If I bypass the relay the 01 blazer will run fine. Swapped different relays, it won't run. Pump is new.

What would get messed up if I jumped the relay incorrectly?

I cleaned the grounds in the back "over the axel" as well as in front left, under the air filter box grounds.

Gauge stuck on empty.

 

How are you bypassing the relay, which wires?


George

 

I use a jumper wire to jump what would be 30 and 87. I can also apply 12V from stud to the fuel pump prime pin. Vehicle runs fine when relay is jumped. I may have caused an issue when attempting to jump relay incorrectly.
Fuel pump was replaced. Gauge needle on E even with fuel in the tank.

Headlights won't turn on. High beam blue indicator lamp illuminated when switch is manually set to on.

Cap and rotor replaced for an intermittent crank no start problem.

 

OK lets work on the fuel pump circuit first. I don't know how you jumped power "incorrectly" so I don't know what damage you may have done but never alter power wiring or jump something unless the power source if fuse protected.

Jumping 30 and 87 causing the truck to run correctly tells us that the power source and wiring to the relay socket are good and the wiring from the relay socket to the fuel pump is good and the fuel pump ground is good. If you already tried a known good relay and your sure that the pinout was the same then the problem is in the energizing circuit that turns on the relay through pins 85 and 86.

Does the fuel pump prime for 2 seconds at key on with everything normal?

Have you tested for 12v at the relay coil and a good ground at the other side (85 & 86)?

George

 

No fuel prime when turning the key.
I have not tried to jump the 85 or 86 to ground. Would i ground 85 first then turn the key? Repeat with 86 separately?

 

No dont jump anything to ground. Pull the relay and test for 12v on 85 and then again on 86 with the meter black lead on the battery negative post and see if you get 12v during the 2 second prime at key on.

George

 

It was raining last night after my son basketball game so I didn't have much time. I quickly checked for 12V at relay socket. Without having anyone turn the key, I had .2 volts on one and 0 on the other.

I pushed relay in, adding a small wire in the socket with 0V and took it to battery negative. It started right up and head light issue was fine. After work today i can look into the problem more and have my kids turn the key as i measure Volts. I'm thinking i have a broken ground.

 

You will only see 12v on one pin (85/86) for two seconds at key on. Then we know the engine computer signal is good and then we know that the other pin is a bad ground. No 12v at either pin at key on and the drive circuit is bad (computer, wiring, power, grounds). The reason I said not to ground anything yet is because grounding unprotected power can damage something. In this case you had a 50/50 chance of guessing the ground side correctly. Had you picked the othe pin then the relay driver circuit in the engine computer would be driving a dead short at key on and I don’t know if it’s short circuit protected,it could have bricked the engine computer. Also, be careful that make shift ground wire may now be taking all the current flow for the ground attachment point for the relay and everything else that uses that ground bolt.


George

 

Copy. I'll get measurements with key on after work today. I won't jump that ground until I know for sure which side is which.
Do you know the location of the ground? Is it at the back of the engine? Hopefully it's tight and hard to get to. Story of my life. Thank you for the help.

 

G114 left rear of engine. Half your truck is grounded there and since you didn't say your truck is acting like its possessed most likely its the ground wire from the fuse center/relay to the ground point.


George