Mechanics

93 4.8 TBI

1993 GMC Sonoma • 6 cylinder 2WD Automatic • 125,000 miles

Hi I have a 1993 GMC sonoma (S15) 2wd pickup. I has been running fine and all of the sudden it wouldn't start. Just spun over. It seem to be geting fuel but no spark. Then I went out the next day and it started and ran fine for about 4 or 5 miles and died. After 15 20 min it re started and I returned home. I am not sure where to start. I replaced the coil last year Control modual mabe? Any imput would be great. BTW it runs fine when it runs.
Avatar
Disturbo
April 30, 2011.



That should be a 4.3, not 4.8.

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.

Wrenchtech
Apr 30, 2011.
Tks for the reply. Yea I pulled a compression test and it was fine. I have power to every thing and the tbi is puting out fuel just fine but no spark at the plug. Reason I asked here really was I'm not real good with electronic bits. On a simple hei system it would be control modual, distributor, or coil. Was wondering if somthing else may cause it on the newer ones like the computer or somthing. The coil is newer but I will check it next lol its running right now. Oh and yes 4.3 ( 90 deg v6) brain fart on my part.

Tiny
Disturbo
Apr 30, 2011.
If you're not going to run the tests, I can't help you.

Wrenchtech
Apr 30, 2011.
Thats what Im telling you I did run the tests and I had no spark at the plug and then it started again and I cant continue until the problem happens again. Did you read my response? I belive I said I pulled a compression test and a power test and I have plenty of fuel pressure. I had no spark at the plug and all of the sudden it started to work again. If this explanation doesn't work for you I will try and break it down alittle more.

Tiny
Disturbo
May 1, 2011.
Believe me, I do this a lot and I know what you have tested and what you haven't. You don't know what your fuel pressure is, although that's not that critical on TBI but you have not used a noid light to look at injector pulse. I'm not sure if you have verified power supply to the coil either.

Wrenchtech
May 1, 2011.
Ok you have a crystal ball and know what I have or havent done. Man I hope your a shut in and dont work with the public. Thanks for bestoing your great wisdome and and psychic abilties apon me. Lol what an ass.

Tiny
Disturbo
May 1, 2011.
Oh and by the way it was the coil it had a crack in it apon removal. Oh but you knew that.

Tiny
Disturbo
May 1, 2011.