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05 Grand Cherokee Li
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Discussion Starter · #1 ·
Hello, Jeople. I recently bought an 05 Grand Cherokee Limited 2WD w/4.7 V8 and have pretty much been throwing parts at it for 3 weeks now. It's been giving me the P0300 since day 1 and about a week ago started the stalling out. To date I've replaced; EGR valve, 8 plugs, 8 coilpacks, crankshaft position sensor, 4 injectors (found cracks in inj body)

It's had a cylinder combustion chamber cleaner performed by shop. Cylinder cutout test that revealed nothing.
Compression test; all checked within spec of each other.
Exhaust shop checked cats and said they're in good shape. Replaced Muffler due to dent.
Fixed small vac leak at throttle body/manifold inlet
2 tanks of seafoam and 1/3 ran through brake boost line.
TPS tested ok
Cleaned IAC but unsure of test proedure.

Newest revelation during latest test drive: where it's normally likely to stall out in traffic (sitting at a red lamp) I changed the mode selector on the A/C from feet to blend and just after I heard whatever actuators behind the dash moving, the jeep idle fell just before stalling and then the vehicle
lurched a bit forward and idled up substantially until it regulated. I was able to duplicate that process many many times whilst on the test drive. Phew! Sorry for the lengthy post. Any help is much appreciated.
 

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05 Grand Cherokee Li
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Discussion Starter · #2 ·
So after having the new muffler installed yesterday and a few successful errands afterwards the P0300 CEL went off on its own. I'm at a loss on that one. I'll wait until it rears it's head again... if it's going to.
Stalling still happening tho. What would changing the A/C mode selector have to do with making it idle low and die? Seems directly related. I can make it happen at will. PLEASE HELP!!
 

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Discussion Starter · #3 ·
Had the jeep back at the shop today for fuel psi test and vacuum test.

Fuel psi was 59lbs at idle
Vacuum gauge read 17.5 in/hg pretty consistantly.

Pretty convinced IAC is the culprit. Installed new IAC
Same issues, stalling out at idle especially when using A/C and mode selector.

I'd appreciate any type of feedback to help me at least brainstorm.
 

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05 Grand Cherokee Li
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Discussion Starter · #4 ·
P0300 just returned. This time with P0123 TP Circuit high voltage. Thoughts?
 

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Do you have a scanner to read fuel trims and O2 voltages?
Throttle position sensor?
 

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05 Grand Cherokee Li
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Discussion Starter · #6 ·
Do you have a scanner to read fuel trims and O2 voltages?
Throttle position sensor?
I sat for about 2 hours today with a scanner hooked up and didn't see anything that raised a red flag.
O2, if I remember right it was constantly toggling between 2.6 and 3.2
Unsure of fuel trims (very unfamiliar with the scanner)
I'm trying to rule out the TPS but can't seem to find a pinout for the PCM.
I have a constant 5V to TPS, unplug TPS and jump signal wire to ground pin and I get 4.7 volts. That should go to near 0v, if I'm not mistaken? :confused:
 

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The beast from Brazil
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Normal O2 values is between 0.2 and 0.8 V, never over 1.0 V.
The fuel trims are shown as STFT (short term fuel trim) and LTFT (long term fuel trim). The fuel trim figure should be below +-10% during steady operation. You should add or subtract the STFT with the LTFT to get the final figure.
( so if STFT = +4 and LTFT = +3, the total trim is +7%)
I don´t know on the WK, but on the WJ I like to compare the fault codes from the scanner with the ones given using the key dance. On the WJ, depending on the scanner, it can give quite different codes then the keydance gives (ignition switch OFF-RUN three times and leave in RUN at the third time. The odometer will show "DONE" when no faults, or each fault at a time)
 
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05 Grand Cherokee Li
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Discussion Starter · #8 ·
Thanks. I was going off memory from earlier today on the O2 value so it could have been .26 - .32? I'll recheck in a day or so when I can access the scanner again. Thanks for the info on STFT/LTFT!

I did notice that several times I've gotten 1 or 2 codes on the DTC report and then something additional with the scanner. Scanner definitely seems more informative.
 

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Discussion Starter · #9 ·
Unhooked battery and uninstalled PCM approx 5:30PM yesterday. Inspected PCM case and connections on bench and didn't see anything obvious. Removed cover screws and attempted to lift cover off of PCM gently but it appears to be completely encased in epoxy inside. Went ahead and cleaned what I could, connectors etc and kept everything unhooked and uninstalled for 24hrs. First trip today was great. I stopped off somewhere and when I restarted the jeep to leave it threw a CEL, P0300 only on DTC.

Should I start accepting that the PCM is intermittently failing? Or does anyone have another suggestion for troubleshooting I can try?

Again, any help is soooo appreciated. Thanks, everyone!
 

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The beast from Brazil
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Does the engine run rough, which would be an indication for the misfires?
It could be a PCM problem, but also other things. The fuel trim is an important value to start with. Due to a faulty O2 sensor, the fuel can be down trimmed that much, that misfires occurs.
But also a problem with the MAP sensor or even an inlet temp sensor could be the problem, so I would check those sensor readings as well. The MAP for example you can compare with the ambient pressure when the ignition is in run, but the engine off.
Do you still see the idle spiking when messing with the AC? Is switching the AC compressor on/off doing anything?
 

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Discussion Starter · #11 ·
Yes, it runs rough at idle once the CEL is on. Also, it's back to feeling a hesitation when you start to lug it a bit. For example, cruising at 45 and attempt to accelerate but not aggressive enough for the trans to downshift I feel stutters/misfires. That's great info on the newly mentioned sensors. I'll try to test them first thing in the morning and update.

The A/C thing is still happening. Although, it will stall without the A/C too but very rare.
 

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Discussion Starter · #12 ·
Just to keep the topic updated:
Jeep dealer has the jeep for the 3rd day. Nothing so far. Stay tuned!
 

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Discussion Starter · #13 ·
Dealer kept jeep for 8 or so days. Recommended PCM but unsure if it'll fix so more diag may be necessary afterwards . 1,800.00 parts and labor.
 

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Discussion Starter · #14 ·
So, installed a replacement PCM from carcomputerexchange and my jeep is having the same issues. P0300 and misc lean bank 1 and 2 codes.

I could really use some advice or suggestions on what to do next so any feedback is appreciated! TIA
 

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Discussion Starter · #16 ·
O2 voltages seem ok.
.2 - .8v min/max
Fluctuates between that range. Front 2 sensors are way more actively calibrating. Rear sensors calibrate but stay steady more. (During spirited driving seen .9)

Below is a screenshot of the fuel trims
And a pretty good summary of what it looks like most of the time. Bank 1 LTFT hit max -25% once but I don't have a CEL currently.
 

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Did you ever sort this out?

I'm currently dealing with a similar issue on my 07 wk with 202k miles.

To date, I have replaced all the spark plugs twice (once under warranty), fuel injector service, replaced the number 7 coil pack, replaced the servo valve for the cruise control (I may have the nomenclature incorrect), serviced transmission and filter (transmission lost prime), and I'm currently waiting on a cruise control switch.

I have received a p0300, p0188, and a p0582 code.

The car has stalled out once within the last 2 weeks and the rough idle kills the cruise control completely until i restart the vehicle.

Received the car back today and it's better but there is still slight rough idle.
 

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Discussion Starter · #18 ·
Did you ever sort this out?

I'm currently dealing with a similar issue on my 07 wk with 202k miles.

To date, I have replaced all the spark plugs twice (once under warranty), fuel injector service, replaced the number 7 coil pack, replaced the servo valve for the cruise control (I may have the nomenclature incorrect), serviced transmission and filter (transmission lost prime), and I'm currently waiting on a cruise control switch.

I have received a p0300, p0188, and a p0582 code.

The car has stalled out once within the last 2 weeks and the rough idle kills the cruise control completely until i restart the vehicle.

Received the car back today and it's better but there is still slight rough idle.
Yes, I finally have a reliable vehicle again. I should have updated thread immediately, so sorry for that. I finally found that the dealer put the wrong spark plug in the initial problem cylinder and just by pure chance I suppose Autozone sold me an entire set of 8 of that same wrong plug. After installing a PCM and still having those issues I pulled the plugs for the 3rd time to quadruple check the gap and p/n, that's when I realized the V6 non-copper core plugs. Simultaneously it must have fried the Crank sensor because it would run great til it warmed up and started relying on sensor data and then ran terrible. Swapped the old crank sensor back in (1 of the many things I had already changed. I saved old parts though just for that reason) and has been running perfectly since.

Purchasing a Bluetooth OBDII scanner was the smartest thing I did because it helped me watch the sensor values in real time and I actually found some other non-related issues during the process. Hope this info helps because I know how you're feeling. Stay persistent!
 
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