A 3.6 Mystery...I am stumped

[Embs]

Another Varioram, OBDI, everything is brand new mechanically or as good as new from the crank out.

The engine was running great for several weeks and then it died and wouldn't restart. It stumbles and backfires a little but doesn't come close to starting.


So far I have checked and verified the following as okay:


DME relays (I have tried 5 different all were new & German)
It is getting fuel
Strong spark (both ignitors are new)
No plug wires crossed (plugs and beru wires are new)
Head temp sensor
DME pick up
Hall Effect
Hot wire
Distributor +slave and belt
ECU/Motronic (verified by Loren at Systems Consulting)


I am LOSING MY MIND (what's left of it) What am I overlooking???

Any suggestions greatly appreciated.

Thanks ,

Todd

[Tinker]

Interesting....

Fuel pressure is at spec? A misfire/backfire would point towards an electrical problem but your list of items pretty much covers everything...... by ignitors you mean those ignition control units??
I have heard/witnessed that when they go bad, the car will behave strangely.

Has the DME sensor moved away from the ring gear??? A vacuum leak??

I'm probably not helping.

Tinker

[Embs]

Originally posted by Tinker
Has the DME sensor moved away from the ring gear???
Tinker

In fact, I am checking that this weekend, it is the last thing I can think of. I did crank the engine with the test leads for the sensor hooked to a scope, it reported the proper pulses but I am checking so see if it has came loose anyway.


Thanks,

Todd

[Mark McClure]

You did not mention checking the timing!

[WERK I]

Did you pull the spark plugs to check if the engine is in a flooded condition?

[Embs]

Thanks so far fellows, I have emailed Loren and hope he chimes in.


Could a defective speed/reference sensor retard timing to the point that it wouldn't run, and yet the DME would still provide injector ground pulses and spark? I can't check the 3V sinewave fluctuations, but I did confirm that the sensor is pulsing with a fluke digital multimeter while the engine cranks over. Also the gap is correct.


I still have four or five hairs left to pull!

Thanks,
Todd

[Tinker]

How did it die?? Tach fell to zero?...slowly lost power like out of gas?

Did you run a compression check on it?

Tinker

[Embs]

Originally posted by Tinker
How did it die?? Tach fell to zero?...slowly lost power like out of gas?

Did you run a compression check on it?

Tinker

All of a sudden it slowly lost power like it was out of gas. I haven't offically checked compression but I know that it's okay, (I have turned the engine over plenty by hand!) and everything is new.

I am thinking that I may have a wiring harness problem??

Thanks,

Todd

[Tinker]

The harness is easy enough to check. You can isolate the engine and DME ends.

A sensor problem? I know you checked for signals, but did you check actual output?

You haven't actually changed anything from when it was running?

You could see if the timing is even close by cranking it with a timing light hooked up. Insures your not getting an intermitent spark.

Throwing ideas.....

Tinker

[Lorenfb]

Try running on just one of the two ignitions, i.e. disconnect one coil (- 12 volts
to it) then the other. A common problem on the twin plug system is one bad
ignition and the engine won't start. Also, bad plug wires cause major problems.
Noise on the pickup sensor is a problem too, The shield wire may be open.

It sounds like ignition/timing related!

[Wayne 962]

Originally posted by Lorenfb
Try running on just one of the two ignitions, i.e. disconnect one coil (- 12 volts
to it) then the other. A common problem on the twin plug system is one bad
ignition and the engine won't start. Also, bad plug wires cause major problems.
Noise on the pickup sensor is a problem too, The shield wire may be open.

It sounds like ignition/timing related!

Hmm, not a bad suggestion, however, I believe that on these cars, the spark timing on both plugs is nearly identical. So, I think having one set of plugs not firing wouldn't make the car run poorly, it would make it knock quite a bit more.

-Wayne

[Lorenfb]

This is common problem on 964s. The bad ignition interferes. I it see all the
time. The dealer/shop puts the tester on and always thinks it's a bad Motronic
unit. A simple 5 minute test resolves the issue.

These cars are VERY sensitive to RF noise, i.e. radiated from the ignition
system into the Motronic unit.

[Speedster94]

hallo
Is the Engine flooded , does it smell bad after Fuel ?
Harald

[ischmitz]

Todd,

the fact that the engine slowly lost power makes me wonder that it is not a wiring harness problem. If wires snap or short it simply stops working. Problems that creep up like yours are less likely electrical on the newer engines. If you have intermittant issues such as sudden cutouts or stumbles it would look electrical.

I would check for a vacuum leak first. Maybe one of the hoses from the crank case breather to the oil tank and to the intake came off and the motor drew more and more unmetered air.

My 3.6 dies when I open the oil tank since I don't have a restrictor installed towards the intake plenum. Consequently I belive I would not be able to start it with the oil tank cap removed (never tried it though). I also have seen that someone (?guess who) using duct tape (duh) to block off various ports on the intake system when doing the conversions.

The reference sensor could be an issue where it provides only a noisy signal due to it not positioned right. If it would be broken, the DME does not switch on the fuel pump (assuming the conversion harness is made the correct way). On 964 and 993 cars the DME relay has two stages. Stage one powers the ignition circuits when you switch the ignition to ON. Stage two activates the fuel pump whenever the DME reference sensor senses movement of the flywheel. If you fuel pump does not run with the ignition set to ON then you have the correct harness. If it runs as soon as you switch the ignition to ON like in the old cars someone cut corners.

Have someone with a scope check if you get a good signal.

Let us know what you find.
Ingo

[Embs]

*****UPDATE*****
Ingo, funny you should post that just as I am writing this!


I have started to unwrap the harness and found many little goodies, like unsoldered splices wrapped in plastic tape (not electrical tape, not heat shrink) we are talking scotch tape! Small residential style wire nuts, etc.


This wiring harness is from the first transplant that I dare not mention for fear of a BBS flogging. As well, I no longer use the T word.


I should have known better. I almost bought a PMS harness before I started this latest project, I have one on the way.


I am suprised this engine ran at all. I'll post pics and conclusions once I wade through this latest mess. Just call me SUCKER.

[ischmitz]

Gotcha.

When I got my main DME to engine harness I completely unwrapped it, had to fix a couple of things and undo an aftermarket alarm connector spliced into it. At least they used solder and electrical tape there.....

I then rewrapped it in that original black guey cloth tape to make it look brand new. I made my own conversion harness from scratch so I didn't have to deal with someone elso cutting corners there. Never had an electrical problem since.

I don't use the T word myself or his stuff but still if he ever had his hands on the motor make sure there is not duct tape used for blocking vaccum ports on the plenum. I had to take some of that stuff off of mike's car and guess where his crate motor came from.....

good luck and post pictures.
Ingo

[surflvr911sc]

Making the conversion harness was so easy using Ingo's diagrams. I don't know what the differences are between your conversion harness and a 964 conversion harness but you already have the connectors. With a little work you could make a new one that you know will be right, using the factory wiring diagrams and Ingo's diagrams. Good Luck!

[ischmitz]

The 993 harness is a little different from the 964 version in how the DME relay is driven by the DME. Nothing big but please give me a shout if you need any diagrams for that.

Ingo

[Embs]

******UPDATE*******

The new harness is in and I have checked and re-checked every wire/ground etc. With the key on, the injectors are staying grounded (ON) all of the time, no pulse ground. I never smelled much gas, but I didn't crank it for very long periods.

I missed this the first time around, I turned the key on and checked each injector for +12 with my multimeter while grounding to the chassis, I never tried the actual injector ground to see if it was staying on all of the time and not pulsing (I am a ROOKIE)!

So I am once again thinking defective DME? What else could it be?

[ischmitz]

Embs,

I know what it is and how to fix it: SEND THE TRIAD AND THE MOTOR TO MY ADRESS. It's a spell. Do not drive a Porsche or think about one in the next seven years but get a used Camry instead!!!