reference sensor
 

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

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?

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

Ref
 

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

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 .

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

Bentley manual has the specs.

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?

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

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

12 14 1 708 618

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.

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.

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

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

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.

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

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.

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.

You did I missed it.

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?

This is my extra dme. Now you have me curious.

http://i475.photobucket.com/albums/r...ps0b4e04cf.jpg

Ops. Too late. I just saw the post. My thought here is to have this one looked over and then plug it in. Leaving the original one in the car. This came out of a donor car for another project. I may send it off at any rate to have it thoroughly inspected for future use.

Bosch 0261210002

Crank Reference/Speed sensor for BMW application. $60 each if you search the web. I have about 6k trouble free miles on a set. -J

Thanks. It looks like the application is an 85 635is. $54 each.

Testing coil is easy.
1. remove '-' wire from coil's '-' terminal
2. turn key to RUN test that you have 12v on the '+' terminal
3. place a spark plug wire from the coil to a test spark plug on the end and ground the test plug. Do NOT go through the distributor, you want just one spark plug hung directly from the coil's hi-voltage output.
4. using a test wire, wire one end to the coils '-' terminal and then ground the other end for no more than 2 seconds, within 2 seconds remove he ground and the plug will fire.

Testing for DME coil pulses requires a simply LED test light. You can get one at Walmart for $5. It must be a a 12vdc LED test light. Then test DME for coil pulses like this:
1. Remove wire from '-' terminal on coil
2. Place test light's '-' to the wire you just disconnected.
3. Place test light's '+' to the coil's '+' post.
4. Crank engine and watch test light, it will flicker as the DME generates coil ground pulses.

Thank you. I will try those.

John

The speed sensor is the main timing device and the reference sensor is required to determine TDC. With an intermittent speed sensor your engine cuts out every time the signal fails. With an intermittent reference sensor you might fare better since it is not always required. It is used to correct timing every once in a while.

Both sensors can fail intermittently with age due to the heat cycling/vibration at the bell housing. Not easy to diagnose since you need to catch the failure "in the act" by having a breakout box with an O-scope. Probably a good idea to replace the sensor when in doubt before embarking on more expensive items.

Ingo

How many cars do you have, John? :)

Ingo and Sal are very well versed in these systems. You're in good hands. Just remembered, I have a new sensor in my toolbox if you need to buy one. Only used for testing.

Tippy,

Too many...

I ended of putting intwo new sensors, the BMW interchangeable one and it fired right up. I took it on a 400 mile drive without a related hitch. I only lost a mirror as if fell of while driving.

Quick question. I just measure the resistance on my reference/speed sensor in my 964. It measures approx 500 ohm. Manual says it should be 960 +/- 96 ohms. The motor fires up and sounds normal. I'm having an issue with the headers glowing (even at idle I see a faint glow). Infrared thermometer shows temps in the 750 range at idle. I've checked most everything trying to narrow down the problem. Would this sensor cause the headers to glow? I'm guessing maybe the ignition timing would be effected by this causing it to run too hot.