reference sensor

[sundevil64]

Is there a way to test with a multimeter a reference sensor for a 3.2 as well as a speed sensor (identical as far as I can tell).

If so, what am I looking for? Ohms? Hz? voltage?

It appears the middle pin is not used, rather it ties to a shield wire. So, it would be 1 and 3 pins that I am inquiring about.

fwiw- I put a mm to a reference sensor while cranking and I got 4hz, 4 volts, but didn't get to Ω. Had to get to a pool party per the "Mrs"

Thank you in advance,

John

[kodioneill]

You want to measure resistance (ohms). But even when in spec they can fail when warmed up. If the car has high mileage I would replace them. What's the problem with the car?

[vince_aust]

John depends on whether sensor is installed or on hand. The sensor is an imbEdded reed switch with high power magnet. The manual advises how to test when installed and running - 2v sine wave on oscilloscope but I guess if it working why would you need to test it unless you suspect it's intermittent.

If you are testing on a workbench a ohmmeter with a piece of magnetic metal to trigger switch will give you a basic test result.

I replaced mine (87) simply because of their age and they switch on every revolution - car is 25 years old so not replacing them was inviting a breakdown. When I removed them all the insulation was broken down due to location near exhaust. They are identical units

These are cheapish! - you only need to buy the cheaper version for BMW or the 928 about $70 from pelican. Use the search tools - there is heaps written on this issue

[sundevil64]

Originally Posted by kodioneill

You want to measure resistance (ohms). But even when in spec they can fail when warmed up. If the car has high mileage I would replace them. What's the problem with the car?

Originally Posted by vince_aust

John depends on whether sensor is installed or on hand. The sensor is an imbEdded reed switch with high power magnet. The manual advises how to test when installed and running - 2v sine wave on oscilloscope but I guess if it working why would you need to test it unless you suspect it's intermittent.

If you are testing on a workbench a ohmmeter with a piece of magnetic metal to trigger switch will give you a basic test result.

I replaced mine (87) simply because of their age and they switch on every revolution - car is 25 years old so not replacing them was inviting a breakdown. When I removed them all the insulation was broken down due to location near exhaust. They are identical units

These are cheapish! - you only need to buy the cheaper version for BMW or the 928 about $70 from pelican. Use the search tools - there is heaps written on this issue

It started out as an intermittent problem, not starting at times. I have checked the dme relay. It's not that. Furthermore, I even replaced the dme relay. I have verified voltage at the coil black wire. I have verified continuity of all related wires back to the dme. I have even swapped out another dme. I have verified fuel at the rail and you can smell it when excessively cranking. I have verified with a timing light no spark. I have air, fuel, but no spark.

This is why I am looking at the reference sensor. I looked in the Bently manual but apparently missed it. I have searched but e is a ton of stuff on "my car won't start" I am looking for a specific item. I will search and read further.

The sensor is in the car. I have another used sensor which is why I wanted to test. No point in putting in if it's shot.

Do you have a part number on the cheaper ref sensor?

John

[theiceman]

i dont have the answer you are looking for but am going to ask this question to provoke more discusion .

On some vehicles the speed and reference sensors not only indicate when the crank and cam are at specific positions to fire the spark , these sensors are also used to fire the injector pulse for the fuel injectors.
If someone knows ( probably Loren ) if that is the case in the Porsches and which sensor does what , it may give you a bit more information since you say you are smelling gas ..

All the best .

[john walker's workshop]

somewhere in the neighborhood of 950 ohms, measured between the bottom 2 of the 3 terminals as mounted in the bracket.

[gamin]

Bentley manual has the specs.

[sundevil64]

Originally Posted by gamin

Bentley manual has the specs.

Found it!

Page 240-14 for future reference. Per the Bently's it says test pins 25 and 26 at the dme plug socket. The range is .6 to 1.6kΩ. I have 987kΩ. So, as I read it. The ref sensor is fine. Now that leads me to the dme. How do you check "pulse voltage". Do you need a scope?

[Joe Bob]

You can use the BMW ones, they are like 1/2 price of the Porsche replacements.

[sundevil64]

Anyone have a part # for the bmw or application I can look up?

[Joe Bob]

Reference Sensors

[john walker's workshop]

12 14 1 708 618

[rick-l]

Originally Posted by vince_aust

The sensor is an imbEdded reed switch with high power magnet.

The sensor is a magnet and a coil of wire arranged so that the flux through the coil changes as a gear tooth or a pin is placed near the end of it. The change in flux generates a voltage, rising and falling as the gear tooth completes and breaks the flux path.

You can see an output for the speed sensor with a good multimeter set to AC because it happens 129 (# teeth??) times per revolution but the reference only occurs once.

[rick-l]

Originally Posted by theiceman

i dont have the answer you are looking for but am going to ask this question to provoke more discusion .

On some vehicles the speed and reference sensors not only indicate when the crank and cam are at specific positions to fire the spark , these sensors are also used to fire the injector pulse for the fuel injectors.
If someone knows ( probably Loren ) if that is the case in the Porsches and which sensor does what , it may give you a bit more information since you say you are smelling gas ..

A DME needs both to do either function.

There is no cam sensor, the distributor routes spark to the correct cylinder.

The sensors tell when the crank is at a specific position (reference ) and how fast it is turning (speed) this sensor also tracking position and speed variations during each revolution.

[rick-l]

Originally Posted by sundevil64

fwiw- I put a mm to a reference sensor while cranking and I got 4hz, 4 volts,

Sounds pretty good to me. 4 Hz would be 240 RPM.
What meter did you use.

[rick-l]

Originally Posted by sundevil64

I have verified fuel at the rail and you can smell it when excessively cranking.

Do a search for "DME solder joints" and determine if you want to take the DME apart or send it to Ingo for test/repair.

[sundevil64]

Originally Posted by rick-l

A DME needs both to do either function.

There is no cam sensor, the distributor routes spark to the correct cylinder.

The sensors tell when the crank is at a specific position (reference ) and how fast it is turning (speed) this sensor also tracking position and speed variations during each revolution.

I guess I should check the speed sensor sensor also. I would imagine that would tell the dme how fast the motor is turning?

Originally Posted by rick-l

Sounds pretty good to me. 4 Hz would be 240 RPM.
What meter did you use.

That was with a low battery too. It would normally turn faster on cranking. Nothing too fancy. It's an IDEAL sold at Lowes. I have heard good feedback and it doesn't cost an arm and a leg.

Originally Posted by rick-l

Do a search for "DME solder joints" and determine if you want to take the DME apart or send it to Ingo for test/repair.

I will thanks. I have a friend that can put it under a microscope to check for small cracks.

[rick-l]

Originally Posted by sundevil64

I guess I should check the speed sensor sensor also. I would imagine that would tell the dme how fast the motor is turning?

If you smell raw fuel when it does not start it means the DME is supllying injector pulses and both sensors are supplying inputs.

You never did say if you had spark however. Usually fuel but no spark is a broken solder joint around the darlington transistor that controls the coil.

[sundevil64]

I do not have spark. Sorry, I thought I stated that. Thanks, that will get me started. Although I have plugged another dme and it too didn't trigger a spark. I don't have a way to test either dme on another car. hmmm I wonder if I can convince someone to let me plug it into their car.

[rick-l]

Originally Posted by sundevil64

I do not have spark. Sorry, I thought I stated that.

You did I missed it.

Originally Posted by sundevil64

I have plugged another dme and it too didn't trigger a spark.

I missed that also.

Might not be time to tear into the DME. Can you think of a way to verify the DME signal at the coil and the coil itself?