Random misfire p300 + p307 CMD +7.1

[Mrich0908]

Im having a random misfire condition.
Now I think the front of the intake is leaking and Im pretty certain it was replaced once before . Black RTV when gm used the white silicone. But its dirty , oily . I dont see coolant pouring out to say 100% its leaking. Its possible . If I cant figure this out ill do it just to make sure.
So I downloaded ScanXL with with the gm pids to see the cam retard offset. I happen to have the ODB2 PC connector. It was showing 7.1 at 1000 1200 rpms.
I guess my question is would the offset of 7.1 cause a misfire condition?

 

[Mrich0908]

Any one who was wondering ... Nope I got it set to 1.4 while the p307 is gone p300 is still there.
Guess im doing the gasket next .

 

[Mrich0908]

Found a broken screw on my rotor head....Hmmmm
While I think that may be part of the problem . I dont think thats it.
I have a horrible feeling its the injectors . I ran the motor out of gas 2 weeks ago . Motor has high miles new 4l60e though. I think it may be time for a lsx.

 

[Mrich0908]

Jeeze , im talking to my self. ne ways..
failed a fuel leak down test. Not the pressure but holding pressure. Purchased a new Mfi system and installed it.
Get this the previous owner installed the distributor gear upside down. It ran like that also. Im not sure how but they timed it and it ran. Gear was chewed up .Grabbed new one. Replaced the leaky lower also.
I think i going to have to re-time it . I think now the gear is right side up it would be 180 degrees to where I marked it . Fun fun....

 

[Mrich0908]

SO I installed everything today ran 100% better but still had a miss . Bad brake booster. Busted it power braking the 4l60e I rebuilt. I believe in a harsh break in after warm up.
I also had the P0307 . Probably be a good Idea to check plug 7 huh? It was cracked . Ill own that when I rebuilt my 4l60e I had to drop my long tubes and must of hit one. Motor runs great now.... Obviously there were allot of little things.

 

[Steve A]

Mrich, glad you got it fixed. Did you happen to get pictures of the distributor gear on upside down? Surprised it didn't spit the oil pump driveshaft out. How did it work out with the new gear, should have lined up pretty much on your marks I would think. That P0300 code seems to be a recurring theme on some of these motors.

 

[Mrich0908]

Sorry no pics . I get working and really dont document much.
Dropped right in and started right up. I was @ 18 degrees cpm my scan tool said ajusted to 2.3 thats good enough for me . I marked the rotor before and after. Really didnt give me much trouble after I found the problem.
P0300 is a generic something is misfiring. I know I had a lower leaking intake gasket. I wasnt sure if my injectors were leaking or it was my fuel pressure regulator regardless it was failing leak down lest. Great excuse for new mfi spider. The motor had allot of carbon also. I cleaned the egr , replaced a cracked plug . Installed a new rotor that was broke . Brake booster I busted. Throw all that together and you have a p0300
I didnt get a pic of the gear upside down. If you look on the net you will see others have made that mistake. I couldn't believe it ran , and ran for a while like that.
Everything lines up including the pump , upside down . The distributor just doesnt sit flush with the intake and gasket.
My gear was also chewed up . I did replace it .While inspecting the gear you can tell it wasn't mating flush with the cam gear. The wear marks wear at an angle .
I mean if some one went through everything I did and still has problems . I would say Check vacuum see if the one way on the intake is leaking . If your positive you have no intake leaks . Buy an elm27 scanner tool . I honestly can say that has been one of the cheapest best investments Ive ever made. You can really read anything the bigger scanners can. Even reading CMP cam offset.
Next would be a (probably should of been first) compression test , look for sticky valves timing chain head-gaskets.

 

[Mangonesailor]

I just went through something similar with my own truck. Right after throwing in a 0411 I got the p0300. After exhausting all sorts of troibleshooting methods I looked at misfire counts as they happened and noted that they were all right next to each other in the firing order. Pulled the dizzy and the gear was toast on about 7-8teeth. New dizzy and no more missing!