3.2 Speed & Reference Sensors...both bad at the same time...

[mziggy16]

After solving a no crank issue (poor wiring crimp by yours truly) I'm now chasing a no start after clutch job, starter, fuel lines, AC conversion, etc. Previous thread is here for reference

We problem solved a lot today on the no start:
- Fuel pump fuse has continuity
- DME is not the issue (swapped the sold state with previously functioning DME)
- Terminal 86 on the DME has 12v
- No fuel smell at the tail pipe
- Fuel pump primes and can feel it vibrate through a screwdriver
- Tach doesn't move on the crank
- Starts with carb cleaner sprayed in the intake
- 36psi at the fuel rail
- CHT: 1.03 ohms at ambient 85 degrees F

Drumroll...

Reference Sensor AND Speed Sensor:
1&2 read 1031ohms
1&3 nothing
2&3 nothing

It looks like BOTH are not properly functioning. Before I go and order these, is this something that happens? We speculated that maybe we knocked them when mating the engine to tranny but don't specifically recall this.

Any thoughts before I go and order new parts?

Appreciate all the help so far.

[dannobee]

Isn't 3 the shielding braid?

Did you connect them up to the harness correctly? They have the same style connectors going to the engine harness and it's easy to mix them up. Switch the middle and lower connectors and see if it starts. These are the three vertical connectors near the #3 intake runner.

[mziggy16]

Originally Posted by dannobee

Isn't 3 the shielding braid?

Did you connect them up to the harness correctly? They have the same style connectors going to the engine harness and it's easy to mix them up. Switch the middle and lower connectors and see if it starts. These are the three vertical connectors near the #3 intake runner.

They are connected in the right order.. The middle connection has a silver paint pen stripe on the plug and receptacle to avoid mis-connection.

The page from the Bentley is below. This is what I was referring to.

Still seems unusual that both would prove faulty at the same time.

[john walker's workshop]

1&2 Should be around 1000, so yer probably in the ball park.

[mziggy16]

Originally Posted by john walker's workshop

1&2 Should be around 1000, so yer probably in the ball park.

What about the other readings returning nothing?

The Bentley makes it sound like the other terminals should return a reading.

[dannobee]

In the Bentley manual, the > symbol means GREATER than 100,000 ohms. Infinite resistance is GREATER than 100,000 ohms. You're good to go.

Like I said, terminal 3 is the shielding braid and it should not be touching either of the two other wires.

[dannobee]

Also, the sensors should generate an AC voltage across terminals 1 and 2 with the engine cranking.

[mziggy16]

Originally Posted by dannobee

In the Bentley manual, the > symbol means GREATER than 100,000 ohms. Infinite resistance is GREATER than 100,000 ohms. You're good to go.

Like I said, terminal 3 is the shielding braid and it should not be touching either of the two other wires.

Helpful, thank you. I was looking for the meter to return a value.

Given that…what are thoughts on the next test? Running a little low on options.

[dannobee]

Swap the two lower harness connectors and see if it starts.

[wazzz]

Originally Posted by mziggy16

After solving a no crank issue (poor wiring crimp by yours truly) I'm now chasing a no start after clutch job, starter, fuel lines, AC conversion, etc. Previous thread is here for reference

We problem solved a lot today on the no start:
- Fuel pump fuse has continuity
- DME is not the issue (swapped the sold state with previously functioning DME)
- Terminal 86 on the DME has 12v
- No fuel smell at the tail pipe
- Fuel pump primes and can feel it vibrate through a screwdriver
- Tach doesn't move on the crank
- Starts with carb cleaner sprayed in the intake
- 36psi at the fuel rail
- CHT: 1.03 ohms at ambient 85 degrees F

Drumroll...

Reference Sensor AND Speed Sensor:
1&2 read 1031ohms
1&3 nothing
2&3 nothing

It looks like BOTH are not properly functioning. Before I go and order these, is this something that happens? We speculated that maybe we knocked them when mating the engine to tranny but don't specifically recall this.

Any thoughts before I go and order new parts?

Appreciate all the help so far.

No sign of life shown on tach means either the Motronic is not powered or it is powered but does not receive correct signals for speed and ref when cranking.

Also, are you sure of the ohm reading for CHT? If so it looks like the CHT is shorted. Certainly doesn't help startup as this simulates a very hot engine. But since ambient temp is 85F it should eventually start. So this goes back to the sensors. Have you tried to swap them as suggested?

[76FJ55]

If it will run on starting fluid then the speed and ref sensor must be working. If either one id dead you will have no ignition spark at the plugs, so it wouldn't make any difference if you added starting fluid or not.

[mziggy16]

Originally Posted by dannobee

Swap the two lower harness connectors and see if it starts.

Swapped them. Same result

[76FJ55]

Originally Posted by mziggy16

We problem solved a lot today on the no start:
- Fuel pump fuse has continuity
- DME is not the issue (swapped the sold state with previously functioning DME)
- Terminal 86 on the DME has 12v
- No fuel smell at the tail pipe
- Fuel pump primes and can feel it vibrate through a screwdriver
- Tach doesn't move on the crank
- Starts with carb cleaner sprayed in the intake
- 36psi at the fuel rail
- CHT: 1.03 ohms at ambient 85 degrees F

Drumroll...

Reference Sensor AND Speed Sensor:
1&2 read 1031ohms
1&3 nothing
2&3 nothing

It looks like BOTH are not properly functioning. Before I go and order these, is this something that happens? We speculated that maybe we knocked them when mating the engine to tranny but don't specifically recall this.

Any thoughts before I go and order new parts?

Appreciate all the help so far.

SO for clarification, per the original post, "- Starts with carb cleaner sprayed in the intake". this indicates that you are getting spark if the engine will run on carb cleaner. when started by spraying carb cleaner into the intake, does the tack show that the engine has started, or is it still dead? will the engine stay running if you continue to feed it with cab cleaner?


You state that "- Fuel pump primes and can feel it vibrate through a screwdriver". There is no prime feature of the original fuel injection system. there are aftermarket DME relays that incorporate a prime feature. what DME relay are you currently running?

[GH85Carrera]

My last pair of flywheel sensors would ohm test just fine when they were cold. Just after warmup and driving for a while, they acted like a demon possessed them. The idle would go up to 2,500 on it's own, then die. I had a heck of a time getting in 1/2 a mile back home to the garage. After I replaced them, I heated them with my heat gun, and they started acting weird. I was happy to send them to the landfill.

I replaced the sensors, and "while I was in there" another head temp sensor and the car run like it should for the last 6 or 7 years and I hope for many more years.

So yea, test the sensors, but when it doubt, replace them unless they are very new. If they are the original ones, replace them just because they will not last much longer. I considered them a consumable item. And they are not that expensive or hard to replace considering how much pain and suffering they can cause. They are like having a flat tire, and a dead battery at the same time. Annoying as can be.

[mziggy16]

Originally Posted by 76FJ55

SO for clarification, per the original post, "- Starts with carb cleaner sprayed in the intake". this indicates that you are getting spark if the engine will run on carb cleaner. when started by spraying carb cleaner into the intake, does the tack show that the engine has started, or is it still dead? will the engine stay running if you continue to feed it with cab cleaner?


You state that "- Fuel pump primes and can feel it vibrate through a screwdriver". There is no prime feature of the original fuel injection system. there are aftermarket DME relays that incorporate a prime feature. what DME relay are you currently running?

I did not look at the tach when we sprayed carb cleaner in there. The tach does not move on the crank though.

We did a second carb cleaner spray/test and it started but when we sprayed more in to see if it would wake up something fuel-related it backfired so we stopped. I think it would run if it were fed an appropriate amount of fuel, whether that be carb cleaner or gasoline.

DME is a Focus 9 Solid State DME with the pump prime feature.

[mziggy16]

Originally Posted by GH85Carrera

My last pair of flywheel sensors would ohm test just fine when they were cold. Just after warmup and driving for a while, they acted like a demon possessed them. The idle would go up to 2,500 on it's own, then die. I had a heck of a time getting in 1/2 a mile back home to the garage. After I replaced them, I heated them with my heat gun, and they started acting weird. I was happy to send them to the landfill.

I replaced the sensors, and "while I was in there" another head temp sensor and the car run like it should for the last 6 or 7 years and I hope for many more years.

So yea, test the sensors, but when it doubt, replace them unless they are very new. If they are the original ones, replace them just because they will not last much longer. I considered them a consumable item. And they are not that expensive or hard to replace considering how much pain and suffering they can cause. They are like having a flat tire, and a dead battery at the same time. Annoying as can be.

CHT was replaced in 2012 at 136k miles (car now has 151k miles).

I don't have a record showing Speed or Reference Sensor replacement and they appear to be original.

[mziggy16]

Originally Posted by wazzz

No sign of life shown on tach means either the Motronic is not powered or it is powered but does not receive correct signals for speed and ref when cranking.

Also, are you sure of the ohm reading for CHT? If so it looks like the CHT is shorted. Certainly doesn't help startup as this simulates a very hot engine. But since ambient temp is 85F it should eventually start. So this goes back to the sensors. Have you tried to swap them as suggested?

CHT reading is in spec with this post’s parameters.

[mysocal911]

Originally Posted by mziggy16

I did not look at the tach when we sprayed carb cleaner in there. The tach does not move on the crank though.

We did a second carb cleaner spray/test and it started but when we sprayed more in to see if it would wake up something fuel-related it backfired so we stopped. I think it would run if it were fed an appropriate amount of fuel, whether that be carb cleaner or gasoline.

DME is a Focus 9 Solid State DME with the pump prime feature.

Then you have a fuel problem the result of;
1. a bad DME ECM (fuel injection section)
2. a bad DME relay - Focus 9s go bad too like the OEM relay
3. a bad fuel pump/fuel regulator
4. stuck fuel injectors
5. no 12V power on fuel injectors

[mziggy16]

Originally Posted by mysocal911

Then you have a fuel problem the result of;
1. a bad DME ECM (fuel injection section)
2. a bad DME relay - Focus 9s go bad too like the OEM relay
3. a bad fuel pump/fuel regulator
4. stuck fuel injectors
5. no 12V power on fuel injectors

It’s not the DME relay. We swapped in my old, functioning, relay.

Pump and Regulator are getting 36psi to the rail.

Could be injectors. What are the odds of ALL of the injectors being stuck? Would assume it’s power delivery to the injectors rather than all of them being stuck.

And then there’s the DME ECM…is there a way to test this without swapping in a new one?

[GH85Carrera]

Originally Posted by mziggy16

CHT was replaced in 2012 at 136k miles (car now has 151k miles).

I don't have a record showing Speed or Reference Sensor replacement and they appear to be original.

If your sensors are indeed original, replace them even if it ain't broke. They will die someday soon, at a very bad time. 36 years is amazing that they lasted that long.

And the head temp sensor s just a while you are right there replacement item. The wire goes through the grommet, and getting the grommet back into place is frustrating enough to do that alone is a good reason to replace the three sensors as a unit. And do them one at a time, and mark the positions of the connectors top and on the flywheel positions BEFORE you do removal.

If your fuel pump is original, replace that as well.