austin9111

Have a 924S that I am still learning.

Currently turning over but not starting: seems like a fuel delivery issue.

I can't remember whether I could hear the fuel pump running in the 924S when key is in "on" position but before cranking.

On several of my cars (911, X1/9) you can clearly hear the fuel pump running with key "on" but before cranking, while other of my cars (Land Rover D2, RX-7), the fuel pump only momentarily runs toi pressurize the fuel system, then turns off and waits until the engine is cranked before running again.

How the 924S fuel pump/DME operates -- continuously or intermittently/on demand -- will help me determine whether I have a bad pump or a bad relay: I'll put the multimeter on it but need to know under what under what conditions I should see voltage at the pump studs.

And is there a pressure measurement schrader valve on the fuel rasil?

Any help/guidance would be appreciated.

Gage

The system is designed to run the fuel pump only when the engine is rotating.
The access to the fuel system is via a 19mm cap nut at the front of the fuel rail. Be sure to counter hold the rail and don't drop the ball bearing seal. There is no schrader valve.

V2Rocket

as stock it doesnt run the pump at key on, only when cranking and then when engine running.
you can use this aftermarket DME relay to get a prime function and basic diagnostic

https://www.ftech9.com/new-products/993-ssr-pp

austin9111

Wow, thanks for the responses.

Good to know that the fuel pump doesn't run before cranking to prime/pressurize the fuel system. For me that's a big ah, hah. (and that pump priming relay is pretty cool)

Starting with the "elephant in the room", how would you approach this diagnosis?

I see the following tests, but not sure what order I should tackle it.

confirming spark (just to address one the 3 things needed for internal combustion engine operation: fuel, compression, spark)
Apply voltage to fuel pump (by jumpering the relay socket?), this will also confirm whether the fuel pump is good without taking it off or putting power directly to it
Measuring pressure at the fuel rail
Checking for signal at the fuel injectors (using a noid kit)
Testing the cam and crank position sensors

I thought I had seen a response/post about a tired pump having lower resistance and therefore drawing more current (V = I x R) thru the DME. This actually scare me because I already have this problem with the AC amplifier: I think my AC blower motor is drawing too much current, which is frying the printed circuit board in the AC amplifier box (I've fried 3-4 of these already and we tried to bypass the line on the board with a heavier gauge wire jumper with no success).

I also thought someone had posted a list of links I should read, but I don't see it anymore.

austin9111

re. the "missing post", an interesting discovery.

When viewing Rennlist using Chrome on my iPhone, at the bottom of the thread it also show me related threads, including one from the 993 (sub) Forum titled "fuel pump issues" that had the comment about a failing fuel pump causing too much current to be drawn thru the DME (I thought the DME controlled the relay, but that the actually current path to the pump is always energized at the relay).

This related thread does not show up in Chrome on my MacBook.

peanut

the first check that I carry out a non start Porsche of this period is to remove the DME relay and measure the voltage on terminal 30 of the DME relay socket with the ignition switched off.
There should be a constant 12v+ on terminal 30 at all times, with the ignition Off , ignition On and whilst cranking. This supplies the fuel pump the ECU , the injectors , the ignition and the various sensors .

A 3x wire bypass will supply everything needed and will either confirm or eliminate the DME relay being a starting or running issue . I convert a spare relay to make a DME bypass and add a switch so that I can switch it on and off during testing otherwise the fuel pump will run continuously until the bypass is removed.

austin9111

Terminal 30 is one of the 3 "amigos" to interconnect: what are the other two?

And after confirming power to terminal 30, wouldn't testing the DME relay itself achieve the same , i.e., putting 12v on the solenoid terminals and seeing if you get a closed circuit, i.e., >1 ohm resistance, on the terminals controlled by the solenoid.

peanut

you will have to check your DME relay I am not familiar with the 924
On all of the 944 models the DME relay is a double relay and you should connect socket terminals 30 ,87 and 87b

To answer your question....if you connect a 3x wire bypass in place of the DME relay and the car starts then you'll know that it is the DME relay that is faulty won't you ! you won't need to test it .
If using the bypass doesn't allow the car to start then move on to the next sequential No Start troubleshoot check still using the Bypass not the DME relay.

Before you install a DME bypass you must confirm that you have 12v+ at terminal 30 or you're wasting your time.

peanut

here is a link to a similar no start situation that I tried to help the 924S owner with way back in 2013 ! ( where have all the years gone. )
You may find something helpful in this thread if you read it right through. It will save a lot of unecessary duplication
https://rennlist.com/forums/924-931-...e-relay-3.html

austin9111

Thanks, going to follow those steps tomorrow.

Which terminal is the fuel pump (87 or 87b)?

Chalt

You may or may not know about Clarks-garage.com...
The Troubleshooting section is a good place to start for methodical testing Here.
Then select "Engine Will Rotate But Will Not Start (Fire)"