Thread: Sputtering and P0300 code

OK so I have done the search and read a lot on this topic but just wanted a little reassurance on this matter.

So car in park starts right up on first crank and idles good and can rev freely, seeing 19 vac on the boost gauge.
While driving and the car is under a load or as soon as it hits anything above "0" on the boost side it starts sputtering and sounds like a machine gun and has no power....then I can get a P0300 code to be thrown. Clear it on the Aeroforce and keep driving and will run fine until again it hits that right load amount and throws it again.

Already have done new 104's and have tried gapping from .052" to .060"..
New fuel filter...
New Delco wires...

my next adventure is new coils and ICM.

Does that sound like the right path?

Try all the rubber "T" fittings around the LIM. I bet you have a vacuum leak tossing around that PO300...if not...try swapping the coils first.

I will check that.
Does the whole starter spray/carb cleaner on the vacuum lines to help find leaks work?

My only concern is that I have 19 vac at idle so if I had a vac leak I would see it then too right?

if you have a consistant 19" of vacuum at idle i bet youre fine. does it feel like its fighting for power up top? what boost numbers are you seeing?

I can pull 8-9lbs with my 3.4 on there right now but I don't dip into it too much.

Also no knock either and its not pulling any timing...

It has no power as soon as I cross into boost or under a load. It is literally puttering and if the hill or load is long enough it will throw the SES light blinking at me.

What other mods do you have for the 3.4"? Enough?

Do the plug gaps tend to be bent by chance? If so...that's a chipped piston. But that's my last resort.

Mod List:
Intense Generation 1 Modified Stock 1.9 ratio rocker arms
Digital Horsepower Custom Tuned PCM
Thrasher Modular Pulley 3.4"/3.25"
Motor Sports Performance Cold Air Induction kit
Custom ported stock manifolds with 2000 degree coating and wrapped crossover
3" custom downpipe with braided flex pipe
3" in/out Car Sound Catalytic Converter (94009)
U-Bend Removed
Resonator removed with 2.5" custom pipe
Dynomax UltraFlo mufflers and Borla Dual-Dual outlet tips
180 Robert Shaw thermostat
Autolite 104 spark plugs


Plug gaps don't look bent from what I can tell.

Car has been in storage since November in the garage. Gas tank (Full) was stabil'd at that time and battery disconnected.
Have been able to run 3.25 pulley in spring and fall until it gets too warm and knock creeps in, then I would switch to the 3.4. Switched to 3.4 off the bat this year with the old gas I figured it was the safe route.

Originally Posted by Thinkmoto

Find out which cylinder is misfiring when you get the blinky SES. Try swapping that coil pack with another 1st. If its multiple cylinders I'd take a look at your cat. Also that gas is over 6 months old? Stabil or not get that **** out.

Blinky SES only triggers the 0300 code...I wish it was cylinder specific then I have somewhere to hunt.

Am picking up new coils and ICM tonight from a friend who had spares from an engine rebuild from the donor car. We shall see how those are. They only have 5k on em.

New coils and ICM in.
Still can pull the same P0300 and it mostly triggers the flashing "real time" SES light from 40-50 under light/medium acceleration.

Going after o2 and MAF tonight.
Also have a new MAP sensor but I don't think that's it.

i got the same thing going on. i have replaced my MAF sensor, bought all new vacuum lines and still got the code. i check the msd coils that i had and they weren't @ spec so i put old stock one on and still the same code! i also checked the spark plug wires to make sure they had ohm resistance. they were good also! the only thing i noticed is that i pulled my plugs to see how they were after replacing them and they were white so i'm either running to lean or i'm guessing that my injectors might be stuffed.... Keep intouch so we can figure this out!!!

i had it with it on and then i took the catalaytic converter off and it still have the problem

If you scan for knock you should be able to scan the 02 or maf. Possibly fuel pump/pressure issue as well.

Fuel pressure is good on the rails...reading 42-50 from idle and into boost.

Dropped new 104's in and did a fuel trim reset (battery pull overnight).
I have not seen the code come back since. Must have been a hairline crack in a plug since they only had 500 miles max on them.

A slight misfire or injector issue uptop @ WOT, but I think it is still related to the gas and cleaning out the injectors from sitting all winter.

After this tank I plan to seafoam and then I should be ready to rock for the summer.

At least the code is gone and the engine runs 95% like it should. Fuel trims are -0.7 to 0.7 so the tune looks good still and knock is still under control with small blips of 1-2 at the very top end under WOT.

Had this exact problem and after changing almost every part on the car did an injector test and i had no negative injector pulse put in a new ecm and shes been fine ever since but the problems your describing were exact as mine mine was cylinder 3 missfire and cylinder inj port open on that 0300 code and it turned out to be the ecm