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Old 10-07-2011, 02:34 PM   #1
WIDESIDE72
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93 350 TBI no spark

I am having trouble with my 93 GMC 3/4 ton 4x4 that I swapped a 97 Vortec 350 into. I kept the TBI by using a Crusader marine intake to adapt the TBI to the Vortec heads. About a week ago, I was driving down a bumpy gravel road and the truck started to cut out, then quit. It would barely crank over like the battery was dead. I have fuel pressure gauge and noticed no fuel pressure. I was afraid that the pump had failed again, but also noticed that the ground strap between the engine and frame had broken. (My buddy pointed out that his truck has a ground from the body to the engne at the firewall, but when I bought this truck, the previous owner had blown the engine and had pulled the old engine, so I was playing it by ear when I installed he ground.) It had been running fine up til this. I fixed this with a new wire and now the starter cranks the truck fine, and I have fuel pressure, but no spark. I tried changing the ignition module, then the whole distributor, and the coil. I am getting power at the red wire at the coil. I wonder if I burnt out the computer or chip with the bad ground. (?)

Thanks for any help you can offer.
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Old 10-08-2011, 07:18 AM   #2
panhandler62
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Re: 93 350 TBI no spark

There is a lead to the distributor that signals it to spark. I think that is going to be from "B5" on the ECM.

If you find the correct lead you should be able to connect a test light to it. The light should flicker when the engine is cranking.
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Old 10-10-2011, 12:49 PM   #3
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Re: 93 350 TBI no spark

I have a running 91 Olds Custom Cruiser with a TBI 305 that I am using to compare to the truck. It has power to the red wire when the key is turned on, nothing pulses when cranking. Several of the wires have power after it is running, though. Popular opinion is a bad ground, module or coil. I guess since I have already tried new module and coil, I will add another ground.
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Old 10-14-2011, 01:24 AM   #4
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Re: 93 350 TBI no spark

I have not had time to work on the truck this week. Hopefully tomorrow I will. Does anyone else have any advice? I am almost ready to pull the intake and install a carb and old style HEI!
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Old 10-16-2011, 12:46 AM   #5
1968robinsegg
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Re: 93 350 TBI no spark

there is also a ignition pickup under the ignition rotor inside the distributor, they are known for the wires breaking from the pickup to the module--not real common but i have seen it happen--could be a possibility since its the only thing you didnt mention?
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Old 10-16-2011, 03:09 PM   #6
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Re: 93 350 TBI no spark

Quote:
Originally Posted by 1968robinsegg View Post
there is also a ignition pickup under the ignition rotor inside the distributor, they are known for the wires breaking from the pickup to the module--not real common but i have seen it happen--could be a possibility since its the only thing you didnt mention?
I replaced the whole dist with a rebuilt dist. I have a new one sitting in the seat to try tomorrow.
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Old 10-21-2011, 07:27 PM   #7
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Re: 93 350 TBI no spark

I stabbed the new distributor in and the truck fired with no problem. The only other difference was I used the new cap and rotor that came with the new distributor. I did not try it with the old cap and rotor, but I couldn't see anything wrong with the old one (cracks, carbon trackng, etc.). I cannot imagine the cap and rotor being affected by a bad ground, but at this point, I don't care!

Just goes to show that you can fix anything if you throw enough money at it (luckily only about $50 this time).

Thanks everyone for the help!
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Old 10-21-2011, 08:09 PM   #8
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Re: 93 350 TBI no spark

So did you see if you had spark from the coil or just that you had no spark at the plugs?
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Old 10-22-2011, 02:37 AM   #9
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Re: 93 350 TBI no spark

I never checked for spark from the coil. I just had no spark at the plugs.
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