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Fuel Pump Relay Wiring Diagram 88 Chevy Pickup

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Topic: 1987 Chevy No power to fuel pump  (Read 4763 times)

I have a 87 Chevy 3/4 ton and the fuel pump will not turn on when turning the key. I put twelve volts to the pigtail on the fuel relay and that turns on the fuel pump so it seems to be fine. I have replaced the fuel relay, and the ignition control module on the top side of the distributor after reading some of the forums in this topic but that did not change anything. What should I look into next, I'm not super mechanical but enough to be dangerous. Would the oil pressure switch be causing this?

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Did you check the ECM B fuse?

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,                           ___
                         /  _ _ _\_
              ⌠�����'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

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,                           ___
                         /  _ _ _\_
              ⌠�����'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Did you check the ECM B fuse?

This has happened many times in my last 87 3+3.

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87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Is the ECM B fuse in the fuse panel? I went through all the fuses in there with a tester and visually inspected them and they all tested ok. I don't know if this is related but the headlights quit working about the same time it quit.

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Can you get the fuel pump to run by jumpering the Fuel Pump Prime circuit 490?  It is a red jumper wire that comes off of the Fuel Pump Relay.  Run a fused wire from the + side of the battery to this wire.

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-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Yes I ran twelve volts to that pigtail and it would turn on the fuel pump.

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That jumper wire completely bypasses your fuel pump relay, so the problem has to be between the relay and your battery.  Circuit 450 off of the relay is black w/ white and is a ground for the coil side of the relay, the part the controls the switching on and off of the power.  Make sure you have a good ground there.  Circuit 440 is Orange and provides power to the fuel pump.  It should have 12 V.  I am not sure if it is there all the time or if it is there when you turn the key on, but it comes through the ECM.  Circuit 120 is Gray and goes to the fuel pumps, so we know that one is working.  Last is Circuit 465 which is Green w/ White.  This is the control circuit coming from the ECM.  It is a signal from the ECM to turn on the fuel pump.  This should have 12 V briefly when you first turn the key on.  It should run the pumps for a few seconds.

I am sure BD can chime in if I'm telling you something wrong or if I'm not being completely accurate.

I would think that you should be able to get your truck to run if you jumper to the fuel pump prime wire and then try to start it.  Once it fires, if you remove that jumper wire and it keeps running, then the Fuel Pump Oil Pressure Switch is doing it's job and keeping the truck running in the case of a failed relay, but you did say you replaced the relay.

If you are getting power to the relay and you have a good ground to the relay, then I would think something is wrong with the control circuit from the ECM.

« Last Edit: October 11, 2019, 08:41:32 AM by ehjorten »

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-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

from the link vile posted

even if the FPR is bad the OPS will still give the fuel pump power. the ecm B fuse is in the fuse box. once you find it make sure its getting power when the key is on.

on another note i dont see how the headlights and fuel pump are related but did you ever fix the headlight issue?

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If you can�t tell yourself the truth, who can you tell it to?~Irish_Alley

When you have eliminated the impossible, whatever remains, however improbable, must be the truth ~Sherlock Holmes

The OPS will only keep a currently running engine running.  If the FPR isn't working and the vehicle isn't currently running, you won't be able to start it.

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-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

The OPS will only keep a currently running engine running.  If the FPR isn't working and the vehicle isn't currently running, you won't be able to start it.

Not true.  With regard to 1987 GM TBI, once the engine builds >5� PSI while cranking, the OPS contacts close and supply power directly to the fuel pump, bypassing the fuel pump relay.  Assuming no other gremlins exist the engine will still start, but after many more seconds of cranking.  The OPS is just a failsafe in the event of fuel pump relay failure.  It's redundant.

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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

More to the point of the original complaint, use Chart A-3 and Chart A-5 supplemented by the explanation provided by...

That jumper wire completely bypasses your fuel pump relay, so the problem has to be between the relay and your battery.  Circuit 450 off of the relay is black w/ white and is a ground for the coil side of the relay, the part the controls the switching on and off of the power.  Make sure you have a good ground there.  Circuit 440 is Orange and provides power to the fuel pump.  It should have 12 V.  I am not sure if it is there all the time or if it is there when you turn the key on, but it comes through the ECM.  Circuit 120 is Gray and goes to the fuel pumps, so we know that one is working.  Last is Circuit 465 which is Green w/ White.  This is the control circuit coming from the ECM.  It is a signal from the ECM to turn on the fuel pump.  This should have 12 V briefly when you first turn the key on.  It should run the pumps for a few seconds.

I would think that you should be able to get your truck to run if you jumper to the fuel pump prime wire and then try to start it.  Once it fires, if you remove that jumper wire and it keeps running, then the Fuel Pump Oil Pressure Switch is doing its job and keeping the truck running in the case of a failed relay, but you did say you replaced the relay.

If you are getting power to the relay and you have a good ground to the relay, then I would think something is wrong with the control circuit from the ECM.

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Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

I haven't had the chance to look at it again lately but I will use that A5 chart to try narrow my problem down. Thanks for the help

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Well I finally got time to look at it and it was the ECM B fuse, my dad had went through all of them and had told me they all checked good... apparently he missed one. I replaced the fuse and the pump is kicking on now. Thanks for all the help

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