electric fuel pump

[drummer]

Hey Members,
My fuel pump primes when I press my horn button. There must be some wire married in the harness to the horn circuitry. This also causes the
idle to increase slightly whenever the horn button is pressed. Where do I start?

[NJ Torque]

The bar.

But really, what kind of car is this? Mods?

[drummer]

This is a LT1 transplanted in an old Ford. The harness is from a 94 Camaro

[LTb1ow]

The 94 PCM just sends a ground to a relay to kick on fuel pump. Find that relay and then follow the trigger lead back to PCM. Anything on that line thats not a direct line to and from, is wrong.

[drummer]

Originally Posted by LTb1ow

The 94 PCM just sends a ground to a relay to kick on fuel pump. Find that relay and then follow the trigger lead back to PCM. Anything on that line thats not a direct line to and from, is wrong.

I located the fuel pump relay. There are 4 wires. Orange= direct 12v
Grey = fuel pump
Black/whitestripe = pcm
green/whitestripe = pcm

Don't see any splices in these wires.

[sweetbmxrider]

He's saying follow the leads. Someone tapped a wire onto the fuel pump circuit and you get to find out where. I would try going off of the horn wiring and either seeing where it goes or cutting the wires, taping the one side off, and running the button side to known sources for both power and ground. Hopefully that fixes your issue. Could even be from the horn connections itself so you may have to play around a bit.

[LTb1ow]

Yea, something is wacky there.

And if the car is running fine, then the horn button messes up idle something is wacky. The pump can run fast, slow, or whatever it wants as long as it maintains 40psi to rail, the regulator will make average FP what you need. So..

A) Your fuel pump is running slow on low voltage and the horn adds normal voltage (too little FP and it gets the OE amount with horn)
B) The horn causes fuel pump to lose voltage and slow down. (normal FP, but horn causes pump to slow down and not provide OE FP)

That being said, on 95 harnesses there is a fuel pump relay prime wire that normally is on pax side harness. That lead is prob what is being tied into the horn.

[sweetbmxrider]

Maybe the horn button is connected to a Nawzzz fogger system? I'd check the intake welds while you are under the hood.

[BonzoHansen]

Are any related wires attatched to the horn relay? A lot of old cars use the horn relay as a common power point. I'm not sure what could be happening but that came to mind.

[drummer]

Originally Posted by LTb1ow

Yea, something is wacky there.

And if the car is running fine, then the horn button messes up idle something is wacky. The pump can run fast, slow, or whatever it wants as long as it maintains 40psi to rail, the regulator will make average FP what you need. So..

A) Your fuel pump is running slow on low voltage and the horn adds normal voltage (too little FP and it gets the OE amount with horn)
B) The horn causes fuel pump to lose voltage and slow down. (normal FP, but horn causes pump to slow down and not provide OE FP)

That being said, on 95 harnesses there is a fuel pump relay prime wire that normally is on pax side harness. That lead is prob what is being tied into the horn.

Is there a fuel pump relay prime connector in a 94 lt1 harness? What color and where would it be?

[LTb1ow]