Mis-Fires driving me CRAZY!! 2002 Chev Astro RV

[andyrud]

2002 Chev Astro AWD Tiger RV


Runs FANTASTIC! Really strong! But my XTOOL OBD scanner shows intermittent mis-fires. Usually Code P0305 shows #5 cylinder, but sometimes P0300-99 shows on other cylinders and the scanner shows intermittent mis-fires on various cylinders. This causes me to not pass the smog test. As long as I drive it everything is fine. BUT, when it idles for a while, various intermittent mis-fires show up on the Scanner. ANY increase of RPMs or when I turn on the air conditioning the mis-fires within 15 seconds go away. Below, are all things I have already done to it. It is driving me CRAZY!



New Iridium GM spark plugs

New GM spark plug wires

New GM Distributer Cap

New GM Distributer Rotor

New GM Cam Shaft Position Sensor located in Distributer

New GM Crankshaft Position Sensor and RE-LEARN done

Compression test done- All cylinders good

All cylinders leak down test was good

Fuel pressure was in range and did not leak down

Fuel filter changed.

Vacuum smoke test was done- no leaks detected

Barryman’s Carb and Choke fluid was used to test for a vacuum leak- none detected.

Used propane gas to test for vacuum leak – none detected

#5 Injector was replaced- no effect on problem

#5 cylinder compression tested again and leak test done again- checked out very good.

Poured 2 bottles of injector cleaner into gas tank, ran full fuel tank through engine- no effect on problem

WHAT WOULD YOU DO NEXT!?!

Any Suggestions are REALLY Appreciated!



Andy R

[MountainManJoe]

Hi Andy. Did you visually confirm good spark on each cylinder? You could have a faulty ignition coil.

[andyrud]

Yes I did. But why would a coil just misfire at idle? The misfires happen after idling for a minute or so. I am starting to think it is the ECM.

[MountainManJoe]

What are the fuel trims at idle? And how about ignition retard?
PCM is the last thing I would suspect.

[andyrud]

What are the fuel trims at idle? And how about ignition retard?
PCM is the last thing I would suspect.
[/quote

At 625 idle and warmed up:

Short term Fuel trim Bank 1 -1 to 0
Short term Fuel trim Bank 2 1 to 2
Long term Bank 1 3
Long term Bank 2 7
Fuel trim cell 4

Short term fuel trim bank 1 average -2
Short term fuel trim Bank2 average 2

Long term fuel trim bank 1 average 3
Long term fuel trim bank 2 average 5



If I foot throttle RPMs to 700 random misfires eventually stop and all show 0

If I turn on the air conditioning random misfires eventually stop and pretty much show 0

Any idea how to up the idle RPMs to about 700?

[MountainManJoe]

you could try cleaning out the throttle body and IAC.

[andyrud]

The throttle body was thoroughly cleaned when the # 5 Injector was replaced.

Here are some other scanner items:
Ho2S Bank 1 sensor 1 bounces between 73 to 868 mv
Ho2S bank 1 sensor2 is steady at 828
Ho2S bank 2 sensor 1 bounces between 86 to 724 mv

Injector PWM bank 1 average 4.65 to 4.84
Injector PWM bank 2 average 4.56 to 5.19

MAF sensor 5.50 g/s
MAP sensor 5.8 psi

Does any of these stand out as abnormal to you?

Thanks for your help,
Andy R

[andyrud]

you could try cleaning out the throttle body and IAC.

The throttle body was cleaned when the #5 injector was replaced.

Injector PWM bank 1 average 4.65 to 4.84
Injector PWM bank 2 average 4.56 to 5.19

Could these be too high causing misfires? Google lookup said they should be between 2.5 and 3.5 at idle.? What do you think?

Thanks for the help,
Andy R

[MountainManJoe]

Nothing really stands out for me. When I had misfire before, one of the problems was the distributor was loose and worn out. Not in it's proper position (which is why I asked about CMP retard value). I've also seen photos of stripped out teeth on the distributor gear (where it meshes with camshaft).

[andyrud]

I check the distributer teeth and when I try to turn it it barely moves. I will try to find the CMP retard value, but I did not see it on the list in my scanner. What should the value be? If I find it?

I want to sell this van but I can't in good conscience sell it until these misfires are solved! The van runs GREAT!

Andy R

[MountainManJoe]

retard should be zero degrees (give or take a couple) @ 1,000 RPM, and it should not change more than a couple more degrees when raising up to 2,000 RPM.

Also note this relevant TSB:

https://charm.li/Chevy%20Truck/2002/Ast ... C%20P0300/

[andyrud]

Just got back from testing it. CMP retard value was 0 at 1000rpm, at 2000 rpm it was 0, but went to -1 for a half second or so.