87 GMC TBI won't start

I have an 87 2wd GMC 5.7 TBI .
I love that truck. I have been not paying attention to it for a while.
I start the truck and drive it around the block, warm it up , move it
in/ out of the driveway so it isn't just sitting there rotting. Recently I noticed that at low speeds(15-40mph) if foot is on gas pedal to maintain speed , and you were rolling , the truck would stumble and sound like it wanted to stall. It would sound like a "lopey" cam hot rod motor . I didn't really worry about that too much until now.
The gas was low so I took some fresh 91 octane from my motorcycle gas can and added about 2 gallons to each saddle tank . It's not registered so I shouldn't driving it around (that's the reason for the gas can) This gas is new and it has been burning in other vehicles with no problems Well I started it and was Idling it in the driveway , and right in front of me it just died. No stumble , no wimper , just clean stopped , like someone turned the key off . No codes..just flashes standard 12 12 12
I'm no expert so I looked at all the basics.(from my GM R/V repair manual I purchased years ago,specifically for this truck) -I hear the fuel pumps from either tank with switch each position for 2 seconds -The injectors each get the pulse voltage. - I replaced the fuel filter (which was really dirty) night and day difference blowing through both(yucky) -I carefully took apart TBI and checked both supply and return lines (air pressure though both) -pulled each injector and applied 12 volts and blew through (yucky) I don't have a fuel pressure gauge so I can't check for the 9-13#s. it seems like a pretty good flow (assuming) I had wife turn it over and the injectors alternate dispensing left/right. The truck WILL fire with starting spray/fluid then dies.
There is a spark which was the first thing to check in the book , but in seems orange. In my younger auto shop days I seem to remember needing a blue spark. could that be it?could I have witnessed some kind of ignition failure? was that low speed stumbling a pre-curser of things to come? I'm sick of gas in my mouth please chime in , any advise greatly appreciated .
Thanks P.J.







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hope I can help, see my post on 11/26/05. was having the same conditionand same diagnostic code.the ignition control module located in the distributor cap was bad, had it checked out at local napa store. replaced and is running fine. easy to replace, make sure clean all surfaces and coat with the silicone that comes with the new module, prevents heat build-up which probably caused the original module to go bad. good luck, and let me know how you made out. thanks

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PeeJay wrote:

    Test the HEI module. Both cold and after truck shuts down. The manuial willl have all the proper testing proceedures. Charles



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Thanks , I 'll give it a try soon and let you guys know.
been very busy at work.


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Hello,I was wondering if i could ask you for help?I have a 1989 GMC Jimmy with the 5.7 I drove it every day.I helped my boss's mom and dad move up north my truck sat for 3 days i come home get in my truck and started it up and let it run a little and was driving it and i started to hear like a pinging noise and or a knocking noise.it does not do it at a idle.could it be lifters and or could it be a timing chain.Lost power and has a miss what could it be?or could it be a cracked Flex Plate?

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