1987 911 Cab won't start

[david3299]

My 1987 911 3.2 Cab won't start.
I had the car sitting without starting for two months. I was able to start the car with a portable charger. The car idle for two minutes and then died. I attempted to jumped the car again using the portable charger. The engine turns however it won't start. I found the following:
1) There is gas fuel going pass the filter to the engine.
2) The voltage across the ignition coil was 3.39 VDC (when trying to jump the car with the portable charger)
I'm assuming the alternator is defective?

Please advised.

Thanks

[FrankM_]

What is your voltage across the battery terminals before starting ? It should be around 12.5V.
When starting it should drop but no lower than 10V ?

Your alternator isn’t really doing much during starting, the energy should come from the battery. I would put the BAT on a charger for at least 24h and try again (charger disconnected, measuring as indicated above). More likely the battery is the problem.
With 3V across the coil you are not going to do much...

[david3299]

The voltage across the battery is 12.6 vdc and when an attempt to start it drop to 11.2 vdc. I had the battery load tested at the local auto store and found no problem.

[david3299]

Does anyone have a copy of the 1987 911 cab electrical schematic?

Thanks

[jlex]

Try your spare DME relay.... you have one, don't you?

[steve911T]

Check all the connections in engine compartment. Make sure they are all seated correctly. Check all of the ground especially the one in the engine compartment. As suggested,check the DME. Good luck !

[david3299]

Can someone send me the location of the RPM and Top Dead sensor location for 87 911 3.2L?

Thanks

[jlex]

Take off left rear wheel. Follow 3 lines leading from the engine tin thru a rubber grommet. Two of those lines lead to the speed and reference sensors which are mounted on a bracket at the flywheel. The third line leads to the head temperature sensor. Connections for those three lines are seen at a vertical "tree" located inside the engine bay on the left side. Check the DME relay first, though.... common no start problem with 3.2's.

[Lyle O]

Originally Posted by jlex

Try your spare DME relay.... you have one, don't you?

This is great advice; check this FIRST. The other items to check (speed and reference sensors, etc.) are much less likely to have crapped out or become disconnected spontaneously. DME relay failure is way more common.

[DNickel]

+1 on the spare DME relay. It's under the drivers seat and bolted down at the tab so not exactly easy to get at. Give it a tap and try again. If you are handy with a soldering iron remove it and resolder the connections inside.
Something I always carry for my 968 and 911 is a DME bypass jumper. This will bypass the relay and permanently run your pump for testing. If you have no spare this will prove out the dead relay.

[cabmandone]

Originally Posted by david3299

My 1987 911 3.2 Cab won't start.
I had the car sitting without starting for two months. I was able to start the car with a portable charger. The car idle for two minutes and then died. I attempted to jumped the car again using the portable charger. The engine turns however it won't start. I found the following:
1) There is gas fuel going pass the filter to the engine.
2) The voltage across the ignition coil was 3.39 VDC (when trying to jump the car with the portable charger)
I'm assuming the alternator is defective?

Please advised.

Thanks

If you have fuel, the DME relay is working. When you hit it with the booster it started but then died?
Battery/Charging System.

Get a spare spark plug and verify that you have spark while cranking. If no spark then you need to look at speed and reference sensors.
Make sure you have the battery fully charged before you start cranking to check for spark.

[david3299]

I performed the wire configuration as DNickel (for my 911) had suggested. I was able to hear the gas pump running, I attempted to start the car and no luck. Car still won't start. It seem as if the either or both the speed or reference sensors is/ are defective.

[cabmandone]

Originally Posted by david3299

I performed the wire configuration as DNickel (for my 911) had suggested. I was able to hear the gas pump running, I attempted to start the car and no luck. Car still won't start. It seem as if the either or both the speed or reference sensors is/ are defective.

You said you had fuel in your first post... You didn't need to jumper the DME relay to verify the pump was working if you had fuel. Check spark.

Do a search on this big beautiful forum and you'll find how to test your speed and reference sensors.

[david3299]

Today I replaced the DME relay. Measured the DME unit at the following pins: 8 to 27 showed 983 ohms @ 2.01 volts AC/ pin 25 to 26 read 1023 ohms @C .3 volt AC. However, I still can't start the car. HELP

[jlex]

Seen this:
https://forums.pelicanparts.com/porsche-911-technical-forum/1057464-resolved-87-carrera-dies-no-start.html
Did you ever check for a good spark?

[david3299]

I just pick up a spare spark plug and will check for spark tomorrow. I will keep you guys posted.

[david3299]

Does anyone know what the impedance /resistance of a good TD or RPM sensors?
I just ran across this thread.
no-spark problem finally resolved
As stated above, my current sensors as followed:
pins: 8 to 27 showed 983 ohms @ 2.01 volts AC/ pin 25 to 26 read 1023 ohms @C .3 volt AC.

[cabmandone]

Found this by googling "how to bench test Porsche 911 speed and reference sensors" First results were from Pelican. First suggestion was a thread asking about Reference Sensor Testing.

"Unplug both black plugs and measure around 1000 ohms resistance between the bottom two of the 3 terminals of each black plug, on the engine side of course."

He's referring to the plugs on the left side of the engine bay the top and middle I think are speed and reference. The bottom plug should be your cylinder head temp sensor IIRC

Here's the thread
Reference Sensor Testing

[david3299]

The battery is new with 10.5 vdc. I tried the used a portable charger and car wouldn't start. Here is the list of things that was checked on my 911.
1) DME pin 1,18,35 had 10.5vdc
2) DME pin 5,16,17 to GND @ .2 ohms
3) Replaced Speed and reference sensors
4) Coil had 10.5 vdc to GND
5) Install new DME relay yesterday
6)When tried to start with the new DME relay I don't hear the fuel pump. However, as soon as the battery is connected with DME relay pin 30,87, 87b jumped the fuel pump become active.
I performed a spark check and noticed the spark was very weak. Please review the picture.
Is it safe to assume the car battery need to be fully charge to @ 12 volt?

[cabmandone]

Unless you have a custom chip, you fuel pump will not run if the engine isn't cranking.
Charge your battery. At 10.5 volts it's low and once a load is placed on it by the starter it's going to go even lower.