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87 silverado no start

X-1

By X-1
in Ask A GM Technician

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X-1 Enthusiast

X-1

Posted
Posted

I have an 87 silverado 4x4 with 5.7 tbi motor, lately it has been slow to start, having to pump the gas when cranking. Last weekend it stalled on highway, so I replaced the fuel pump in drivers tank and everything was fine for a couple of days. Now it won't run at all. I have replaced the drivers fuel pump ( this truck has two tanks), relay, selector valve, selector switch, ignition module, oil pressure switch, throttle body, iac valve, still no start, no codes and all fuses good. with a volt meter I am getting 8 volts at the pump. What am I missing, I have replaced everything I can think of :fume: Any help would be apreciated,

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted
with a volt meter I am getting 8 volts at the pump. What am I missing

 

I'd say you're missing the fact that 8 volts is not good. It should be battery voltage or darn close.

 

I'd have to see a schematic on the dual tank system to offer a suggestion as to where to check, but I don't think I have anything that old. I'll look tomorrow when I get to work.

X-1 Enthusiast

X-1

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Posted

Thanks,

I think I read that a bad pick up in distributor will also cause a problem, if it helps I am getting 12 volts at relay, and 1 1/2 out to ecm. At the plug coming out of firewall to the pumps I get 8 volts, some thing in between relay and firewall is not doing what it is suppose to do, thinking maybe switch for tanks was bad I replaced it and nothing. Hope maybe this will help with diagnosis, I have never run into something like this before.

X-1 Enthusiast

X-1

Posted
  • Author
Posted

Hooked it up to a snap on scanner, and showing no codes, cel flashes code 12, but would with motor not running, troubleshooter taked about bad grounds and or bad fuseable link, so I will start checking them also look for open ground at ecm, I am still stumped so if anyone has had similar problems please post, I am now on a wild goose chase.

Jerther Enthusiast

Jerther

Posted
Posted
No more ideas here.  Wish I had a schematic handy, but I don't.

 

 

 

 

And I did a quick search and they're impossible to find for free.

 

If it could be of any help, and even tough we're talking about a '87, I've got some diagrams (Haynes Manual) right here that covers most 1988 to 2000 GMC & Chevy Pickups. Just ask :dupe:

X-1 Enthusiast

X-1

Posted
  • Author
Posted
No more ideas here.  Wish I had a schematic handy, but I don't.

 

 

 

 

And I did a quick search and they're impossible to find for free.

 

If it could be of any help, and even tough we're talking about a '87, I've got some diagrams (Haynes Manual) right here that covers most 1988 to 2000 GMC & Chevy Pickups. Just ask :dupe:

 

 

 

 

I found diagrams, and it shows a hot fuel module in the circuit, I don't know what this is, basically my problem is the fuel circuit is not working, it runs with gas piured into throttle body, but the pumps won't run on either side.

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