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I have a p0300 code and the tuner said it was cylinder #2 and 3 miss firing. I had the injectors cleaned and new plugs and wires. It did overheat last year before I put it away so I did a compression test and it says 180 cold on 2, and 3 and the cylinders next to them....I dont see any coolant missing , but is it possible I have a head gasket leaking and causing the miss fire or does anyone have any ideas....It runs at 185 deg. and doesnt overheat....but I dont know too much about these engines. It is a LQ4 with a ls6 intake, and corvette accesories. Please let me know if you have any ideas...it seems like it runs good but the tuner said he can see it on his scanner. Thanx
You might try a fuel injector coil test. Just check the resistance of the fuel injectors with a multimeter (preferably a digital) - the difference between the highest and lowest should be no more than 3 ohms.
im sure youve looked at this but for a month or two after i bought my camaro i had the same problem with p0300 and i replaced plugs and wires and relearned the crank position as well, fuel filter (possible clog causing it to go lean). so i threw it at GM they tore it down checked the valvetrain swapped injectors and coil packs and did a compression test and EVERY thing came back normal.
as it turned out it was my injector seals... thats what fixed mine and it hasnt come back since. maybe it will help
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I didnt use new seals on the intake but I did do the 2 step torque process, also I have no idea how to do the other things your talking about....can you explain more....should I have bought new intake gaskets?
no to the software...44inch pounds/ 89 inch pounds...I guess I will replace the intake gaskets....any chance I blew the head gaskets when it overheated and its burning water....the code seams to blink just cruzing....not when I am on it....seems like it is running good when I get on it...pretty fast for a stock 6.0 motor...thanks for the ideas so far
I just found a cracked hose...its the hose that goes from the throttle body all around the motor and ends on the back of the driverside valve cover. the cracked part is the part that goes to the passenger back tube thats on top of the valve cover....Could that cause the miss fire....if so do i just block those ports off and drive it to see if it doesnt show up?
Ok here is the update, all fuel trims were the good, also I moved the coils from the missfire cylinders to cylinders 6 and 8....the mechanic said almost all the cylinders are missfiring. The only other thing he said was the maf was reading 6 grams at idle and it should be 1 or 2...he took out the maf and cleaned iy....no change. So I called PSI who mail tuned the computer and he said to put another ground from the battery to where the bolt is where the grounds go from the harness. No change....Mike at New Era is still saying its probably the pushrods or valves are bent or the seats are dirty...does anyone have anymore ideas.....I also changed the pvc hose with a GM new one...and changed the intake gaskets....
Have you done a ckp relearn yet, I had issues with my lq4 throwin a p0300 for the longest time and everything was good,did the relearn last summer and its never come back. I also showed a few cylinders with higher misfire counts. After the relearn it was normal
Ok here is the update, all fuel trims were the good, also I moved the coils from the missfire cylinders to cylinders 6 and 8....the mechanic said almost all the cylinders are missfiring. The only other thing he said was the maf was reading 6 grams at idle and it should be 1 or 2...he took out the maf and cleaned iy....no change. So I called PSI who mail tuned the computer and he said to put another ground from the battery to where the bolt is where the grounds go from the harness. No change....Mike at New Era is still saying its probably the pushrods or valves are bent or the seats are dirty...does anyone have anymore ideas.....I also changed the pvc hose with a GM new one...and changed the intake gaskets....
Unsubscribing so I don't waste any more time. Good luck anyway.
Well I dont know what I did wrong to get that response.....Ive taken this to the tuner, and a shop with tech 2.... this is what they have told me....I reported the parts I bought that people said could be the culprit...I was looking for help....Im not a tuner...just trying to get my car right...its been a $8700 project....useless right now. Any ideas or direction would be great.
Just wanted to update people of the result of this P0300 code....I went from drive by wire to drive by cable on this engine.....For some reason when I took the car to the shop the first time the computer only said the car was in 1st gear....so I could not do a crank relearn....The good guys at PSI swaped computers and retuned the new one for free even though my warrentee expired. After that it read park and after the crank relearn I have had no codes for almost 200 miles, where as before it would come up in around 3 miles......So my advise is to everyone changing computers to have a crank relearn done....Cost me $20. As for those who came back saying they were wasting there time.....try to be more helpful...us guys that are new to these engine dont have a clue and are trying to learn. Thanx for the reponses
There's misfires, and there's misfires. Even stock you'll see
a few random misfires popping. Add a lightweight converter
or flywheel / clutch, add a cam, and you'll see a lot of
-reported- misfires. These are not failure-to-fire type
misfires, they're just false counts from the motor getting
more crank ripple.
The only thing you worry about is when a cylinder always
shows many misfires and the rest don't, or show only low
level random counts.
Crank learn is all about getting the misfire detect baseline
clean, by fine tuning the timing of the crank sensor. It
can help. But you'll still likely see some rolling random
counts, which is OK unless they're elevated enough from
motor mods to start bugging. Then you want to mess with
the tables.
JAs for those who came back saying they were wasting there time.....try to be more helpful...us guys that are new to these engine dont have a clue and are trying to learn.
It's a waste of time when:
a.) you didn't do a single diagnostic I recommended.
b.) you didn't tell us that it was a PCM swap case.
Glad to hear the shop got it running right, congrats.
Your right, I didnt know the computer change made the difference. Drove the car for over 200 miles the last 2 days beating the crap out of it several times, took it to work 63 miles 1 way and the car got 18.3 MPG with that 3600rpm stall. I thought that was pretty good....but I can tell it still needs a tune. Anyone know a tuner in the Rochester, NY or Buffalo area. Just found out New Era had a big fire and lost there Dyno.
I have a P0300 code...help !! 
