As the title says, I need to disable the fuel pump while cranking the motor for a compression test. I have the carb off the engine, so just an open intake at the moment.

I thought pulling the fuel pump relay would do the trick, but fuel started gushing out shortly after starting.

What's odd is that I'm using a heavy gauge wire to jump the battery (+) terminal straight to the starter wire on the solenoid, so that I can see the gauge without having to sit in the truck doing this blindly. I thought this would bypass all electrical accessories but I cannot seem to kill that damn pump.

Please help!

 

Pull the relay, and also a small wire over at the solenoid connected to the same terminal as the large wire going to the starter or the "I" terminal. It should have a fusible link there and turn into a pink/black wire.

 

It's on the I terminal. I will try this, thanks for the tip!

Also, I know I'm shooting compression values that are within 5% of each other, but what are appropriate or average compression readings for this engine? The first one I did before fuel started pouring at hit a solid 148 PSI.

I'm also at a high elevation, I suppose they will read slightly lower than normal, or does this not affect it?

 

I know this may be beyond the scope of my original question, but I'm curious if these compression numbers are considered decent for this model year engine (1985).

Cyl Number | PSI dry/wet

1. 147
2. 138
3. 139
4. 144
5. 150
6. 137
7. 120/160 (performed wet test on this one cause of the low #)
8. 130

Supposedly the engine has 97k and is original to the truck, but may have 197k; hard to tell.

Is there any surefire way to determine if the engine is original to the truck, or a replacement / reman unit?