Pelican Parts Forums - Crankshaft Sensor issues

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..