Here's my problem...i need help quick. I'm in the middle of swapping out my 89 tbi setup for an 88 TPI setup. When we layed the 2 wiring harnesses side by side, we noticed that the TPI harness has a fuel pump relay and fuel pump boss primer plug (that's what it's called in the haynes manual), and the TBI setup didnt. This means that the plug on the TPI harness has nowhere to plug into. So how is the fuel pump going to come on? I'm thinking that maybe the plug is something that can be bypassed, or i'm going to have to splice the wires off that plug into the wires leading to the fuel pump. What I dont get though is...how did the TBI pump turn on if it didn't have a fuel pump relay?? It had to have some other method. If anyone knows anything, help me out...thanks

 

TBI should have the relay. It is held closed by the oil pressure switch. The primer may be what the large TBI vans had, a module that kept the fuel pump on an extra 20 seconds to get fuel up from the tank. If that is the case, not having the module will only shorten up the time the pump runs before it has to be controlled by the oil pressure switch. If this is what the primer is, it will run with out it.

 

I've read that the fuel pump is actually activated by the Oil pressure switch....if that's so, then Its not absolutely necessary to have the fuel pump relay hooked up....it'll just take longer to crank right?

 

The computer closes the relay for the first coupla seconds. I would have to look at the wiring diagram to see if the oil pressure switch would actually close the relay or if it just maintains it once it is closed.