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
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
-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
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