Mechanics

MISFIRE

1996 Chevrolet Cavalier • 4 cylinder 2WD Automatic • 86,600 miles

1996 Chevy Cavalier ls misfire
error code P0300 multiple random misfire. The catalitic converter and the area around the the oxygen sensor is red after a mile, is this a symptom or the cause of the misfire?
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Gjewell
November 29, 2010.




Yes it is. It means raw fuel is being dumped into the exhaust and burning down stream. You need to get this fixed before it fouls the converter.

Most likely your coil pack is faulty. Have it tested before replacing it.

Ernest Clark
Nov 29, 2010.
I have replaced coil pack, plugs, I.C.M, and injector seals.
Could it be fuel pump regulator or fuel pump?

Tiny
Gjewell
Nov 29, 2010.
No. You are getting fuel in the cylinders, but it's not firing. You can however test the pump pressure to be sure, but then pull the plugs one at a time and see if they are being fouled by fuel. If they are, look for a leaking pressure regulator, as sometime it will introduce too much fuel into the intake and foul the plugs.

Next look for leaking injectors. This has nothing to do with the seals around the outside of the injectors. This will be an internal leak that allows fuel to go into the cylinders at the wrong time, which will then go out the exhaust valve unburned.

Ernest Clark
Nov 29, 2010.
Its random but there are usually 2 'sooty' plugs and 2 'wet' plugs. Random asto in what order.
Injectors checked o.K. While out, compression is o.K. Also.
Fuel pressure regulator is discolored.
The fuel pump can be heard but I did try without fuse and it made no difference to engine performance?

Tiny
Gjewell
Nov 29, 2010.
The fuel rail is also discolored around the base of the regulator!

Tiny
Gjewell
Nov 29, 2010.
That would be an external leak. That may also be a problem, but keep in mind, there are two kinds of misfires, ignition and lean. An excessively lean condition will cause your exhaust to overheat and glow red, but it's not as common a condition as unburned fuel entering the exhaust and being burned inside the tail pipes or causing your cats to light off.

I'm not always 100% correct, as no one is perfect. But I believe your misfire is causing this second kind of condition. Unfortunately it's not always easy to hunt down. You just have to go one step at a time until you find the problem. But remember to test, not just replace parts. Only replace when you know that part is faulty.

Ernest Clark
Nov 29, 2010.
I have replaced 2 coils, coil pack housing, I.C.M, plugs and boots what else could cause a misfire?
What should fuel pressure regulator pressure be if a gauge was used?

Tiny
Gjewell
Nov 29, 2010.
First pull the vacuum line to the regulator and check for the presence of fuel. If there's any, replace it.

Fuel pressure should be 41-47 psi.

There are MANY things that can cause a misfire, including but not limited to: Bad computer, failing sensors, you forgot to put the dielectric grease around the insulators of the plugs when you replaced them, there's a bad ground to the coils, the coils wires, connectors are bad, the injectors are clogged/leaking, etc.

The thing to do is eliminate one thing at a time, beginning with the ignition system, then fuel, then sensors, then computer.
AD

Ernest Clark
Nov 29, 2010.
Thankyou for the help, it is much appreciated.

Tiny
Gjewell
Nov 29, 2010.
P.S. There is no moisture in the pipe, but there is some brown residue in the groove on the top of regulator, in which the pipe slides into?
I shall buy a fuel pressure guage set tomorrow.

Tiny
Gjewell
Nov 29, 2010.

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