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1994gm truck start problem


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jamesg1551
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Nov 27, 2017, 2:55 PM

Post #1 of 3 (368 views)
1994gm truck start problem Sign In

1994 gm 1500 truck elec. problem. will not start. checked most common things to check. manual said. white wire coming from ecm should have 12 volts to supply modual in distubator , and this wire goes to the ecm unit only and I have no voltage. but wire shows around 200 ohms. is that normal to drop the voltage . have traced wire from dist to ecm no breaks. if I cut wire tape up going to ecm and put 12 volts to pcm unit ( on dist. modual ) would truck start and run or burn up dist. modal ? wire coming from coil and ignition switch has 12 volts. please help, this is getting old. thanks. james


Hammer Time
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Nov 27, 2017, 3:18 PM

Post #2 of 3 (360 views)
Re: 1994gm truck start problem Sign In

Before doing anything, make sure the check engine light is coming on for bulb check when the key is first turned on without starting it.


after that

All "crank, no start" conditions are approached in the same way. Every engine requires certain functions to be able to run. Some of these functions rely on specific components to work and some components are part of more than one function so it is important to see the whole picture to be able to conclude anything about what may have failed. Also, these functions can ONLY be tested during the failure. Any other time and they will simply test good because the problem isn't present at the moment.
If you approach this in any other way, you are merely guessing and that only serves to replace unnecessary parts and wastes money.



Every engine requires spark, fuel and compression to run. That's what we have to look for.

These are the basics that need to be tested and will give us the info required to isolate a cause.

1) Test for spark at the plug end of the wire using a spark tester. If none found, check for power supply on the + terminal of the coil with the key on.


2) Test for injector pulse using a small bulb called a noid light. If none found, check for power supply at one side of the injector with the key on.


3) Use a fuel pressure gauge to test for correct fuel pressure, also noticing if the pressure holds when key is shut off.

4) If all of these things check good, then you would need to do a complete compression test.

Once you have determined which of these functions has dropped out,
you will know which system is having the problem.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Nov 28, 2017, 11:50 AM

Post #3 of 3 (316 views)
Re: 1994gm truck start problem Sign In


Quote
white wire coming from ecm should have 12 volts to supply modual in distubator , and this wire goes to the ecm unit only and I have no voltage.



NOOOO!! Don't do that! The white wire is the coil trigger wire from the distributor ignition module. If you short power to that wire, it will blow the transistor in the module. There is another white wire from the module to the ECM. That circuit is the timing circuit that supplies a 5v digital square wave signal for triggering the ignition module in EST mode. If you short that wire to 12 V, the ignition module will definitely not work. It will also blow the IC output transistor in the ECM.

I suggest you have a professional check it out if you are not familiar with the system and how it works.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Nov 28, 2017, 11:51 AM)






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