Crankshaft Sensor issues
 

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?

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.

Is the tach needle the rpm needle?

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

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.

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

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!

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

Haha that's true.

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?

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.

http://s20.postimg.org/vssxinmd5/IMG_1604.jpg

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.

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.

944 Speed Sensor, 944 Reference Sensor
 

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

http://forums.pelicanparts.com/uploa...1466011697.jpg

http://forums.pelicanparts.com/uploa...1466011727.jpg

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.

Did you ever get ypour 944 started
 

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

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.

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..

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.

http://https://cdn11.bigcommerce.com...=1&imbypass=on
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.

http://forums.pelicanparts.com/uploa...1725023126.jpg

Hope this is of value to you.

Hello, where can I get that part?

Dealer item... 944 101 335 00 ... US price is about $7 USD.

I had to muck with the sensor in my volvo, I found a reference for the air gap between the sensor and what its sensing, then used a vernier caliper to check the distance down the hole to the thing it senses ( might require turning the flywheel if it senses a pin)

then I could measure from the base of the sensor and subtract to know the air gap.

also the sensor was basically a coil of wire, it was referred to as a magnet , I suppose a coil of wire can be considered an electromagnet , so since it is a coil of wire it has a defined resistance. if its the same part the resistance through both should be about the same. you can measure the ohms between the 2 pins, id expect 1500 or 2000 ohms or something similar, at least not open circuit or a dead short. If you found that one had lower or higher resistance than the other then I'd suspect that. you might make a resistance comparison between your old one and the new one just to know.


with it out of the car I found I could hook the 2 wires to a meter, then pass a screwdriver near the end, then Id see a pulse of current maybe a volt or two.

the sensitive electronics int he ECU can sense the pulses, I think one is reading the gear teeth and the other is looking for the pulse from the pin that tells it when it is at TDC. ( or some defined position) the pulses to the coil are then timed to the engine speed and position. if it looses the signal even intermittently you'll see problems.


if you wanted to look at the pulses you could use a scope but failing having a scope you can probably hear them if you connect instead to the input of a radio, like a ghetto blaster that has a line in. that should give an audible pulse when cranking.


If you check the pulses at the coil you can see if you are getting a pulse of power to the coil , that verifies you have a pulse, which basically means the ECU is synching up with the input of the sensors and doing its job. If you do have a pulse at the coil and engine won't start then I'd check if you have spark at the wire for cylinder 1 if you are getting a spark then the no start issue could be no fuel , too much fuel or bad compression maybe an air leak causing a messed up air fuel ratio.

if you do have a spark try quick start, see if it fires up. if it will run on quick start then that proves your issue isn't with those sensors.

you can remove the plugs and look at them, see if they are wet with fuel or if they are blackened indicating rich fuel or white indicating lean.

if you've been trying to start it with no ignition then it may be that the plugs are wet with fuel , if you see that dry things up and try again.

there is a spark plug thing ( spark tester) that can be used to test for spark or you can ground the plug and crank watching for a spark, ( nice if you have a helper to hold the plug but you can rig it up so you can see it..
another way is to connect a timing light , tape down the button so you can see if it flashes , if you are alone it may help to be able to see the timing light flashing, from the driver seat.

there is a little amplifier thing that is mounted somewhere around the left front fender. it has a bit of heat tape to conduct heat to the body, you can check the terminals, see if they are clean. possible that can fail but they are pretty dependable, if you remove it you may want to refresh the heat transfer putty. I think volvo uses the same one. I mounted two of them in one of my volvos so I can switch the wires to it if I suspect it but I never found a failure in that.

I think the ECU is providing a pulsed ground and you mentioned the coil has no ground, I think that's normal because I believe it is the ground side that is pulsed not he hot. the coil is not simply always seeing 12 V, it needs to be provided a pulse so don't expect to see 12 V across the 2 coil terminals.

that pulsed ground from the ECU ( or MCE) is not able to carry a lot of current so the transistor or something like it is used ..basically a bridge that isolates between the sensitive electronics and higher amp pulse through the coil primary..

its basically pulsing power on and off to the coil and subsequently the coil is amplifying the voltage to a high voltage so it can provide a spark with enough volts to jump the plug gap.

I had a mysterious no start and found that I had a pulse at the coil but the problem was that the nuts on the coil were rusty so even though the terminals had the pulse, the coil itself wasn't seeing the pulse .. cleaning the coil posts solved that. Ive never had a coil fail, they can but I think they are more often replaced needlessly as part of shotgun troubleshooting.

so Id unscrew the connectors and make sure the lugs on the coil itself are clean.

in my 88 ford van i ran a couple of small and well protected wires from those coil wires, up to the dash and connected to a little tiny LED permanently.

now when I crank I see it flashing , that tells me I have an ignition pulse, when I start it it glows because the filament isn't; able to really respond that quickly. the reason I did that is because if I get stuck somewhere and it wont start I can see straight away weather I have ignition pulses. In 80's fords, sometimes the ignition module can suddenly fail and cause a no start..

the ignition module in my 88 ford is strapped to the distributor itself. probably comparable to that "transistor" on your fender. I've heard it called a power stage amplifier, or an ignition amplifier. in ford its called an ignition module.

I'm not sure what term porsche uses. That thing is involved between the ECU and the coil... I'd clean the spade terminals up. if you get an intermittent in that current path then the car can stall , choke intermittently, or not start.

before messing with the timing sensors it may not hurt to take a vernier caliper and measure how far it is from the block or housing to start with , but you have removed it ,,,
you can do the math should the replacement is different dimensionally, what should be important is the air gap between the sensor and what its reading, that might be something like 1.5 or 2 mm or so, someone here may know the correct spec. point is you can check that by it, measure the protrusion of the sensor and subtract the difference to know the air gap. if the sensor did touch something it may wipe out the sensor.

if you have the wrong air gap , that may affect it and you probably don't want it just on the edge of working or not working, otherwise maybe you'd have some trouble in the future. the distance may affect the pulse, maybe the intensity of the pulse or pulse width etc. you can't analyze that easily, probably easier to measure the distance and do the math by measuring the new sensor.. the gasket could be made to suit. maybe the one posted will get you right exactly where you need to be, I don't know.

it probably is possible to check the pulse with a scope and move the adjustment to see a change and optimize the distance by way of examining the pulse itself, but just measuring it is easier for one of us " back yard mechanics" without such equipment and diagnostic experience.


in general if you move the engine to the firing position for cylinder 1 then the distributor rotor should be pointing to the terminal for plug i in the cap.
if plugs are out, turn engine in its normal direction until you feel air blow out of plug 1 and continue to TDC, that means cy1 has just finished its compression stroke and is about ready to fire. the rest follow suit in the firing sequence. You can make sure the plug wires haven't gotten mixed up. I've seem people take a distributor apart and put it back together incorrectly..

"Hello, where can I get that part?"

personally I'd just cut it out from a piece of gasket paper, how hard is that? but my question may be - how thick is it?