UPDATE!!!!!! P0300 WONT STOP...GOING BACK TO THE DEALER!!!!!

Jeep Dawg · **Posted:** Fri Jul 03, 2009 12:28 pm

Ok REAL LONG STORY SHORT with repair details.....

Few months ago I got a P0300 misfire code. replaced pluge. went away. a few weeks later P0300 06 and 05 flashed. Checked coil packs. Moved 1 and 2 coil over to 5 and 6. Same misfire code 5 and 6. Checked injectors with tester. OK. Checked for plug gap and was ok. Checked for broken or loose wires. OK. CEL now flashes on a decline and gives P0300. PCM tested OK.
Once in a while when I come off of a decline the CEL would flash and the engin will loose almost all power. I shut it off and turn it back on and it will work for a few weeks untill it does it again....

I know i have read other people in last last few weeks were starting to have this same problem. Who has figured it out yet?

I have over 140K on the engin. first issue like this. What have others done at this point?

Could it be the MAP sensor behind the A/C compressor?

Edvalencia · **Posted:** Fri Jul 03, 2009 12:52 pm

I posted this before and I don't really know how it all correlates, but I was having the exact same problem.
What I found:

I had flushed the radiator and used regular green stuff instead of Zerex. Shortly after, I started having the P0300 problems. I tried everything, but could not get the problem to go away. When I found out that I should be using Zerex, I flushed the cooling system and refilled it with the proper coolant. My P0300 problem immediately disappeared and never returned.

Whether or not it's just coincidence, I don't know. I'm thinking the green stuff was somehow getting burned and setting off the code, as I was constantly having to refill the coolant. That also disappeared after switching to zerex.

Anyway, just thought I'd throw that in.

Jeep Dawg · **Posted:** Fri Jul 03, 2009 11:27 pm

Serious, that is intresting. It is worth a shot. it is either I try that or I try a gallon of tiki torch fluid (regular gass cost too much) and drop a match and tell the INS co a bolt of lightning hit it HAHA

Jeepjeepster · **Posted:** Mon Jul 06, 2009 4:36 pm

Check the compression in that cylinder.

Jeep Dawg · **Posted:** Mon Jul 06, 2009 5:50 pm

how do i check the compression in the cyc?

does any one know how much pressure the MAP sensor should have?
I checked mine and it is 9.4" hg Shouls it be more or less? I am suspecting the MAP sensor. Maybe Troy could chime in on this one

tjkj2002 · **Posted:** Mon Jul 06, 2009 7:54 pm

Jeep Dawg wrote:

how do i check the compression in the cyc?

does any one know how much pressure the MAP sensor should have?
I checked mine and it is 9.4" hg Shouls it be more or less? I am suspecting the MAP sensor. Maybe Troy could chime in on this one

That depends on your altitude what the MAP sensor reads.If the MAP sensor was bad it would effect all cylinder equally.Checking compression is way to easy,pull all the spark plugs,remove ASD relay,screw in a compression tester(found at most auto parts places or sears),crank the engine for 2-3 seconds,then read what that cylinder is reading and do the same for all 6 cylinders.Do this test once cold(all cylinders) then do another when the engine is warm.The cold cylinder psi should be 170-225psi for your 3.7 with no more then about 25% difference between the cylinders,warm test should be closer to the max spec then the cold test.If that test is showing all normal then it may be time for a cylinder leakage test,much more involved though.

Jeep Dawg · **Posted:** Mon Jul 06, 2009 9:41 pm

tjkj2002 wrote:

Jeep Dawg wrote:

how do i check the compression in the cyc?

does any one know how much pressure the MAP sensor should have?
I checked mine and it is 9.4" hg Shouls it be more or less? I am suspecting the MAP sensor. Maybe Troy could chime in on this one

That depends on your altitude what the MAP sensor reads.If the MAP sensor was bad it would effect all cylinder equally.Checking compression is way to easy,pull all the spark plugs,remove ASD relay,screw in a compression tester(found at most auto parts places or sears),crank the engine for 2-3 seconds,then read what that cylinder is reading and do the same for all 6 cylinders.Do this test once cold(all cylinders) then do another when the engine is warm.The cold cylinder psi should be 170-225psi for your 3.7 with no more then about 25% difference between the cylinders,warm test should be closer to the max spec then the cold test.If that test is showing all normal then it may be time for a cylinder leakage test,much more involved though.

tonight I got a misfire on all 6. and it ran like CRAP. turned it off and gave it a few and fired right back up with out a problem.

tjkj2002 · **Posted:** Mon Jul 06, 2009 9:59 pm

Jeep Dawg wrote:

tjkj2002 wrote:

Jeep Dawg wrote:

how do i check the compression in the cyc?

does any one know how much pressure the MAP sensor should have?
I checked mine and it is 9.4" hg Shouls it be more or less? I am suspecting the MAP sensor. Maybe Troy could chime in on this one

That depends on your altitude what the MAP sensor reads.If the MAP sensor was bad it would effect all cylinder equally.Checking compression is way to easy,pull all the spark plugs,remove ASD relay,screw in a compression tester(found at most auto parts places or sears),crank the engine for 2-3 seconds,then read what that cylinder is reading and do the same for all 6 cylinders.Do this test once cold(all cylinders) then do another when the engine is warm.The cold cylinder psi should be 170-225psi for your 3.7 with no more then about 25% difference between the cylinders,warm test should be closer to the max spec then the cold test.If that test is showing all normal then it may be time for a cylinder leakage test,much more involved though.

tonight I got a misfire on all 6. and it ran like CRAP. turned it off and gave it a few and fired right back up with out a problem.

If the MAP sensor was going out or messing up you should also get a P0105-P0109 code also.

Jeep Dawg · **Posted:** Mon Jul 06, 2009 10:19 pm

yea that was what I thought. So far I have never gotten that code. I was playing around before and it feels like my MAP is slightly loose. It was too dark to get a driver in there to adjust it.

tjkj2002 · **Posted:** Mon Jul 06, 2009 10:34 pm

Jeep Dawg wrote:

yea that was what I thought. So far I have never gotten that code. I was playing around before and it feels like my MAP is slightly loose. It was too dark to get a driver in there to adjust it.

The MAP sensor give the PCM a altitude reading to set up a basic air/fuel ratio setting which is tweaked by the O2 sensors,engine temp sensor,cam,crank sensors,TPS,and other sensors.Basically the MAP sensor is like re-jetting a carb without having to actually do any physical work.

Jeep Dawg · **Posted:** Thu Jul 09, 2009 12:42 pm

OK, I did what you said. Everything seems to be almost dead on.

I have noticed the last 2 days as I am coming down a hill, I let the KJ coast and when I start on the gass, it will spudder and almost stall.

Jeep Dawg · **Posted:** Fri Jul 10, 2009 11:23 am

I can not take it any more.
Time to bring it into the dealer.
A friend of mine let me borrow his code reader which is a very good one, but not the best and all it will tell me is the P0300 01-02-03-04-05-06

it will not sayanything else. no possiable causes or why it is showing these codes. It will say the code is being showen when engin is on a decend/roll with no throdel action.

tjkj2002 · **Posted:** Fri Jul 10, 2009 9:11 pm

Sounding like a PCM problem,right from the '03 FSM......................

Quote:

DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
PCM receives the following inputs.
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto.
trans. only)
² Vehicle speed
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply a ground to the injectors. If a hard deceleration
does not exist, the PCM will determine the
proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust
engine idle speed through the idle air control (IAC)
motor.
The PCM adjusts ignition timing by turning the
ground path to the coil on and off

Jeep Dawg · **Posted:** Fri Jul 10, 2009 10:43 pm

tjkj2002 wrote:

Sounding like a PCM problem,right from the '03 FSM......................

Quote:

DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
PCM receives the following inputs.
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto.
trans. only)
² Vehicle speed
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply a ground to the injectors. If a hard deceleration
does not exist, the PCM will determine the
proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust
engine idle speed through the idle air control (IAC)
motor.
The PCM adjusts ignition timing by turning the
ground path to the coil on and off

YES!
I just found my FSM and was reading that a few moments ago. That sounds EXACTLY what is going on with my KJ.

I gonna look at PCM prices. Do i need the dealer to re-program the PCM/flash?

tjkj2002 · **Posted:** Fri Jul 10, 2009 11:11 pm

Jeep Dawg wrote:

tjkj2002 wrote:

Sounding like a PCM problem,right from the '03 FSM......................

Quote:

DECELERATION MODE
When the engine is at operating temperature, this
is an Open Loop mode. During hard deceleration, the
PCM receives the following inputs.
² Air conditioning select signal (if equipped)
² Air conditioning request signal (if equipped)
² Battery voltage
² Engine coolant temperature sensor
² Crankshaft position sensor
² Intake manifold air temperature sensor
² Manifold absolute pressure (MAP) sensor
² Throttle position sensor (TPS)
² Camshaft position sensor signal
² Park/neutral switch (gear indicator signal—auto.
trans. only)
² Vehicle speed
If the vehicle is under hard deceleration with the
proper rpm and closed throttle conditions, the PCM
will ignore the oxygen sensor input signal. The PCM
will enter a fuel cut-off strategy in which it will not
supply a ground to the injectors. If a hard deceleration
does not exist, the PCM will determine the
proper injector pulse width and continue injection.
Based on the above inputs, the PCM will adjust
engine idle speed through the idle air control (IAC)
motor.
The PCM adjusts ignition timing by turning the
ground path to the coil on and off

YES!
I just found my FSM and was reading that a few moments ago. That sounds EXACTLY what is going on with my KJ.

I gonna look at PCM prices. Do i need the dealer to re-program the PCM/flash?

Yep

Jeep Dawg · **Posted:** Fri Jul 10, 2009 11:31 pm

probally gonna cost a few bucks.

thank you Troy for your help.
I will let you know the out come

lilblkblt04 · **Posted:** Mon Jul 13, 2009 2:29 am

I had that code and the dealership replace the engine, cats and torque converter.

Jeep Dawg · **Posted:** Mon Jul 13, 2009 3:53 pm

lilblkblt04 wrote:

I had that code and the dealership replace the engine, cats and torque converter.

I hope you were under warranty at that time.

Jeep Dawg · **Posted:** Mon Jul 13, 2009 3:56 pm

Over the weekend, I was doing some more trouble shooting with a friend of mine who is a DC tech and he was saying jeep is knowen to have moisture/water get in the computer contacts. We took it all apart and cleaned the contacts. some had a slight build up on them. After it was all cleaned, the codes went away. (I GUESS IT IS BECASUE WE DISCONNECTED THE COMPUTER) I hope that did the trick. I also noticed a little bit better power in the KJ when going up hills.

Not too sure if it will hold up, but I HOPE!

Jeep Dawg · **Posted:** Mon Jul 20, 2009 7:57 am

seems how another KJ member just had the same P0300 code and running like KRAPP over the weekend, he had a valve spring problem.....

DO I?
I have tryed everything else except gas and a match

UPDATE!!!!!! P0300 WONT STOP...GOING BACK TO THE DEALER!!!!!

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