I've had lots of different opinions on this problem. I've tried to take logical steps towards solving the problem. the engine (longblock) is new. it was installed by NECO in Woburn,MA. I think they did a great job and had my car running the best I've ever seen it. this was an external ignition problem that was going on before the engine exchange. I could drive it one day and it would be running fine,the next day it would go bizerk,run like **** and the tach would flicker. eventually it got so bad that the car would die because the ignition was so currupt. when it finnally died and wouldn't fire up at all,I disconnected the 4-wire harness at the distributer. it starts up and runs ok with the ESC harness disconnected,it just has no timing advance. driving it like this uses way to much gas and can't possibly be any good for the engine. by logical means of trouble shooting,I've determined it is the computer causing this problem. the ESC module (electronic spark control module) could cause, this but all that does is convert a the signal from the knock sensor to a retard signal to the ECM,the ECM recieves the retard signal from the ESC and the timing reference signal from the HEI distributer,the result is the advance signal back to the to the HEI distributer. if the engine smoothes out and runs with those four wires disconnected (ground,dist. reference,advance,module bypass) from the distributer,then the problem can only be between that 4-wire connector and the ECM. I've tested continuity to ground in all 4 wires,only the ground is grounded, so I'm sure there is no shorts to ground,an open would do nothing...so I didn't check for opens. I'm certain it's a faulty ECM after all it is a 17 year old car it wouldn't be unlikely. the knock sensor and O2 sensor are new,as well as everything inside the distributer. how does that distributer advance timing via an advance signal from the ECM anyways? the rotor is integral with the shaft right down to the cam....so this tends to get me very confused

 

JYD,

Basically, the system works in this way:

The distributor shaft reluctor induces a slight current in the pickup coil every time one of its rotating poles passes the fixed poles. This signal is sent to the HEI module, which conditions the signal and sends it out terminals 'A' and 'C' to the ECM.

The detonation sensor sends a ground signal to the ESC module whenever a knock is detected. The ESC module conditions the signal to a 5VDC pulse and signals the ECM.

The ECM interprets both signals and sends a pulse back to the HEI module on terminal 'D', which controls the timing of the HEI module switching transistor. All of this occurs within about 0.03mS, or 33,000 times per second.

If the ECM is given a detonation signal, the timing of the pulse is delayed briefly to retard timing. Lacking the pulse, the ECM will time the spark signal based on engine RPM and temperature.

Because of this, a faulty ESC can cause unnecessary spark retard. The lack of distributor reference pulses to the ECM from the HEI module can also cause erratic operation or no ignition signal.

You mentioned the possibility of an open circuit, which can include the card edge connections at the ECM itself. Don't overlook those, as well as the HEI connection quality and the wiring between. The ECM grounds are also important to the operation of this system.

If you discover the ECM is FUBAR, let me know via email - I may have your solution.

------------------
Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

thanks, Vader!! I couldn't find your email address,I'd still like to know what your solution to the bad ECM is. I replaced it already and the engine will run with everything connected and no codes. but something still isn't right. the motor knocks no matter what the timing is set to. mostly reving up from idle and accelerating under load. I've heard that a bad EGR can cause this,but I just put in a new one today.if an EGR is bad,does that mean it's stuck open or closed? will an ESC module that doesn't isn't functional at all cause knock or should a good running engine manage on it's own w/out a knock sensor? is the ESC & knock sensor essential for proper timing or is it extra protection.

 

so... the distributer won't physically change the position of the rotor in proportion to the cap,during acceleration? how does the limited time that the rotor is in contact with the cap offer enough room for the computer to effectivly change timing? the reason I ask is because a vaccume advance distributer seems to have much more freeplay in the rotor. I've been told by two people that I'm missing the advance mechanism in my distributer??? I know it needs some form of advance,I always thought it was done electronically,it is an electronic HEI w/ a 7-pin module, WTF?? missing advance mechanism? I've had this car for three years,how could this be overlooked?