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manitouboat
New User
Mar 10, 2012, 6:47 AM
Post #1 of 8
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no fuel 1991 S10 2.5
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Truck would sputter sometimes like it was out of fuel. Then when I shut it off this last time it wouldn't start at all. Lucky it was in my driveway.
So i disconnected the fuel line from the bottom of the fuel filter and cranked it over, no fuel from line. So i started reading and find out the relay maybe bad.
Found two relays on firewall by brake booster, one for the AC one for the FP. Thought there should have been a grey wire on one. No grey wire? I switched relays because I read they where both the same. Thought they both can't be bad. Still no fuel.
All fuse are good.
No power to pump when key is on. Checked grey wire along frame wire with test light
No click from relay.
Also tried putting power directly to grey wire that runs along frame so fuel pump was running (it ran). Then primed truck.
It started but quit when it ran out of prime.
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Hammer Time
Ultimate Carjunky
/ Moderator
Mar 10, 2012, 8:43 AM
Post #2 of 8
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Re: no fuel 1991 S10 2.5
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That gray wire only powers for 2 seconds when the key is first turned on. Check that.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 10, 2012, 9:27 AM
Post #3 of 8
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Re: no fuel 1991 S10 2.5
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The colors at the fuel pump relay are:
dark green/white
orange
tan/white
black/white
where are you getting grey from?
Check at the relay connector.
dark/green white: should have 12 volts for a few seconds with key on. This circuit is powered by the ECM. Do not connect a 12 volt test lamp to this circuit. Use a logic probe or volt meter. You can burn the quad driver up with a 12 volt test lamp on this circuit.
orange: should have 12 volts with key on or off. Power on this circuit is protected by the ECM B fuse in the fuse block.
tan/white: is the circuit that goes to the pump. You should be able to see 12 volts on this circuit when you jump the prime connector near the battery to power. Jumping the prime connector to battery power should also cause the fuel pump to run. That is what it is for.
black/white: is the ground circuit for the relay's coil. The ground goes to an eyelet. Make sure this circuit has close to 0 ohms or can brightly illuminate your test lamp with your lamp connected to battery power.
Another thing to consider is that the oil pressure switch is in parallel with the fuel pump relay. If the fuel pump relay doesn't work, the fuel pump should run when the oil pressure gets high enough while cranking the engine.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 10, 2012, 9:55 AM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Mar 10, 2012, 11:53 AM
Post #4 of 8
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Re: no fuel 1991 S10 2.5
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You're right. I just expected gray because most of the GMs are that color.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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manitouboat
New User
Mar 11, 2012, 9:05 AM
Post #5 of 8
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Re: no fuel 1991 S10 2.5
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Ok this is good info. one step at a time. I checked Orange with meter at relay no power. ignition off. Checked fuses again they are all good.
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 11, 2012, 9:09 AM
Post #6 of 8
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Re: no fuel 1991 S10 2.5
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Check for power in the fuse cavity?
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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manitouboat
New User
Mar 11, 2012, 10:28 AM
Post #7 of 8
(6047 views)
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Re: no fuel 1991 S10 2.5
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Great news truck runs.
Had no power a fuse. Checked again ran tests you suggested.
Put power to tan and white wire pump ran.
Don't know what happened but when I put it all back together and it ran. Guess it had bad connections.
Your very good I have been chasing this for a week. Your the only on who knew what color the wires where and gave a concise way to check them.
Thanks to you my truck runs.
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Discretesignals
Ultimate Carjunky
/ Moderator
Mar 11, 2012, 11:29 AM
Post #8 of 8
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Re: no fuel 1991 S10 2.5
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That could be a good thing or that could be a bad thing, but good to see that you got it running.
One thing that you do know is if it ever has the problem again to check for power at the ECM B fuse. You may want to inspect the fuse panel really good. Check the bus bars on the back of it and make sure you don't have some type of corrosion going on. There is also a pass through connector at the firewall that you might want to inspect. If you take the pass through apart, clean the terminals really good with some electrical contact cleaner and then lube the terminals with dielectric grease using a small nylon brush. Don't use too much grease or you can actually hydrolock the connector when you go to put it back together.
With the vibration and thermal contraction and expansion of the terminals in the connector fretting corrosion can occur and cause a poor connection which causes intermittent electrical problems. If the connection gets enough resistance, it can actually get hot and melt the terminal and the connector material around it.
Its odd, but electrical connectors are one of the most neglected items in the electrical system. They actually do need periodic maintenance. Especially with an older vehicle such as yours.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Mar 11, 2012, 11:30 AM)
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