Control Module?

[fireplug]

Does anyone know why a control module might fail? I had one go on me last weekend while replacing plugs, wires, cap, and rotor. Then grabbed a used one, tested spark, all was good but very briefly before that module seemed not to work. Replaced it with a new one and everything was fine until today.

I brought the truck in for a rad flush and they couldn't get it started afterwards. Unfortunately the mechanics were already gone and they wouldn't allow me to use the tools in the shop so there it sits. I don't know for sure that it is the control module but it seems to have no spark again.

 

[1979jimmy350]

check the pick up coil, it plugs in to the modual and tells the computer the engine is cranking, it is very easy to test with a vlotmeter, check it for execissive restance and short to ground

 

[readymix]

Exactly, plus check the wiring out of the module

 

[fireplug]

Thanks! Will do.

 

[diesel4me]

module failure..

The most common causes of module failure is ...

1. Voltage Surges..alternator putting out excessive voltage,or bad grounds ,causing flare ups of voltage..faulty voltage regulator can pop one..
2."Tach" terminal wire grounded momentarily..a bad tachometer can pop modules ,but not always right away..
3.Ecessive heat due to little or no heat transfer compund between distributor housing and module's underside...
4. Poor ground between distributor and block..
5. Radio noise suppression capacitor shorting to ground intermittently..
6. Cheap "China" modules seem to fail easily,and for no apparent reason..I'd use a GM module from the boneyard over an Auto-Zone cheepie..
7.A failing pick up coil can mimic a bad module,and only act up intermittently(or the ignition coil)....they too can cause voltage surges,or damage the module if they short to ground..so can an ignition coil with a short in its primary windings that only grounds out intermittently..


There is a fusible link on some HEI ignitions..the "big pink" wire that goes to the "BAT" terminal on the dist.cap,its inline somewhere between there and the fuse box...not all have one,but if your does and its half fried,(or that wire itself is broken or corroded anywhere,it will cause you to rip your hair out,and replace every part for nothing!..

I know,I had one car that did this to me!....put a rebuilt distributor in,with all new parts,cap coil,etc..next morning it wouldnt start back up after a short drive!..finally found the bad fuse link..it would only pass a few amps before it heated up ,and broke the connection..took me hours to find that out!.. ..

It threw me for a loop,because it had 12V when I tested the wire with a voltmeter...but when I tried using a headlight for a test lamp,it would only light the bulb for several minutes,then it would sometimes go dead!!..after it cooled,it worked again..I ripped out the big pink wire and put a new peice of 10 ga wire in,and it was cured...probably all it needed to begin with!..

 

[fireplug]

Great info thanks a lot! I think that post is worth keeping in the vault!