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1993 GMC Seirra Z71 4X4

Tiny
AALATA01
  • MEMBER
  • 1993 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
My truck will not run even though fuel is reaching the injection unit, fuel pump relay has been changed, fuel pressure regualtor been changed, the fuel injectors do have power to them, and the fuel system puts out 14 psi, it will fire when gas or ether is manually injected into the t.B.I. Unit, but will stop immediately. It also has been scanned but is not giving any trouble codes, the number one spark plug does have spark, what else is going wrong that will not let it run?
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Sunday, March 27th, 2011 AT 9:21 PM

7 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,916 POSTS
Sounds like the Engine Computer isn't firing the injectors. You can verify that by plugging an injector connector into a "noid light". That will flash when the injector is pulsed. If it doesn't flash, suspect the crankshaft position sensor. (I have to defer to my Chrysler experience here, but in that respect, GM and Chrysler do things similarly).
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Sunday, March 27th, 2011 AT 10:20 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
This one doesn't actually have a crank sensor. The pickup coil in the distributor performs that function. If that were bad, you would lose spark also so if it runs by priming it, you do have spark. Check all your fuses and make sure the check engine light is coming on for a bulb check when the key is turned on.
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Sunday, March 27th, 2011 AT 10:47 PM
Tiny
AALATA01
  • MEMBER
  • 3 POSTS
We checked all te fuses under the dash and fuel pump relay fuse. Are there any other fuses we are over looking and where are they. Is there an ECM fuse? ANd if the computer is bad is there a way we can test it, or does the EPROM chip have something to do with it? What do you mean by "bulb check" my check engine light comes on when the key is on.
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Sunday, March 27th, 2011 AT 11:34 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
It's sounding like a bad computer but all the power and ground inputs to the ECM would have to be verified first.
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Sunday, March 27th, 2011 AT 11:49 PM
Tiny
AALATA01
  • MEMBER
  • 3 POSTS
Everything seems intact in regards to inputs and grounds. The computer also has what I think is a EPROM chip. I noticed that on new computers that you can buy this blue chip is not included. Would the truck need it to run, or is it an optional power chip? The chip says AC Delco right on it, so it makes me think it's a stock part.
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Monday, March 28th, 2011 AT 3:18 AM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
The Prom is the personalization for your particular vehicle and that has to be transferred from the old one to the new one.I have to say that you could not have checked this out thoroughly enough yet. You need to verify every input and output of the PCM systematically.

Here is the pinout to do that.

This is with the 4L60E trans
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Monday, March 28th, 2011 AT 12:51 PM
Tiny
WRENCHTECH
  • MECHANIC
  • 20,761 POSTS
That didn't work out as planned. I'll try it a different way.
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Monday, March 28th, 2011 AT 1:05 PM

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