x98boardwell

Hello,

I have a problem with my fuel pumps. Sometimes when I turn the key on they fire right up, and then other times they do not come at all.

Yesterday, I could pull one of the fuel relays out and then the other one would turn on. If I removed that one and put the other one back in that one would turn on. But, when I installed both, neither of them would come on.

So, I bridged the fuse for the pumps with a new inline fuse (thinking that it was a power issue) and the car started right up. Then today while driving home, the car just died at the light with the same problem... fuel pumps would not come on. Waited 30 minutes and they worked fine. Please keep in mind that my car was not warm by any means and had been driven about 4 miles on warm up so that cannot be the answer.

What I'm looking for: I would like the wiring diagram for a 930 for both fuel pumps so I can figure out where they get their power from and where they ground at. I think that is the issue and I would like to try and solve it. Otherwise, I currently own a very unreliable car.

Thanks for your help in advance.

Bryan

JFairman

It's not the answer to your querry, but the answer to your problem may be in the yellow overboost relay on the back console.
It shuts off the fuel pumps when the overboost signal wire becomes ungrounded by the offwhite colored overboost sensor at somewhere around 1.2bar when they it's working properly.

Some people have fixed it by taking the yellow cover off and resoldering the terminals inside at the bottom.
They may have inconsistant cold solder connections from the factory.

I think the yellow overboost relay shuts the fuel pumps down by disconnecting the grounds to the 2 front red fuel pump relays.

x98boardwell

JFairman, (feedback to help figure this out)

If you are correct, why would one pump come on when the relay for the other was taken off and visa versa when I had the problem yesterday?

Also, would the switch prevent them from coming on when the key is being advanced to just turn them and not when turning over the motor or when the motor is actually running?

Lastly, the problem was solved when I added the in-line fuse connector. Is this just coincidence or could the overboost still be it?

Thanks for the very quick response. Advice welcomed.

Bryan

Ferrari1

I had a similar experience lately, but mine was with my lack of spark. It was the run on relay next to the overboost relay.

The problem with a relay going bad is that it makes it an intermittent problem. Some times it takes the logic out of it because one minute it runs, then the next there is nothing.

If it is your overboost relay it would explain your problems if it is "down stream" of where your jumper is.

Just my .02.

JFairman

The only one of your questions I can answer accurately is that if the wire going to the overboost sensor is not grounded by the switch or by grounding it directly, the fuel pumps will not run in any ignition key position unless someone has rewired something else.

If I copy and paste wire diagram pages from the factory manual than it might be frowned on by a forum moderator.

x98boardwell

Isn't the way to check if it's the overboost switch is defective is to disconnect the wire from the switch and ground it? That way, I would be bypassing the switch and could determine if that was the cause.

Can someone tell me where the power for the fuel pumps is supplied from (besides the battery as an answer) and where each fuel pump is grounded.

Also, is there any other components (fuses/relays) to the fuel pumps besides the ones (2 relays & 1 fuse) in the front fuse block?

Thanks again for the quick help.

Bryan

PS. What would the "green" ignition wire do from the distributor if it was faulty? Could this be a cause based on my description in the above posts?

A930Rocket

The green wire from the dizzy goes to the CDI box. It shouldn't have any bearing on the fuel pumps.

Here's the link to the Lee Rice upgrade: http://www.pelicanparts.com/techarti...amblings-2.htm

This will bypass the old fuse box and give you power right from the battery.

x98boardwell

Can't thank you enough. I will keep everyone posted on my findings. I should have an answer by Wednesday... hopefully.

Bryan

x98boardwell

Jim,

Can you explain how the overboost switch could/would come into play if I was just trying to turn on the fuel pumps with the key/ignition (motor not running or cranking over)? Would a defective Overboost switch still not allow the fuel pumps to come on when turning the key to the ON position?

Also, if I wanted to bypass the Overboost switch to check if that is the issue, do I pull off the wire to break ground or do I need to pull off the wire and ground it to bypass the switch? I'm not sure which way is the correct way.

Anyone know the answers... please chime in.

Thanks in advance,
Bryan

JFairman

You ground the wire going to the overboost switch to remove it from the loop if it becomes over sensitive, or to make the pumps run regardless of boost levels.

But, it's the yellow overboost relay on the back corner of the driver side rear console that I was referring to that might be the problem.

Maybe do a search on the overboost relay or yellow relay.

They are known to become flakey eventually, and start leaving you stranded with a car that won't run. Alot of people resolder the connections inside of it and/or carry a spare even though they are expensive.... like around $175.

You may be able to jump pins 30 and 87a on it to bypass it but i havn't tried that so I don't know if that could hurt anything electrical besides a fuse doing that to this relay.

x98boardwell

Can you explain what "rear corner of drivers side console" means? I'm confused as to where to look.. in the trunk, in the cabin, or in the engine compartment? I don't see a "yellow" relay anywhere.

Thanks,
Bryan

Mark Houghton

Engine compartment, left hand side closest to the rear of the car. A bunch of relays are located there.

x98boardwell

Gracias Senor' (have no idea if I spelled this correctly.

Bry

A930Rocket

Yellow relay here:

x98boardwell

My Yellow relay just dangles around behind the cover. It is not mounted into that plate at all. It has the rubber gromet on it, but is not stuck in the hole. The wires that feed to the relay have another plastic switch that connects them to the relay. I have attached a photo of what mine looks like. The Pins on the relay appear to be fine, So I'm not sure what would be making this happen unless it can fail some of the time???

Also, it looks like a new rubber gromet has been added. If you look closely you can see spme black shrink tubing where it was added. I'm guessing (by the way it looks) that the black rubber gromet is brand new.

Let me know your thoughts,

Bryan