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1993 GMC Sierra Unable to read ECM

Tiny
SIRDANOMAN
  • MEMBER
  • 1993 GMC SIERRA
  • V8
  • 4WD
  • MANUAL
  • 216,000 MILES
My mechanic is unable to communicate with the ECM on my truck. He says the ECM could be failing but it is very rare. Would it be worthwhile to change the ECM and PROM?

Overall, the truck runs very well despite having 216, 000 miles. Thank you
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Friday, July 30th, 2010 AT 12:24 PM

5 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Hi
System is OBDI was he using an ODBI scanner? if not an OBDII will not comunicate. Jumper a wire between term. A and B on ALDL see diagram


https://www.2carpros.com/forum/automotive_pictures/198357_Graphic_536.jpg

key on does check engine light flash?
Let me know
Thanks for donate
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Friday, July 30th, 2010 AT 12:42 PM
Tiny
SIRDANOMAN
  • MEMBER
  • 3 POSTS
Thanks for the quick reply. I have now used an OBDI coder reader (glorified jumper). I simply get code 12 (the handshake code), but nothing else. My idle continues to flucuate primarily when I've been driving the vehicle for a number of miles and have shut it off. When I restart, the idle "hunts" from 200 to 1000 RPM and will settle but the engine still sounds like it is surging mildly. I've had several vacuum leaks repaired, leaky injector cover reparied, and replaced nearly every sensor but MAP sensor. I'm stuck!

Thank you!
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Wednesday, September 8th, 2010 AT 9:02 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Was IAC replaced or cleaned? EGR checked and cleaned? ECT checked or replaced?Fuel pressure good?
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Thursday, September 9th, 2010 AT 10:21 AM
Tiny
SIRDANOMAN
  • MEMBER
  • 3 POSTS
IAC replaced and TBI removed and cleaned with new gasket. EGR cleaned and no carbon buildup anywhere. Diaphragm seems to be intact. ECT (both) replaced, but haven't checked with multimeter. Fuel pressure check was good. I'm stumped. Will check the timing next week. Could a failing pickup coil and/or distributor problem be an issue? Thanks.
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Thursday, September 9th, 2010 AT 8:14 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Two things to check Ignition, module can be tested at Auto Zone the other pick up coil check wires to coil for cracks in insulation if present replace
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Friday, September 10th, 2010 AT 12:21 PM

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