'84 3.2 Li No Start / no spark

[Skip1]

Well hello again all,

It seems like I've been here before, but this time the car was completely tuned, proper valve adjustment, vacuum hoses tested etc and ran perfectly for over a month with excellent power and performance. Initially I had an intermittent no start (mainly when warm). Mech said that reference sensor failed testing once it warmed up - replaced both speed and reference and engine hummed like never before. The other day I parked the car to vacuum it out, and when I tried to start it about an hour later, it just turned over and over, but didn't start - some fuel smell in the exhaust after I cranked a few times. Over the next couple of days I tried it periodically on the off chance the same thing happened with a warm engine, but no dice - engine just turns over and over.

Today, a friend of mine gave me a hand to test a few things, results as follows (I bypassed DME relay for fuel pump to start to ensure no issues there - confirmed later all good):

(1) Spark Plug test at cylinder end (after distributor) - no spark
(2) Spark Plug test at coil (before distributor) - no spark
(3) Coil tested - Primary coil (terminal 1 and 15) 0.57 ohms - within spec according to Porsche manual
(4) Coil tested - Secondary coil (terminal 1 and 4) 5.9 kohms - within spec according to Porsche manual as well
(5) testing green wire from DME and got pulse signal while cranking
(6) tested Black wire to fuse #8 under hood - resistance confirmed and live when in start / run

Tried to test the sensors again, but having a heck of a time - expect that'll be the job on the weekend. Can anyone see if I'm missing anything that I should test on the ignition side?

[Chuck.H]

Hi Skip -

What do you mean by test number (5) above - what pin on the DME do you mean here?

Have you checked your DME for cracked solder joints? This will cause a random no-spark condition, you can search the forums for info.

Chuck.H
'89 TurboLookTarga, 363k miles

[Crude Rudy]

Check the resistance in the engine bay of the speed and reference sensor per the Bentley manual. The connectors are on the left side by the fan. If either of the speed or reference sensors went bad they can cause a no spark conditions. Just because they were OK a month ago does not mean they are OK today .... rule them out. Then try and swap the DME with a friends or another Pelican to rule that out.

Good Luck

[Skip1]

For test (5) my friend held a voltage meter between the green wire that goes to pin 1 on the coil and ground. As I cranked the engine, he got voltage, so I assume that that means I'm getting a pulse from the DME.

Will try to test the sensors as per manual (will have remove heater hose first) too tight for my sausage fingers otherwise. If it is a sensor, that would be two in a little over a month. Could something be frying them?

Thanks for the responses.

[Chuck.H]

Pin 1 on the DME is the coil ground wire - it will go to ground to fire the coil... So a little hard to check with a meter. With an osilloscope it will bounce between 12v and ground. Maybe you can see this with a test LED, but the pulse to ground will be very small compared to the time it's at 12v.

One thing to keep in mind with the reference and speed sensors, if they are too far from the flywheel they will not trigger... so check them first for resistance and second that they pulse when the engine is cranking.

Chuck.H
'89 TurboLookTarga, 363k miles

[Skip1]

OK. Will do that. How can I check if they pulse while cranking? Which of the 3 on the connectors in the engine bay do I use?

Thanks again.

[Chuck.H]

The way I check them is to open the DME and put probes right on the back of the DME connector; there are large pins that go from the connector to the PCB. Just be careful you don't cause a short between pins, they are a little close together.

I would start with an Ohm test between pins 25/26 and 8/27. In case you aren't aware, on my '89 the pins are numbered on the DME connector...

Here are my notes regarding DME pins:

1 coil ground (1)
2 micro switch (throttle, idle)
closure to ground at idle position

3 micro switch (throttle, wot + throttle valve) test connection b
closure to ground at wot

4 t54, starter active
+12 volts while cranking engine

5 gnd
6 gnd, air flow sensor, ntc I

7 air flow sensor +
8 speed sensor +
0.6 to 1.6 kohms between pins 8 and 27

9 air flow sensor -
10 plug for exhaust data (ground) (t0, p3.4)
11 t54, speedo
12 engine bay test connection 'a'
13 ntc II (head temp)
1.4 to 3.6kohms at 70oF
160 to 210ohms at 212oF
591ohms measured 1h after hot, and increasing
2.1k ohms measured the next morning, 62F. 3.02v koeo

14 t55, injector control signal
15 t55, injector control signal
16 gnd
17 gnd
18 +12v

19 gnd
20 fuel pump control signal, dme relay (also puts power on o2 sensor)
dme provides ground signal on pin 20
21 t54 pin 2, starter engaged - also goes to speedo
22 air flow sensor, ntc I +
23 .75ohm connection to pins 5, 25, 26, 8 & 27
24 oxygen sensor
25 ref mark sensor +
0.6 to 1.6 kohms between pins 25 and 26

26 ref mark sensor -
27 speed sensor -
28 altitude sensor
29 a/c compressor clutch 'on'
30
31
32
33 idle speed positioner +
34 idle speed positioner -
35 +12v

Chuck.H
'89 TurboLookTarga, 363k miles

[Skip1]

OK, so pulled the heater fan hose off to get better access to the reference and speed sensor connections. Tested pins 1 and 2 to start on both. Results for reference sensor were around 500 MOhms vice 960 +/- 96 Ohms according to Bentley Manual. Then tested speed sensor and it was at 1.011 KOhms so well within the spec.

So, dug out some old ones I had (have two new on order) and tested them, both within spec, so decided to jack up the car take the rear driver tire off and get to work. Pulled the connector for the reference sensor through the tin and tried to access the allen bolt that mounts it, but no way, am starting to strip it, so stopped (a lot of rust too). Was contemplating removing the entire bracket in order to get it out, but not comfortable trying to re-gap properly as the transmission is still on and I can't get my sausage fingers around all the parts, nor get a feeler gauge between the flywheel and the sensor.

I saw the option in the manual to glue a 0.8 mm washer onto the end of an old sensor as an alignment tool, but then it also says the gap is 0.08 mm which makes no sense to me.

Any ideas on how to get the reference (top) sensor out without further stripping or removing the bracket?

If not, any ideas on how to ensure I re-gap it properly with the engine and transmission still in the car? I was so close too.

Thanks.

[Chuck.H]

Is your car currently in it's nostart condition? I ask because I find these sensors, when they go bad, are often working when cold and then go to zero ohms when they heat up...

Regarding spacing, 0.8mm sounds like the right one to me but I'm away from my factory manuals now. If you don't have a spare sensor you can glue or tape a piece of .8mm cardboard to your sensors and install them touching the flywheel.

I just went thru this in my jeep for the flywheel sensor and I can attest they don't pulse if they are the least bit too far from the flywheel.

Chuck.H
'89 TurboLookTarga, 363k miles

[Skip1]

Car is currently in complete no start. When it first died it wouldn't start hot, now of course it's cold and still won't start. Once I remove the old sensor, I'll have a spare no functioning one, so could give that a try, just a little nervous on that part, in case it won't go after at all. I do have a box of washers that I may measure tomorrow and perhaps try again. Had to lower the car to put it back into the garage for the night as the garage is very narrow here in Germany, so have to do it in the driveway.

My previous reference sensor issue was cold start, hot no start.

[SiberianDVM]

I just replaced my malfunctioning speed sensor (actually replaced both) that caused a no start. If you just paid a mechanic to replace them, they should not be seized up and the allen head bolt shouldn't be that hard to remove. I did have to remove the mounting bracket to get mine out as I think they were original, and I epoxied a 0.8mm washer to the dead one to use as a spacing tool. Are you sure the mechanic replaced both of them?

[Skip1]

I thought they had, but in checking the bill, I only got charged for one (update: Further inspection on bracket removal, the mechanic replaced it with a functioning used set - good and not good), so a failed assumption on my part. I bought some new bolts as well (stainless), as well as some other cool tools to hopefully make the job a little easier in the future and will use the dead reference sensor as a guide to expoxy an 0.8mm washer (have lots of small washers and a micrometer). Let's hope it doesn't fall off. Seems to me like the sensors have a rounded tip though, if memory serves.

Picked up two new sensors this morning at my local Bosch dealer. Back up the car goes.

Thanks much. Will post how it goes.

[Skip1]

Update: Managed to remove the entire sensor bracket without any difficulty, which yielded the explanation of why I couldn't get the sensors out individually. Rusted solid and with final removal outside the car (compliments of the my mechanic), loctite on the threads as well. Bracket completely cleaned, used the dead sensor to glue on my newly reduced 0.8mm plastic washer, adjusted, replaced, and crank. Instantly started - then put all the pieces, rubber grommet etc back together.

End result - happy camper and back on the road. many thanks for the support folks.

One question - not sure if this has been asked before. Based on the apparent frequency of sensor failures I've had, is there anything that could cause my ignition system to fry the sensor that I should check now that it's up and running again?

Cheers from Germany.