2003 Jeep Liberty- Random Misfire Troubleshooting Help Neede

JkolKJ · **Joined:** Tue Apr 01, 2014 4:45 pm **Posts:** 5

Hello Jeepsters,

We have recently aquired a 2003 Jeep Liberty 3.7 4x4 Sport. We bought the rig knowing it had a P0300 Code issue. Having own another one--and still do-- we thought we could figure it out. The Jeep has 174,000

Issue:

The jeep's motor runs absolutely flawless, yet it'll through the Error Code: P0300, P0301, PO302, PO303, PO303, PO304, PO305, and PO306. Which for those who don't know means a random misfire is detected in all 6 cylinders. Once this is detected it goes into "Limp-Mode", and to clear this issue you can simply turn off the ignition and turn it back on and it'll run flawlessly again.

Occurrence:

The Limp Mode comes sporadically, though once it begins the CEL flashes for awhile then goes in. This could happen every mile, or go 60+ miles in between. Just depends on what outlying factors are influencing it. What I found is that if you "Rev" the engine one the CEL is flashing you can prevent it from going into Limp Mode. Also, if you stay above 2200 RPMS the CEL normally won't flash. CEL Flash comes right around 55 MPH, then if you go above 65MPH it's typically not an issue. Limp Mode immediately follows after any sort of load due to incline.

We tested Fuel Pressure, and Cylinder Compression and all are up to Factory Spec. So There is no issue there.

Issues we thought caused the Limp Mode and fixed:

Fuel Filter
Fuel Pump
Battery
Injectors
Plugs
Replaced all Coils
Previous owner stated that it overheated and they replaced the head gasket. We took the heads off to have them rebuilt.
Replaced all O2 Sensors
Replaced Cam Shaft Position Sensor
Removed Catalytic Converter (Not Required to have in my State)
Replaced Evap Module
Replaced Evap Canister on Tank as well
Replaced all Vacuum Lines, and their respective Connections
Replaced Air Filter with K&N Air Filter
Flushed all Fluids
Decarboned the Top End
Adjusted the Timing (Checked the Three Chains, all three were Okay)
Adjusted the Shift Linkage, and currently the Transmission is being looked at. Currently in the shop with these guys, but last I checked there was no issue.
Replaced Gas Cap
Checked ECU with a donor. Numbers matched, and issue still occured with new ECU.
Checked all electrical Connections for a possible short.
Checked and cleaned up all ground connections.

Note: All Sensors are Mopar, because we heard sometimes aftermarket ones cause issues.

I've spent hours upon hours researching possible reasons, and have tried almost all of them. Seeing how we've spent Several Thousands of dollars trying to troubleshoot this issue we are a bit lost. Could there anything that we've missed that could cause a similar issue?

We greatly appreciate any input you guys might have in solving this issue.

Keep On Jeep'n!

pshivers · **Posted:** Sat Jul 12, 2014 3:28 pm

My first thought was the crank position sensor, but you said the engine is running flawlessly. I would imagine that if the signal was bad, it would cause the engine to stumble as well. I've got an 08 KK manual at home (out camping right now). I'm curious as to what computer / input reports the misfire. I thought it was the cps to the ecu? Running at a higher rpm would change the signal thus preventing limp mode. Curious?!?

jimymc · **Joined:** Thu Dec 17, 2009 7:51 pm **Posts:** 248

I have a similar problem with my '03 Liberty. The only time it does it is when l am on a downhill grade that is pretty steep and I let off the gas to help it slow down. I have gone through some of the same things you have done to no avail. I did replace the vacuum check valve for the heating system and this seemed to fix it for awhile. It is located on the firewall behind the glove box. You have to pull the glove box down and push in on the sides to get at it. You can remove it and blow through both sides to see if it is good. Air should only pass one way. Make a note of which way it was in so you can get it back right. It's worth a try. A parts guy at the dealership said they had a problem with these in one of their other vehicles except it would sputter going uphill.

Bubba Fett · **Posted:** Mon Jul 14, 2014 10:13 am

Could be a simple coil pack issue.

JkolKJ · **Joined:** Tue Apr 01, 2014 4:45 pm **Posts:** 5

pshivers wrote:

My first thought was the crank position sensor, but you said the engine is running flawlessly. I would imagine that if the signal was bad, it would cause the engine to stumble as well. I've got an 08 KK manual at home (out camping right now). I'm curious as to what computer / input reports the misfire. I thought it was the cps to the ecu? Running at a higher rpm would change the signal thus preventing limp mode. Curious?!?

We thought it was a CPS as well, and we replaced that sensor accordingly.

JkolKJ · **Joined:** Tue Apr 01, 2014 4:45 pm **Posts:** 5

jimymc wrote:

I have a similar problem with my '03 Liberty. The only time it does it is when l am on a downhill grade that is pretty steep and I let off the gas to help it slow down. I have gone through some of the same things you have done to no avail. I did replace the vacuum check valve for the heating system and this seemed to fix it for awhile. It is located on the firewall behind the glove box. You have to pull the glove box down and push in on the sides to get at it. You can remove it and blow through both sides to see if it is good. Air should only pass one way. Make a note of which way it was in so you can get it back right. It's worth a try. A parts guy at the dealership said they had a problem with these in one of their other vehicles except it would sputter going uphill.

Interesting, perhaps once we get it back from the shop again we'll try that.

JkolKJ · **Joined:** Tue Apr 01, 2014 4:45 pm **Posts:** 5

Update:

Transmission specialist determined nothing was actually wrong with the Transmission. All internals where up to spec. Shift linkage was out a little, that was fixed. However, problem still exists.

My only rational explanation is that there must be a wire shorting out periodically. The Jeep performs as you'd expect until the CEL flashes. (Just throws the code mentioned above.)

Anyone have any further suggestions?

As I learn more, I'll keep you guys updated. This P0300 Troubleshooting is an expensive endeavor in which I hope I can provide insight to others with the same issue.

Half tempted to just replace the whole powertrain with a 3.0 Turbo Diesel out of Dodge Sprinter, or the Mercedes counterpart. Anyone know if this will fit?

JeepinJarhead03 · **Posted:** Wed Jul 16, 2014 6:13 am

the coil pack wiring is dinky as heck and where the wires mate to the plug that plugs into the coil pack is more prone to being damaged / cracked internal wiring next to the plug to the coil pack the older the orig. engine was when the headwork was done

in a way, it sounds like theres circumstances where the wires around the intake have had a chance to absorb enough heat from the engine for the crappy covering on the wires to soften up enough to allow the internal wire fault to "break" creating an open momentarily during vibration

or, during an overheat they got enough melt to partially fuse the wires between the ECM (source of spark signal) and the plugs to the coil packs

I personally, would replace coil pack wiring from ECM to the Coil Packs including new connectors

I doubt you'd be able to force it to fault out by jiggling or tugging them at an idle but you may after getting them good and warm, they are 11 year old small gauge wires afterall! at the least very meticulously inspect that wiring end to end - I had to replace part of mine as it had rubbed on the injector rail

I know you said you checked all the wiring for a possible short but the short simply may be playing opossum or it may be something as simple as a hairline break in the internal wire - the wiring at the firewall grommet and the wiring at the coilpacks themselves and the adjacent bends would be the first two places I'd look

do they make hand held wiring X rays for mechanics yet? lol thats something I wish I had occasionally years ago

2003 Jeep Liberty- Random Misfire Troubleshooting Help Neede

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