1982 3.2 Carrera crank, no ignition

[romster]

Last Friday we made the great plan to drive to a nice spot to see the sun rise. Got out of bed very early, packed up some swim gear, got to the garage, in the car, and lo and behold, the lovely thing didn't start.

I've been doing some digging here and already tried some recommendations, but still found it useful to create a thread to see if anyone has suggestions for the current state of troubleshooting.

Issues observed:

• Engine cranks, but no ignition.
• Fuel pump does not seem to engage during crank. Only hear a hissing sound (what's that?)
• There is no change in rev meter during crank.

Tests performed:

• Cold start spray, no effect.
• DME Relay replaced, no change.
• Fuel pump confirmed working by jumping pins in relay. Nice strong hum.
• No spark observed from spark plug test.
• Was able to test some connections in ECU cable harness. Got accurate resistance reading out of reference sensor (pin 25, 26), but could not get a reading from rpm sensor (pin 8, 27). Voltages to ECU seem OK.

I am by no means an electrical expert but I'm thinking there is an issue with the RPM sensor or its wiring. I am not could not find 100% clear answers, but read that when there is no reading of the flywheel, both the fuel and spark will not engage. This could also explain the rev meter not showing an increase during crank.

Does anyone have advice? I am limited in my options. The car is in a public underground car park, I cannot lift it to check the sensor itself. At most, I can perform basic electronic tests or maintenance (cleaning, inspection). I am hoping to be able to troubleshoot, as I think the process of getting it transported to my garage will be costly.

[wazzz]

If it is a 3.2 (1982 ?), sounds indeed like the rpm sensor is shot. Where do you plug your ohm meter wires to measure it? It could also be a bad contact at the connector on the 3-connector vertical ramp.

[romster]

Oh, I'm not sure what happened in my brain. It's an 1985 Carrera, not an 1982.

I tested at the ECU harness, pins 8 & 27. I re-plugged the connectors at the vertical ramp, no change. Anything I can test there?

[wazzz]

You mean you get not value at all (infinite resistance) when measuring at the connector? If so, you found the culprit for sure. The engine cannot start without this sensor.
There are 3 pins on the connector. One is the cable shield and is meaningless for test purposes. It is only connected to ground when connector is plugged back.
The other two pins are the sensor terminals and should yield some 900-1000 ohms.
This is applicable to both sensors (rpm and ref sensor). They are identical. So if you can measure one ok and don't get the same result with the other one, search no more.

[romster]

I will check, thanks very much. Infinite indeed, or whatever is causing it to not get a reading at all.

Hopefully back in an hour or so. Any thoughts on fixing, if this ends up being the culprit? Could it be a faulty cable still, or would the whole sensor need replacing?

[wazzz]

Probably the whole sensor. But to be sure, take measurements at vertical ramp. Unplug connectors again and ohm them both. That's the closest point to sensors and if measurement is still wrong at this point, rpm sensor is probably shot. Kind of a PITA to replace with car on jack stands but doable. You'll probably need to replace both anyway.
They are cheap if you google the Bosch reference 0 261 210 002. Should get them for 60 euros each.

[brianlay]

The speed and reference sensor harnesses are delicate and deteriorate with heat and age.
You should replace both while you’re at it.
Probably not a job to be done in a car park.

[romster]

Checked the vertical ramp and indeed I'm getting 1000 ohms on the reference and 0 on the RPM. Did some other checks on fuses, ignition coil and all seems fine there as well.

So, next step, I can either get it jacked up and try it myself with the help of a friend or get it to my garage. Will call and get an indication of a price tomorrow. I have never laid beneath a car but I'm willing to give it a shot, but the set of manuals I have all show pictures and instructions for a removed engine. @wazzz would you happen to know some material I can read up on, on how to go about performing this task while laying beneath my car?

[wazzz]

I don't know how good you are at wrenching. You need to at least jack up the rear, lay the car on safe jack stands and remove the rear left wheel, then do your best to reach the pair of sensors and their bracket on the fly wheel. You need a 1/4" ratchet, extensions and a 10 mm socket. Easiest way is to remove the whole bracket (held by two 6mm screws, 10mm hex head) with both sensors still on it and then work on a bench to remove both sensors held with an allen head screw. Sensors can be a real PITA to remove from bracket and you may need to destroy them with a 15mm drill bit. This is what I ended up doing.
I did it with car on jack stands like I explained above and this is not my best wrenching memory. Access is tight there and you can never really see what you are doing. So you need to feel it more than you see it.

[romster]

Thanks, I'll see what I can do! I read that the sensor position is quite important with a strict tolerance. How'd that come into play when it's as obscured as you say?

[wazzz]

Found a short procedure here : https://www.porscherepair.us/porsche-911-1984-1989/crankshaft-sensors-removing-and-installing.html

Not very detailed. The trick to get a 0.8 mm play is to use one of the old sensors, preferably one that didn't have to be destroyed, glue a 0,8 mm thick washer or coin or whatever on its tip, put it back in the lower sensor position, put the bracket back and have the washer rest against the flywheel. Secure the bracket, then remove the old sensor and install the new sensor instead. Then the space occupied by the washer will become the 0,8 mm play needed.
Have fun!

[wazzz]

More info on this page of the Bentley manual.

[romster]

Yes! That's what I found as well. I'll have to see how they match with what I can see from below.

Ordering the sensors at least.

[romster]

Ok, a little update and with that, a request for advice.

I managed to remove the sensors, though had to take out the bracket as I could not get both bolts out from my position. They came out fine, I've cleaned them, and I'll use the "glue a 0.8mm washer on the old sensor" method to get it back into position. I disconnected the wiring from the harness in the engine bay as well hoping to just pull the wires through.

Now however, I seem to have found my new mortal enemy. The grommet that transfers the sensor cables from the flywheel mount to the engine bay refuses to come out. I've tried pulling it, pushing it, even going as far as to getting the rear end of a hammer behind it to try and yank it out, but it simply does not give.

Does anyone have any advice to get this thing out? Image for reference (taken after putting the wheel back on)

[wazzz]

That's weird. It looks like melted rubber. May be the PO glued it to the engine tin?
It normally comes out in one piece and can slide on the CHT cable (white center cable). It is actually part of the CHT and sold with it. Don't know if it can be bought separately.
There are cuttings on both sides so the rpm and ref sensor cables can be removed and refitted easily.
Now your grommet looks so bad that you'll probably need to change it anyway, meaning you may have to also buy a new CHT.

[romster]

It might look worse on the picture. I don't think it's melted or glued, I can grab the edges and pull on them, but it's just very tight.

The CHT cable in the center is indeed sliding. Do you mean to say both cables can be removed with the grommet in place, or would I still need to get it out to remove them?
I might try wrapping some wire behind it and pull it out so the force comes from all sides.

[wazzz]

Both cables can be removed from the grommet, but not when the grommet is in place on the tin.

So the grommet first needs to be pulled out from the tin. Then you'll see or feel thin side cuttings on left and right sides of grommet that will allow you to remove old sensor cables and push in new sensor cables.
Only the center CHT cable cannot be removed from the grommet, because of its connector that is too wide to go through the center hole.
Good luck!

[romster]

Gotcha, that's what I thought. I'll see if the wire method works...

[romster]

Well, got them out. It was the hammer that in the end dealt the final blow. Pretty clear why it failed, the whole cable came apart.



Quite interestingly, when I wanted to attach the 0.8mm washer, I noticed the original sensors clearly have a more curved top, compared to the new ones which are perfectly flat. This is definitely in the range of 0.Xmm, so I wonder how I should continue with the spacing. I'm guessing that the spacing from the edge needs to be used for consistency, so that means the 0.8mm washer is out.

See below. Left is old, right is new.

[proporsche]

you should really use paint or some other tool to make the images smaller...