slivan

At idle, 900 rpm +/-, after chasing down a tail light issue I discovered the fuel pump relays 'fluttering' I could hear them as well as feel them vibrating to the touch. I have rewired the pumps and fused them remotely. Is this due to low idle or could this be indicative of another looming issue? Both pumps are newer bosch units, both relays are new. Seems like the fluttering disappears when the rpm's increase, intermittently shows up at a stop light. Anyone have any experience here? Much thanks!
Tom

A930Rocket

Sounds more electrical if they are fluttering or cycling off and on very fast. I grounded my relays on a impact switch and haven't looked back. Turn the ignition on and the pumps start up.

slivan

Drove the car tonight, the fluttering is intermittent and appears when coming off throttle slowing and stopping for a signal. Touch the accelerator once or twice and the cycling will stop. Otherwise the car is running runs very strong. Rocket, what is an impact switch and where did you tie this in? Got an image lying around? Seems with these cars proper grounding is critical. Thanks
Tom

PorscheMD

It could be your sensor plate is fluterring at idle cause you to intermittently lose ground to the relays. I have seen this before, particularly on cars that don't get driven alot. I also have fixed the problem on other occassions by replacing the relays. Disconnect the sensor plate connection at the back of the plate and see if the problem goes away.

nathanUK '81 930 G50

That was my thought too when he said it happens coming off the throttle. Try it. Disconnect the connector to the CIS metering plate and take it for a drive.

A930Rocket

slivan,

I got mine from the local Ford dealer as it's a fuel impact switch off a late 80's early 90's Mustang. Pegasus Racing carries one as well.

Pull that green/blue plug off the back of the fuel metering plate first.

See the attached pics. One is the impact switch. One is the back of the fuse box showing the mess of wiring for the fuel pump relays and the last is the green/blue plug.

slivan

Thank you gentlemen! And thank you for taking the time to post a couple pics Rocket! What exactly is the purpose or function of the impact switch? Gonna see if I can get this wrapped up before the snow flies again this week....details to follow!
Tom

A930Rocket

By running the ground wires off the two red relays through the impact switch, you bypass all the relays and switches in the engine compartment. In case you have an accident, it will shut off the fuel pumps to the engines. Do you have a wiring diagram?

rbennett

Rocket is a genuine go to guy!
Thanks Jim for helping me in the past!

Your pics and expertise is greatly appreciated

slivan

Hence the 'impact' portion of the switch. I do have a diagram, sounds like an easy install. Thank you again for the input!
Tom

A930Rocket

Oh no! It's not expertise. It's trial and error with lots of luck some times.

Thanks guys.