I get P0300 Random/Multiple Cylinder Misfire Detected...... - North American Grand Cherokee Association

Steven · 08-28-2002, 07:00 AM

WHen I runs the ODB-II. What would cause this? Bad gas?

Mrfreeze5 · 08-28-2002, 09:01 AM

I got that problem when I installed new plug wires. One of the wires did not seat properly on the plug and the spark was arcing and melted the boot. A new plug wire solved it though.

SKEETER · 08-29-2002, 06:22 PM

From memory I believe the code breaks down like this:
P=PCM computer reporting problem
0=Generic OBDII code available to all scanners (not chrysler specific)
3=Ignition system fault
0=misfire
0=multiple cyls. are misfiring (if it was a 1 then it would be cyl one, etc)

Basically it means that the computer detects that you have at least 2 different cyls misfiring to the point to set the check engine. A higher end scanner (Genysis, SnapOn, etc) will allow you to go into the misfire counter and see which cyls are missing.

Causes can be bad plugs, wires, cap, clogged fuel injectors, water in the gas, crank or cam sensor. The computer looks for certain "pulse" pattern from the crank sensor to coincide with the lighting of the combustion chamber. When a cyl doesn't fire and produce power it causes the engine to momentarily stop causing a long "pulse" as compared to the properly firing cyls. Notice that I said when the cyl does fire & produce power. So the plugs might be sparking away but with a clogged fuel inj(s) there is still no power hence a skip or misfire.

Hope this helps.

Mrfreeze5 · 08-30-2002, 11:56 AM

Mine reported multiple cylinder misire when only the #4 cylinder wasn't firing.

SKEETER · 08-30-2002, 12:42 PM

Well no system is perfect, but the multiple cyl misfire is set when the computer system detects more than one cyl missing. I have scanned my own vehicles and have had several cyls missing without even setting a code or being able to feel it. Like I mentioned, the system isn't perfect or fool proof but technically that is what SHOULD

have happened.

08-28-2002, 07:00 AM	#1
Steven Member Grand Rookie Join Date: Aug 2002 Posts: 43	I get P0300 Random/Multiple Cylinder Misfire Detected...... WHen I runs the ODB-II. What would cause this? Bad gas?

08-28-2002, 09:01 AM	#2
Mrfreeze5 Senior Member Grand Master Join Date: Jun 2002 Location: Denver, Co Posts: 1,093	I got that problem when I installed new plug wires. One of the wires did not seat properly on the plug and the spark was arcing and melted the boot. A new plug wire solved it though. __________________ 96 GC Laredo

08-29-2002, 06:22 PM	#3
SKEETER Senior Member Grand Junkie Join Date: Mar 2002 Location: Southern, Maine Posts: 234	From memory I believe the code breaks down like this: P=PCM computer reporting problem 0=Generic OBDII code available to all scanners (not chrysler specific) 3=Ignition system fault 0=misfire 0=multiple cyls. are misfiring (if it was a 1 then it would be cyl one, etc) Basically it means that the computer detects that you have at least 2 different cyls misfiring to the point to set the check engine. A higher end scanner (Genysis, SnapOn, etc) will allow you to go into the misfire counter and see which cyls are missing. Causes can be bad plugs, wires, cap, clogged fuel injectors, water in the gas, crank or cam sensor. The computer looks for certain "pulse" pattern from the crank sensor to coincide with the lighting of the combustion chamber. When a cyl doesn't fire and produce power it causes the engine to momentarily stop causing a long "pulse" as compared to the properly firing cyls. Notice that I said when the cyl does fire & produce power. So the plugs might be sparking away but with a clogged fuel inj(s) there is still no power hence a skip or misfire. Hope this helps. __________________ ASE Master Tech/L1 99 WJ limited v8 4" Teraflex, 265 Trxus, 247 to 242j hd swap 90 YJ vortec 4.3 on 33's 94 ZJ limited v8 -sold 89 XJ lifted w/chevy 350...SOLD http://community.webshots.com/user/extremeoffroad

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08-30-2002, 11:56 AM	#4
Mrfreeze5 Senior Member Grand Master Join Date: Jun 2002 Location: Denver, Co Posts: 1,093	Mine reported multiple cylinder misire when only the #4 cylinder wasn't firing. __________________ 96 GC Laredo

08-30-2002, 12:42 PM	#5
SKEETER Senior Member Grand Junkie Join Date: Mar 2002 Location: Southern, Maine Posts: 234	Well no system is perfect, but the multiple cyl misfire is set when the computer system detects more than one cyl missing. I have scanned my own vehicles and have had several cyls missing without even setting a code or being able to feel it. Like I mentioned, the system isn't perfect or fool proof but technically that is what SHOULD have happened.

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