Lizard928

TBF should be checked.

But you will have to remove the cover from the maf connector to check the wires.

SteveG

Thanks Rich for that diagnosis. Second, a crank position sensor this old might be dying when hot.

928GTSM

I'll 2nd the crank position sensor as well having had the exact same problem recently on my 93 GTS. As soon as it reached operating temperature it would die and you couldn't restart it until the engine cooled down. It was an SOB to get out but once replaced it's run like a good'un.

CJs 928

is there an ops check for the crank sensor?

John Speake

See the diagnosis section at the end of Vol 1A of the WSM.

CJs 928

thank you.

Mrmerlin

CJ order a new starter relay and a new crank position sensor. If you had to replace the knock sensors then you should have also replaced the CPS as well.
Its made of the same connector material as the knocks.
Also if your going to go to the trouble of testing it you should just replace it since your going to have to remove the air cleaner and disconnect the CPS connector


The reason for the starter relay??
Since you have been cranking the car for extended periods the starter relay has gotten very hot and probably melted,
it is now just a matter of time before you put in the key and have a no crank situation this is due to a failed starter relay.

CJs 928

Damn, it just gets better. Thank you for the advice. I started looking at the price for the CPS-seems that there is a BMW version (or 944?) that has a longer cable for half the price. Anyone have any luck with the "alternate" version?

the flyin' scotsman

Talk to Roger at 928sRus..............he has great pricing on all sensors.

The CPS is a while your at it when removing the intake..............the car will run with a probmatic ISV or TPS but the CPS is critical.

Hope it works out for you.

CJs 928

Sorry for lack of progress, in the middle of a big inspection at work-long shifts and weekend for next week. To answer some comments/questions.

Tank has new gas 91 Oct (old stuff was drained).

I had the car for a few years, but have driven it about a mile (seriously-total 1 Mile). I bought the car and a lot of hoses and stuff were perished/gone. So, little by little I started replacing stuff-i.e intake refresh pluse valve cover seals. The original owner stopped responding to phone calls/e-mails as soon as he got paid, so I have no idea if he thought there was an issue or not. I only write this due to the comment stating that I would have known if it was TBF-seriously wouldn't have in my opinion (the PO however, would have). One thing of interest is that the car has stalled since the first time I started (3 years ago or so). I just thought it needed tune up and maybe a sensor or two.

I tried to check the crank play again yesterday-and damn, how the hell do you measure .0?? anything acurately on your back with no real fixed palce to set the caliper. I don't have a dial gauge with a plunger, only a digital caliper guage. Just venting over the tight tolerances. What I think I got was in the neighborhood of .010 to .020. At one point I got .040 as I was still prying the flywheel towards the rear of the engine-I'm praying that that was not accurate.

This is the rest of what I have tried so far. Car stalled yesterday and I replaced the XX relay with brand new one-still no start.

I checked the voltage between XX 30 and 87 and got 2.83 VDC. I went from XX 30 to chasis gnd-same reading. After about 3 hours it read 3 VDC and 24 hours later, it reads 3.98 VDC. The flap receptacle next to it reads -12.3 VDC and other accesories read 12 VDC. I assume the battery is not the issue-car is still turing strong, just no start. I will spray starter fluid next to ensure I have good spark.

Rich9928p

Do not spray starter fluid into the intake, it can damage the mass airflow sensor. Spark should be checked with a tool made for that - otherwise you risk getting the shock of your LIFE ... or shock to take away your life.

Please double check that you are testing the 30 position at the relay socket.
The voltage between ANY 30 relay socket position and chassis ground MUST be battery voltage (~ 12V). Check the + terminal at the battery cable and make sure all the connections are in place. The car will not run unless there is 12V at the 30 position. Investigate this issue before doing ANYTHING else.

928GTSM

CJ's 928 do yourself a favour, start the car let it tick over, or go for a short drive but get back before the temp gets too high, and sit back and observe. If once it gets to operating temperature it cuts out then I can only re-iterate that when mine did this it was the CPS.
It cranked like a beast and even with the fuel pump wired directly to 12V's it was still a no start as your ignition is not receving a signal from the sensor. When I had this problem John Speake kindly went through what to test over the phone with me and tracked it down to this.

CJs 928

Guys, thanks for all the inputs and ideas. The crank sensor connector was pretty well perished so it probably needs replacement eitherway. Gonna order it tomorrow.

On another note, the voltage at the fuel pump relay connector is the strangest thing. Started at 2.8 VDC the day of the stall, has slowly climbed in voltage and as of this morning, it is 9.2 VDC. Weird. At the battery, still reading 12.3 VDC. Another note. I put about 4 gallons of gas in it, but it resgisters empty on the fuel gauge (no low fuel light though). Gonna check the wires to the sender and make sure they are in the right place--maybe this is self induced by a wiring issue to the sender?

I understand that the crank sensor can cause this issue (thanks for the tip), but the lack of correct voltage at the XX 30 makes sense as to why the car would stall-no power to the fuel pump. Is there a circuit I should be looking at that could keep power from this connector? BTW, the pump is new (well only been used for about 30 mins).

Rich9928p

When I had a stall/no start condition with my '83 928 due to no voltage at the 30 position at the relay the problem was the connection of a cable to the + cable to the battery. I haven't traced the actual wiring on the S4s, but somehow 12V must show up at every 30 position ALL the time. It could even be plugs going into our out of the central electric (fuse panel) - check the wiring diagrams and they'll tell you where you need to probe.

AO

If you haven't looked at it already, you should look at the LH/EZK diagnostics proceedure (there's a link in my signature for quick refernce.)

Aside all the pointers that people have given you so far, I would also look at the throttle posiiton switch. As the engine warms the trottle cable will expand slightly and could cause it to not make contact for teh idle position. This can cause a poor idle and possibly stall the engine.

Flex plate and crank end-play to determine thrust bearing condition shoudl also be on your list of to-do's.