no-spark problem finally resolved

[jclporsche]

How did you figure out the BMW part was the same? I see others under BMW - this one is $46.50 : 12-14-1-710-668-M85, says for Motronic also. The one you used is now up to $70.75. My 1988 needs two new ones because the insulation crumbled and fell off the wires during removal for my engine rebuild. Will the one you used or this other one work for my 88?
Thank you so much for the great write up!
John

[bjohnst0]

There are a lot of threads on this part being interchangeable with the Porsche sensor. Only difference is a half inch longer and much cheaper. Pelican says they sell a lot to Porsche guys, only downside is that you get a BMW decal.

The part number is 12-14-1-708-619.

I changed both sensors, only the speed sensor checked out bad. Going the hassel of change, doing them both made sense.

Bob

[JJ 911SC]

Originally Posted by bjohnst0

... Only downside is that you get a bmw decal.

btdt

Originally Posted by jj 911sc

when i opened my last pp order, i could not believe my eyes.

They came with the "blue" stickers So i threw them on the desk.





das babe was furious

Well next morning when i walk-in the garage , i noticed that she was much more relax :d:d




p.s. I mentioned it in the survey and got immediate apology from judy and she offer to send me some in the mail right away of course i declined as i got a few more orders on my wish list.

[scarab]

Thanks to Tom Stiller for the amazing step by step to faulty sensor detection. I am confused. I drive an 84 carrera 3.2 or I did. It started on first crank for the last 15 years. The other day just stopped. I have no spark. I replaced the DME and have done all the rudimentary checks to no avail. My problem is the DME pin nos.referenced in Toms description differ to mine. The DME socket pins are 1,3,5 top and 2,4,6 bottom. The corresponding pins on the DME read 87b,85b,30 top and 87,85,86 bottom hence my confusion when trying to check the ohm reading.
PLEASE HELP

[mreid]

Really excellent write up, Tom. On a side note, the reason the oscope showed a waveform is that these sensors employ a strong fixed magnet with an inductance loop. The fixed magnet provides reference and amplification of the signal. Often when the sensor goes bad, the fixed magnet field is still influenced by the teeth on the reference wheel passing through the magnetic field. This induces a small amount of current flow from the sensor. Not enough to signal the DME, but plenty to see on the oscope.

Now back to your regularly scheduled praise for such a fine write up!

[scarab]

Speed sensor was the problem. The sensors in Australia retail at $330 each. 2 sensors from Pelican parts delivered to Oz $160. Put them in last night and fired up first crank. Thanks Guys WOO HOO. The scarab is on the road again.

[greglepore]

Just some comments after having just done this job today. First, I wouldn't buy the FAE sensor that is available under the BMW p/n. Only one of mine worked (the one in the ref position). The speed sensor ohms ok, but the car wouldn't run. Runs fine on the old ref sensor placed in the speed position, so I have a Bosch BMW sensor on its way.

Second, ain't nfw that my speed sensor would come out, even after overnite with PB and persuasion with a hammer after removing the bracket. Had to destroy it to get it out.

A tip-I cut the head off a longish bolt to create a stud, and put that in the upper bracket mount hole in the case to hang the mount from, then put the lower pivot bolt in, removed the stud, loosely threaded in the upper bolt and set gap. It made hanging the bracket a piece of cake. Not sure I could have done it without the stud, at least not without throwing things.

Car started first try..well, after I got the connections right at the upper end.

Not a fun job, but doable. Didn't remove the shock, did remove the heater hose going to the flapper.

[Missed Approach]

Hi Tom- Just a huge note of thanks for the excellent write up! Luckily, I was able to remove both sensors from their mounting bracket with copious amounts of WD40 Penetrant Release (their version of PB Blaster). The old wires were completely devoid of insulation! (see photo) I marked the old leads front and rear, and used trimmer line to snake the new wires. I kept losing the mounting bolt on the top sensor (it would fall into the abyss, once even ending up in the muffler pan) I used a length of fishing line to keep it in place for the initial tightening. Again, your write up made this a fun and rewarding project!

[A horse with no name]

A big 'hats off' to Tom for taking the time to make such an excellent step by step procedure; photo's and all!

I did it 'my way' the first time around and it was a pig of a job. I did it 'Tom's way', this time around, and it was just about what I would call a breeze.

I wonder which way 'Frank' would have used

[Gsteven]

Tom: Thanks so much for your post. Just wanted you to know it is still being used and appreciated. Just changed out my sensors and the 85 Carrera started right up. This my first Porsche, and although a very low mileage one, I am sure I will be making more parts replacements. Thanks to the knowledgeable folks in the forum, I am learning a lot. Sure is harder to work on than my old Austin Healey though.
Thanks again.

[jlex]

Great write up and pictures. Replaced both sensors along with the CHT sensor over the weekend. Insulation was worn off the sensor wires on my '88 so I thought I'd do the replacement before I had a problem.
I'd like to add that it's not necessary to use anything to fish the new sensor wires thru the tin into the engine compartment. The connector end of the old wires are pulled thru the tin into the wheel well (can't be done the other way as the sensors won't fit thru the hole). Once the old wires are out, simply push the new sensor wires thru to the engine compartment. Those wires are plenty stiff so they will emerge within easy reach just about next to the connector holder. No danger whatsoever of the wires getting lost in the abyss...

[GH85Carrera]

It is not a simple task to replace the sensors for a first timer. I was struggling with even getting mine out. I am fortunate to have a friend that is an experienced Porsche technician. I called him and asked if he had any tricks or suggestions. He told me to step away from it, and he would swing by.

His biggest trick was to use 1/4 inch drive ratchet and extensions. The same basic "rig" in the original post, but all made from 1/4 inch drive parts. That makes them smaller, and gives more room to maneuver.

My buddy lay down next to the rear wheel well and within a couple of minutes had the old sensors out and I handed him the new sensors. He had them back in in a couple of minutes. It was like he was a magician. I had stared and cussed at the sensors longer than he took to replace them.

I know my friend is a pro so I paid him for a full hour of work because he saved me from a day of struggle, and he made a house call!

My only real contribution to this thread is to use 1/4 inch drive tools for that task. The torque needed is low and 1/4 inch drive is up to it no problem.

[A horse with no name]

Quote from Glen: "My only real contribution to this thread is to use 1/4 inch drive tools for that task. The torque needed is low and 1/4 inch drive is up to it no problem."

+1 Big Contribution -> This 'is' the secret = 'easie-peasie'

[Discseven]

Threads like this make this the forum it is. Way to go Tom!

[Erichter]

Great write up. Thank you, just replaced mine. Bottom sensor much easier than the top. I couldn't get the 5mm socket with extender up there but it's not that bad even with an Allen and turning it small bits at a time.

[Pigeye]

Are the #'s on the sensors in the pictures on first post from "Step 3" and "Step 7" correlated?thanks.

[A horse with no name]

Hi..Are you referring to?..

7. Remove brass key on sensor holder in engine compartment

[Pigeye]

Originally Posted by A horse with no name

Hi..Are you referring to?..

7. Remove brass key on sensor holder in engine compartment

Correct -do the plugs go (top to bottom) CHT, Speed, Crank. Or CHT, crank, speed. I thought I would be able to find that in manual, but having some trouble. Hope that makes sense

CHT is easy - it’s white, ha ha.

EDIT - DUH.....Should have just looked at Step 8.

[A horse with no name]

Hi...I see that you now have the info you were after... I can only suggest that you do two things:

1. Make sure not to remove the sensors bracket on the fly wheel - Just the sensors...If you do, then it becomes a lot more fiddly as they have a very fine depth fitment.
Other auto manufacturers have a 'stop' in their castings - You just pushed the sensor in until it 'stopped ...Porsche had them manually gauged as they assembled the engine =

2. Make sure to mark which one they plug into on the 'brass bracket' -> #7.

Other than that, other than turning your arm/body into a pretzel, it's really not that hard of a job...I would also suggest that you change the head heat sensor while you are at it.

[Pigeye]

Originally Posted by A horse with no name

Hi...I see that you now have the info you were after... I can only suggest that you do two things:

1. Make sure not to remove the sensors bracket on the fly wheel - Just the sensors...If you do, then it becomes a lot more fiddly as they have a very fine depth fitment.
Other auto manufacturers have a 'stop' in their castings - You just pushed the sensor in until it 'stopped ...Porsche had them manually gauged as they assembled the engine =

2. Make sure to mark which one they plug into on the 'brass bracket' -> #7.

Other than that, other than turning your arm/body into a pretzel, it's really not that hard of a job...I would also suggest that you change the head heat sensor while you are at it.

All good - thanks - got them out last week and have marked the both the cable ends with red or white paint (depending on Speed or Crank) and ready to go back in tonight. Did the CHT sensor are well - "while I was there". The actual hardest part of this was getting the old grommet out where the 3 cables go through the engine tin. That and the hand cramps from the tight working area.