Confirmed fuel starvation, now what?

JP911 · JP911's Garage

I posted earlier that I was having my first CIS problems (My first CIS problem...please help). The car had been sitting at an angle on jack stands for quite a while, so it was suggested that I may have a fuel starvation problem and I should hold open the throttle plate with the ignition on. I didn't hear much, so I pulled an injector, put it in a bottle and repeated the process above. No fuel came out! I repeated this with another injector and the same thing happened. I think I hear the fuel pump, but I don't know exactly what I should be listening for. I wonder if I may have loosened some sediment in my tank when I was bouncing the car to settle the shocks? Or maybe my fuel pump is dead and I just don't know what to listen for? What would you do first?
Thanks,
Jon

johnco · 01-25-2004, 07:06 PM

sometimes after I don't run my 74 for months at a time, I get no fuel flow. You might try blocking the tank fill with a rag or something and slightly pressurize the tank with an air hose or by blowing into a hose thru the fill. you'll hear the pump start to pump fuel after a short while. at least this worked for me a few times when I couldn't get fuel. doesn't cost anything to try

DavidI · 01-26-2004, 06:26 AM

"it was suggested that I may have a fuel starvation problem and I should hold open the throttle plate with the ignition on."

As I understand it, don't you have to have the ignition in the "start" position as opposed to the "on" position?

You may also want to check the fuse in the block.

Good luck, David

Jim Smolka · 01-26-2004, 06:43 AM

If you fully press the plate up, there should be a good flow of gas.

First, check that the FP is running
If FP is running and still no flow from the injectors, then measure pressure if possible. It is possible to remove an inlet line and catch the gas as you turn on the pump (use good safety precautions). Should be a good stead flow of gas.

vash · vash's Garage

disconnect the fuel line at the accumulator or something easy to reach and stick that into a bottle. have a friend flip the ignition, because if you FP is working, gas will really jam outta the line. if it just trickles then you FP is anemic.

cliff

vash · vash's Garage

you know, i was thinking (rare), maybe you just need to prime the fuel pump. on my car, the FP is in the back, not near the steering rack, but near the rear suspension. that is alot of fuel line that needed to be filled up, before the pump could work properly. i disconnected the line before the filter and had my girlfriend flip the ignition until i had a decent flow (it took a few minutes). then i buttoned it up, and bled the injectors. there is gas in the car right? (i have made this mistake before, very embarassing)

cliff

JP911 · JP911's Garage

There is gas in the car, 3/4 full. My fuel pump is bolted to the suspension cross member in the front of the car, but maybe I'll try running a line from the accumulator into a bucket to see if the pump is working.

David-
When you say start, do you mean that the engine should be cranking? I had the key turned to the farthest position without cranking the starter.

Good thoughts from everyone. I appreciate it!

DavidI · 01-27-2004, 01:32 PM

"David-
When you say start, do you mean that the engine should be cranking? I had the key turned to the farthest position without cranking the starter."

Yes, I believe the engine must be cranking. I was told it had to do with a safety issue so that in the event the car was in an accident and the engine stalled, the fuel would stop.

I think you need an assistant to crank the engine.

I'm sure someone with more experience will chime in...

Good luck, David

JP911 · JP911's Garage

David-
This is interesting. I've read a few past posts and a tech article on Rennlist that makes it sound like it does not have to be cranking to spray fuel, but it's a little vague. I'll try it with the starter cranking tonight...but would the spark in the cylinder ignite any fuel vapor in the engine compartment if I had the injector pulled?

Anyone care to clear this up?

Oldporsche · 01-27-2004, 02:34 PM

Are you sure your fuel pump is up around the front cross member?

On my '75 its located at the rear of the car inbord of the left rear wheel well. Porsche moved the fuel pump around quite a bit.

You didn't say at what angle your car was parked. This could give you a fuel starvation problem.

David Duffield

David · David's Garage

I believe the engine must be cranking, either way it's better to jumper the fuel pump relay.

Another way would be to turn the key to the on position and lift the fuel distributer flapper.

I forget the fuel amount you should get, but it's something like a cup in 10 seconds. It should be pretty obvious if it's not flowing.

If the pump is running and there's no fuel flow, the strainer at the bottom of the tank may be clogged. I think it's a 19mm allen wrench to remove the strainer, of course the tank must empty or close to it. BE SURE AND HAVE A GOOD FIRE EXTINGUISER NEAR BY. I asked a vender at work a few months ago what happened to his bandaged hand. He said he was working on the fuel pump on his SC when his flashlight ignited some fuel on the ground. He lost the car and his garage and nearly his house. I bought a 20lb extinguiser after that story.

JP911 · JP911's Garage

Old_Porsche-
I recently did a bunch of front end work and the fuel pump is definitely in the front on my 76. I had the front end jacked up at a fairly steep angle for about 2 to 3 weeks, and then the rear end for about a week.

125 Shifter-
I did turn the car to the On position and lift the (throttle?) plate inside the airbox. This is where I wasn't sure whether the car had to be cranking or not for fuel to flow. I really hope I don't have to drain the tank as it is about 3/4 full.

porschetech · 01-27-2004, 04:09 PM

To test the fuel pump, fuel flow on a cis car:

reach behind the air flow sensor, going in and around from the left and you will feel a wire/plug that attaches to the air flow sensor. This completes the circuit and allows the fuel pump to run without the sensor plate off it's stop.

you can now turn the key on and you should hear the fuel pump run.

to check for flow out of the injector, remove and injector, put into glass container, turn on key, raise sensor plate by hand and you should have fuel out of the injector.

CAUTION: DO NOT ALLOW FUEL TO SPRAY TO LONG OR YOU WILL FLOOD THE MOTOR.

Hope this helps.

JP911 · JP911's Garage

Just got done working on the 911 for the night. Checked the injectors again following the advice above and no fuel. Removed the fuel filter and blew air through it in the opposite direction and no clog. Attached hose to "out" end of fuel filter, used bleeding procedure and got nothing. Removed fuel level sender from tank to visually check that I had gas (thinking gauge or sender could be bad) and there was a 3/4 full, clean tank. This weekend I will check the line from the pump to the engine and the pump itself. Sometimes you gotta just hate the weekend warrior thing

-Jon

vash · vash's Garage

hey, you are getting warmer. i hate being a weekend warrior too. arggh! i would put a test light on the fuel pump connections and see if you are getting juice. that way you know if it is the pump or a bad connection.

JP911 · JP911's Garage

Put the test light on the connections at the fuel pump?

Groesbeck Hurricane · 01-28-2004, 08:27 AM

Jon,

Are you sure you are pushing up on the correct plate? If I remember correctly, when you remove the air filter the plate you need to move is on the left (driver's) side as you are facing the motor.

When you put the key in the "on" position (final position before engaging the starter) do you hear the whine of the fuel pump? Do not try starting the car while doing the next item! With the key in the "on" position, go to the rear of your vehicle and push up on the throttle plate. You should only have to do this a couple of times. You should hear a rush of air as you are bleeding the system. As the fuel is coming in there will be a loud noise like a screaming cat. It is very easy to flood the car at this time.

If air is in the fuel line or the pump is not starting then you will not have fuel coming through the injectors. Let us know how it goes!

JP911 · JP911's Garage

Sounds like I may be pushing up on the wrong thing (can you tell I'm new to this?). I've been pushing on a curved arm that attaches to a plate in the right-center of the airbox. I'll have another look tonight.

David · David's Garage

If you have a good amp meter you can check the amps of the fuel pump. The correct value is in the Bently manual which I don't have in front of me. If the pump is drawing too many amps, it's bad.