Need help, fuel pumps not getting power

[jwakil]

My 81 930 was running fine until today. Never had this issue before but this morning the car cranked and cranked and wouldn't start. Checked spark and it was good. I swapped the fuel pump relays with known good ones and still no start. After some further diagnosis, I found that the fuel pump relays are not getting power. If I jump power directly to the 87 pins of the relays, then it starts and runs normal. I'm trying to figure out why the pin 30's are not getting power. Does anyone have any idea why? I'm looking for a diagram of the wiring for the fuel system, and what feeds the relays. The scans of the factory diagram are too hard to read.

[Jeff NJ]

Do you have a yellow over boost relay in the rear left of the engine bay? They can go bad or they can just make a poor connection.
Search here for the yellow relay and you will see common issues and fixes, including how to jump it.

[kevin930t]

I would check the wires themselves for corrosion and the terminals.

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[JFairman]

There's a chain of pathetic old relays that can interupt the fuel pump relay grounds like the yellow relay in back and the speed relay under the left seat. The whole system really sucks.

I had so many problems with it 8 to 10 years ago I installed a hidden 30 amp toggle switch that will supply 12 volts directly from the battery to the fuel pumps bypassing the entire electrical nightmare that comes in these cars that left me stranded on the side of the road many times or on a single lane bridge over the intracoastal waterway... that one finally made me install the backup switch.

When needed I can flip the switch and drive on. Comes in handy when fiddling with fuel head adjustments or filling a gas can from my gas tank while the motor is off too.

[kevin930t]

That is a great idea,also as most of know there is a mod that can be done to take the load from one circuit #6 fuse and split it up.I just did this and was successful,hopefully ronnie will chime in as he was alot of help.

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[jwakil]

I don't see a yellow relay near my CD box. I just have an orange one which I replaced with a new red one and it didn't change anything. I'll look for the one under the seat

[jwakil]

I found the perfect wire diagram here:
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/547032-sticky-common-answers-why-my-car-doesnt-start-4.html

Would there be any difference with a Euro 930?
Looks like I need to check the airflow sensor contact, and airflow sensor relay. Does any know where these would be located?

[kevin930t]

Just to let you know,i dont think your car has the yellow speed relay under your seat,being 81 year

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[JFairman]

If the car has a factory rev limiter that abruptly shuts off the fuel pumps at 7200 rpm that's the speed relay. I don't know what all years it was under the left seat next to a couple lambda relays but it's in an '87.

It's not yellow plastic like the one in the back of the car, it has a grey zinc plated steel cover and has an expensive multi pin connector plug like most Bosch relays and old external voltage regulators.

[jwakil]

I'm also trying to find my airflow sensor relay. Supposed to be besides the yellow relay. Seems I have neither?

Latest development. I seem to not have any interior lights and the window switches are not working either. What could be linking all of these? Also, if I bring power to pins 30 of the relays, I still don't have the pumps running, but only if I bring directly to 87.

[kevin930t]

You might want to check the relays themselves the pins get coroded and need to ne cleaned with emory cloth also you might want to try prying them open with a razor blade as they might not be making contact with the female end.

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[jwakil]

Originally Posted by kevin930t

You might want to check the relays themselves the pins get coroded and need to ne cleaned with emory cloth also you might want to try prying them open with a razor blade as they might not be making contact with the female end.

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Already swapped known good relays for both fuel pump relays and the one orange relay in the engine compartment I could find. No changes. I think my relays are ok, except I haven't found the mysterious yellow over boost relay, and there is no speed relay under the driver seat. I assume the MSD probably takes care of the speed relay.

[kevin930t]

Have you tryed opening up the terminals,its possible that its not making good contact.How is your fuse block itself does it hold the fuses well i ask because my fuse block cracked at #6 fuel pump fuse because it got so flippin hot from bothe of the pumps being on 1 circuit.

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[kevin930t]

Your car never came with a yellow relay under the seat or any where.

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[jwakil]

Originally Posted by kevin930t

Your car never came with a yellow relay under the seat or any where.

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Ok, just to be clear, my understanding was the yellow relay was the overboost relay which is supposed to be in the engine bay. The relay under the seat is the speed sensor relay. Since I don't see either, does that mean my car has no speed sensor relay or overboost relay?

What about the airflow sensor charging relay. This is shown on the wiring diagram and explained in the other link to be next to the yellow relay in the engine bay. Is that the orange one in my pic by any chance? I don't see any other relays anywhere.

Anyway, I'm getting very frustrated. I'm getting no interior lights, no horn, and I can only get pumps to work if I jump power to terminals 87, but not 30. All the fuses look ok. I'm suspecting the source to the fuses might be bad. Is there one source that would feed all these circuits? A wiring diagram for the fuse panel would be helpful showing the source feeds.

[kevin930t]

There is a switch behind the fuel head,try unplugging it to see if the pumps run with the key on,

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[kevin930t]

I know how frustrated you are,i have been through this

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[kevin930t]

Hoping someone else could chime in,i think most of us have had this problem

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[kevin930t]

Do u have a circuit tester?

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[kevin930t]

There is a way to test your relays,pin 30 is battery pin87 is your component pin 86 is your ign &pin 85 is your grnd.

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