Hey guys I need a bit of help
I am doing a temporary carb swap on an 88 f250 with a 7.5l.
I need to know what the ECU needs to see in order to run the fuel pumps. They work fine, I jumped the relay. I need to know what the ECU would normally want to see to allow the pumps to run continuously. Oil pressure? Vacuum signal? RPM? I just want to jumper the harness to get it up and running. I am planning an aftermarket efi upgrade down the road to go with DOVE heads and a cam, but i need to get the truck moving around.
Thanks.

 

The ECU uses the PIP signal from the distributor to run the fuel pumps

 

Is there a way to fake a pip signal? I an using a gm style hei distributor, and it has a tach output. Would this create the same signal?

 

If it's a EEC-IV setup the pumps should run continuously when engine RPM is above ~100-200 RPM. It energizes them for 1 second in KOEO to prime the fuel system and re-energizes it during cranking, and will continue to run them as long as engine RPM is sufficient. Arse_sidewards is correct on the PIP being the input to the PCM.

Also, there are two wires w/ fusible links that feed power to the fuel pump relay. The links are near the fender mount solenoid. I had an issue with one/both of the wires breaking, it set a code 543 and caused a crank/no start.

 

What I am most concerned about is burning up my ecu by feeding it a signal that is too high a voltage. I don't have a stock distributor to test output. Can anyone tell me what the pip signals parameters look like?

 

It's a square wave, with the peaks at around 12v or battery voltage. Keep in mind, it would be far easier just to run a little jumper wire from the main PCM relay to the fuel pump relay.

 

A waveform to reference:


I agree, for a short term solution this is the easiest.

 

This is a good point.

I was originally trying to preserve the safety feature that you get by only allowingthe pumps to run when the engine is firing. I can just see myself forgetting to turn the key off and having the pumps run until the battery dies or the old carb im recycling leaks until it fills the motor with gas or something ridiculous.

 

Why not just leave the EFI system on until you're ready to do your swap?

 

I bought the truck without a motor or transmission. It sat around for a very long time and now I need to get it moving. I found a very low km (rebuilt) 460, that was 70'S vintage. I scored a set of DOVE heads to go on it for $300.
Unfortunately top end 460 stuff is not interchangeable between efi and non-efi to changes in port location and combustion chamber volume. The end goal here is a tow rig motor that makes 9.0:1 compression.