it's not doing it where it did it evert time w the old pump. I did reset pcm when replacing pump as I had battery disconnected and so its still Relearning I think while testing. Emissions ready status was incomplete so maybe my issue is fixed and pcm is still recalibrating, so I thought, I stopped on way home at grocery store I got home and saw the P0300 was pending again
injectors w new, oems were leaking and worn out giving high neg fuel trims, replaced w new bosch injectors long term trims are both now around 5% vs -15%
Only use gas from top tier station 87octane
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Ignition
Tested spark strength
Tested waveforms for primary and secondary
Replaced plugs w oem
New coil packs
*** only thing my untrained eye noticed w the secondary ignition is that the burn line is jumping up and down every 2-5 seconds and even looks to drop out but could be my scope or an issue w triggering. I uploaded video clip of the waveform sp you can see what I'm talking about
Video of secondary ignition waveform
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Timing
Replaced cam and crank sensor
Tested cam crank correlation waveform looked good compared to known good
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Sensors Tested and replaced
All 02 sensors Replaced
Map sensor is only year old and live data looks correct, checked w vaccum guage on intake too No issue I could see map matches load changes
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Engine breathing
Smoke leak Tested intake and exhaust system
Checked catalytic converter is good
Zero exhaust back pressure
New air filter
Cleaned throttle body and plate
*Tested cleaned egr valve, I did find leak coming out pintle vent hole and plugged that, even though it seems to be part of its design? no change, but mine and salvage yard one both leak outside air from pintle shaft seal through vent hole, I think it's designed to leak there a little?
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System voltage good 14.2v
Battery load test good
Grounds
Block and body Grounds all good no voltage drop
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Mechanical
Compression test looks all within spec
Cylinder Leakdown test, I've checked some with bad leaking harbor freight tool but seemed ok, retesting today w better tool
Evap purge valve seems fine
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PCM
Only odd thing I'm noticing is that it doesn't go into open loop drive deceleration mode ever unless I turn off overdrive by hitting shifter button. I'm assuming deceleration mode in pcm only works with overdrive off by design, but there's no detailed pcm operation information anywhere I can find. Service manual is vague, and I don't know anyone with a Jeep liberty I can compare to.
Also I rarely see scanner show me going into open loop drive deceleration mode w overdrive on, but occasionally it does for no reason. It happen today for a few seconds going 50mph onnflat stretch and my first thought was oh crap something is wrong w new fuel pump as i felt it engine brake and not coasting off the pedal. Normally it only does it w overdrive off, but I tried for an hour test drive to get it to do it again trying various speed changes etc and wouldn't do it, even on 2 mile downhill where I can almost also get the misfires and flashing cel and p0300 to set, usually takes me coasting a while before it happens like not till the final stretch of hill by right before it transitions to flat so that could be 1 minute of coasting at 60mpg no throttle in closed loop w overdrive on.
If I coast downhill w overdrive off its in deceleration mode i get no misfires when i tried it.
