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.