Reference Sensor Testing

[CCM911]

I have been looking at information on how to test my reference sensors in my 1984 Targa. I saw the clip on YouTube where he does the test on the plug to the ECU.

Do I have to test there? Or can I test from the engine compartment as well?

My search did not provide any concrete answers.

Thanks.

[McLaren-TAG]

I know it's not the technical answer you're looking for but after much trials and tribulations in my chasing a no start while warm issue.

When the car is cold, If you heat up the area of the sensors with a heat gun to operating temp, you'll duplicate the no start when warm issue.

[john walker's workshop]

Unplug both black plugs and measure around 1000 ohms resistance between the bottom two of the 3 terminals of each black plug, on the engine side of course.

[CCM911]

Thanks, John Walker! I knew I could do it from there, but was not sure.

You just saved my back!

[CCM911]

OK, I got out this weekend and tested my sensors. They each were at 986, which is well within tolerance.

Next, I will try my ECU in my buddies car.

And I also have set out to remove the UNGO box from my car. Good lord! Where do some of these wires go???

[Porsche 2]

Why are you testing your flywheel sensors?

[CCM911]

Originally Posted by Porsche 2

Why are you testing your flywheel sensors?

No-start issue.

[Porsche 2]

I had a no start hot engine problem. Sensor resistance checks at cold and hot condition showed correct resistance amounts (per Bentley). Replaced both sensors, no further start problems. See my postings last week.

[McLaren-TAG]

Hence the real world test recommendation ^^ up there.

[steely]

If this is the same problem you had in June, I'd replace the sensor - that is, if your fuel pump stopped firing.

[Quicksilver]

To completely test the sensors you need to get an oscilloscope, crank the engine, and see what kind of voltage the pulses have. It should be 2.5 volts. If you aren't getting that much you should look at the gap between the sensors and the teeth/pin on the flywheel.

BTW "Fun Fact" - If the reference sensor has no pulse when the TDC pin goes by check the pin with a magnet. John Walker found a flywheel that had been made with a stainless pin!

[gwinnch]

I have a similar issue with my '85, need some help on testing my sensors:
I get a good resistance reading at each sensor for terminals 1/2 but get nothing in any meter setting for 1/3 and 2/3. Bentley says these two pairings should read greater than 100,000 ohms, so does that mean mine are over 2M ohms, or bad?

[rick-l]

Originally Posted by gwinnch

get nothing in any meter setting for 1/3 and 2/3.

Is that nothing the same nothing your meter reads when you measure high resistance, like with the probes laying on the table not touching anything? If so your resistance tests have passed.

[CCM911]

Yes, Steely, I am not the fastest repair guy out there. I got sidetracked with motorcycles and the new Lotus Europa, so progress has been slow.

This week, we are going to remove my ECU and try it in my friend's car.

Hopefully, it will prove bad, and then I could ship it out to Ingo for some TLC.

Originally Posted by steely

If this is the same problem you had in June, I'd replace the sensor - that is, if your fuel pump stopped firing.

[gwinnch]

Rick, it doesn't change when I hit it with the probes, so same as when probes are on the bench not touching anything or each other. I put some heat on it and the resistance at 1/2 goes up to 1200-1300 then goes back to about 960 cold. Is that a problem?

Chris, not trying to hijack your thread-thought this would be useful to both of us! Thanks!

[CCM911]

No worries, it's all good.

I am in the middle of bumbling my way thorugh so I'll read anything.

Originally Posted by gwinnch

Chris, not trying to hijack your thread-thought this would be useful to both of us! Thanks!

[gwinnch]

Finally got time to get back to my no start issue:
Went ahead and replaced my ref sensor with the less expensive bmw part-it started right up. New and old sensor meter at the same values...