Good idea! 
No Fuel Pressure
TECH Regular
Joined: Dec 2022
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If the engine starts and runs with a jumper in the relay spot then you have an issue with relay or the control side of the relay... you can use a headlight bulb across the control side of the relay terminals and if it's bright when you key on then it's good and if it's dim then you have a problem there... you can then narrow it down to the power or ground side
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From: Bostwick, GA.
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Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
Ok so I finally got around to doing the drop test and here are the numbers. Hopefully someone can tell me if they are good or not. Ill start with the ground side:
Key off: KOEO:
Pin 1 .005 V Pin 3 .005V Pin 1 .05 V Pin 3 .03 V
Pin 5 12.56 V Pin 2 .005V Pin 5 12.25 V Pin 2 12.02 V
Power side
Key Off KOEO
Pin 1 12.59 V Pin 3 12.6 V Pin 1 12.27 V Pin 3 12.3 V
Pin 5 .001 V Pin 2 12.00 V Pin 5 .01 V Pin 2 .25 V
I installed an aftermarket FPR and the pressure gets gauge reads pressure. I installed a walhbro 255 fuel pump so everything is new. Ive got a 98 which had the stock FPR in the tank on the return but since I added the asdjustable one in the engine bay I can just chuck the old one correct?
TECH Regular
Joined: Dec 2022
Posts: 444
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Kinda confusing the way you wrote that out but...
Pin 1 and 2 are the control side of the relay
One should be ground all the time and one is power from the pcm
Voltage drop should be tested with the load on the circuit. An easy load test is to use a headlight bulb across those pins. When you key on the bulb should light brightly during the pump prime cycle for like 2 seconds. If it's dim then you can put that bulb between the ground side of the relay and battery positive- should be bright - if so then swap the bulb so it's on the power side of relay and battery negative then it should light brightly during the prime cycle.
This tests circuit integrity quickly. A poor Connection or bad wire will show full voltage and low ohms unloaded but not be able to support the current requirements when loaded with an amp draw
Pin 1 and 2 are the control side of the relay
One should be ground all the time and one is power from the pcm
Voltage drop should be tested with the load on the circuit. An easy load test is to use a headlight bulb across those pins. When you key on the bulb should light brightly during the pump prime cycle for like 2 seconds. If it's dim then you can put that bulb between the ground side of the relay and battery positive- should be bright - if so then swap the bulb so it's on the power side of relay and battery negative then it should light brightly during the prime cycle.
This tests circuit integrity quickly. A poor Connection or bad wire will show full voltage and low ohms unloaded but not be able to support the current requirements when loaded with an amp draw
Since you mentioned you have a bulb handy, here is best way.
Put a bulb with leads in 1 and 2 (as shown on the relay picture).
Just sitting, the light should be OFF. Key off, then key on and you should see the bulb light for right around 2 seconds and go out. That should happen on each and every key cycle. Bulb should be bright and solid for 2 seconds then go off.
Then when you crank it you should see the bulb light again only while engine is spinning.
That tests the control side.
Your jumper has already tested the load side I believe, I think you said if you jumper 3 to 5 the pump works.
If this all works then your relay is broke. If not, then find out why, maybe bad power isn't lighting the light etc....
Note: I am basing these pin numbers off of that relay pic. If you have the wrong relay then the pins may be different, I didn't look up the fuse box ping numbers I am trusting that relay pinout.
Put a bulb with leads in 1 and 2 (as shown on the relay picture).
Just sitting, the light should be OFF. Key off, then key on and you should see the bulb light for right around 2 seconds and go out. That should happen on each and every key cycle. Bulb should be bright and solid for 2 seconds then go off.
Then when you crank it you should see the bulb light again only while engine is spinning.
That tests the control side.
Your jumper has already tested the load side I believe, I think you said if you jumper 3 to 5 the pump works.
If this all works then your relay is broke. If not, then find out why, maybe bad power isn't lighting the light etc....
Note: I am basing these pin numbers off of that relay pic. If you have the wrong relay then the pins may be different, I didn't look up the fuse box ping numbers I am trusting that relay pinout.
Last edited by mk3cn4; Feb 16, 2024 at 03:38 PM.
Thread Starter
Staging Lane
Joined: Nov 2023
Posts: 90
Likes: 5
I appreciate all the help. I have pressure just weird how it never goes back to the same psi . I havent been able to start it because for some reason my injectors arent pulsing. Ive got 12v at the red wire on the injector coil when KOEO and i ground the multimeter to the neg battery. When IU test the ground on the coil its 6.65 so idk if thats right or not. I have checked all the grounds and cant figure it out but the injectors wont squirt
TECH Regular
Joined: Dec 2022
Posts: 444
Likes: 158
Really dude? Is that repeatable? Starts and runs vs ran for 2 secs and died are completely different... thats why you got people running in circles telling you how to test the control side of a relay when bypassing the relay didn't even fix your no start issue...