I've been running on a Pettit ECU that has a problem reading the knock sensor...basically, it thinks it is missing or dead, but its the ECU...a stocker works just fine, and in fact this one used to. From my reading, it seems that when the ECU gives this error code it simply retards timing a bit just to be safe. This doesn't bother me too much, because the car runs much better with this ECU than the stock one anyway...not sure why, but it does. Anyway, this morning I suddenly started having a problem...if I gave it gas it would "pull back" like it was severely retarding ignition, and it would backfire a lot when I let up. Also, the check engine light, on permenantly due to the knock sensor code, went out briefly and then came back on. It was somewhat reminiscent of a MAP sensor hose popping off and entering limp mode. Idle speed was low and faintly pulsing. Then, as I'm sitting at the light...the idle returned to normal and the problem vanished completely. No codes other than that for the knock sensor were returned.

Any ideas? Clearly it was not the MAP sensor hose, as it repaired itself. If the ECU thinks it sees knock, does it have the capability to take measures this drastic? I didn't think so, but perhaps it was getting fooled into thinking it saw massive detonation, and put the car into limp mode briefly?

jds

 

I think I am right ,the stock ecu can hear the knock but does NOT retard the timming . It may give a code and limp mode, I do not know. If the stock ecu could retard the timming ( this is not why I think that the ecu does not retard timming ) no one would need a J&S knock unit .

 

Well, my understanding was simply that the stock ECU could not precisely determine knock early enough, so by the time it could actually be sure it was too late to do much good. The FSM claims that timing is retarded when there is an error code due to failed or missing knock sensor...or at least I could have sworn I read that.

jds

 

is the knock sensor the only code?

 

i think the book says something about retarding like 3-4 degrees, its not really enough to do much

mike

 

The knock sensor was the only code, yes...I was actually expecting something else to pop up.

I'm pretty sure what I saw was not such a small retard of ignition...anyone know if the ECU will ever enter limp mode based on something from the knock sensor? The more I think about it, the more like limp mode it felt. However, I would expect the ECU to throw some kind of code if it enters limp mode.

jds]