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88 K5 will not start...need help.

T

THEMCGUIRE

1/2 ton status
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This truck last ran about 6 years ago when it just died.

It will start and run while using starting fluid...

I do not see fuel coming from the injectors.


New stuff installed since then:

1. spark plugs and wires.
2. control module.
3. Fuel pump assembly. then just in case another new fuel pump :(
4. 2 new fuel filters
5. Fuel pump relay
6. battery
7. Starter

I have about 8.6 volts coming to the fuel pump from the front of the car to the connectors behind the driver rear wheel.

When I connect to the fuel assembly wires and check voltage at the fuel assembly it drops to 1.5 volts.

I am so confused. Help !!!!!
 
Fab54:

I got the 8.6 at the connector with the key on. it was not connected to the fuel pump assembly... that is it was unplugged.

I got the 1.5 v by piercing the wire at the assembly when plugged in with the key on.

does that help ?

Eagle Mark: thanks for the diagrams will print and check them asap.
 
Not to be condescending, no idea what your experience level, but key in run, engine stopped, voltage at the fuel pump is meaningless since it only has a 2 second prime, then nothing.

As Mark said, put 12V to the red wire at the relay, then measure voltage again at the connector near the rear of the truck.
 
I know how to do a tune up and replace parts but electrical diagnostics is alien to me.

With truck jumped to a running car to save the battery I put positive power to the fuel relay bypass. tested at the rear connector and got 13.4v (key on or off) then reconnected and got zero volts on the purple wire that goes into the fuel pump assembly.

Next I put positive power directly to the purple wire and I could hear the fuel pump wirring. So pump is good !!!!

Then I reconnected and twisted the connector some (also cleaned the connections with carb cleaner) after twisting I got 13 + volts at the purple wire right at the pump assembly.

attempted restart and do not see fuel coming from the injectors ?

BTW after sending the 12v directly from the battery to the purple wire and let the fuel pump wirr for a second or 2 then reconnected the wires to the harness I tried to start it. It seemed to start for a split second.

Would it be ok to hard wire (as a test only) the 12v directly to the purple wire causing the fuel pump to work and then try to start the car and see if I get fuel from the injectors?

Will that damage anything? I suspect it will not but want to be sure.
 
Not sure I'd do that.

If putting power to red prime wire worked, then did not? It's a bad relay!
 
I installed the relay about 4 years ago but truck never started anyway. I gave up for a while when I was working on rebuilding the body.

Can a relay go bad if it is never used ?

Can it be tested at napa, autozone etc ?

Wait !!! I have power to the fuel pump assembly when I use the red bypass but when I crank it I DO NOT hear the fuel pump go on.

It only goes on when I put power directly from the battery to the purple wire at the pump assembly.

I only want to power the pump directly for a very short time to determine if I get fuel to the injectors when cranking.
 
If you put 12V to the relay bypass, the pump should be running at all times, no matter what the key position. If you can hear the pump over the engine cranking, your hearing is better than mine. If it is not working with 12V to it, stop and fix that problem first. You know the pump works, but if it does not work consistently, you have to solve that before you do anything else. No reason to wire the pump directly when the relay bypass is the same thing.

Once the pump is known to be working correctly, every time, then you can worry about whether or not the injectors are actually pulsing as they should be.
 
Disregarding all advise because I NEEDED TO KNOW, I connected 12v directly to the purple - in connection at the fuel pump. Engine started... plenty of fuel coming out of both injectors (although droplets not a fine spray). But it stayed running until I remove the power to the pump.

So bought and installed a new fuel pump relay. NO change. Now I must point out that my old fuel relay was installed 4 years ago but truck never ran.

Therefore would you agree that it must be the wires from the fuel pump relay to wherever they go ????
 
Have you checked the power into fuel pump relay? Have you checked the fuse for fuel pump relay?
 
When the key is on, and I disconnect the plug from the bottom of the fuel pump relay and test for voltage on the wire that goes to "A" I have 12 volts. since that wire comes from the ignition doesn't that mean that the fuse is ok ?
 
THEMCGUIRE said:
Disregarding all advise because I NEEDED TO KNOW, I connected 12v directly to the purple - in connection at the fuel pump. Engine started... plenty of fuel coming out of both injectors (although droplets not a fine spray). But it stayed running until I remove the power to the pump.

So bought and installed a new fuel pump relay. NO change. Now I must point out that my old fuel relay was installed 4 years ago but truck never ran.

Therefore would you agree that it must be the wires from the fuel pump relay to wherever they go ????
Click to expand...


you need to verify where your power loss is... the pump runs when energized at the back... does it run when you put 12v to the relay red jumper? you need to know that before assuming it's in the feed to the relay.. even if you've put a relay in... verify function from the relay back, than move to the power feeding it..

isolating the issue, it's what diagnostics are all about..
 
According to the wiring diagrams that Eagle Mark provided above when power is applied to the red wire going to the fuel pump relay it goes directly to the "E" connection and out to the fuel module. I am going to go and test voltage at the "E" wire coming out of the relay and will report back.
 
Last edited:
ok sending power to the red wire "aka "C"". I checked for power at "E" and have 12v +. Then I checked at fuel pump assembly purple wire. also 12v + but pump does not operate.

This is crazy. when I apply 12v to purple directly from battery the pump "wirrs".

I must be crazy or incompetent but this does not make sense.

New plan ???? Splice into the E wire as it exits the relay and run it directly back to the purple wire on the fuel pump assembly. See what happens.
 
take apart and clean the grd connection for the pump...
 
Will do, Sir! :)

When I put the new fuel assembly in last year I made sure to grind down the frame under where the ground gets connected to the cross member to be sure I had a good ground.

was thinking about the ground earlier but then I thought that since the engine runs when I connect the battery directly to the fuel pump doesn't that indicate that the ground is ok.

is there a way to test the ground ?
 
continuity test is usually good enough.. and yes, 12v applied, and running would indicate good grd, just covering my bases...

you just need to work farther and farther from the pump and ensure it runs.. ok, it runs when you put 12v to it at the back... and you say it checks 12 there when the red is hot... go to the other side of the relay, to the output, put 12 there and verify the pump runs and starts the rig... ya may have a shoddy wire from the relay back...
 
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