Hello 1952Chevy,
I appreciate your detailed status report. I like the fact that you monitored the CMP Offset both before and during the misfires. So although we don't know what it
is, we know what it isn't.
However, re-reading everthing that you've posted would lead me to believe that you are experiencing thermal-related electronic intermittent failure.
Please correct me if I get any of the following wrong, but since the beginning, haven't all these issues occurred only after say, 10-15+ minutes of
operation? During the first few minutes of operation, doesn't your vehicle always give you that "I'll never quit" feeling, only to start misfiriing a few
miles down the road?
By the way, if you were to put a thermometer under the hood, while driving you would be observing pretty close to whatever the exit temperature is
from the radiator. (180-190+ degrees F.) But when you shut down, all the coolant stops circulating, and all the heat stored in the exhaust manifolds
just sends the underhood temps skyrocketing. This has been proven ever since engineers were trying to solve vapor lock and fuel boiling in carburetors
down at the AZ proving grounds way back in the day. The engineers always talked about these 'rest stop' driveability issues, especially with high-HP engines.
In English, it looked like your vehicle was doing pretty good until you stopped for lunch. No doubt during that stop the underhood temps soared.
So would it be possible to do the following?
1) Flip your normal schedule, and drive at night instead of during the day?
2) Any time you stop for any reason, immediately pop the hood open and don't allow the heat to build.
If you are stopping at a rest area, getting gas, any reason at all, don't forget to pop the hood wide open.
3) If you have a place to carry the hood, consider the proven Roadkill trick of driving home with the hood
removed. This is one of their workarounds when they are having tough overtemp issues.
NOTE: I've personally never done #3, but I *have* done #1 & #2 when I was suffering from thermal issues
a long way from home. I'll bet you a chicken mcnugget ($1) that if you had fully opened the hood during your lunch
stop you might have not suffered any misfiring afterwards?
4) This may or may not help, but since the engine bay temps are set primarily by the air exiting the radiator,
would it be possible for you to find a 160° thermostat for a 'one time flight' back to home base? It sounds
like we're flirting with the edge of success, and driving late at night with a 160° thermostat, and also being
vigilant in not letting the engine bay bake during stops...maybe we can still get you home under your own power?
It seems that the CASE relearn that you are referring to is not normally done UNLESS a DTC kicks that the
FSM would bring up the need to do this? Again, because your vehicle seems to be well behaved both Closed Loop
and Open Look until the heat starts to build, I'm thinking that you are suffering from a thermal intermittant.
Grasping at straws, IF the CMP Offset went wacky during the misfire, I might be inclined to suspect that the
VCM is the one failing at high temps? But it didn't, and a lot of the VCM has be running right in order to make
those measurements/perform the compares/store the results, and communicate it to your plugged in test equipment?
I've lost the picture of what you've tried so far (I'll go back and reread this thread after posting this) ...but unless
you have a known-good ICM and Coil I'd be wondering about those. And checking them with a *light misting* might
uncover a problem, if not *the* problem.
Whaddaya think? 160° thermostat and then a test drive in the evening, always popping the hood at any burrito break,
refueling, or rest stop? Last but not least, if you take the hood off then please be sure to take pics and share them with
your remote support team. :0)
Keep us in the loop. Safe returns --
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