Van

At this point, would it hurt to drain the gas and replace it with fresh stuff? Far cheaper than throwing electronic parts at it.

roman944

Mark - honestly, I don't know

Van - you think? gas was fresh, Mobile gas station, filled up just a few hours before this "no start" happened ... not "old gas" or anything like that ...

Van

That is precisely why I'm suggesting it... I've seen bad gas cause weird problems before.

Mike C.

At least throw a couple can of dry gas in there just in case.

joes

After reading this thread I suprised that you haven't figured out what the problem is. Let me help, your reference sensors are not working. Check, clean, remove, repair, replace.

AKCJ

I'm thinking the same thing. It could be that the fact that the tach bounces indicates that ONE of the sensors MAY be working. That's not the same thing as BOTH ARE working.

I assume tach bounce is related to the speed sensor so . . . change out the reference sensor first.

roman944

will try this "new" AFM, and get some fresh gas first

thanks guys!

roman944

got the "new" used AFM in, still no start

have "new" used computer, but before then, we'll drain the gas ... if its none of these things, will order new speed/reference sensors

Mike C.

Did you test the speed and ref sensors with an ohm meter per Clark's? And take a close look at the connections- the connectors on these are notorious for cracking and causing intermittent operation.

roman944

I looked at them and they look normal, I didn't try to unplug anything though

tried wiggling it and starting the car, to the tune of nothing

Kerry Chadderton

Roman- Hold tight. I pulled my hair out doing this same shiznit on mine. I came up with a way to "see" the Ref and Speed sensor signals at the DME using $2 worth of Radio Shack LEDs and a magic marker.

I gotta get to the shop, set it up and take some pictures. Then I'll post with the part numbers and pictures. Hope you can wait 24 hours. At least then you'll know that the signals are getting through.

roman944

Thanks Kerry, I got all the time in the world ... LOL

Kerry Chadderton

Okay Roman. I hope I don't confuse you here. I had a no start problem a couple of months ago. I went through everything. The car was new to me and I had never seen it run, so there was a huge learning curve. Along the way I had to determine if, in fact, the reference and speed sensors were working since I could not "test" the DME. Incidentally I have a 1984 N/A, so this all applies to your car.

The following information refers to Clark's Garage document IGN-02 and the Porsche shop manual section on testing the DME and associated sensors. Porsche uses an oscilliscope to test everything. I don't have one, could not find one and I certainly wasn't buying one! So, lets use LEDS to test.

First, start by buying two LEDS. Radio Shack #'s 2760022 & 2760041


One lead on each LED is shorter that the other. That is the negative side, which is important. Mark that one black with magic marker on each. Now remove your fuel pump fuse and disconnect the 35-pin connector from the back of the DME. Using Clark's Garage document IGN-02, page 5 "DME plug connector" locate and mark pins 8,25,26,27.

8 & 27 are the Speed Sensor outputs; 8 is negative, 27 is positive. Insert your RED LED (2.6 volt) between the two. Remember your + & - !

25 & 26 are the Reference Sensor outputs; 26 is negative, 25 is positive. Insert your GREEN LED (2.1 volt) between the two. Remember your + & - !

It should look like this:



Make sure the leads don't touch. Now crank the engine over as you would normally. If everything is kosher your green LED should be blinking and the red LED should be almost steady as the engine spins.

This worked like a charm for me, helping me to determine that the DME was bad and ultimately solving my problems. If I didn't explain well, please ask for clarification. I'm no teacher! Good luck sir!!!

shiners780

^^^ Great post.

roman944

that sounds like an easy test - I should have enough time on Sunday to pick these up and do this ... THANK YOU !

so did it end up being your sensors or?