1985 911 crank no start issue after sitting

[ischmitz]

One (or both sensors bad) will cause no spark and no fuel pulses. However, the fuel pump is turning on as soon as the DME sees the starter signal. So if your observations that you have no spark and no fuel pump activity during cranking you either have both a bad sensor and a bad DME relay or something more fundamentally wrong with the DME.

Have you checked for fuel pulses. If only spark is missing it would indicate bad DME. If both fuel and spark signals are missing it points towards the sensors. And unfortunately you can’t “jump” them. The speed sensor is needed as its signal directly defines the fuel and spark pulses. The reference sensor is needed to correctly synchronize the signals to TDC.

I’d get replacement sensors and start from there.

Ingo

[55rag]

I'm going to order those sensors and get the car towed to my garage. Hopefully those will fix it up.

[jlex]

Save money by replacing the sensors yourself.... no big project.
And do the CHT at the same time.... they go thru the same grommet.

[ClickClickBoom]

Did you try the jumpstart?

[jlex]

Originally Posted by ClickClickBoom

Did you try the jumpstart?

He did...

[55rag]

I got the car home and got it jacked up after work today. I took a quick look under the car to look for the speed and reference sensors but don't see them. Do I have to remove this engine tin under the drivers side?

[jlex]

No need to remove engine tin.
put the rear wheels up on jackstands, then remove the left rear wheel.
Just follow the wires that come thru the wheel well that lead over to the flywheel.... you can't miss them. Two of those wires lead to the speed and reference sensors. The third wire leads to the cylinder head temp sensor. You can't miss them...
From your photo, the two wires that lead to the sensors appear with the cht sensor wire. The two that have the insulation crumbling off of them and are showing silver underneath are the ones that will be replaced with the new sensors. From the looks of those wires, that's probably your problem.

[55rag]

Thanks Jlex, I'll hopefully be able to get under there and take a better look this weekend.

[Missed Approach]

Hi @55rag- this is still one of the best reference posts on the sensors. Helped me tremendously.

no-spark problem finally resolved

[55rag]

Very cool! Thanks for the write up. I didn't see that thread when I was searching but maybe I didn't read far enough down. That will help out a lot.

[GH85Carrera]

The project to replace the sensor is not super hard, but tricky. I had the biggest challenge in getting the new grommet back into place. Lube is your friend for that. Dose it all with WD-40 and it all pops back into position easily. The WD-40 evaporates. Everyone has it around.

[jlex]

Try not to use petroleum products like WD40 on rubber parts.... it deteriorates rubber. Instead, use liquid soap or silicone spray. The grommet isn't a critical item, so no big deal using WD40 on it per Glen's suggestion, but for other projects be mindful of oil's effect on rubber parts.
Come to think of it, since you'll be working so close to the oxygen sensor, I probably wouldn't use the silicone spray either...
may be best to go with the liquid soap.

[55rag]

I got a spare 30 minutes to work on the car today and was able to get the sensors out of the bracket with minimal cussing. I had to use a regular allen wrench on the top sensor since the engine tin got in the way of using a socket. Hopefully I'll have time tomorrow to finish up the removal. While I was working I did find a torn axle boot so I'll have to replace those too.

[55rag]

I swapped out the sensors today and the car started right up. Thanks everyone for your help getting this thing going. I need to replace one CV boot and then I'll be on the road again.

[proporsche]

good to see..looks a like someone did some work on that sensors wires..that could have been the problem

Ivan

[jlex]

Now aren't you glad you did the job yourself instead of having the car towed to a shop?
Although my car wasn't disabled due to bad sensors, I replaced them anyway when I saw the insulation was crumbling off.
Have fun with the boot replacement.... bit of a messy job, but doable if you don't mind working on your back. Do both sides. Hopefully, dirt hasn't infiltrated the CV joint... if so, disassembling, examining and re-packing the joint may be necessary. Luckily, I caught mine just as it tore (from stress on the joints from jacking the car up).... old rubber does that.