SurWagon

So I was trying to figure out why the fuel pump didn't prime or run. After reading the wiring diagram I saw that pin 85 was getting 12v+, but pin 86 was not grounded. The ground looks to be good, but there is intermittant connectivity between pin 86 of the relay and F7 on C2. It shows an open circuit and then will blink to connectivity for a split second.

I made a jumper from 86 to ground and the relay clicks on (during run) and the fuel pump turns.

Anyone had this problem before? Anyone see a problem with leaving the extra "jumper" ground attached?

Next time I do a swap I'm buying the fusebox with the engine and taking it directly out of the car. Having to guess about the harness and other wiring sucks.

Pop N Wood

iTrader: (1)

I run a carb so I don't know much about the computers, but I thought the computer grounds the fuel pump relay on EFI motors? I think the computer turns the pump on to prime the fuel system for start up, but then kills it again if the motor isn't running. If that is the case you just bypassed that safety feature.

Hopefully someone will correct me if that is wrong.

SurWagon

From the diagram it looked like it supplied positive signal through a green and white wire. But what you said makes sense. It should just prime....right?

68 SS

iTrader: (23)

According to your wiring diagram 86 is a full time ground witout an interrupt if it works correctly then problem solved. Does the pump prime the shut off like it should when you put the jumper in?

SurWagon

I haven't tried to start it yet. I disconnected the starter relay signal and turned it to RUN and the fuel pump runs for at least a couple seconds, I didn't try any longer than that. The fuel pump also runs during START.

I would think it would only prime for a second, maybe two. Does anyone know how long the PCM primes it?

mantycarguy

The fuel pump should prime for approximately 2 seconds and then turn off unless the pcm sees a crank sensor signal which will then restart the pump again. In older versions the pcm would control the ground side of the relay. It makes no difference on how it is controlled, but in your case running a jumper to ground will work as you are essentially replacing a faulty constant ground anyway. This would not work on earlier pcm ground controlled versions.

dkbmxer002

iTrader: (5)

check the plug at the top of the fuel hat where the 4 wires go through for the fuel level sensor and the fuel pump. mine has an issue with melting. i am going to upgrade to a setup racetronix sells that helps. from what i have read it is a common problem.

SurWagon

This is a 2003 LQ4 and harness from an express van with a 2004 sierra 4l80e going into a 88 Jeep Grandwagoneer. The computer was retuned by wait4me performance. It's a red/blue. I'm still using the Jeep's fuel level sender and have a high pressure pump on the frame rail that moves the fuel. When jumpered fuel flows through the rails.

So....when I jumper 86 of the relay the pump just stays on. Boo...

Also, when I crank it, it doesn't fire. I'll have to hook up the obd port and see what's going on.

dkbmxer002

iTrader: (5)

ahh nevermind.

SurWagon

Dkbmxer - any ideas or help are always welcome!

I still don't understand why I have no connectivity between F7 and 86?????

SurWagon

Got this off of autozone's diagrams (great stuff there)

Looks very different, like blue green PCM connections instead of red/blue.

SurWagon

Pulled a spare fusebox I pulled from some S-10 and guess what....F7 and 86 have connectivity. Crap, guess I have to figure out which fuse box to use with my harness by checking the wiring diagrams against the actual wires.

SurWagon

BTW, this is the fusebox I'm using (I think)

SurWagon

Spent a good portion of tonight trying to rewire the thing and still just had the fuel pump run constantly.

I'm going to just buy an 02 fusebox from a silverado. I was trying to make this easier by using stock parts!

Moral of the story....buy all your stuff together.

SurWagon

For future reference....the van fuse box is completely different. This probably explains all of the issues. I gites the only thing it has in common its out uses the same connectors as the truck.....but pinned differently.