Crankshaft Sensor issues

[MikeWCallahan3]

I have a 1983 Porsche 944 with a starting problem. I've replaced the DME, DME relay, ignition coil, starter, and the distributor cap, still no spark. The car is attempting to start but it just keeps trying to turn over. I've been told that it's probably my crankshaft sensor or "reference sensor" so I went ahead and ordered two sensors because I(this is the first car I've ever worked on, so I'm still a noob) thought that they were both the reference sensor lol. My problem is I ordered two of the same parts, is there a difference between the crankshaft sensor and speed sensor? Do I need to order a different sensor?

[dgcantrell]

There are two reference sensors mounted in the same holder on the bell housing. One is the reference sender for the DME to determine TDC. The other is the engine speed (RPM) sensor. One good way to tell if they are working is is when you spin the engine over to crank it, the tach needle should jump just a little. This indicates the reference senders are working. If not it could be them.

The DME relay you got, is it a URO brand.. If it is, that might be the problem too. They are grade A effin' junk. When you turn the key on (not starting the engine), do you hear the fuel pump come on for a few seconds and go back off? If so, the DME and DME relay are working correctly.

[MikeWCallahan3]

Is the tach needle the rpm needle?

[MikeWCallahan3]

Also are the speed sensor and reference sensor two dofferent parts? I ordered two of the same exact sensors to replace both.

[dgcantrell]

Yes, the tach is the RPM needle. Replace the sensors one at a time and do not get the connectors crossed or in the wrong hole in the holder. While they are physically the same part, they read two different locations on the fly wheel. The reference sensor reads the one little set screw that is screwed into the flywheel and indicates TDC. The other one that reads the engine speed reads the teeth on the starter wheel from what I remember.

[dgcantrell]

Looking at the repair manual now.. Yep. The front sensor is the reference sensor. The rear one is the speed sensor. There may be some labels on the harness near the connectors that read DG and BG. BG is the reference sensor connection. DG is the speed sensor connection. Don't get them crossed up or the thing will not run. LOL

[MikeWCallahan3]

Awesome, that's helps a lot. Up until now I've kinda been guessing on what's wrong and have spent over $1100 on parts that weren't broken lol. The tach needle is not moving at all, so I guess that is the reason. Thanks!

[dgcantrell]

I look at it this way, you now have a good selection of spare parts that you will need at some point.. LOL

[MikeWCallahan3]

Haha that's true.

[MikeWCallahan3]

I replaced the reference sensor and speed sensor and still no tach needle movement. Also, I just noticed that I'm not receiving power to the negative coil on my ignition coil. What else could be the problem?

[dgcantrell]

There is a 9 pole connector that connects that green wire to the coil. See if you can locate it. That could be the source of the problem.

[MikeWCallahan3]

Could you send me a physical picture of what a 9 pole connector looks like? Because I don't know what I'm looking for.

[dgcantrell]

I'm not sure. man. All of my 944's are 87-88 models. It's got to be in the engine bay somewhere. Probably along the firewall.

[Leo944]

Mike,

Installing new speed & reference sensors is not a huge challenge. Suggest you check out a terrific step-by-step guide at: Clark's Garage Home Page

Here’s a tidbit to consider while diagnosing your problem. I recently rebuilt the head on my 86 NA and during the installation I somehow cracked one of the sensor’s connectors and it took me a while to figure out why the car would not start.

You can imagine my Aha! Moment when I pushed the connectors together and voila!

Too cheap to buy a new sensor; I simply wrapped a cable tie around the connectors to keep them from pulling apart. So far so good.

I’m posting a photo of the sensors courtesy of Clark’s and a photo of my fix.

Good luck!

Leo

[Leo944]

Mike,

Reading my recent post it occurs to me that I neglected to make my point clear... make sure the sensors' connectors are securely attached to the wiring harness connectors.

[cloudskillz]

Reading this post and I have the exact year and model and issue, and wanted to know did you ever get that 944 running?

[Monkey Wrench]

Here's what I'd do .

find a little 12V light bulb, not great big brake light but a small one like you might find in the dash.

connect 2 wires to the bulb and wire that across your 2 coil terminals. don't disconnect anything

crank the engine and watch the lamp, it should flicker.

if the lamp flickers then you have an ignition pulse and you have eliminated problems with the MCE MCE relay, those sensors you are int he process of changing..

if you have a pulse at the coil, you are basically spending money and time chasing down the wrong problem.

this pulse also influences the tachometer needle so normally when you crank you will note that the needle moves, it will blip a little as it sees the pulse. this is normal and the previous poster was trying to get you to take note.. that blip of the tach needle is basically similar to the coil pulse.

If the lamp does not flicker then yes you may be on the right track.

if the car starts the lamp will glow but not at full brightness.

I think this is a more simple and less expensive approach as you are then breaking down the possibilities very easily and without spending money on stuff that has not failed..

replacing the engine sensors and the DME relay may be done for reliability reasons but I think you went into this because you wanted to start the car..

troubleshooting is a process of elimination, the objective should be to find the problem.

if you shotgun a bunch of parts for reliability reasons, fine , but I'd do that in steps with a drive between so if you do introduce an issue, the cause of your new problem is obvious.

If you happen to introduce a second issue then you can have two reasons why the car won't start at once, You don't want that situation..

to answer your previous question, the coil will have a hot with key on. the negative is pulsed on and off by way of the DME and it goes through a little amplifier thing near the left front fender.. it is grounded intermittently ..

those two wires with small nuts on the coil are the primary coil, when it gets power it energizes. when the power is interrupted it introduces a spark in the secondary coil.
the secondary coil has many turns of copper so that coil acts like a transformer changing a 12 V pulse into a high voltage pulse , this is distributed to the appropriate plug by the distributor's rotor..

an easy way to make a car not start, remove the rotor in the distributor, then you can crank all day and there will be no spark.. I' ll do that to prevent theft sometimes.

[Monkey Wrench]

reasons why you dont have a pulse can be , the DME electronics are nto properly greounded to the body. the speed or reference sensors are not providing a pulse to the DME. the powerstage transformer after the DME and before the col is bad.

remember the engine shakes and oil and heat causes wire rot so visually inspect all related wiring.. look for cracked insulation anythign tht may rub, make sure your battery connections are tight and clean and if there are two hot wires on the positive battery post , make sure BOTH are connected properly..

[curtisr]

I didn't see an answer to your original question -- probably just me -- anyways, there is no difference in the required sensors. The part number is 944 606 115 00. A search will indicate that these are available from different manufacturers. There may be, however, differences in the length of the sensor body (containing the magnet). I found this out the hard way. Best if you buy Bosch. Should the replacement you choose be a bit shorter you'll have to adjust the reference sensor bracket. This requires an allen key. The bolt is located in the alley pictured at the right. Naturally the other bolt needs to be loosened... You will also see from the picture located here that in '88 (?) a sleeve was added to protect the one sensor from electrical interference. The absence of this may be source of a no-start condition.


Your search may also turn up a 0.8 mm shim. Since this is the required distance from the sensor to the flywheel, you can adjust the bracket to have the sensor make contact and then add this part.



Hope this is of value to you.

[Porsche94483]

Hello, where can I get that part?

Originally Posted by curtisr

I didn't see an answer to your original question -- probably just me -- anyways, there is no difference in the required sensors. The part number is 944 606 115 00. A search will indicate that these are available from different manufacturers. There may be, however, differences in the length of the sensor body (containing the magnet). I found this out the hard way. Best if you buy Bosch. Should the replacement you choose be a bit shorter you'll have to adjust the reference sensor bracket. This requires an allen key. The bolt is located in the alley pictured at the right. Naturally the other bolt needs to be loosened... You will also see from the picture located here that in '88 (?) a sleeve was added to protect the one sensor from electrical interference. The absence of this may be source of a no-start condition.


Your search may also turn up a 0.8 mm shim. Since this is the required distance from the sensor to the flywheel, you can adjust the bracket to have the sensor make contact and then add this part.



Hope this is of value to you.