Ron6519

Still working on this. Came across a possible source with the Blue Driver scan tool. Watching the distributor advance in #1 cylinder. Advance moving along in a 15- 18 degree range. Hit the accelerator and the advance goes up to about 30 degrees. Watching the graph at idle and all of a sudden the advance angle drops like a stone to -64 degrees for a second and pops up to the 15-18 degree range. Goes along for 3-5 minutes and repeats. Some times to -84 degrees. Short and long term trim drop as well, just for a second, then return to normal.
So:
1. Is it the distributor? If so how to test?
2. Is it the coil sending power to the distributor? How to test?
3. Is it the PCM sending a dropped signal? How to test?

Distributor was replaced in 2013 by mechanic
Thanks
Ron

mountainmanjoe

those dizzies were always a pain in rear. Pull it out and inspect for moisture, corrosion, cracks or signs of arcing. They're so cheap you might as well just drop a new cap in.
check that the rotor shaft gears aren't chewed up too.
Ignition can be tested by pulling plugs out, cranking, and watching for spark.

Ron6519

spark was checked as well as plugs. Both are 3 years old. Distributor on order. So far component testing has not been guided along. You tube and the internet have not addressed the issue. Useless generic advice perpetrated.
Hope fading fast and expect to have to deal with this myself.

mountainmanjoe

who else is supposed to deal deal with it?

Ron6519

With the less esoteric things, you might get a leg up with others who have come across a similar issue. Then you can take their experience and try out previous solutions.
I think this is a signal issue. So I want to test the signals through the system to the distributor. The signal drop(blip) to the distributor occurs every 3-5 minutes. It would seen the engine rotates far too many times between the signal drop for it to be a mechanical part failure, such as the distributor as it's gears are turning constantly. I did order one but did so as a "hail Mary" due to the lack of electrical testing material I'd come across. This should be able to be diagnosed with a VOM meter, but you need to know what values you're looking for. Can't find anywhere, voltage, amperage or resistance figures for the pathway. Might try a subscription service for a month if they have the information.
I haven't seen any detailed electronic trouble shooting on the auto forums I've come across. The highly technical forums the professionals use scanners/oscilloscopes I don't have. So far on YouTube with Scanner Danner, Eric the car guy and South Main Auto with Eric O have been most informative, but have not shown this particular graphic with the accompanying misfire issue. It seems a random misfire can be caused by a myriad of things. Almost everything.
And yes, I will deal with it, just like I've been dealing with it in the past. Am appreciative of the useful advice and ignore the non useful.
The Internet is no different then anything else. Chaff and wheat.

oldchevy

A random misfire can be caused by many things, some of which are not electrical. My son had an 05 Pathfinder with a P0300 random misfire. After going through the electrical components with no success, we found it to be a clogged downstream cat. There were no codes for the cat, just a P0300. It had a bad coil which damaged the upstream cat and the debris from the upstream cat clogged the downstream cat. This might not be your problem, but it is something to think about.

Ron6519

At this point I'm concentrating on the graphing anomaly, which seems to be electrical. The advance angle drops to -64 degrees for an instant and then resumes at the 15-18 degree range. So far this is the best possibility. At least it shows up on a graph.
Wouldn't a clogged Catalytic convertor have an effect on the fuel trim and oxygen sensor readings?
Looked up catalytic convertor failure and the van doesn't have any symptoms . Starts right up, plenty of power on acceleration, no back pressure or rotten egg smell and the oxygen sensors are working as though the convertor was fine.

mountainmanjoe

Please start at the beginning.

What symptoms are you experiencing (besides the check engine light)?
Does the vehicle drive?
What exact actions have you taken to troubleshoot the issue ?
what vehicle are we even talking about?

It takes 2 minutes to rap on the cat-conv with your first.

Ron6519

2001 GMC 2500 Savana van with a 5.0 liter.
Only symptom is the engine light comes on. And DTC P0300 pops up. Along with a low output for the B2S2 downstream o2 sensor. The sensor was 9 years old and stayed at 430-450 mv. Replaced it and code disappeared. Cleared all codes and drove the van. Starts right up, idles smoothly and has plenty of power on acceleration. After 15 minutes of driving the check engine light comes on. Once the DTCP0304 came on. Checked the plug and exchanged it with the one next to it. Checked spark at both cylinders. Spark was orangish in color. Not white hot. Checked cap and rotor, which were replaced in August 2019. Replaced coil wire to distributor. Old wire tested for continuity and it was fine. Cleared codes and drove the van. Code(P0300) came back.
. Opened a "Distributor advance Cylinder #1" window on the Blue Driver and found the advance would drop to -64 degrees every 3-5 minutes, for a split second and then return to the 15-18 range. Upon throttle snap the advance would go to 32-37 degrees and drop back after going back to idle.
Distributor is about 8 years old and was replaced by my mechanic trying to find a crank, hard start, an stalling at lights and stop signs. Turned out to be the wiring harness going to the cam sensor on the distributor. That was replaced and the problem disappeared.
Current theory in that the issue comes about through the electric path from the PCM to coil to distributor to plugs. Since I can't find testing methods for the coil and PCM and distributor, I'm going to replace the distributor and ignition coil. Could be the PCM. That was replaced due do moisture getting into the old one and a crusty white paste( aluminum oxide?) covering many electrical components. Rebuilt PCM was programmed to VIN number by seller. DTC P0300 was showing before the PCM swap last August 2019.. Communication(transmission) codes disappeared upon PCM swap.
And that's the story.

mountainmanjoe

so the new distributor solved the P0304 you were getting, and now you have a white hot spark?

You could try a timing light to see if the advance is in fact that low, or if it is being misreported.

Make sure the ignition module has a good ground. It could also have an intermittent short.

Abnormal HO2S readings will cause misfire.