About '93 GMC Sierra 5.7 v8 automatic.
Please, correct me if I am wrong, but my understanding of the 'pure mechanical' pre ignition system consists out of 3 techniques to provide proper pre ignition:
1. fix pre ignition, set with timing light to specification bij turning the distributor
2. vacuum pre ignition system, to provide suitable immediate pre ignition when revving the engine (to avoid hesitation of the engine)
3. centrifugal pre ignition system, to take over from the vacuum system when engine stays on higher rpm.
The '93 GMC Sierra is equipped with an electronic advance spark timing system that takes over the various stages of the mechanical system as describes above.
I would expect to see those stages when I check pre ignition with my timing light on this '93 GMC truck.
When checking the pre ignition on idle I notice some degrees of pre ignition, which looks normal to me.
However, when revving the engine, I would expect to see immediate increase of pre ignition degrees. But that did not happen. i.s.o. advancing the ignition time, the ignition time retards, causing hesitation of the engine at revving time.
Holding the engine on higher rpm, shows me again a normal amount of pre ignition.
My question, as the complete pre ignition timing is controlled electronically on this car, what could cause this ignition timing retard, and as such hesitation of the engine, when revving the engine.
Thanks a lot in advance for any help in solving this problem.
Please, correct me if I am wrong, but my understanding of the 'pure mechanical' pre ignition system consists out of 3 techniques to provide proper pre ignition:
1. fix pre ignition, set with timing light to specification bij turning the distributor
2. vacuum pre ignition system, to provide suitable immediate pre ignition when revving the engine (to avoid hesitation of the engine)
3. centrifugal pre ignition system, to take over from the vacuum system when engine stays on higher rpm.
The '93 GMC Sierra is equipped with an electronic advance spark timing system that takes over the various stages of the mechanical system as describes above.
I would expect to see those stages when I check pre ignition with my timing light on this '93 GMC truck.
When checking the pre ignition on idle I notice some degrees of pre ignition, which looks normal to me.
However, when revving the engine, I would expect to see immediate increase of pre ignition degrees. But that did not happen. i.s.o. advancing the ignition time, the ignition time retards, causing hesitation of the engine at revving time.
Holding the engine on higher rpm, shows me again a normal amount of pre ignition.
My question, as the complete pre ignition timing is controlled electronically on this car, what could cause this ignition timing retard, and as such hesitation of the engine, when revving the engine.
Thanks a lot in advance for any help in solving this problem.