PerryB

Van,

I used the original flywheel. There is a roll pin in the back of the crank that fits into an asymmetrical, offset hole in the flywheel ensuring that the flywheel can only go on in one position. Also, I'm testing for spark at the coil and still get nothing--so even if the spark came at the wrong time in terms of rotor to cap orientation, I would still see the spark at the coil wire.

Scott--I have seen that connector above the brake booster and have no idea what it does. I have taken it apart and cleaned it to make sure that it has a secure connection. It has made no difference, but I'm still curious as to where those wires come from/go to. I don't see it on the engine wiring diagram.

Perry

Van

Look in zone F48 (at least for NA cars).

It's the plug to the right of the DME in the diagram.

See 1:48 of this video:

Lemons racer

Man you have put so much time and effort into getting this fixed you should get a medal.
Long story short I put a 944 motor into an 1978 924. I did not want the headache of trying to get a 30 year old system running .I replaced the computer with Electromotive Tec-Gt system .One day in building a new harness to wire system .Plugged in my laptop programed computer and turned key and it ran.
Now what I have is all the wiring that was removed .The reference sensors and such your welcome to any or all of the stuff .The 944 ran but body was garbage rusted out and not worth rebuilding .
Where the 924 was stored in a barn for thirty years plus and was solid. I don't think the DME will work as it was a NA car.

PerryB

Van, Lemons,

Thanks for your replies. Van, believe me I've gotten good at reading the Porsche wiring diagrams over this last year. The connection that Scott talked about I believe is on page 8, section J48 of the Turbo wiring diagram and goes to the starter and alternator. At any rate, I don't think that this has any effect on the no start.

As I mentioned in a previous post, I am looking at some weird ohm readings, but I have come to no conclusions on this aspect of my testing.

Lemons, I have sent you a PM. Please respond when you get a chance. Thanks!

Perry

Scott at Team Harco

Perry - that connector would prevent power from reaching the starter. That is not related to your no-start issue. Sorry for the non-usable information.

Good luck!

PerryB

SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The car is up and running!!!!!!!!!!!!!!!!!!

I have discovered a truly marvelous solution to this, which, however, the margin is not large enough to contain.

I post a full write-up later. Thanks to all the posters for their help and support.

Perry

divil

Thanks for the update Fermat

This is great news...I can't wait to hear what the solution was.

Scott at Team Harco

That's great news! Congratulations.

Van

Every time I see this thread move up the list, I hope its for this reason. I'm glad it finally is!

I look forward to your writeup.

Tiger03447

Perry: Glory BE! So glad it is alive! What perseverance! I am so proud as to be in the council of such fine gentlemen! I hope and pray that my old 944 will not put me through such a flaming hoop as yours has done to you, Perry..Great work and a big SHOUT OUT to all the guys who contributed...Can't hardly wait for the results...Tiger03447

thomasmryan

Closure after 10 months)) congratulations)))

PerryB

Friends,

First off, let me thank all the people that responded to this thread either with concrete suggestions or with moral support (or both). Without both, I would have given up months ago in baffled frustration. I especially want to thank Specsalot, Divil for testing my computers in their cars, and to Van for his patience and suggestions.

So, here's the solution: It was the speed and reference sensors.

I know, that's a bit boring and expected, but there's a twist--which I'll get to in a minute.

First a quick recap for anyone that is coming into this story nearer the end than the beginning.

I took my 1987 off the road in December of 2013 to do a clutch job. I also did the timing and balance belts, rebuilt the torque tube, repacked the CV joints, replaced the O2 sensor, and did a few other small items. This took about two months working nights and weekends. During this work things went mostly smoothly. However, I broke the reference sensor trying to remove it before removing the clutch bellhousing. It snapped off in my hand as I was twisting it in its mounting block. I replaced it with an FAE equivalent bought from Autohauz AZ. I gapped it at .8mm and assembled the rest of the car.

I completed all the work in early February of 2014. I went to test drive my car only to discover that it wouldn't start. I determined that the car was not getting fuel or spark. I then tested everything that I could think of that could possibly prevent the car from getting fuel or spark. This process took about two months and involved all the usual suspects--the DME relay, the speed/reference sensors, the coil, the ignition switch, etc. I used the Porsche factory diagnosis algorithm and determined that the DME itself was at fault. Over the next months I had the DME and the KLR both rebuilt by Specialized ECU repair in Florida. This did not cure the no start. I then went back and forth with Specialized as well as some other Rennlist posters as they all tested my computers in their cars. The last test, done by Divil a month or so ago, showed that the computers functioned normally.

At this stage I was really upset and ready to give up. I had no fresh ideas or theories to test--I was tired of having my hopes raised then dashed, I was tired of having my money spent on parts that didn't fix the problem, I was tired of seeing a 3,000 lbs. paper weight everytime I went down into my basement, I was tired of not diriving my sports car, I was tired of endlessly and fruitlessly poking my car's wiring with an VOM, I was just tired of it all.

I decided that since everything checked out I would start again with the most likely culprets, the speed and reference sensors. This did not seem like a good idea so much as just something to do rather than just to continue to stare at the car. I conducted (no pun intended) these Ohm tests at the DME harness connection in the passenger's footwell. Here's what I found...

5 8 23 25 26 27 28
5 X X X X X X X
8 881W X X X X X X
23 Infinite Infinite X X X X X
25 873W 1753W Infinite X X X X
26 1.6W 880W Infinite 873W X X X
27 1.6W 878W Infinite 873W 3W X X
28 0W 878W Infinite 873W 1.6W 1.6W X


I hope that this chart copies onto the forum without being unformatted.

The numbers on the top row and the left most column are the pin numbers at the DME harness, the "W" is supposed to be the Ohm (omega) symbol. What you'll see here is that the resistance between pins 8 and 27 is 878 Ohms--exactly what it is supposed to be. Ditto with the resistance between pins 25 and 26--870 Ohms. I also redid the oscilloscope test and found them, like I have every time since March of 2014, performing correctly. However, this time I also tested resistance between all the other pins involved in the reference/speed sensor harness. What I noticed after filling in this chart was that there seemed to be resistance between pins of one sensor and those of the other, like the sensors were in some kind of contact with each other. You can see this in the "8" column. The resistance between pin 8 (the center pin of the speed sensor) and pin 26 (the center pin of the reference sensor) was 880 Ohms. I thought that there should be infinite resistance between between these two pins. The wiring diagram shows that the sensors are completely seperate! Also pin 26 had 1.6 Ohm resistance to ground. It seems that the sensors are grounded, but the wiring diagram shows that the only grounding is for the shielding--pins 5 and 23.

During my previous attempts to fix this problem I also replace the speed sensor, again with an FAE part. I now have a total of four sensors--two FAE ones installed in the car, the broken one, and the original (but unbroken) one. I tested the new FAE ones and found that they had continuity between the center pins (8 and 26) and the metal shielding tube on the end of each sensor. The original Bosch did not.

That's it. The FAE sensors produced the correct resistances as called for in the Porsche manual, produced the correct cranking AC voltage as demonstated on Specialized ECU's Youtube video, produced the correct sine waves on the oscilloscope screen, but failed to get the DME to fire the ignition.

I cut off the metal shield tube of one of the new FAE sensors, installed it, installed the old, unbroken sensor and the car started right away. So, the FAE sensors have continuity between there center pins and the shield tubes but the original Boshc ones do not. That's what prevented my car from starting this last year. All the repairs I did were unnecessary.

I hope that I wasn't too long winded with this description. Please contact me if you want further details.

And thanks again.

Perry

divil

Wow...I've been waiting for this all day Congratulations!

But it's certainly confusing...I don't think pin 8 is the center pin of the speed sensor - that should be pin 27 according to the manual I have. But then, I have had a few drinks...

I can see how a short from the signal to the shield in each sensor (or even just one of them) could cause your problem - when the plug is disconnected, it wouldn't matter...your signal would show up just fine on the scope. But once the plug is connected to the DME, the shield would be grounded, and so your signal would disappear, and the car could not start. But how the wires from the 2 sensors could be connected together when the DME plug is disconnected...I have no idea!

Regardless, your perseverance has paid off and you should be proud of your results. Few people would have stuck with it this long. It's easy for those of us who have running cars to overlook how hard it is to try something for the millionth time. At this stage, going back and checking resistances again must have taken phenomenal will power.

I wouldn't feel too bad about the repairs either...having the DME and KLR looked over was probably no harm, and you might have saved yourself some trouble.

Remember2

I have followed this thread for months (looking for an update daily) - and I'm so happy to see you finally found the solution !!!

I (have?) had a period problem closely related to yours for some time - so I know the feeling of investing time and money in replacing parts that make no difference.
However I have been able to drive (and enjoy) my car - so in no means compared to what you have had to go through, having your car of the street for more than a year.

I hope you can finally enjoy a very long problem-free period with your 944

I took the liberty of converting your ohm-table in to a more userfriendly layout:

tempest411

It sounds like the FAE sensors were defective, yes?

I appreciate your endurance in working through this. I have to wonder how many others out there that have bought the same sensors are having similar issues? How many have decided it was the last straw and sent the car off to be parted out