P0300 Code Please Help

[98_lumina]

I have a 98 Lumina 3.1 sedan with 110,000 miles. It has been running rough at low speeds and in idle, has the P0300 misfire code indicating a random/multiple missfire, and has also been a little sluggish under any condition. I had a full tune-up performed by a professional and it did nothing to help. Parts replaced include plugs, wires, pcv valve, air filter, and fuel filter.

This may be a separate issue as it started occuring after the missfire. But my radio is also shutting off and powering on every once in while by itself. It never looses the time, so I'm thinking that is indicative of either a bad accessory wire, or a bad iginition switch. Could this be related?

[maxwedge]

Try and pin it down to one cyl. if possible, have you or your mechanic can run a power balance test on a scanner, this will tell you which cylinder, then proceed from there.

[wafrederick]

It is a fuel injector,but which one is the answer.If you know anyone that has GM's factory scan tool Tech 2,Gm's factory scan tool has a misfire chart and the aftermarkets do not have the misfire chart.

[maxwedge]

Snap on scanners can do a power balance test by cutting out 1 injector at a time and watching the rpm drops, to pick out a bad one. Also make sure all battery ground and engine grounds are good.

[bishop5307]

Originally Posted by 98_lumina

This may be a separate issue as it started occuring after the missfire. But my radio is also shutting off and powering on every once in while by itself. It never looses the time, so I'm thinking that is indicative of either a bad accessory wire, or a bad iginition switch. Could this be related?

I know your radio deal is not related. A bad ignition switch would cause the whole engine to glitch. I probably work with the guy who calibrated the misfire code for that year.

The 300 means more than 1 cylinder saw a misfire, more related to something like a coil or module, not an injector that would only misfire on 1 cylinder. A bad injector could also set a P0200 type code under certain conditions, but not always. Grounds are a problem and can cause most anything you can't explain to happen. They are easy access on the 3.1, on the trans studs under the air cleaner.

If you don't find anything, I might be able to get you a misfire chart and schematic from either a GM manual or AllData. You can get AllData for a year for like $15 for 1 car.

Randy
[email protected]

[richtazz]

The problem with random misfires is that you have to be able to access the frequency of the mis-fires. After total random mis-fires reach a certain number, it will trip this code. But if you consider that your spark plugs fire 250 times each per minute at 3000 rpm (3000rpm/6 cyl/1 spark per 2 revolutions) , it doesn't take long to reach the code threshhold.

[corning_d3]

I'm thinking it might be EGR related, which will cause a multi-cylinder misfire and a rough idle if the EGR valve is open at idle. Just inspect or test all the things that would affect every cylinder, not just one. Things like MAS, EGR, Fuel pressure AND flow, stuff like that. I would suspect that the fuel pump may be getting weak. A weak pump can cause a misfire if pressures or flow is low. I would test it first to rule out the fuel system if its good.

[maxwedge]

Originally Posted by bishop5307

I know your radio deal is not related. A bad ignition switch would cause the whole engine to glitch. I probably work with the guy who calibrated the misfire code for that year.

The 300 means more than 1 cylinder saw a misfire, more related to something like a coil or module, not an injector that would only misfire on 1 cylinder. A bad injector could also set a P0200 type code under certain conditions, but not always. Grounds are a problem and can cause most anything you can't explain to happen. They are easy access on the 3.1, on the trans studs under the air cleaner.

If you don't find anything, I might be able to get you a misfire chart and schematic from either a GM manual or AllData. You can get AllData for a year for like $15 for 1 car.

Randy
[email protected]

I suggested the power balance test to isolate the cylinder since he said he felt the misfire at idle, no suggestion it was an injector.

[wafrederick]

It is a fuel injector.My father has one customer same problem and it is a fuel injector.Luckily my father has a GM tech 2 and #5 fuel injecter is bad showing on the misfire chart.The Snap On scanners are JUNK!I have been hearing problems on the Snap On scanners.The 3.1 has fuel injector problems once in a while

[corning_d3]

I didn't think one bad injector caused a random, multi-cylinder misfire.I agree with you on the snap-on's. We have 2 in our shop, along with a Chrysler OBDII, GM Tech II and a Ford Rotunda. They're ok for pulling codes and viewing streaming data, but not much good for anything else. My gripe about them is the tiny screen. My top choice is the GM.