Barely Running Believe its a CMP issue.

[1952Chevy]

I have attached some pictures of the plugs as well.
Cylinder 5

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Cylinder 7

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Cylinder 2

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Cylinder 4

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[Schurkey]

Well, about half the porcelain is darker than I'd prefer. Maybe that indicates some amount of oil-burning. Modern gasoline, modern feedback fuel injection, and low-rpm overdrive transmissions don't tend to put much color on the plug otherwise. Takes tens of thousands of miles for the white to turn light-grey.

 

[Road Trip]

Update, I just had a thought, and maybe it's worthless.

I have a timing light. I put the timing light lead on each of the 8 plug wires. They were all very sporadic. It's getting late and I have other things to do, but I will go back out and look at that again.

Does this seem like a decent way of determining anything? My thought process was that if the ignition is working properly then I would get a steady rhythm on each cylinder. Instead of steady and then nothing for a few seconds, or slow and steady with a faster portion.

I like your troubleshooting thought process. (And the approach is valid, for I have personally seen timing lights pulse
perfectly steady for minutes at a time with no dead spots.) But what you've observed could be an artifact of either the
ignition system -or- the timing light trigger circuitry.

In order to be able to put more trust in the timing light, IF you were to try the timing light on a smooth, misfire-free
vehicle and you get a steady flashing, then now we know that the test equipment is capable of continuous, steady flashing.

NOW if you put that same timing light back on your truck and you again see sporadic flashes, now we have some actionable
info to work with. (!) On the other hand, if the timing light is also sporadic on a smooth-running car, then we know that
for whatever reason the test equipment is no longer up to the task we need to execute. (!)

****

For what it's worth I've reread this string from the beginning. In my next reply I'd like to dig a little deeper into
the reported full-scale swings in the CMP <> CKP comparison, while at the same time no DTC 1345 is flagged?

The preceding is about the cold OK, hot FAIL symptoms first observed in Las Vegas back on May 26th.

Now we're back at home base in Idaho, the hot fail has yet to resurface, but now we have a random miss
that presents either hot or cold? Don't know if this is related to the original road trip malfunction or possibly
a 2nd issue to resolve?

More to follow once I figure out how to boil it all down to something more concise. Just wanted to check in and
let you know I'm still following this tough intermittent.

Cheers --

 

[1952Chevy]

I like your troubleshooting thought process. (And the approach is valid, for I have personally seen timing lights pulse
perfectly steady for minutes at a time with no dead spots.) But what you've observed could be an artifact of either the
ignition system -or- the timing light trigger circuitry.

In order to be able to put more trust in the timing light, IF you were to try the timing light on a smooth, misfire-free
vehicle and you get a steady flashing, then now we know that the test equipment is capable of continuous, steady flashing.

NOW if you put that same timing light back on your truck and you again see sporadic flashes, now we have some actionable
info to work with. (!) On the other hand, if the timing light is also sporadic on a smooth-running car, then we know that
for whatever reason the test equipment is no longer up to the task we need to execute. (!)

****

For what it's worth I've reread this string from the beginning. In my next reply I'd like to dig a little deeper into
the reported full-scale swings in the CMP <> CKP comparison, while at the same time no DTC 1345 is flagged?

The preceding is about the cold OK, hot FAIL symptoms first observed in Las Vegas back on May 26th.

Now we're back at home base in Idaho, the hot fail has yet to resurface, but now we have a random miss
that presents either hot or cold? Don't know if this is related to the original road trip malfunction or possibly
a 2nd issue to resolve?

More to follow once I figure out how to boil it all down to something more concise. Just wanted to check in and
let you know I'm still following this tough intermittent.

Cheers --

It's getting just as hot here in Idaho now, but the AC quit again(compressor seal) so I haven't been driving it. But I will do the same thing one day this week when it's just as hot out to ensure the problem doesn't resurface. I will also run the timing light on another vehicle. Smart idea considering this was the first time I've used it.

As always I appreciate the help and response.

 

[1952Chevy]

Update. I tested the timing light on the coil wire to the distributor and got a steady light non-stop. Rechecked the wires and was getting inconsistent flashes.

I went ahead an replaced the cap and rotor. Initially I put the drivers side wires on incorrectly, which drove a misfire. My scan tool picked up the misfire, and showed misfire counts for Cyl 3,5 and 7. All 3 of those wires were in the wrong place. I corrected those wires, and adjusted the distributor to get the CMP Offset correct.

Started the truck back up and no misfires. Everything seems good. I let it run and get warm. Now it is sitting in the sun, hood closed. In a little bit I'm going to go for a drive and see how she does. It's over 100 degrees here today, very similar weather to Las Vegas when the issues started.

 

[Road Trip]

Update. I tested the timing light on the coil wire to the distributor and got a steady light non-stop. Rechecked the wires and was getting inconsistent flashes.

I went ahead an replaced the cap and rotor.

Given that you are driving a '99 Vortec 7.4, this means that you are using the Vortec dizzy crab cap,
and we've seen that it's favorite way of failing is burn-through/arc-over from the center terminal to the #3 spark
path. (which crosses the cap nearest the center terminal.) Given what you observed with your timing light test,
I'm wondering if your cap shows visible evidence of why you saw steady flashes on the coil wire vs. sporadic
flashes on the spark plug wires? Here's an example of a cap that failed bad enough that it kept the engine
from starting:

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Q: Do you still have that original cap, and if so, is there any visual indications of arc-through
like the above?

Initially I put the drivers side wires on incorrectly, which drove a misfire. My scan tool picked up the misfire, and showed misfire counts for Cyl 3,5 and 7. All 3 of those wires were in the wrong place. I corrected those wires, and adjusted the distributor to get the CMP Offset correct.

Good on you for calling out this error and how you figured it out via the misfire counts. This gives us more confidence
in the scan tool you are using, and also it's a good learning moment for others troubleshooting similar issues, researching
this thread, and demonstrating how live data can really speed up misfire troubleshooting.

Started the truck back up and no misfires. Everything seems good. I let it run and get warm. Now it is sitting in the sun, hood closed. In a little bit I'm going to go for a drive and see how she does. It's over 100 degrees here today, very similar weather to Las Vegas when the issues started.

So it looks like you have successfully addressed the 'hot and cold' misfire issues that you first mentioned after returning to Idaho.
In my next reply I'll focus on the 'hot fail' issue, just in case it decides to return.

 

[1952Chevy]

I just got back from a 75+ mile test drive, multiple stops allowing for a chance for the engine bay to heat soak. The ambient temp(according to the truck) was 102, so right around the same as Las Vegas when the issues began. The only real difference now is that the AC is not running, so no additional heat from the condenser.

Results are no CMP Offset swings up and down. Cyl 2, 4, 6 and 8 do still have occasional misfires. According to the live read, 2-10 misfire count. I only physically noticed 1 instance of the misfire, and that was Cyl 8 at a count of 10. So still have some more to track down. There seems to be some remaining issue on bank 2. Still no codes, just observed misfire counts. No misfires on bank 1 at all.

Given that you are driving a '99 Vortec 7.4, this means that you are using the Vortec dizzy crab cap,
and we've seen that it's favorite way of failing is burn-through/arc-over from the center terminal to the #3 spark
path. (which crosses the cap nearest the center terminal.) Given what you observed with your timing light test,
I'm wondering if your cap shows visible evidence of why you saw steady flashes on the coil wire vs. sporadic
flashes on the spark plug wires? Here's an example of a cap that failed bad enough that it kept the engine
from starting:

You must be registered for see images attach

Q: Do you still have that original cap, and if so, is there any visual indications of arc-through
like the above?

Now that I think about it. Cyl 3 was the fastest flash during my initial testing. I will attach a picture of my cap(it's on my phone).

Good on you for calling out this error and how you figured it out via the misfire counts. This gives us more confidence
in the scan tool you are using, and also it's a good learning moment for others troubleshooting similar issues, researching
this thread, and demonstrating how live data can really speed up misfire troubleshooting.

I am glad I was able to give myself that confidence as well.

So it looks like you have successfully addressed the 'hot and cold' misfire issues that you first mentioned after returning to Idaho.
In my next reply I'll focus on the 'hot fail' issue, just in case it decides to return.

I will continue to drive it and see if the hot fail issue comes back. Obviously I am hoping that it doesn't.

 

[1952Chevy]

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[Road Trip]

Troubleshooting electronic-related Cold OK / Hot FAIL scenarios

For what it's worth I've reread this string from the beginning. In my next reply I'd like to dig a little deeper into
the reported full-scale swings in the CMP <> CKP comparison, while at the same time no DTC 1345 is flagged?

If the 'hot fail' symptoms re-occur, then here are some things to keep in the back of your troubleshooting mind.
(First stimulated during a road trip to southern Nevada -- see attached for my crib notes of this thread.)

Good for you that you were monitoring your VCM/engine bay while the error occurred. This way you
caught the CMP <> CKP sync value ("CMP offset") varying wildly between the limits at both ends while
the misfire was occurring. Given the rest of your reporting this feels like a electronic component that
has become thermal sensitive, especially given that if you let the vehicle cool off it will return to normal
operation.

Given that the CMP sensor has already been replaced (a good place to start) with no change in behavior,
we will need to decide whether the problem is on the ICM side or the VCM side of this circuit.

But before we get into specific troubleshooting, I'd like to discuss electronic thermal failures a bit more.
The first thing is that most electronic components are available that are spec'd to work at different temperature
ranges. And the ones that require the most research, verification, and testing to work reliably at temperature
extremes also (for obvious reasons) cost the most money.

So the delicate dance is for the design engineer to specify electronics that will work at the expected temperatures
plus a safety margin (headroom) so that the vehicle is reliable, whether deep in Alaska in the middle of winter, or
while traversing Death Valley in the heat of summer. But at the same time, as a good corporate citizen he
knows that he can't specify the use of ruggedized Mil-Spec or aerospace-quality electronics, for these parts
are much more expensive than the lower-tier stuff.

NOTE: In the price-sensitive aftermarket, in the race to the bottom all this nonsense about wide temp range
capable electronics sometimes takes a back seat to the goal of making the most attractively-priced ignition bits.
(And they use a longer warranty to overcome the 'you get what you pay for' customer expectation + cover the
scenario where a non-spec part is sold to the rare HD user who works the vehicle hard enough to precipitate
a stress failure. The corporate bet here is that the vehicle in question is parked at the lake cottage and used
gently/infrequently, -or- is sold before the part reaches a premature end of life from heavy use.)

Anyway, here's a little hand-drawn chart that attempts to show how we can end up with a tough thermal
intermittent buried in the ignition and/or control system for our powerplant that plays peek-a-boo with the owner:

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(I'm on the 3rd rewrite. I decided to replace several screens of blah blah blah with this hypothetical graphic. Hope it illustrates how some electronic parts that fade too early from
heat can lead to 'intermittent' behavior. (And why I used to fervently wish that electronics were purely good/completely broke like the old incandescent light bulbs of yore. :0)

Seriously, no matter what type of intermittency you are diagnosing, you really can't fix an intermittent sans parts cannon or vehicle trade in
until you first figure out how to break it at will. Simple as that.

Anyway, if the above causes any questions concerning electronic-related thermal intermittents I'll be happy to elucidate.

****

The remainder of this discussion will be based upon the first page of the P1345 DTC in the '99 FSM:

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(from the '99 FSM, Vol 3 & 4.pdf)

Alright. In the TBI era the all-important Reference Signal to the computer (aka 'RPM signal') came from the
distributor sensor as an analog signal to the 8-pin ICM, where it was converted to a Square wave, which was
forwarded to the ECU/PCM, which in turn enabled both spark & fuel injector pulses. Wicked important signal. :0)

EDIT: In the '96+ Vortec/VCM world, the VCM is the Master, and the ICM is simply the (coil) Blaster. The Vortec ICM is now
down to only 4 pins, all of which can be seen in the diagram above. (See attached for Vortec ICM pic.)

For those keeping score, the input from the CKP (CranK Position) sensor is now the source of that all-important Reference signal.
Meanwhile, the sensor in the Vortec distributor is now only responsible to supply the CMP (CaM Position) signal that the VCM uses
to help identify where we are in the firing order, enabling SFI and accurate misfire error reporting.

Instead of attempting to turn us all into ignition system designers, for brevity I will instead just identify what
problems need solving, so that when they aren't solved we know which direction to head.

The first problem is that both the CKP & CMP sensors output an analog signal, which for timing purposes
needs to be converted into square waves. Here's a good illustration of what I'm talking about:

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(credit: thirdgen.org Ignition signal discussion)

1) I bring this up because if the VCM circuitry heated up and lost the ability
to correctly trigger on the positive-to-negative zero crossing, then you
could easily get those wild CMP offset readings. (If you happen to be a
scope dope it's easy to visualize what a loss of trigger sync does.)

* First possibility identified: circuitry involved in signal conversion heats up
and we lose sync with the engine rotation. All other VCM functionality
is unaffected. But why wouldn't this flaky Reference signal not create a
miscompare triggering a P1345 DTC & SES light?

Troubleshooting hint: If the failure is CMP related, the CMP offset is
goofed up, but the engine still runs right/close to right. (VCM reverts
to Batch fire, and also can no longer discern which cylinder is misfiring.
Maybe error reporting degrades to P0300?)

On the other hand, if the CKP is the affected signal, you will experience
noticeable roughness, for everything is timed off of the CKP 'Reference'
signal. (!)

2) Input power to CKP, ICM, and Ignition Coil (circuit #439) is flaky. IF
the coil were to heat up and this was to cause the secondary to arc
back into the primary (+12v power circuit) ...this could create havoc
downstream with the CKP sensor. How old is your coil? Any signs of
distress? Will it pass the fine mist test?

* Second possibility identified: Flaky high voltage coil causing CKP
reference signal disruption via shared +12v circuit? But why wouldn't
this flaky Reference signal not create a miscompare triggering a
P1345 DTC & SES light?

3) ICM heats up and loses ability to properly drive Ignition Coil.
But how does this cause flaky CMP offset readings? (Unless normal
flyback from coil primary is coupled back to weakened ICM, and now
RFI is in turn coupled back to the VCM?

Third possibility: ICM heats up, loses high voltage gatekeeper functionality,
and is polluting the VCM with coil-generated RFI.

****

And although I've been trying to avoid going here, when all else is proven
good, then we have no choice but to consider the VCM as the root cause
of the failure. The fact that VCM hasn't been kicking a P1345 despite you
seeing wild CKP<>CMP sync swings all the way to +/- 40° is a concern.
Is the VCM no longer capable of kicking DTCs and lighting the SES light?

What happens if you disconnect the MAF? (The engine should continue to
run on the MAP and also kick the SES light and log a P010x DTC? If the
DTC is kicked, can you shut the engine off, wait 10-15 seconds, restart
the vehicle, and the DTC isn't lost across the power cycle? How about
a P1345 if you were to misadjust the distributor assy ~15°?

I could continue, but I think this is a good stopping point for this evening.
Some parts have been changed, including the CMP sensor on the new(er)
distributor, which was a good starting point. IF the hot fail were to return,
then we need to try to figure out if the VCM is the victim of a bad input,
a hot coil flaking out and throwing lightning bolts back into it's coworkers,
or a previously overlooked failure in the power or ground circuits?

Or is the aging VCM heating up and flaking on us, mishandling good
input signals while not telling on itself with 1 or more DTCs?

****

Anyone still reading this who has an anecdotal story about a similar failure
and eventual fix please share it here.

And circling back to an earlier comment I made earlier, IF you can figure
out how to make the heat fail occur at will, then maybe we could also
figure out a temporary work-around to confirm our diagnosis?
(Only fails during extended heat soak with hood down. But always
starts when hood is popped at every stop?) Or a bag of ice on the VCM
shortens the wait/fixes the issue every time?

Sincere apologies for the length. Paraphrasing Mr. Hendrix,
'ther-mal mal-func-tions is a fru-stra-ting mess'
:0)

As always, thanks for the detailed status reports, and please
continue to keep us in the loop on this.

Every trip a round trip!

Cheers --

 

[1952Chevy]

@Road Trip I really do appreciate your input! Well written and easily understandable(at least for me). I have read all of your posts. I am glad(with your help) that this very valuable information will be available to others in the future.

I am intrigued by your thought that maybe the VCM isn't capable of kicking out DTC's now. When I started it earlier and with plug wires in the wrong spot, I did not get any DTC's for the misfire or CMP offset(which was -10). My understanding is with the CMP over 5 degrees off, it should kick a code. I may go out tomorrow and readjust the distributor to force a -10+ offset and see if I get the P1345 that I once got. I will also do the MAF sensor separately. Both are easy to accomplish.

It's also supposed to be 107 tomorrow so I will do some more driving and see if I get any more heat soak problem.