Different CIS fuel pump operation methods when testing

[Forza]

What are the different methods to run the fuel pump (with the engine not running) to test cold CIS fuel pressures? Any consensus on which ones are preferred?

1) The Bentley manual suggests building a jumper with 14 gauge wire, an inline fuse, and a toggle switch.

2) The Porsche Factory Workshop Manual suggests using an spare fuel pump relay with terminals 87a and 30 bridged.

3) A local independent Porsche mechanic I spoke with suggested unplugging the air flow sensor on the fuel distributor.


Of the three, the third one sounds the easiest as it's free, but I'd like to know what others have done during these tests.

[T77911S]

#3

just remember, unplug the power to the WUR to check CCP. and if you ever lift the sensor plate to run the FP, that is spraying raw fuel into the intake.

[Gunter]

#3 sounds easier but.......................getting the tiny wire clip off to unplug is another story.
Considering how hard it is to reach, you may find #1 and #2 easier.

The WUR doesn't get power with ignition ON, only with engine running.

#1 is o.k. but I would go with #2. It's not too hard to bridge the terminal on an extra relay and BTW, it doesn't have to be red, a black one will do.

[boyt911sc]

Originally Posted by Forza

What are the different methods to run the fuel pump (with the engine not running) to test cold CIS fuel pressures? Any consensus on which ones are preferred?

1) The Bentley manual suggests building a jumper with 14 gauge wire, an inline fuse, and a toggle switch.

2) The Porsche Factory Workshop Manual suggests using an spare fuel pump relay with terminals 87a and 30 bridged.

3) A local independent Porsche mechanic I spoke with suggested unplugging the air flow sensor on the fuel distributor.


Of the three, the third one sounds the easiest as it's free, but I'd like to know what others have done during these tests.

John,

There are many ways to test run the FP without running the engine. So it's a matter of choice. Your choice of #3 would be my last choice because it is not that convenient to unplug the AFS (air flow sensor/switch) with the motor installed. My favorite method is jumpering terminals #87A-#30 (ignition SW @ ON position not START) using wiring set-up mentioned in your #1 procedure. You don't need a spare FP relay to test the FP!!!!.

Once your FP starts to run, WUR, AAR, and TTV (optional) would be all energized at the same time regardless the engine is running or not unless you have disconnected or unplugged them before hand. The difference in the cold control pressures between plugged and unplugged the first few seconds is very minimal. However, I suggest that you unplug it if you're just starting to learn CIS troubleshooting to prevent you from mis-reading the data. So the choice is yours.

Tony

[Forza]

Originally Posted by boyt911sc

John,

There are many ways to test run the FP without running the engine. So it's a matter of choice. Your choice of #3 would be my last choice because it is not that convenient to unplug the AFS (air flow sensor/switch) with the motor installed. My favorite method is jumpering terminals #87A-#30 (ignition SW @ ON position not START) using wiring set-up mentioned in your #1 procedure. You don't need a spare FP relay to test the FP!!!!.


Tony

What type of electrical connectors would you put on the end of the wires for hooking up to the fuse box?

[ninelevenick]

Electronic supply stores (Radio Shack for instance) sell "alligator clips." I don't know the official name for them, but it's a wire with a jaw-like prong on both ends. These jaws clamp down on wires, connectors, fuses, or whatever will fit within the jaws.

[Gunter]

Originally Posted by boyt911sc

John,

Once your FP starts to run, WUR, AAR, and TTV (optional) would be all energized at the same time regardless the engine is running or not unless you have disconnected or unplugged them before hand. The difference in the cold control pressures between plugged and unplugged the first few seconds is very minimal. However, I suggest that you unplug it if you're just starting to learn CIS troubleshooting to prevent you from mis-reading the data. So the choice is yours.

Tony

Tony,

The Bentley SC Repair Manual on page 201-5 says nothing about disconnecting the WUR for the pressure test. Is that just omitted by mistake?

Does Porsche mention anything about disconnecting WUR for pressure testing?

When jumpering the pump to run as described, does that complete the circuit to give power to the WUR?

If that is so, it would have an effect on pressure.
But I think leaving the AAR and TTV (if applicable) connected should be alright.

Your thoughts?

[Forza]

I think Tony means to say that one should disconnect the electrical wire to the WUR that helps to heat the metalic strip more quickly under normal operating conditions. Cold pressure check would fluctuate with the strip being heated by this circuit.

[boyt911sc]

Originally Posted by Gunter

Tony,

The Bentley SC Repair Manual on page 201-5 says nothing about disconnecting the WUR for the pressure test. Is that just omitted by mistake?

Does Porsche mention anything about disconnecting WUR for pressure testing?

When jumpering the pump to run as described, does that complete the circuit to give power to the WUR?

YES. Jumpering

If that is so, it would have an effect on pressure.
But I think leaving the AAR and TTS connected should be alright.

Your thoughts?

Gunter,

The Bentley SC Repair Manual on page 201-5 says nothing about disconnecting the WUR for the pressure test. Is that just omitted by mistake?

NO. The Bentley Manual does not mention that for a fact. I don't usually disconnect the plug when I check the cold control pressure provided you read it the very first few seconds otherwise, the heater will help increase the control pressure after 10 to 20 seconds of running.

Does Porsche mention anything about disconnecting WUR for pressure testing?

YES. Please read Workshop Manual 911 (vol.III- sec.2) it's in there. I'll post the exact page if I get the chance to look for it.

When jumpering the pump to run as described, does that complete the circuit to give power to the WUR?

Yes. Terminal #87A gets power from the ignition switch @ RUN or ON position. So when you bridge terminals #87A and #30, you are supplying power to terminal #30. Thus all the CIS components that are connected to #30 would be energized. Terminal #30 is not exclusively used by the FP, there are several CIS components namely WUR, AAR, & TTV (optional) that are connected to terminal #30. This explains why WUR should be unplugged during cold control pressure measurement. Otherwise, the heat generated by the heating element inherent in the WUR would give a 'heated' control pressure.

If that is so, it would have an effect on pressure.
But I think leaving the AAR and TTS connected should be alright.

Yes. The heat generated by the heating element (WUR) will have a direct effect on the cold control pressure but very minimal on the system pressure based from my limited experience. AAR and TTV (thermotime valve) have no effect on the fuel pressure test.

One of the few guys in this forum that I helped and walked thru the basic CIS troubleshooting procedures was Rich911S. He has documented his work by posting a video about the change of the control pressure when the heating element is plugged.

Tony

[Gunter]

Tony,

You da man.

That makes sense. Looking at the diagram for Terminal # 30, it does supply the other components like you say.

I'll make a note in the Bentley to that effect.

Many thanks.