I've been working to cure a cylinder 5 misfire and found that my ignition timing is fluctuating widely at idle. The timing advance jumps around from 8 to 25 degrees at idle (600 RPM.) It steadies out nicely at higher RPM. My error code is always thrown at around 650 RPM...

Is this normal for these engines? If not, I'll assume the camshaft position sensor is the first thing to change.

Thanks in advance if anyone knows if this is a normal idle condition (1997 5.9L engine).

Here's a graph of the timing advance at 600 RPM over about 15 seconds (scale on right is 0 to 25 degrees.) This is captured with car stopped. Manifold vacuum, throttle position, temperature, and RPM are very stable:

 

when my camshaft position sensor started messing up it made the CEL come on.
advance and autozone call it a pick up coil and its much cheaper than the dealers.

i believe that a big change in the timing can be blamed on slack in the timing chain because the pcm controls the timing.

 

does it go back to the same pattern after a while? because i think these have 4 strokes right? so does it go back to the same pattern after it completes the strokes?


i could be wrong

 

It doesn't look like much of a pattern and it's jumping around pretty fast. The chart above is from the OBD connector, so that's what the computer reports. I also put a timing light on it and the crankshaft pulley mark is also jumping all over.

I read some other posts here that suggest this is normal, but I have my doubts. Seems like having a cylinder fire 25 degrees early at idle could cause misfire. It's basically firing while the piston is still coming up on the compression stroke, way before TDC. Seems like that could slow the piston down. The computer measures small changes in engine speed to detect a misfire and throw one of the P030X codes.

I've already spent bucks shotgunning this problem, but I guess $27 more for a CPS won't kill me. If that doesn't do it, the next step is pull the heads and rebuild the top-end, and maybe the whole engine (it's got 150K miles.) I just want to make sure I've done all the basic stuff before I tear into the engine.

 

hows the Harmonic Balancer since yours is a 5.9? does it wobble around whe running? because this could mess up the crankshaft sproket for the chain and cause this.

 

you won't get a steady check at idle, that's normal.

The standard way to check the timing is to rev the engine to at least 1K. The dealer's DRB III and a snap-on scanner all raise the "idle" to 1000 rpms automatically to set the distributor fuel sync.

 

I think the balancer is OK. Engine is rock steady at idle. Balancer is not wobbling when running and feels solid.

I was afraid of that --- I'm running out of easy fixes. I've got a CPS coming in tonight, so I'll give that a try anyway.