83 911 SC fuel pump performance.

[sjheinz]

Trouble shooting why I have a fuel pump that works with a direct power connection but does not seem to work when cranking the engine.

Have verified that relay is working with swap from the horn relay. But nothing seems to be working when I go to start the car. Car starts momentarily but then dies.

120k miles.

Does the 83 have a cold start valve. I can't seem to find it. Have found the "warm" valve between cylinder 1 and 2 intakes.

Bentley manual doesn't help me much. Help appreciated.

[sjheinz]

Previously posted that the FP wasn't working. Well shoot, the car has to be running or cranking for the relay to kick in with power to the FP. I have power when the car starts before dying.
I have fuel pressure at the filter. There are two what would appear to be fuel filters in the engine compartment, at least fuel seems to be running through both. Do these cars have 2 fuel filters?

[Woodyhfd]

My memory may be failing me here, but I think in 1983, the fuel pump might have shared a fuse with the dome light.

[Woodyhfd]

'83s have a fuel filter and an accumulator.

You may also want to check the relay next to the Jetronic control box under the passenger's seat. If it's bad, the car may start for a moment, but won't run. Water can accumulate in that area, especially in Targas, and the relay will fail.

Mine looked like this:



Removing it ruined the connector:



I carefully labelled the connections, replaced the connector with female fittings and swapped in a good relay:

[sjheinz]

Checked and no fuel at the #2 injector.
Fuses good shape.
Dome lights work.

Was not aware of the second relay. I completely replaced all the carpet with seats out and may have leaned on the connections inadvertently. Starting problems seemed to occur while carpet was being replaced. It ran before the project and then had it down for almost a year while I did the re-carpet and other tasks. So this might just be the TICKET. Great explanation and will advise.

[Woodyhfd]

It's also a cheap fix, just a generic relay. Good luck. Let me know how you make out.

[na2ub]

If you have already tried the pump with a direct electrical feed, why not turn the car on and see if it is receiving voltage at the pump? If it is, it is probably just failing. They don't last forever. Replaced mine at about 80,000 miles. They can fail intermittantly and cause you to chase your tail cause sometimes they work, and sometimes they don't.

[boyt911sc]

Steve,

The second relay beside the ECU is the FV (frequency valve relay) and has nothing to do with FP operation and also the fuse #18 that supplies power to interior lights, clock, etc. would not be a factor to consider. There are several simple ways to test the FP in a CIS.

If you have a fuel gauge hook it up and test run the FP. Aside from hearing the FP runs, you'll know the delivery capacity of the pump under test. You could test run the FP as:
a). Turn ignition switch @ ON position (not start):
a-1: Remove air filter and lift up the AFS (air flow sensor) very briefly (no more than a couple of seconds) and listen to the fuel injectors. Or pull out one of the FI and observe fuel flow.
a-2: Remove FP relay and bridged terminals 87a and 30. FP should start to run.

b). Supply power to terminal #30 (FP relay socket) or directly to the FP's (+) terminal.

c). Check if FP is getting energized when you turned the ignition switch to START.

d). Bench test the FP.

There more ways to do this evaluation but these should be suffice to find the problem/s. Keep us posted.

Tony

[sjheinz]

Thanks Tony:
I have checked the relay, fuses, removed the Fuel Pump from the car and direct wired it and it works in that condition.
However, after disconnecting the fuel line at the filter, and turning the key to run, I get no fuel delivery.

Jumping the relay pins between 30 and 87A with the relay in the socket turns the engine over but no sound of a fuel pump working and no fuel discarge in engine compartment. Jumping from 87A to 30 no fuel pump activity.

Your help is appreciated. Heck the pump is only 29 years old. 120,000 miles with lots and lots of down time for extended periods.

Again, car will start momentarily and then die. Lifting the sensor plate does provide a hissing sound of injector discharge when the system did have pressure in it.

[Woodyhfd]

After a little more thought, I think that the relay that I mentioned above is what gets its power through the dome light fuse, not the fuel pump. Sorry for the misinformation.

[boyt911sc]

Originally Posted by sjheinz

Thanks Tony:
I have checked the relay, fuses, removed the Fuel Pump from the car and direct wired it and it works in that condition.
However, after disconnecting the fuel line at the filter, and turning the key to run, I get no fuel delivery.

Jumping the relay pins between 30 and 87A with the relay in the socket turns the engine over but no sound of a fuel pump working and no fuel discarge in engine compartment. Jumping from 87A to 30 no fuel pump activity.

Your help is appreciated. Heck the pump is only 29 years old. 120,000 miles with lots and lots of down time for extended periods.

Again, car will start momentarily and then die. Lifting the sensor plate does provide a hissing sound of injector discharge when the system did have pressure in it.

Steve,

You need to pull out the FP relay from the socket to do the test. Of course, the engine would turn over when you bridged terminals 87a and 30 (ignition switch @ ON). Why? When you turn the IS (ign. SW) @ ON position, the normally closed (NC) terminals 87a-30 would switch to normally open 87-30 (NO). Now visualize this, the relay is now @87-30 orientation and power present @ 87a (from ignition switch)............when you bridged 87a & 30, power is transmitted from 87a to 30 and since terminal #30 is also connected to 87 (yellow starter wire terminal) the STARTER would be energized causing the engine turn over.

Have you tried or tested the procedures I suggested to you in the earlier post? You need to pinpoint where the root cause of the problem. It maybe just a simple loose or bad connection. Or something else. Test and confirm. Keep us posted.

Tony

[sjheinz]

Thanks Tony,
I only checked for current at 30 and 87A with the relay removed.
Now that I have gone and bridged as in Bentley 240-11, I have power to the FP.
So.. with that known, why doesn't the pump run when the IS is in the run position? It ought to run just to pressurize the system right?
I think we are getting close. I can feel it.

[boyt911sc]

Originally Posted by sjheinz

Thanks Tony,
I only checked for current at 30 and 87A with the relay removed.
Now that I have gone and bridged as in Bentley 240-11, I have power to the FP.
So.. with that known, why doesn't the pump run when the IS is in the run position? It ought to run just to pressurize the system right?
I think we are getting close. I can feel it.

Steve,

The FP is not suppose to run when the ignition switch @ ON position!!!!! Have you done test A-1 (post #8)? Since you have a Bentley manual, read it and you'll understand how the system works. The system is already pressurized after the FP stopped running. So for the next start, you need some residual fuel pressure to facilitate starting. CSV (cold start valve) activates when engine is cold.

So what problem are you trying to fix? Keep us posted.

Tony

[Dklever48]

If you have a pop off valve in your air box make sure the o'ring is sealing. If not you won't create a vacuum and switch will not close in the air box to run the FP

[sjheinz]

Tony,
thanks again,
Learning here.
a-1: Remove air filter and lift up the AFS (air flow sensor) very briefly (no more than a couple of seconds) and listen to the fuel injectors. Or pull out one of the FI and observe fuel flow.
Yes have. can hear fuel in the injectors and when lifting the AFS it does seem to Prime the cylinders and the car will start.


Problem is: car will start momentarily and then die. Occasional backfire on start.

[boyt911sc]

Originally Posted by sjheinz

Tony,
thanks again,
Learning here.
a-1: Remove air filter and lift up the AFS (air flow sensor) very briefly (no more than a couple of seconds) and listen to the fuel injectors. Or pull out one of the FI and observe fuel flow.
Yes have. can hear fuel in the injectors and when lifting the AFS it does seem to Prime the cylinders and the car will start.


Problem is: car will start momentarily and then die. Occasional backfire on start.

Steve,

Check the following:
1). Fuel pressure (control and system).
2). Pressurize the system (engine) and locate the source of your air/vacuum leak.
3). Check the ignition timing and sparks.

I'll put my bet on #2. Keep us posted.

Tony

[Quinlan]

Another cheap, easy test is this:
1. Remove the air filter so you have access to the "flapper".
2. Carefully disconnect the fuel line at the connection to the fuel accumulator. Assuming you have pressure in the system, even with the ignition off gas WILL spray a bit until the pressure is relieved, so make sure you do this outdoors, and have a tray underneath the accumulator to catch any leakage.
3. Once the fuel line is disconnected, put the loose end in a container (I used a glass 1 liter measuring cup).
4. Turn the ignition to "run", and tweak the flapper. Fuel should flow into the measuring cup. Haynes says it should be 1 liter in 30 seconds, so if you can get 1/2 liter in 15 seconds or less, the FP is delivering as it should. If not, you may have identified the FP as the culprit.