fuel problem 930; please help!

scphelps1 · scphelps1's Garage

Some of you may remember me inquiring about a muffler nut last week. Well with an s-wrench I was able to get to it and the new one is on and the engine is back in the car. Went to fire it up and the engine just spins, but does not fire. I had changed the fuel filter while the engine was out for easier access, so I thought it might take a minute to fill. Kept the key in the on position for a while - still nothing! Cracked the line on top of the filter and there is no fuel present. I've tried replacing the relays with a spare, but I cannot hear the fuel pump(s) running. I have seen indications that there is a front and rear pump. Can anyone direct me to where the rear one is located? Does anyone have any suggestions for what to try next?

Thanks,
Clayton

TurboRuf · 05-01-2002, 04:43 AM

>I have seen indications that there is a front and rear pump. Can anyone direct me to where the rear one is located? Does anyone have any suggestions for what to try next?<

The rear pump is in front of the drivers side rear wheel, at the lower side of the fender well. It's hard to see because it has a cover over it. Just follow the fuel lines down and you should find it.

Try turning on the ignition and depressing the CIS plate, you should hear the fuel pumps turn on. If not, time to dig deeper.

E Ray · 05-01-2002, 04:56 AM

Clayton: I've been down this road before, the rear pump is on the drivers side, back near the rear shock, kinda boxed in and hidden, look for wires and fuel lines.

There is an air flow switch tied to the air flow plate in the CIS system, the pumps will only run when this switch is triped by air flow. there are three ways i know of to get the pumps to run without air flow, (1) with the ignition on and the air cleaner off move the air plate, you should hear the pumps whine. (2) jumper the air flow switch, it is on the back of the CIS air box (3) jumper the pumps at the front relays, 2 of them, the red ones, I don't remember the pin #s, there should be a schematic on the relay to give you a starting point, as a note the black and red relays are interchangable, the red have an additional noise supression feature.

Good luck

Eric

lendaddy · 05-01-2002, 07:18 AM

I am going thru a similar thing with my '77 930. I did a search and found one of Lelands posts which was very similar. It got a tremendous amount of response and they finally solved the problem. There was air in the fuel system.

To hear your pumps run. Here is what you do, pull the air box, right behind the sensor plate and just to the right is the air flow safety switch. It's like two inches from the plate. Anyway to make your pumps run all you need to do is disconnect this switch, you dont have to jump it or anything like that just pull the switch and turn the ignition to the run position. As a side note in order for this to work you must have the other switches on the aluminum intake body The large one that comes from the turbo output to the throttle body) connected and the aluminum body grounded (ask me how I know). Now your pumps are running(I really only see this test as useful to determine that they are indeed runnng or to check fuel pressure) Anyway back to the problem of purging the air from the system.

This part can be kind of a pisser for us turbo guys due to all the plumbing that has to be removed in order to access the injectors, but it's not that bad I have it down to a science now maybe 8-10 minutes.
You need to pull your injectors (17mm line wrench usefull here)and place a rag or paint can top under each. Then with the ignition in the run position push down lightly on the sensor plate. You will hear and see fuel coming out of the injectors. Hold the plate down until all injectors are spraying fuel equally. System is now air free.

This is where I have a question as well, To replace the injectors you must remove or atleast loosen them from the fuel lines again. Havent we just created more air in the lines? Or is it so minute hat it is not a problem? I will know tonight as I pickup my injectors from being cleaned and tested tonight I will post my results tomorrow.

scphelps1 · scphelps1's Garage

Thanks for the replies so far. I will try these suggestions tonight and hopefully it will 'trigger' the pumps. As for air in the lines, wouldn't the system take care of this via the return line to the tank? As the pumps pressurize, doesn't the excess fuel return to the tank? At which point I would think this fuel would bring air with it, in much the same manner as cracking the injectors would. Just a thought.

lendaddy · 05-01-2002, 09:58 AM

Ok, I just reread your post and I misunderstood you the first time. The air I was referring to is after the pumps between the fuel distributor and the injectors(which may still be a problem for you later). I would make sure that you have all the sensors hooked up as they need to be for the pumps to run. Good luck. Also try the thing I recommended earlier about disconnecting the air flow safety switch to make the pumps run. You see just turning the ignition to run does not activate the fuel pumps, the engine must be turning over first so your not seeing fuel at the fiter connection is normal( unless someone was cranking the motor at that moment or you had just cranked it within the last half hour or so in which case the accumulator should have held some pressure.), there wouldn't be any if everything were working correctly. Trust me though you Will hear the pumps if you pull the safety switch and everything else is ok(don't forget to turn the key to run with the switch pulled.)

lin7310948 · 05-01-2002, 02:10 PM

all may be correct, but I had a similar problem as described bu eRay..the air switch was the problem.

john walker's workshop · 05-01-2002, 03:12 PM

make sure the cutoff relay is plugged in all the way. it's on the rear electrical panel. the white wire needs to be attached to the overboost switch too. it's on the intake bypass housing, under the turbo vent hose, close to where it attaches to the air cleaner. the wire can also be attached to ground to bypass the switch, but it needs to be one or the other.

1bar · 05-01-2002, 09:54 PM

I had the same problem the last time I put my '77 930 engine back in the car. It took 2 days to track down a bad red relay on the plate back in the engine compartment - I don't recall right now if this was the cutoff relay or the rear fuel pump relay.

Do the fuel volume flow test that's in the Hayne's or the Bentley's manuals - actuate the CIS plate (by removing the air cleaner) and measure the fuel volume delivered - you can figure out if one or both pumps are working pretty easily. Just don't do it with the garage door shut if you have a water heater in the garage...

The really wierd thing is that the engine was running fine, so how did the relay fritz out while sitting for 3 weeks in the garage?

BTW - I diagnosed this by palying with all sorts of things, but swapping "known good" relays into the fule pump relay sockets front and back was what caught it finally.

scphelps1 · scphelps1's Garage

Thanks again for all the good suggestions. Trying the trick with the plate seemed to activate the pumps, but fuel was still not getting to the back of the car. After getting under the cover at the front of the car, and to the front pump, it was determined that the relay was activating and the pump was trying to operate, but was not. The pump was warm and I could feel the click when the plate was pushed down, but no whirring from this pump. After 1 stuck clamp slowed us down we finally have the pump out of the car. Unfortunately, there is no way to see anything in the pump. It is definitely not serviceable! We sprayed some PB blaster in the pump (probably not Porsche's recommended fix (or mine for that matter)) and let it soak overnight. We will check operation of the pump tonight and if need be, I will buy a new one. Thanks again for the responses!