924Board.org

[kris]

Okay, we have progressed a little bit towards getting this dog gone car running!

I have removed the TPS unit from the throttle body of my 1981 931. I am wanting to check it to see if it may be faulty before sticking it back in & moving on to other possible problems (As I have posted in my previous posts, the car runs smooth at idle speed, but as soon as the throttle cam is moved, it wants to sputter out & die...so this is the next test on the list).

From what I am understanding, an Ohm Meter will be needed to check this unit. My question is, what terminals do I use to check the ohms of the "running circuit" (the idle circuit seems to be fine since it doesn't mis fire at ALL during idle).

The Haynes Manual is worthless for this application, so Im appealing my case to a higher court!!!

Im becoming so eduacated on this 931 Ignition/Fuel System, I almost want to PUKE! hahahaha

Any ideas?

[kris]

I will be damned!

Page 286 in the Haynes Manual has updates for the 81-82 931!!

I just read the whole chapter. It talks about a continuity test on the flywheel sensor that runs to the timing control unit.

When testing the sensor itself. Does the car need to be in the "on" position when jumping over terminals 13 & 15? Same thing when jumping 14 & 15?

Or should I do one of these checks with the car "off"?

Also, when locating the mark on the flywheel, and making sure the ignition distributor is lined up right on the #1 spark too. Is the mark hard to see with a flashlight? Does anything need to be taken off the motor to make it easily visible on the flywheel?

[dwak]

Kris,
I just went through this procedure with my mech and we found my sensor to be bad. Took it off to test. It was a month ago but I can dig up details if you want. We managed to locate a new replacement for this rare item in California through a friend of a friend ad nauseum. Just about to install.dwak

[924 turbo]

"If the flywheel sensor fails, the entire ignition system will not operate" P43, Service Information, Model 81.

Just trying to narrow down your problem. Does the car run?

[kris]

Yes, the car runs fine AT IDLE SPEED. But as soon as you start to move the throttle body (even the least little bit) the car starts to sputter & die. If you keep "popping" the throttle cam, you can eventually bring the car upto higher RPM ranges, but the car misfires badly, surges & backfires when you do this. And the Air Mixture Control Unit Plate hops up & down (you can hear it popping around as the car misfires). I am trying to find means of testing the throttle positioning sensor. I am also going to pull the injection & air box unit out & inspect the main boot from the turbocharger to the air mixture control unit & see if it is damaged at all....

Would an air leak on EITHER of the air mixture control units rubber boots ("to air box" or "to turbocharger") Cause this problem?

[kris]

Dwak,

How did you figure out that it was bad? Did you have the same symptoms that I do?

If you tested it off of the car? What terminals did you have to jumper over to check for continuity?

So YES, ANY info you have on how to test this thing. Kick it my way if its no trouble for you....

Thanks

THIS CAR WILL NOT BEAT ME!!!!!

[Smoothie]

You should be able to see the TDC ("Z1" mark on a 924t) with just a flashlight.

To test the flywheel sensor, leave the ignition shut off. Unplug the sensor* from the DITC box behind the radio (accessible from the drivers side foot well without removing anything). Check for continuity (with either a test light or an ohmmeter) between the terminals given in the Haynes. The top terminal is #14, middle is 15, bottom 13. I get .01k ohms between 14 and 15, 0 ohms between 15 and 13, .01k ohms between 14 and 13 (checked with a digital multimeter) - and the car runs great.

* - To get the sensor unplugged, first unplug the 12 pin plug to the right of it, then pry off the sensor plugs' wire clip with a flat blade screwdriver. If you don't do this, and pull hard enough, the whole circuit board will come out of the DITC box** with the flywheel sensors' plug still attached. Straighten any bends in the clip and reattach it to the plug before replugging the plug. (Add this to your Haynes manual.)

If you need to remove the DITC box, there are 2 screws on the right side (when facing the connectors).

** - Don't ask me how I know this.

_________________
'82 93

[ This Message was edited by: Smoothie on 2002-10-18 07:09 ]

[Smoothie]

By the way, that 12 pin plug on the DITC box is a common source of problems - just unplug-replug or remove it and wirebrush the pins with a clean fine-wired brush.

[dwak]

Kris,
I'm pretty sure 924turbo is right. I'd leave the flywheel sensor alone. Mine wasn't sparking and tested out unequally, indicating a continuity problem. Probably had been manhandled at tear down. Engine would not fire.
dwak

[kris]

Well the flywheel sensor is fine. I jumpered over the terminals as explained in the Haynes Manual (just to be thorough) and I had NO resistance between the contact points on EITHER check. So it must be ok (the car runs at idle anyway).

(See My Post on "A Look Inside the Throttle Position Sensor" for the other checks I did today).