2005 tahoe p0300 HELP! With freeze frame and mf data

[Bjsetz89gt]

Hey everyone, I have an 05 tahoe, t vin 5.3 w/o get system with a p0300. The misfire is happening at idle, then goes away completely over 1200 rpm. Bank 1 is leaning out, and ltft b1 reads high at idle and drops when driving.
Here's my freeze frame:

Fuel Status = 0 byte
Engine Load = 19.608 %
Engine Coolant Temperature = 197.6 °F
Fuel Trim Bank 1 Short Term = 0 %
Fuel Trim Bank 1 Long Term = 12.5 %
Fuel Trim Bank 2 Short Term = 0 %
Fuel Trim Bank 2 Long Term = 8.594 %
Intake Manifold Pressure = 5.221 psi
Engine RPM = 632 rpm
Speed (OBD) = 0 mph
Timing Advance = 17 °
Intake Air Temperature = 96.8 °F
Mass Air Flow Rate = 5.82 g/s
Throttle Position(Manifold) = 12.157 %

Fuel pressure is at 48 key on engine off, and jumps to 58 at idle.
Cleaned maf and throttle body, inspected the bank 1 injectors (clean), vacuum is at 18.7 and I can't find a leak, compression test is good too, lowest was 159, and highest was 166. Been doing all the diag work myself, but I'm not all up on how to interpret it. Could anyone make anything out of this?

Attached misfire data from after I replaced both upstream o2 sensors

 

[Bjsetz89gt]

Update: replaced camshaft position sensor, with no changes

 

[iamdub]

Crankshaft position sensor?

 

[Bjsetz89gt]

I suppose that's next on the list to mark off....

 

[bottomline2000]

Intake manifold gasket?

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[Bjsetz89gt]

Common problem, but no. Sprayed carb cleaner around the intake and all the vacuum hoses.
forgot to mention it has new acdelco plugs, and tried switching coils and wires on the missing cyls and misses stayed put.

I watched my o2 graphs today and bank 1 and 2 are jumping rich to lean like normal, but both downstreams are reading rich (like .8-.9v). Do the downstreams have any control on injector pulse on these?

 

[bottomline2000]

Common problem, but no. Sprayed carb cleaner around the intake and all the vacuum hoses.
forgot to mention it has new acdelco plugs, and tried switching coils and wires on the missing cyls and misses stayed put.

I watched my o2 graphs today and bank 1 and 2 are jumping rich to lean like normal, but both downstreams are reading rich (like .8-.9v). Do the downstreams have any control on injector pulse on these?

A lot of people have tried the carb spray and i cant say ive seen that sppray test work on our trucks. Rear sensors just monitor the condition of the cats. Long shot but have the cats been tested? My ltft were maxed out when I had bad cats. Maybe yours are starting to clog?

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[Bjsetz89gt]

I haven't had the cats actually tested, but I have an ir thermometer and figured them good just off the temp readings at the front and back. It was actually the first thing I thought when it threw o2 codes with the 300 at first. But that was just a dead sensor and the 0153 hasn't come back.

As far as the intake gasket, is it possible to have a bad gasket and still get good vacuum tests? Even the old cigar trick turned out good...

 

[M1Gunner]

I would be willing to say that cyl. 1 miss is due to cyl. 7. Have you check injector pulse to inj. 7?

 

[Bjsetz89gt]

I tried checking the pulse. Torque pro won't pick it up with the pid' s for maybe this tahoe? Would a noid like work as well?

On another note, ran a can of seafoam through the intake and saw an improvement. My cyl1 misfires seem to be gone, and cyl 7 misfires are down from around 100 per "cycle" to about 30 or 35. Definite improvement. Is it worth it to run another can through?

 

[M1Gunner]

I tried checking the pulse. Torque pro won't pick it up with the pid' s for maybe this tahoe? Would a noid like work as well?

On another note, ran a can of seafoam through the intake and saw an improvement. My cyl1 misfires seem to be gone, and cyl 7 misfires are down from around 100 per "cycle" to about 30 or 35. Definite improvement. Is it worth it to run another can through?

Makes you want to suspect the injector on cylinder 7. Now that 7 has calmed down, it's no longer affecting cyl 1.

Well you could test the theory and swap a known good injector from another cyl and see if it follows OR just go ahead and replace it.

 

[Bjsetz89gt]

Update- so I got together with a friend that's an ase tech at the chevy dealer, hooked it up to his scanner, and it shows misfires on 2 and 7, with 2 most likely caused by 7. All signs point to the cam. It's getting centrifugal force above idle, allowing the lifter to get some action, but it's missing 85% of the time at idle. Looks like I may be in for a top engine rebuild. Next move is a running compression test and leakdown test to confirm.

 

[retiredsparky]

The seafoam improvement certainly points toward injector issues. If a second can doesn't clear it up, why not remove the injectors and clean them. There are multiple utube videos on easy methods to use carb cleaner on them.

 

[Chubbs]

Update- so I got together with a friend that's an ase tech at the chevy dealer, hooked it up to his scanner, and it shows misfires on 2 and 7, with 2 most likely caused by 7. All signs point to the cam. It's getting centrifugal force above idle, allowing the lifter to get some action, but it's missing 85% of the time at idle. Looks like I may be in for a top engine rebuild. Next move is a running compression test and leakdown test to confirm.

Bummer. I was hoping you would find something simple as part of the engine management system: i.e. Faulty MAF sensor, vac leak. Please keep us posted on your findings of the compression values

 

[camperhead]

any updates to this?

 

[ivin74]

Hey everyone, I have an 05 tahoe, t vin 5.3 w/o get system with a p0300. The misfire is happening at idle, then goes away completely over 1200 rpm. Bank 1 is leaning out, and ltft b1 reads high at idle and drops when driving.
Here's my freeze frame:

Fuel Status = 0 byte
Engine Load = 19.608 %
Engine Coolant Temperature = 197.6 °F
Fuel Trim Bank 1 Short Term = 0 %
Fuel Trim Bank 1 Long Term = 12.5 %
Fuel Trim Bank 2 Short Term = 0 %
Fuel Trim Bank 2 Long Term = 8.594 %
Intake Manifold Pressure = 5.221 psi
Engine RPM = 632 rpm
Speed (OBD) = 0 mph
Timing Advance = 17 °
Intake Air Temperature = 96.8 °F
Mass Air Flow Rate = 5.82 g/s
Throttle Position(Manifold) = 12.157 %

Fuel pressure is at 48 key on engine off, and jumps to 58 at idle.
Cleaned maf and throttle body, inspected the bank 1 injectors (clean), vacuum is at 18.7 and I can't find a leak, compression test is good too, lowest was 159, and highest was 166. Been doing all the diag work myself, but I'm not all up on how to interpret it. Could anyone make anything out of this?

Attached misfire data from after I replaced both upstream o2 sensors

Swap out the coils on the good cylinders to the bad cylinders to see if the misfire changes, if it does your coils are bad

 

[Bjsetz89gt]

Yeah so being a newbie, my vacuum showed 18 in., but I didn't pay attention to how it was jumping. Didn't need do running compression at that point. #7 exhaust lobe scored, with a bad roller lifter to go with it. Replaced my cam, lifters, timing chain, and my gaskets. Runs great now...