Newbie with 911 3.2 No Start No Spark Questions

[Franki]

Hi All,

It was with great pleasure I joined this forum. Thank you for all your contribution of great information.

I have a 1984 911 3.2 and am having the common no start/no spark problem after storing the car over the winter. Through researching this forum I had done some preliminary tests and have ruled out DME relay and coil. I did the ohms and AC voltage tests on the ECU plug through pins 25&26 and pins 8&27 for the reference (TDC) sensor and Speed (RPM) sensor, respectively, based on this video: https://www.youtube.com/watch?v=zeFOOcLSk60

From the results of doing the above ohms/Voltage tests, it was clearly indicated that the speed sensor is not working whereas the TDC sensor is OK.

I now have a couple of quick questions for you Porsche enthusiasts:

(1) Can a defective speed sensor alone cause no spark problem?

(2) Does anyone of you know of a link or video that shows the location of and how to replace these two sensors while the engine is in the car?

Many thanks in advance.

Frank

[GH85Carrera]

If one sensor is bad, replace them both. Many people (me included) also replace the head temp sensor “while you are in there” if it has not been replaced recently.

The sensors are easy to remove. Jack up the rear and put on jack stands. Remove (driver’s side) left side tire and look at the area where the flywheel is. Mostly done by feel.

And yes, one flywheel sensor will prevent the car from starting or running.

[cabmandone]

Not sure of a video but on the driver's side just in front of the engine where the trans and engine meet at about 1 o'clock you'll see the speed and reference sensor. Hope that makes sense. The wires from the engine bay go toward the front of the car, through a rubber grommet in the engine tin and then to the housing on the transmission.

[Rotoyz911]

Hi Franki

Did you fix the no start no spark issue?

[PeteBrown]

My '87's DME motherboard had a few cracks in the soldering that caused the no start issue. Sal (scarceller) was able to replace my DME with a newer motherboard from a 944. At 30 years old our cars are relying on the equivalent of a Commodore 64.

Pete

[GH85Carrera]

Originally Posted by PeteBrown

My '87's DME motherboard had a few cracks in the soldering that caused the no start issue. Sal (scarceller) was able to replace my DME with a newer motherboard from a 944. At 30 years old our cars are relying on the equivalent of a Commodore 64.

Pete

A commodore 64 had 64K of RAM. The early Carreras came with a 2K DME. Later replaced with 4K because no one was making the 2K chip anymore. The 4K chip motherboards can be jumpered to the 8K version. Whooo Hooo, 1/8th the RAM of a Commodore 64.

[Franki]

Thank you so much for all the replies and info. As I mentioned before I had done some test and it was indicated that the speed sensor is defective thru testing the voltage and resistance. I ended up having to remove the sensor bracket from the car as the speed sensor didn't want to come out from the bracket while the bracket is on the car. I used a vice and a hammer to finally remove the speed sensor from the bracket. I am keeping my fingers crosses it was only the speed sensor. Will find out once I have the new sensors in.

Meanwhile I am playing with the idea of replacing also the coil, the distributor cap, the rotor, spark plugs and the fuel filter. All the parts have been ordered and should have them in about couple of weeks. One thing I am not sure if I will eventually replace the spark plugs myself. Attempted to remove no. 1 plug and didn't have much luck the first trial. Seems pretty tricky in getting the factory spark plug wrench in place to remove the plugs.

[Walt Fricke]

Franki - spark plugs on these cars aren't difficult to remove. While lots of guys like to use the factory plug wrench from the stock tool kit, it makes more sense to purchase a 14mm spark plug socket (long socket with a magnet), a short 3/8" socket extension, and a 3/8" socket wrench for the job.

You may find it convenient for access to remove some of the heating air tubing on the left side, and to unfasten and (without disconnecting hoses) rest the air conditioner pipe on a pad or something on the right rear fender.

[Franki]

Originally Posted by Walt Fricke

Franki - spark plugs on these cars aren't difficult to remove. While lots of guys like to use the factory plug wrench from the stock tool kit, it makes more sense to purchase a 14mm spark plug socket (long socket with a magnet), a short 3/8" socket extension, and a 3/8" socket wrench for the job.

You may find it convenient for access to remove some of the heating air tubing on the left side, and to unfasten and (without disconnecting hoses) rest the air conditioner pipe on a pad or something on the right rear fender.

Do you think I should take off the silver metal cover before attempting removing the spark plugs (See pics)? Also from the spark plug picture I could not figure out if the plugs are sitting flush with the cylinder head or the swirl lines surrounding the spark plugs are actually part of a cone shape cavity where the plugs sitting at the center?

[Walt Fricke]

You are overthinking this. Leave those round "nut" like pieces on the ends of the plugs. They are there to let the plug connectors grip. Your spark plug wrench will fit over these just fine.

You are looking at the hole which is machined through the cooling fins of the cylinder head. Your wrench fits over the hexagon, which is the spark plug itself.

Some spark plug sockets have a circular magnet to grip the plug's metal hex once it is threaded all the way out. Others have a rubber ring which grips the white ceramic part to do the same thing. But if a plug is unscrewed and gets loose down in that hole, you can fish it out with a magnet or some other simple tool.

[911pcars]

I believe a BMW speed sensor is pretty much equivalent at an un-Porsche price tag. Reference Dempsey's engine rebuilding book.

Sherwood

[Franki]

Originally Posted by Walt Fricke

You are overthinking this. Leave those round "nut" like pieces on the ends of the plugs. They are there to let the plug connectors grip. Your spark plug wrench will fit over these just fine.

You are looking at the hole which is machined through the cooling fins of the cylinder head. Your wrench fits over the hexagon, which is the spark plug itself.

Some spark plug sockets have a circular magnet to grip the plug's metal hex once it is threaded all the way out. Others have a rubber ring which grips the white ceramic part to do the same thing. But if a plug is unscrewed and gets loose down in that hole, you can fish it out with a magnet or some other simple tool.

Thank you Walt Fricke, I was actually trying to figure out should I remove the head cover (with the name Porsche on it hold down by 8 bolts) before I try removing the plugs.

[pete3799]

No....that's the valve cover. No need to remove it to change plugs.

[Walt Fricke]

Plus it is held on by six nuts with six washers on six studs. It is easy to remove, but only if you plan to adjust your valves, or inspect to see if a head stud has loosened or broken, or a rocker shaft has gotten loose. I would respectfully suggest you figure out how to remove the spark plugs before you consider the slightly more complicated procedure of checking the valve lash.

[Franki]

Yay what a feeling!!! My Porsche started right up after I put some in many hours and some new parts. The culprit was a bad speed sensor. I took the opportunity to also replace the reference sensor, a new distributor rotor and cap and a new coil. All parts are German made new old stock except for the coil. My next attempt will be spark plugs, fuel filter and valve gap adjustments.

THANK YOU so much again for all your help and the info found in this forum!!!

[hughc]

Originally Posted by Walt Fricke

I would respectfully suggest you figure out how to remove the spark plugs before you consider the slightly more complicated procedure of checking the valve lash.

Very good point. What's even more fun is trying to get the plugs back in. You'll no doubt say a few " Hail Marys" by the time all plugs have been replaced
🤣