The dreaded P0300 [Archive] - GrandAmGT.com Forum

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Mr.BeefySE
02-06-2013, 03:59 PM
Hello all,
My 1998 GAGT with the 3100 has the dreaded P0300. I was told the car ran rough and needed plugs. I bought the car with the assumption that a simple tune up would take care of it but no dice. I replaced the plugs with Autolites and delco wires. I removed the ICM and Coils and tested them at Autozone. I tried replacing them with a used ICM and coils, still nothing. I'm suspecting it's a fuel issue. Plugged injector ? I don't want to buy 6 injectors at $100 totalling more than the car is currently worth. I'm currently trying to change the fuel filter. It seems the filter is rusted on the nut side and the plastic clip on the other side turned into shrapnel when I touched it lol. I soaked it in WD-40 yesterday, going to hit it with another soaking today and hopefully it breaks loose. Any suggestions ? Comments ? Concerns?

Mr.BeefySE
02-06-2013, 04:01 PM
I also cut off the Catilytic converter and replaced with a test pipe, no effect.

geldartb
02-06-2013, 04:06 PM
that's the multiple misfire code.

ignition or injectors.

plastic_indian
02-06-2013, 07:57 PM
If you've replaced/swapped/whatever basically the entire ignition system with no change, look at mixture next. Check fuel pressure with an actual gauge (not by just poking the schrader with a tech driver to see if it squirts) and compare to spec (41-47psi). Check for other DTCs. If you have access to a decent scan tool, check fuel trims.

Assuming base ignition has been properly eliminated as the culprit, random multiple is most commonly due to a lean condition (vacuum leak if fuel trims indicate starvation but fuel pressure is good), followed by advanced internal wear (low compression) and then perhaps a timing issue (with a DIS ignition, I would expect cam and/or crank sensor codes set concurrently if this is the case).

In example of the last scenario, I've seen 60 degree engines come in with 'mystery' 300 codes only to find out the owner/owner's brother/dave the neighborhood mechanic/whoever did the intake three weeks ago and accidentally pinched the CMP wire harness when he put the steering pump back on...

On a far less likely note, if the engine has had a crank sensor replaced before the problem manifested, it may be possible a CKP variation relearn was never performed after the new sensor was installed - I cannot remember if that is necessary on that engine for certain, but if all else fails it may bear investigation.

Brendan is certainly not wrong with his suggestion of an injector problem - waxed up injectors can cause this as well (this would be bourne out by lean fuel trims). If you go this route, use the proper GM injector detergent through the rail - most generic in-the-tank additives will not resolve this in my experience.

dagenais
02-08-2013, 05:47 PM
Had the same problem with ICM and coils they tested ok but still had problem... Change plugs, wires, clean TB and did Sea Foam treatment and tripple check all vacuum houses and nothing... went to junk yard paid 15.00 for a USED ICM - Coils and replace as a test and car runs GREAT...

Mr.BeefySE
03-03-2013, 12:35 PM
Got the filter changed, no effect. Probably going to take to the garage. I've done all the simple, easy stuff that I can handle doing without buying major tools. I do want to try another icm and coils though.

Mr.BeefySE
03-04-2013, 05:24 PM
Ok, i found an ICM and coils off of a car with 61,000 miles on it for $25 off of Craigslist. Swapped it and she runs like a dream!!

jonny
03-04-2013, 05:57 PM
yeh i have learned with these cars when in doubt change the icm and coil.

GTfiend
03-04-2013, 09:09 PM
Don't mean to hijack but my cars engine feels shaky/bumpy at idle but I have no stored codes... I did just about everything I could do/check. If my ICM or coils were crappiin out wouldn't I have a code?

Mr.BeefySE
03-05-2013, 10:58 AM
They usually throw a P0300 random misfire detected. Maybe you have a bad motor mount?

GTfiend
03-05-2013, 02:09 PM
They usually throw a P0300 random misfire detected. Maybe you have a bad motor mount?

Possibly since the coils and icm just tested fine at auto zone
I'm testing fuel pressure next

rocketfast123
03-05-2013, 02:24 PM
When i worked at autozone I always tested coils and icms like 4 times in a row. It get them pretty hot. And i did find a few DOA parts.

GTfiend
03-05-2013, 03:13 PM
When i worked at autozone I always tested coils and icms like 4 times in a row. It get them pretty hot. And i did find a few DOA parts.

The guy that did my icm tested it 25 times

Mr.BeefySE
03-07-2013, 06:03 AM
The guy that did my icm tested it 25 times

Might want to try it anyway, my ICM tested good.

AaronGTR
03-07-2013, 03:52 PM
As a side note... don't always trust those testers at the auto parts store. They are VERY limited in what they can test. Their testing machines don't full replicate what the parts go through on the actual car. I've taken in batteries for them to test that they said were ok, and they didn't work in the car. I've taken in alternators that passed on their machine, but in the car the voltage regulators were shot. Learn how to diagnose the problem in the car... don't trust the machine! ;)