TDC Sensor No start Help me Solve the Mistery
 

I spent the whole day today troubleshooting my TDC and RPM sensors and trying to get my car to start with no luck. The two sensors are newish, I bought them two months ago and the car was working fine with no problems.

We took the engine out for a refresh and Now I got a No Start problem.

I tested both sensors at their plug and here is what I got so far:
Tested RPM sensor Ac voltage output while cranking = +2.5V
Tested TDC sensor AC voltage output while cranking = +0.1V

The I switched the sensors and got the following readings:

Tested RPM sensor Ac voltage output while cranking = +2.5V
Tested TDC sensor AC voltage output while cranking = +0.1V

So as you can tell the sensors are working fine, so I think it must be the position of the TDC sensor. I moved them, adjusted them, got them closer, no luck. Then I went technical and looked up the specs.

I placed both sensors at a calibrated distance of 0.8mm and got the same readings.

Now here is where it gets intersting. If I crank the engine with a wrench (slow) the TDC sensor reads +2.5V, but as soon as I start cranking the engine with the starter, the sensor reading goes down to +0.1V.

Why is the TDC reads when cranked by hand and not when the engine is cranking faster? It is doing this with both sensors if I moved them around, they read the RPM but not the TDC???

Any clues?

Pretty sure you should be observing a dc output not ac. Are you sure you don't have the the two connectors criss crossed?

Got the test procedure from this video.

https://youtu.be/zeFOOcLSk60

I am taking the readings at the sensor itself, not plugged to anything. They do not have any DC voltage reading, they explain that by getting AC from the (2) wires of the sensor you can get dinamic reading and for static readings you look for Ohms.

Both my sensors pass the static Ohms test but fail the dinamic test when placed on the TDC slot.
They give a good dinamic reading when placed on the RPM slot.

Did you do this?
It will not hurt anything.

Yes, I did.

Can't explain the v-out difference cranking vs wrenching.
Sensors sound new if you bought them recently and get similar results when swapping them.
They worked before, you did something called a refresh to the engine, now it won't start, but you suspect the new sensors.
Can you start at the top and give us the no-start symptoms?
Do you have spark or fuel?
Did you change the flywheel? Are the iron pins in place? Are they ferrous? (There was at least one example here where the pin was not).

Your sensors are fine and no mystery at all. I doubt you can reach similar speeds with your wrench compared to cranking with the starter ;)

These sensors are VR (variable reluctance) sensors where the passing metallic teeth change the magnetic flux in a soft iron core inside the sensor. That results in a voltage swing.

The DME only looks at the zero transition and doesn't care about the absolute magnitude of that swing. The speed sensors sees many teeth and hence you get around 2.5V AC equivalent to a continuous stream of pulses, 128 per rotation to be exact. The reference sensor only sees one tooth per rotation and thus gives only one pulse. Your volt meter averages and you only see ~ 0.1V. When you hand-crank that pulse is larger and you see a higher reading.

Back you your issue: I'm assuming you attribute the no-start to the engine removal and re-install. Start with the basics:

Do you feel the DME relay click when turning the ignition to ON - No, bad DME relay or no power to DME relay
Is the ICV vibrating with the ignition in ON - No means no power to the DME, bad DME relay or DME harness connection to engine
Is the fuel pump running during cranking?
Are you getting fuel pulses during cranking but no spark? Bad coil, bad DME
Are you getting spark but no fuel (spray starter fluid)? Bad DME, fuel pressure, stuck injectors
No fuel and no spark pulses - DME or sensors

Ingo

Steely
They worked before, you did something called a refresh to the engine, now it won't start, but you suspect the new sensors.

Originally the car had a no start problem, we did a complete no start trouble shoot and found the problem was the TDC sensor wire plug. We reached this conclusion by doing the same test we are doing now, we installed (2) new sensors and both new sensors were giving the +2.5V reading.

And I test drove the car with no problems for about 2 weeks before taking the engine out.

The refresh was take down the engine, paint, clean, hoses, ect..
http://forums.pelicanparts.com/uploa...1480256440.jpg
http://forums.pelicanparts.com/uploa...1480256790.jpg

Once we were ready to start the engine we primed it
Tested for spark (ok)
Got fuel pressure (ok)
But no start.

Then we spayed some carb cleaner into the intake and started in one turn of the engine.

We then tested the injectors and found out they were not pulsing (no intermittent ground)

Then I went to the DME and started testing input voltage (ok)

Then I proceeded to test both TDC and RPM sensors pins on the DME harness as before, both passed the static test and the TDC was not giving me the same voltage as before.

Then we tested the wires on the harness for continuity to the engine bay plugs (ok)

Then we started trouble shooting the sensors itself and their position.

Did you change the flywheel? No - only new clutch

Are the iron pins in place? Are they ferrous? Looks ok see pic

http://forums.pelicanparts.com/uploa...1480257359.jpg

[QUOTE=ischmitz;9373735]Your sensors are fine and no mystery at all. I doubt you can reach similar speeds with your wrench compared to cranking with the starter ;)

These sensors are VR (variable reluctance) sensors where the passing metallic teeth change the magnetic flux in a soft iron core inside the sensor. That results in a voltage swing.

The DME only looks at the zero transition and doesn't care about the absolute magnitude of that swing. The speed sensors sees many teeth and hence you get around 2.5V AC equivalent to a continuous stream of pulses, 128 per rotation to be exact. The reference sensor only sees one tooth per rotation and thus gives only one pulse. Your volt meter averages and you only see ~ 0.1V. When you hand-crank that pulse is larger and you see a higher reading.

-That makes a lot of sense, but why when I changed the sensors a while back I
Was getting +2.5V on both the RPM and TDC?

Do you feel the DME relay click when turning the ignition to ON - No, bad DME relay or no power to DME relay
-Yes clicking

Is the ICV vibrating with the ignition in ON - No means no power to the DME, bad DME relay or DME harness connection to engine

-Checked this morning. No I do not feel it vibrating.

Is the fuel pump running during cranking?

- Yes fuel pump is running strong

Are you getting fuel pulses during cranking but no spark? Bad coil, bad DME

- Injectors are not pulsing

Are you getting spark but no fuel (spray starter fluid)? Bad DME, fuel pressure, stuck injectors

- Yes, injectors not pulsing. (Closed all the time)

No fuel and no spark pulses - DME or sensors

- Spark ok, it starts with starter fluid.

If you have spark both sensors are working ! And the DME is powered. The sensors are common to fuel and spark. If one sensor is bad NO fuel pulses and NO spark.

If the injections don't fire they are either stuck close (common on 3.2 sitting for several month) or the harness or the DME are faulty.

And your ICV must vibrate with ignition on. Make sure it's plugged in. Else the engine won't idle.

The more I think about your story the more I lean towards DME harness not connected to injectors and ICV. Check that you plugged everything back into the correct place.

Ingo.

Ingo:

I got a little more testing done today. And at this point I have ruled out the sensors because the car starts with starting fluid. I got fuel on the fuel rails but the injectors are not opening.

I tested the voltage on one injector plug and got the following results:

switch on, engine not turning: 12V on both pins.
engine turning trying to starts : 12V on one and pulsing ground on the other.

I got 3 injectors on with paper cups, and they are not opening.

Took all injectors out and clean them with starter fluid and cycle them with pulsing 12V until they were working properly.

I installed them and the car started, but with a really rough idle.

I do not feel the ICV vibrating I took the voltage at the plug and reads 5V.

Is this the proper voltage?

I will look into ICV test procedures to troubleshoot.

I will like to officially close this tread. As always the great members of this forum guided me to properly solve my non start problem.

To recap:

Both the TDC and RPM sensors were reading within acceptable range all along.
The Ohms readings were in range and as I learned the dinamic test should give +2.5 volts for the RPM sensor and +0.1v for the TDC sensor.
The ICV and the trotle plugs were mistakingly switched that is why the ICV was not pulsing with the key on.
And last the injectors were stuck. I has to removed them and apply started fluid and cycle them with 12v. I also put some Miracle Oil in the fuel to keep them lubricated.

Once I solved those issues, the car started right up!

Ingo was right there was no mistery after all

Thanks for the help

Awesome - glad you found it, and thanks for letting us know.

Look like you got it all sorted out. Good job