1990 k5 wont shut off

[big_black_blazer]

a couple of weeks ago, my truck died and i determined it wasn't getting power to the fuel pump. the pump checked good, so i traced it back to the relay, where it still wasn't getting power.(no power to relay) so just to get it home, i hard wired my fuel pump in, with its own relay, so that it would come on when the key was turned to "on". (i determined the computer was the problem, because the power to the relay problem dissapeared when i put the computer from my other truck on it. but shortly after, the new computer acted up too.)

the fuel pump has worked fine ever since and the truck has ran good. but now sometimes the truck will start to run rough and when i try to shut it off it keeps on running. it doesn't do it every time i drive it. there is no SES light showing, and i have verified that the SES lamp does work.

thanks

evan

 

[1985_K5_Silverado]

Ignition switch, perhaps? Did you mess around with that when you were wiring up the relay-picking lead for the fuel pump?

 

[mouse]

The computer provides a ground to the injectors. The injectors have 12v at all times (ign switched). I would suspect a grounding problem. Double check all of your ground wires on the engine - back of the pass head, and on the intake. I bet you find one broken or corroded.

 

[big_black_blazer]

thanks to the both of ya. the ground sounds like the suspect, since it has been intermittent until last night. not to challenge your idea, but where does the spark come from if the ignition is off? it still runs strong, just like the key is on. you can drive the thing.

thanks

evan

 

[1985_K5_Silverado]

Consider the possibility that an increasingly faulty ignition switch is letting power still pass through, even though the key is in the off position. Check it out with a multimeter. I hope it's an inexpensive part like an IS that's causing your trouble, rather than something more pricey.

For reference, a couple of wiring diagrams:

88 - 90 R-V Chassis 1.pdf

88 - 90 R-V Chassis 2.pdf

 

[mouse]

I agree, the power circuit for the injectors is controlled by the ign switch. I would replace that and look at the grounds.