Been a long time member and need some help guys this one has me stumped. I have a 89 formula 350tpi I just installed the fitech ultimate standalone ecu and harness. I removed the factoy ecu and harness. Car runs excellent BUT now immediately after installing this kit the fuel pump will do a 2 second prime everytime I turn on the headlight switch. Fitechs system uses there separate fuel pump relay with 1 wire that I connected to the tan wire with white stripe in the c100 harness.. anyone know what I'm missing here? Fitech was pretty simple and straight foward install im wondering if theres a leftover wire somewhere from the factory ecu harness that needs power or ground idk im lost lol Thanks

 

The brake warning lamp in the instrument cluster also uses a tan/white wire. It would be good to verify which is which.

 

Thanks Vader! I'm going to run the fp wire from there relay straight to the pump and that should take care of it.

 

Vader so I took fuel pump wire straight from the fitech fuel pump relay and ran it straight to the fuel pump and samething. Key on, the headlight switch still primes the pump for 2 seconds then again when I turn the headlight switch off it will not do it with the key off. Fitech system doesn't have anything to do with the lights in the car. Really confused. Any help is greatly appreciated!

 

The problem isn't the wire from the relay to the pump (the "output" of the relay, so to speak); it's the coil circuit of the relay. The "command". The one that tells the relay to operate.

The wire from the original ECM that tells the relay to operate is the same color as the other wire that's involved with the lights. You have the new harness' FP relay coil wire connected to the wrong (the other) tan/white wire.

 

I ran the wire from fitechs fp relay in there fuse box under the center console to the back of the car straight to the fuel pump. There's got to be something I'm missing here

 

That's the relay OUTPUT. That's not what's wrong. You can change that wire every day from today until The Rapture, and twice on Sundays just for good measure, and it will NEVER address the problem you have. Your problem is the relay's INPUT.

Imagine that you have a switch on your kitchen wall and you flip it but no lights come on. Instead the garbage disposal starts to run. Miraculously enough however, you flip the switch located in the upstairs bedroom, and voilà! the kitchen lights up. THAT'S the way your problem is. Your relay's COIL circuit, the thing that tells it to come on, is wired to the wrong source. You're sending the relay the wrong command. Instead of sending it the FP command, you're sending it some headlight-related command.

 

My guess is you've wired the Key wire (page 4, install manual) to the headlight switch instead of ignition.

 

Thanks komet, I have it wired to the red wire on the coil plug like the manual recommends. They want to have 12v while cranking. It's so easy to install and not many wires to screw up lol this is what's frustrating. This is how I wired it from the manual.
1) pos red wire to battery (ecu needs 12v all times)
2) both grounds at the back of the head
3) fuel pump wire ran directly to the pump
4) red wire 12v on/off 12v while cranking went to the red wire on coil plug as recommended
5) tach wire to white on coil plug
6) white fan wire relay ground - ran it to a dakota digital 70amp fan relay for my Taurus fan. I don't get how any of that would have anything to do with the headlight switch.
Thats all there is to it. Pretty simple install. I have alot of experience working on these cars. Worked at a vette f body shop for 11 years and have restored for 89 formula that I've owned since high school 20 years ago. After thinking about I guess it really doesn't matter if the switch primes the pump while the car is already running bc the pump is already getting 12 volts. It doesn't have any effect on it while it's running. Other than this issue the car runs amazing (fully built 350tpi with a g force T5)

 

I don't know about your specific setup, but typically an ECM controls a relay by grounding the field coil circuit, and there is always (+12V) on the high side of the coil with key ON. Mis-wiring the high side of the coil with the wrong (+12V) source won't make the pump turn ON in that situation, only the ECM can command the pump ON by grounding the field coil.

Typically an ECM primes fuel only after the switched power is cycled. And then it turns pump ON again whenever there is engine speed (engine cranking or running).

Sounds like it has something to do with your pop-up headlight motors. Those are the only thing that run when the lights are turned both on and off.

My guess is that either your ECM is somehow power cycling (which initializes fuel prime again), or the headlight motors are somehow providing an alternate ground for the fuel pump relay coil.

Few questions for you:

1. Does the pump prime during a normal key ON, or is it only when you cycle the head lamp motors?

2. And is your normal prime longer than 2 seconds?

3. Does this "prime event" turn on and off at the exact same moments as your headlamp motors turn on and off?

 

Yes the pump primes normal with the key on. My headlight motors are hard wired to a window switch (I did that years ago since the headlight module died)

 

Normal prime probably 2 to 3 seconds

 

Oh, I see. LOL! ​​​​​​You're one of those people.

I can't help you with this because I cannot guess at all the hacks you've done to that car over the years.

For what it's worth, a C5 Corvette headlight module works in my 89.

 

Smart ***. Its not a hack if you know how to wire it up correctly and not half *** it. Not f*cking rocket science. When you own a car for 21 years and NEW headlight modules are OBSOLETE and I've been through 4 used ones at $100 a piece it makes since to me. Maybe it makes since to you to use a 28 year old headlight module from a 1985 corvette doesnt to me.

 

 

Real hack job restored from the ground up. Moron

 

That's pretty big talk for somebody who's fuel pump turns on every time they touch the headlight switch.

When you own a car for 32 years, you learn that a C5 Corvette is 1997-2004 and you can buy the headlight modules NEW. That's why that was such a useful piece of info.