Car randomly dies

[aza]

Hi ive had my 944 turbo for a couple of years now but recently it started to die after about 10mins, so far ive replaced fuel pump, DME relay, fuel filter, plugs and wires, distributor cap and rotor, I have replaced one of the reference sensors when i pulled the old one out and it looked like this

that was the sensor closest to the firewall. That is the sensor that reads the teeth on the flywheel I assume.

Couple of questions with how these 2 sensors work.
1. Does the sensor closer to the engine need to be connected after the engine is running? Reason I ask is if I have both connected and unplug the one closest to the engine the car still runs but won't start unless it's plugged in.
2. Is there only 2 sensors? A picture of the bracket looks like there is a 3rd sensor further round but I can't see on the car.

Another question also after I had a look around where the ECU's are in the footwell, behind one of them there was a black box with alarm some german writing on it. Is this a stock alarm? When I purchased the car I never had to use the alarm remote that came on one set of keys so I assumed the alarm was disabled.

Couple of other weird things as of late that are happening the fuel needle will jump around a small amount and the indicators now seem to flash at different speeds from left to right.

Could I have a huge electrical issue in the dash causing everything?

[John_AZ]

I'll take the easy Qs.

Have you ever reset the gap on the sensors?
Speed and Reference Sensors - Checking, Replacement, and Adjustment

The third sensor you may not be able to see is the "factory" TDC sensor. Not used--NLA
The sensor wire connection goes over to the rear of the cam housing by the firewall.

You need to change the damaged sensor. A BMW interchange is cheaper than the OEM.

I do not know about alarms.

The fuel sender in the fuel tank is dirty. You can clean the contacts if you take out the entire fuel sender. Get a new gasket first. Very delicate. Usually the top wire contacts inside the fuel sender are corrorded and you may not get it fixed. I am 1 for 2 on my fuel tank senders.

Clean all your grounds---every one.

GL
John

[SolReaver]

Dies after ten min? Hmmmm...

+1 on the grounds. I would have done both sensors WYAIT. Replace or at least check the connectors to the sensors. You need both sensors to start and the computr MIGHT be able to figure it out from there to run IIRC. Test the sensors from the DME plug. The third sensor is for some mysterious factory tuning thingie and there is a plug that goes to it. The plug is a large roundish thing with a cap and it is on the passenger wheel well under the hood. But, that isn't your problem.

Please leave the sensors plugged in. The furthest back IS the FW tooth or Speed sensor and the forward one is the Ref sensor that picks up a pin on the Flywheel. You need em both...OK?

Next...figure out WHAT dies after ten min. No spark..no fuel pressure...does it have signal to the injectors as tested with a noid...lets get technical here.

It could be temperature related, so check the thermo connections and, yes, there are a few of them.

Indicators flashing at different speeds is a short or burnt bulb. (best guess)

Alarm system? Oh dear... I don't have one of those. Never seen one. They all died years ago. Trace the wires and make your call as to whether or not you want to remove it. Honestly... Today you can replace it with a better unit for short money IF you really want an alarm system.

[aza]

I ordered another 2 sensors as the speed senor i replaced seemed to contact the flywheel like the orginal which I worked out there was a missing washing for this sensor. Now I know an easy way to set the distance for the sensors then I can replace both and reset the distance from there.

When the car dies it sometimes starts again from the monentum of the engine spinning this only happens sometimes and does this within 1sec of it dying. When the car dies and does not restart right away there is no spark.

I have also noticed it plays up ie. dies and goes again off and on when I drive over a fairly rough bit of road.

I also ordered a new coil incase the old one doesn't like vibration anymore.

Another thing about the alarm module i found was it has 2 plugs going into it, from what I can gather 1 is power with only a red and another wire going in. If I pull this plug the car stays running but if I pull the other plug which has about 8 wires going in the car dies, so it still part of the circuit it was a lil warm so im also wondering if this unit might be part of my problem.

[SolReaver]

Hmmm.. If you remove it the car won't start...But you suspect it is making the car die...Quite the dilemma. However, as you pointed out you can disconnect the unit and the car remains running...so...not your problem.

"gapping" the sensors is as easy as gluing a piece of plastic or a matchbook cover to the ends. When they bottom out...you have your clearance.

So it dies when it goes over bumps...well...you COULD have mentioned that earlier.

No spark? When you go over bumps you loose spark? The difficulty is that you need to test it when it is "dead" and intermittent problems can be tricky. Check for voltage on the hot side of the coil with the ignition on. Signal difficulties can be checked with a noid on the fuel injector.

[aza]

what is a noid? maybe we call it something different here in australia.

I read somewhere i think on another forum about having no spark and when you turn the key to start and the engine turns over and doesn't fire and the tacho does not move then the issue is narrowed down by checking something but I for the life of me can't find this information again.

Today I replaced the 2 reference sensors again and also installed a new coil problem still the same.

I also bought a multimeter today to be able to check voltage and resistance but i'll need some help on where to start and what to look for.

Also is there a PDF somewhere of the service manual I lost the copy I had when my house was flooded back in January, would like to check all my earths

Also would a dry solder in the DME computer cause no spark?

all help is greatly appreciated

[SolReaver]

Noid= a little LED thingie that plugs into the fuel injector harness and lets ya know if signal is getting to the injectors. Or you can scrounge an oscilliscope..... you might call it something else in Australia...It is a common diagnostic tool and you can pick em up cheap. A whole kit is 40 american...individual bosch are 3 to 10. Good to have. A Fuel pressure gauge on the rail is neat to have as well.


Just a thought...Spend some quality time cleaning the fuses and relay connections..All of em. Corrosion can create some odd intermittent connections Grounds....do a search...I saw them around here somewhere...especially check what I call the PITA ground... just trace the neg batt cable to where it disappears behind the engine. Run an extra ground for giggles.

Check power to hot side coil with ignition on.

YOU WILL need a good multimeter. Nothing fancy mind you....

[P944GUY]

your in need of a new computer...mine did the same thing intermittently to start then just died one night

[aza]

Originally Posted by P944GUY

your in need of a new computer...mine did the same thing intermittently to start then just died one night

the DME computer?

where abouts inside do the dry solder joints happen that can cause this issue?

also which is the DME and which is the KLR they arent labelled but I assume the KLR has the vacume line running into it??

[P944GUY]

Hmm...KLR ..is it a turbo car...I just have a measly no horsepower non turbo..over the years heating and cooling and humidity corrode the electronics i would imagine...it's under the dash passenger footwell behind the carpet and piece of wood is where it's located..

[aza]

after deciding to check if the alarm was the issue i tapped the alarm which was resting on the bracket that holds both computers the car played up, then i tapped just on the DME computer i assume its the one without the vacume line running into it and the car played up.

Has anyone repaired dry solders in theirs? I'm in the middle of pulling it apart to see if I can find any dry solders and fix them

[John_AZ]

A couple...
Early DME repair write-up with pics. - Rennlist Discussion Forums

OR
DME Repaired w/pics - Rennlist Discussion Forums

Finally...
DME Computer - Testing and Inpsecting

GL
John

[aza]

thanks for the links i can't access the pics in 2 of those but the one i could see of the big resistor i think is/was my issue, I had to get between the 2 boards and remelt the solder in there as well as on the board. about to go for a drive and test sitting in the driveway and tapping the computer now fairly hard only made it stumble slightly a few time but didn't completely die.
I have a mate coming over tomorow to have a look at it also he knows alot more about soldering and fixing these kinds of things im a crap solderer lol

[John_AZ]

Sorry, you can/could become a member of Rennlist. Many Pelican members use both. Pelican Parts is a forum sponsor on Rennlist.

John

[AKCJ]

I agree it sounds like a failing DME. But I would also change the DME Relay first. (If a turbo is anything like the early.)

[PorscheKitty]

Just a random thought- might be good to check the air flow meter while you're at it.

I agree with the other guys- definitely get all your grounds/electrical clean up out of the way-ultra important

[Dan Himan]

This might sound crazy, but did you check the connections on the bottom of the fuse box. Mine would die as if it was the TPS or DME, and after resoldering the DME, and testing the DME and TPS, and getting pissed, I did a through wire check and found to plugs loose under the fuse box, popped them back in and problem solved. Luckily!