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Discussion Starter #1
Hello everyone,

I have a 99 that has a very strange issue. It has the wait to start delay problem going on which would tell me the ECU was damaged by a bad alternator.

But the problem is it only happens when it's warm outside anything below 50F and the problem goes away. It doesn't matter if the truck is hot or cold either.

I've checked the ECU ground behind the starter and it's good. There's no ac output on the alternator. There's no codes.

I'm out of ideas as to why the ECU booting would be delayed when the ambient temperature was above 50F hoping you guys have seen this before.
 

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An ECM(u) can have another issue where certain connections in a circuit board go bad after too many "heat cycles" AKA bad soldering of the 90's. It is still bad and needs replacement/rebuilt. Even though it may not be ACv related, but check that too. If you send it specify likley hood of that problem
 

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Discussion Starter #3
An ECM(u) can have another issue where certain connections in a circuit board go bad after too many "heat cycles" AKA bad soldering of the 90's. It is still bad and needs replacement/rebuilt. Even though it may not be ACv related, but check that too. If you send it specify likley hood of that problem
That would make sense if it did it while the truck was hot. But it has only ever done it when the outside temp is above 50F. The truck doesn't care if I spent all day pulling 20k through mountain roads 30 miles. If you park it after and it's below 50F outside the WTS light is instant on. If it's even 55F out and the trucks been sitting overnight the WTS light takes 5-30 seconds to come on. Same if you were hauling anything and it's 55F out and parked it.

I'm wondering if the IAT sensor has anything to do with the ECU booting.
 

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The ECM should boot as soon as key on is made IAT tells the ECM when grid heater is needed.
 

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The ECU is checking the AIT and the Battery Temp sensors when deciding how long to turn on the WTS and thus the grid heaters. However, I have not found anything about the delay you describe.

Something may be waiting for a reply that never comes.
Or electronics can get into a "thrash state" where communication can get caught up in a back and forth until something matches up finally or there's a default re-try.
Theoretically, and this is only a theory, this might be what's going on when the temperature aligns.
But I have found absolutely nothing so far that describes this state specifically.
It sure sounds like there is a communication issue somewhere.
 

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Why does not matter much. If the ECM is not instantly booting up every time if is going or gone bad. It can be intermittent or get worse overtime. It can be caused by AC, Heat cycles, other shorts and so on. Either way it is going bad and why does matter other than preventing a new one from being damaged.
 
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