P0300 Code :Random/Multiple Misfire HELP!!!!

[JAM25]

Ok guys this is for my 99 cutlass. Seems that I have the notorious random misfire code. With my emmision test coming up in less than a month.

How can I fix this? The car seems to hesitate at startup a bit so what im planning on doing is do a full tune up.

Replace the ignitjon coils
Spark plug wires
Spark plugs
Air filter
Oil
Oil filter
Ill try the fuel filter but the filter is rusted and sonare the gasblines. Im.afraid if I twist it I may break of the fuel line


O2 sensor


What else or what can I do to get this code go away. I do mainly city miles with less than 100 miles a week.

 

[JAM25]

What plugs should I use. My friend at autozone can get me Autolite Double Platinum plugs and the autolite wire set for 50 dollars. Should I do that or stick with ac delco

Im.currently running autolite on my lincoln and mitsubishi with no problems whatbso ever cars drive smooth.

 

[demarpaint]

Originally Posted By: JAM25
What plugs should I use. My friend at autozone can get me Autolite Double Platinum plugs and the autolite wire set for 50 dollars. Should I do that or stick with ac delco

Im.currently running autolite on my lincoln and mitsubishi with no problems whatbso ever cars drive smooth.


Not quite the same car, but that combo is exactly what I'm running in my 2000 Century w/o issue.

 

[Ironduke4]

First i would start by replacing the wires and plugs if that does not cure your missfire problem then look at replacing the coils but i bet new wires and plugs should fix it.

 

[The_Eric]

You're off to a good start. Always best to cover the basics. If you can't manage the fuel filter, then take it to a garage and have them do it. Either way, make sure it's done. It's been my experience that even if they look bad, the nut on the fuel filter will spin loose. I believe you'll need a 20mm wrench and 16mm wrench.

If that doesn't fix your issues, then report back. Actually, report back even if it does take care of your issue, so we know the fix.

edit: I would skip replacing the coils for now. They don't tend to go bad that often. You should only check the terminals where the plug wires snap on for rust or corrosion.

 

[NHGUY]

Intake leaks?

 

[HerrStig]

Bad injector?

 

[bdcardinal]

With a P0300 I would be looking at a systemic problem, especially since the PCM cannot narrow down the cylinder that is misfiring. Vacuum leak, low fuel pressure, check LTFT and STFT, maybe even excessive carbon on piston tops.

 

[JimPghPA]

If you can't get the fuel filter off dump two cans of SeaFoam gas treatment in a full tank of gas and run it until the tank is down to 1/8 or less.

If the fuel filter is clogged enough to cause the problem the SeaFoam will open up enough passageway for the fuel to flow well enough for the problem to go away for about 6 month. And it does a good job on cleaning the rest of the fuel system.

If the filter is the problem it will come back and repeated use of the SeaFoam will clear it up but each time the time of good use with no problems will decrease.

We had that problem with out 2001 Impala, and after several rounds of cleaning with SeaFoam the problem never came back after the fuel filter was changed.

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I think that the engine on that vehicle has a crank position sensor that can go bad. The plastic that holds the sensor tends to break. The long drawn out high labor way to fix it is to take the engine apart. The quick low cost way to fix it is to get a new sensor, remove the part of the mount that prevents you from inserting it easily, clean the area very well with rags and some alcohol (91 percent from any drug store or Wal-Mart). And use JB-Weld epoxy on the part to hold it in place. Let the JB-Weld cure for at least a half a day. You probably can find some YouTube videos about this fix. My brother did that on his Cutlass of that year, and he never had the sensor problem again.

 

[Falken]

Keep nailing all the basics that would be considered overdue maintenance items anyway.

Change off that fuel filter if it is really old. It can be a culprit or at least be putting undue load on your fuel pump and may burn it out.

Have your fuel pressure checked afterwards to make sure your fuel pump is ok. This is an old vehicle.

 

[Trav]

Go through all the basics then if it still has P0300 look at the intake, the 3.1 is a notorious leaker.
A partially clogged cat will also throw a P0300, you can do a basic check on it with a cheap vacuum gauge.

vacuum gauges they are a great and cheap diagnostic tool, they can help pinpoint all sorts of problems.
Fuel trims and misfire count would be a big help if you have access to a scanner.
Although the misfire code is for random misfire a count of the individual cylinders may help locate the general area or bank most affected.

 

[yonyon]

Fuel trims and misfire counter would be very nice to have.

From what I can remember of the days when those cars were all over the place, some common causes of P0300 were:

-Carbon deposits on the pintle of the EGR valve keeping it from closing all the way. This will give you misfires mostly at idle. It takes only a couple of minutes to remove it and clean the pintle, so may be worth trying just to eliminate the possibility. No parts are needed.

-If you do a lot of short trips or use "whatever's cheapest" gasoline, dirty injectors. Again, misfires will be mostly at idle. If you have that usage, buy a bottle of injector cleaner.

-Worn spark plugs and deteriorating wires. They really do tend to go bad at about the same rate and that PCM will be happy to give you a P0300 rather than multiple codes in the P0301-P0306 range. Misfiring will be worse under load, will be worse when cold, and may be worse in damp weather.

 

[JethroBodine]

Do your tune up and use the same plugs specified by the factory. Clean EGR. Clean fuel system with Techron.

Reevaluate.

 

[yonyon]

Oh, and if you decide to remove the EGR valve to clean the pintle, don't worry too much about the gasket. It will probably look like the most ruined gasket you've ever seen. Go ahead and reuse it; it'll seal up just fine.