bound to happen, carrera no start, possibly speed sensor?

[gunlover05]

Hello all,

After 10 years of uneventful and blissful ownership, my 85 Carrera (107k miles) left me stranded for the first time at a red-light a few weeks ago with the dreaded "no start". It has been running fine for years. Got her home and did research here a lot. I am now suspecting the speed sensor, but unsure if that really will cause a no start/spark? here is what I've narrowed down:

Car turns over fine, not starting at all
Possibly a very little fuel smell after cranking but not really strong
No spark at a test spark plug, or off of coil wire to a ground.
New dme relay installed, feel it softly click once on start
ICV valve vibrates when ignition on
Fuel pump runs (I hear it) when fuse is jumpered at fusebox
12 volts gets to coil when ignition on
Can't see a pulse from coil though across posts with test light when starting
Tach is not moving when cranking

so unless I'm missing something based on research, I am suspecting reference/speed sensors are not letting spark/fuel happen.

Just checked resistance across bottom two posts of the reference/speed plugs in engine bay. Reference sensor I get 1k ohms (bottom I think), speed sensor (middle) I get no resistance at all. And the rubber around the plugs started crumbling when I unplugged them, imagine from old age and heat, obviously making me suspicious (pic below). Question: does a bad speed sensor stop any spark/fuel like a reference sensor (which reads ok I think)? am I missing something else to check before I make an order?



gratuitous pic

[Chuck.H]

Search here for cracked solder joints on the DME, it's an easy visual check once you open the DME...

The solder going to the coil transistors that are up off the board are under vibration and crack after time.

Chuck.H
'89 TurboLookTarga, 392k miles

[Jcslocum]

DME relay is an easy swap and you should be carrying a spare anyway. It can be fixed by resoldering if your handy. Lots of info on the interweb.

Speed sensors are a PIA to change.

[CCM911]

Turn the factory alarm off and on a few times. That solved my no-start issue.

It may not work for you, but it is easy and free.

[DRACO A5OG]

To test the DME, find a 3.2 Pelican and ask if you can test your DME in their car. If it starts then it may be the sensors, replace both. Note do not not put their DME in your car.

BTW, she is a Beauty

[JTL]

I would recommend changing the sensors if they have never been replaced. They got me twice in the past, one at a time. The first time, I wasn't too far from home when the car started revving wildly. I turned around to go back but the engine quit shortly after. I coasted into a gas station and changed out the dme relay but no go. I had the car towed back home and started troubleshooting. One of the ref sensors didn't check out and there was no spark. The car fired right up after replacing the sensor. The second time, the car just didn't start at all. No tow needed that time as I was at home. Replaced the second sensor and all has been ok since.

[SiberianDVM]

If you are getting different ohm readings on the speed/reference sensors, then one is bad. My 84 died at the track with the exact same symptoms: no spark. I changed both sensors when I got home and she fired up 1st try.

It is a fiddly repair, as working position is awful, but easily doable at home. I also changed CHT sensor while I was in there.

[Targa Me]

I believe I have a spare speed/crank sensor if you want to try swapping it out.
Let me know.

[wwest]

Yes, DME relay first, but don't be surprised if a brand new one also doesn't work.

Shoddy workmanship abounds!

[89PS911]

I just changed my oxygen, speed, ref, and CHT sensors. Did this mainly because of age, while I am also chasing the cause of an occasional temporary no-start problem/stall problem when the motor is warm. DME relay is next.

As others have noted, the last three sensors are a bit awkward to replace and take some time. For the ref and speed sensors, it is easiest if you just remove the whole bracket with the old sensors in it, though this means you will have to gap the new sensors properly (see below).

The crucial step is to leave the cylinder/flywheel ends of the old sensor wires dangling by the flywheel so you can use those old wires to pull the new sensor wires through the engine bay and up to where the sensors plug into the connectors for the wires that feed the information to the DME. Another important step is to gap the sensors properly, which can be done easily by cleaning off your old sensors and gluing a 0.8 mm washer to the end; then slip that old sensor back in your bracket, position the bracket so that sensor, with washer, is up against the flywheel teeth; tighten down the bracket; remove the old sensor and insert you new sensors, and then pull the plug ends of those new sensors up through the engine bay.

Good luck and please don't hesitate to send any specific questions you may have as my memory is very fresh on this job.

Jonathan

[Chuck.H]

OP and 89PS911 - to easily check for cracked solder joints, you can also try this test; unbolt the DME and shake it slightly, this should cause/fix your no-start issue, even if temporarily...

Hope this helps,
Chuck.H
'89 TurboLookTarga, 392k miles

[gunlover05]

Thanks to everyone for the info so far.
I will check on the DME solder joints this weekend. Thanks Chuck.H for the shake test idea
It sounds like I should replace the speed/ref sensors, they are original and now the rubber around the plug is crumbling! Targa Me I definitely appreciate the offer to swap, but all things considered I think I will bite the $ and time bullet and order and replace both, just to be sure. It is evidently a pain to replace them, and 89PS911 appreciate the tips. Maybe while i'm in there i'll do the CHT sensor and get all three.
I never thought of the factory alarm being an issue, but I don't think mine is hooked up though will need to look.
I also never thought about a new DME relay possibly being bad! I do feel a soft click, would be a real shame to go through all of the sensors and that be it.

[gunlover05]

ouch.
these sensors are very expensive.
assume I need two of these for both speed and reference: 911-606-215-01-M14
I read an older post that a bmw sensor is the same but cheaper. 12-14-1-708-619-M14
is that true and has anyone use the BMW one? the BMW part sold here is half as expensive. sorry if this question offends the host.

[gtc]

The BMW part is the same but with a slightly longer wire.

[Jcslocum]

The DME relay is easier to swap and I would start there. The URO made ones have been known to be bad out of the box.

Search the Bosch part number for the speed sensors. They can be had for about $60 each. I just bought 2...

bosch 0261210002

[sugarwood]

Originally Posted by 89PS911

The crucial step is to leave the cylinder/flywheel ends of the old sensor wires dangling by the flywheel so you can use those old wires to pull the new sensor wires through the engine bay and up to where the sensors plug into the connectors for the wires that feed the information to the DME. Jonathan

Do you mean, rubber band the old sensor head to the new sensor wire plug?
Then pull on the old sensor cable from above to fish up the new sensor wire plug?

[plumb4u2]

Originally Posted by gunlover05

ouch.
these sensors are very expensive.
assume I need two of these for both speed and reference: 911-606-215-01-M14
I read an older post that a bmw sensor is the same but cheaper. 12-14-1-708-619-M14
is that true and has anyone use the BMW one? the BMW part sold here is half as expensive. sorry if this question offends the host.

I used the BMW parts when I swapped my sensors, have worked perfect for last couple yrs

[cabmandone]

If you're thinking of pulling the sensors, I'd hit them with some penetrating oil and let them soak. Mine pulled out like a mofo and I had my engine out when I replaced them. If you can salvage one of the original I believe you glue a washer to the bottom and set your gap with it, then pull the old one and install the new ones.

BTW, I'm also running with the BMW sensors.

[gunlover05]

thanks all very much, I will try the bmw sensors

[tomphot]

Originally Posted by plumb4u2

I used the BMW parts when I swapped my sensors, have worked perfect for last couple yrs

Same here - I should have just changed the sensors right off - after all the car is over 25 years old, instead I went ahead and did the DME inspection and walked down a few other dead-ends first.