Fuel Pumps not working with Ign.

[timc]

When my car is operating properly, turning the ign key to position 2 both pumps will run for approx 1-2 seconds then stop, this creates sufficient fuel pressure to start the car. Or, of course, if I just turn the key to pos 3 to start the car, the pumps run for 1-2 sec, then stop, until the engine fires then the pumps come back on due to the AFM plate moving from the airflow. This car was my daily driver, but now that it has been sitting the pumps don't always run when turning the key, so sometimes I will have to turn the key on and off several times to get the pumps to run to start the car. The car has now sat for about two weeks (first time ever in the last 6 years) and the pumps will not run when turning the key, so the car will not start. I have tested the following:
1) replaced both FP relays, and the yellow overboost relay.
2) removed each FP relay and jumped 30/87 to run each pump by itself. This also proves the fuse is good, as well as both pumps.
3) Turning the key to pos 2 and pushing down the AFM plate the pumps will NOT run.
4) Turning the key to pos2 and removing the plug on the rear of the AFM the pumps will NOT run.

There is a relay under the drives seat that I can feel one click when key is turned to Pos 2. Have no idea what this relay is, but is is located under the seat and closest to the dr door.

Is there another relay that I am missing that would receive signal from the ign to run the pumps?

[mark houghton]

Originally Posted by timc

When my car is operating properly, turning the ign key to position 2 both pumps will run for approx 1-2 seconds then stop, this creates sufficient fuel pressure to start the car. Or, of course, if I just turn the key to pos 3 to start the car, the pumps run for 1-2 sec, then stop, until the engine fires then the pumps come back on due to the AFM plate moving from the airflow. This car was my daily driver, but now that it has been sitting the pumps don't always run when turning the key, so sometimes I will have to turn the key on and off several times to get the pumps to run to start the car. The car has now sat for about two weeks (first time ever in the last 6 years) and the pumps will not run when turning the key, so the car will not start. I have tested the following:
1) replaced both FP relays, and the yellow overboost relay.
2) removed each FP relay and jumped 30/87 to run each pump by itself. This also proves the fuse is good, as well as both pumps.
3) Turning the key to pos 2 and pushing down the AFM plate the pumps will NOT run.
4) Turning the key to pos2 and removing the plug on the rear of the AFM the pumps will NOT run.

There is a relay under the drives seat that I can feel one click when key is turned to Pos 2. Have no idea what this relay is, but is is located under the seat and closest to the dr door.

Is there another relay that I am missing that would receive signal from the ign to run the pumps?

That relay under the seat is called something like the "over speed relay". It's supposed to shut off the pumps if you over rev past some mysterious point. Sounds like it's working, since you can feel it clicking.

Check your overboost sensor/switch near the front of the BOV housing. Single wire going to it. If it is faulty, has a poor ground, disconnected, or broken wire then your pumps won't run....period.

[timc]

i unplugged the overboost switch, and grounded the wire, which should bypass the switch, still no pumps. I'm going to go back thru all the relays again just to double check. Seems like it has to be something mechanical due to it slowly failing from not being driven, as after the car sat for several days, I would have to turn the key on/off several times to get the pumps to run, then it would be fine as long as I drove the car on a regular basis, but then after sitting for several days same prob again, now after sitting for several weeks no pumps at all.

A friend once told me, to keep a Ferrari running you hire a mechanic, to keep a Porsche running you drive it. Apparently there's some truth to that...

[JFairman]

The part nimber on the relay you hear clicking under the seat is called a "speed relay" when you search the part number here. It's expensive if toast and you can work around it. I opened mine up by peeling the aluminum back on the bottom edges and there are 2 small relays on a circut board inside.
It is the factory rev limiter that kills the fuel pumps around 7000 or 7200 rpms and the overboost sensor and yellow relay seem to interface with it to some degree.

My '87 used to just shut off completely in the worst places like when crossing a bridge or somewhere in traffic... very dangerous.
Eventually I accidentally dicovered the problem was the multipin plug going to that speed relay under the seat wasn't making good contact even though it looked perfectly clean. If I tapped the plug or the relay the pumps would go on and off. After cleaning all the contacts on the plug and relay I've never had the mysterious fuel pumps shut down again.

When I took the aluminum cover off and looked inside the relay everything looked new and clean still so it was just the plug I think.

[911boost]

Also check all of your grounds. I know on my 91, the intercooler ground was bad, and it was making the car act like it was overboosting all the time.

Bill

[timc]

looks like it is the speed sensor relay that is under the seat. With pins 1&2 jumped, the pumps now run a few seconds when ign is turned on. I don't see this relay on this site, anyone know where I can find one?

[T77911S]

the drawing i have shows the speed relay or rev limiter side cuts out at 7k, and the other side is for the O2 sensor. it shows it cutting out at 3k.

tim's relay had several broken solder joints. one was on the coil for the FP's. the others where on some of the major pin joints. some even for the O2 side. so for those that have bad relays' pull them apart and just resolder the points i mentined.
you can apply 12v to pin 7 and ground to pin 5 to test the relay. both relays should pull in.
(i actually used a 9v battery)

my explanation to tim on how it worked:
look at the fuel circuit as 2 seperate circuits. one is the 2 FP relays, the yellow relay(contacts), the rev limiter, and the pressure switch. the other circuit is the yellow relay(coil) and the AFM switch.
the AFM switch removes ground from the yellow relay, de-energizing it when the engine is running.
the FP circuit gets its ground through the contacts of the yellow, then the rev limiter then to the pressure switch.
all the yellow relay is doing is energizing the 2 FP relays. the yellow relay is also (?) what gives the 1-2 sec FP run before starting.

to trouble shoot: no particular order.
with key on
1 ground the wire at the pressure switch. FP should run
2 remove the connector on the AFM or push down on the plate to energize the yellow relay. FP should also run.
3 check for power and ground on the connector to the AFM.
4 jumper pins 30 to 87a on the YEL realy:
the FP relays should energize
power on pin 1 of the rev limiter
power on the wire going to the pressure switch. (wire removed from switch).
(if there is no power on this wire, but there is power on pin 1 of the rev limiter, the rev limiter is bad)
5 jump pins 30 to 87 on both FP relays to test FP's

( this is assuming fuses and wiring are good)

you can really start anywhere.

i am not a 930 guy, this is just based on the drawing and what little i have done on tims car, mostly over the phone.

[JFairman]

this is very good and if everythiing you wrote is correct (i think it is) you're the first person on this forum to figure all that over engineered afterthought ___ out.
even more amazing is you say you don't have one of these cars to check out the wiring in person- you did it from a drawing or wiring diagram.

excellent

[T77911S]

thanks.
it really is a simple cricuit. just remember, the yellow relay drives (energizies) the 2 FP relays, the AFM switch controls the yellow relay and the rev limiter and pressure switch, (along with the yellow relay contacts), provide ground for the 2 FP relays, with the pressure switch being the final ground contact.

guess i could have cut the above shorter.

[oilonly]

This is one great site. Thread saved.

[j930]

does anyone know if the same 1-2 second fuel pump run when turning the key is the same on a 84? i have never heard my pumps run prior to actually engaging the starter? I have noticed on my 84 that it will take a few seconds to start as it seems it needs to build up pressure or get fuel period. if i remove the wire going to the back of the fuel head(forgive me as i don't know the terminology)so that the pumps run when you turn the key then you have no delay in it starting. maybe the 84 did not have that 1-2 sec run of the pumps?

[mooney265]

My '79 doesn't run 2-3 seconds, either. when i began reading this thread, I felt left out. Mine takes about 2-3 seconds to start when cold, but fires right up when warm.

My guess is, it's because I don't have the dreaded "speed" relay under the seat, either. ????

[mark houghton]

Originally my pumps wouldn't run unless cranking the engine or removing the plug at the air flow metering arm. That's normal. But, back when I was trying to diagnose a problem (that eventually pointed to the speed relay under the seat) I was throwing coin at it and bought a new yellow relay. With the new relay, the pumps now run for a second or two when you turn the key on. I suspect some updated circuit in the relay or a different manufacturer. I actually like it, since it gives you a clue that the pumps are working before you crank it over.

[timc]

The 1-2 second delay is normal and due to the the relay getting energized before ground is applied to de energize. Mine has been doing this since I owned it and every 930 that I have driven with the yellow relay does the same.

[mooney265]

Ok, well I don't have a yellow relay - - so, i guess that explains it... And, i seem to remember that the PO had the relay's rigged so that the FP's would fire up [and stay fired up] with the turn of the key. My mechanic said that wasn't a good idea and put it back to stock... Obviously, no one wants fuel pumping the the engine not running and key on [in the event of a wreck/fire]...

[T77911S]

you would have to post a wiring diagram for the earlier cars, and euro cars for me to say what might be going on. i know the 86 is even different than the 87 so i doubt they are the same.

this is based on the 86 only. when i talked about this with tim and looked over his diagram, there are only 2 reasons i could come up with as to why his FP's run. one was the relay's could have a delay circuit in them, but if i remember correctly, he took one apart and there was nothing else in it, but i am not sure.
my explanation to him as to for the other reason was that since the relays take a short time to energize, that might be giving him the short run of the FP's.

[j930]

dumb question but relay do i replace with a yellow one?

[Noah930]

Originally Posted by j930

dumb question but relay do i replace with a yellow one?

There's a rectangular yellow relay in the engine compartment. It's under a black plastic cover held in place with a butterfly nut on the driver's sidewall of the engine compartment, aft of the silver cylindrical fuel filter.

[j930]

i know the area but i think i have a red one in there, dont recall seeing a yellow. will check

[Noah930]

There are 2 relays there. The traditional round one (in black), and the yellow rectangular one.