Carrera 3.2 (Old reliable) Left me Stranded!

MOMO3.2 · 04:58 PM

I was driving home from work last Thursday. I stopped at a light and my 1987 Carrera changed from a steady idle to an anemic deiseling for maybe 4-7 seconds as I pumped the gas pedal in an attempt to help it regain composure. No luck. She left me stranded!

The motor cranked over fine, but never even gave a hint of wanting to start again. This resulted in the humiliating flatbed tow home (fortunately only 1 neighbor witnessed my shame...).

Anyway, I immediately ordered a new DME relay from Wayne. It came today and I hastilly installed it, but no luck this time. I checked the fuel pump by jumping the fuse box and the pump ran fine. I also smell gas after cranking, so I am pretty sure there is fuel.

I pulled a spark plug and there is no spark (Does one have to have the spark end of the plug near to or touching bare metal to check for spark? I held it next to the motor mount and could not see a spark in dark conditions).

Finally, perhaps someone can help diagnose the problem more expeditiously by factoring in the way the engine died?

Thank you in advance for your help.

Sincerely,

Mike

TroyGT · TroyGT's Garage

Take off the #1 plug wire (front left engine compartment).. stick a spare plug in the wire and then touch the plug to your ground point on the intake runner while a friend cranks. Should see some spark there. If not, pull off the distributor cap and then pull off the rotor. Pulls straight up and will only go back on in one position. Check for excessive wear/damage, etc. Clean if necessary. Check the contacts inside the distributor cap... clean if necessary. Look for cracks or other damage. Replace rotor, replace distributor cap. Try another spark test. Report back your results.

Do a search on 'stranded 911' I've practically written a book. My 86 died on me right before xmas. Tons of info in this thread.

-Troy

MOMO3.2 · 01-29-2007, 05:26 PM

Thanks Troy.

jorian · 01-29-2007, 05:27 PM

I had this exact issue. Swaped out the spare DME with no luck. Car would diesel a bit and quit. The starter would crank to no effect. I finally diagnosed faulty plug wires. The # 2 was grounding itself out against the heat shroud. As I pulled the other wires it was obvious they were OEM originals and all had issues. Installed new cap, rotor and wires and it runs as it should.

ZOA NOM · ZOA NOM's Garage

+1 on the wires/dizzy/coil area.

Early_S_Man · 01-29-2007, 08:46 PM

http://www.pelicanparts.com/911/technical_specs/911_DME_troubleshoot.htm

mambodave · 01-30-2007, 08:29 AM

dumb question.. but is your fuel gauge working? Sure you have gas in it?

88911coupe · 01-30-2007, 08:56 AM

Check the easy stuff first but it sounds like you may have the same thing I did which was a broken solder in the DME unit that would occasionally cause the car to stop running. However in my case it was pretty sudden, it did not run rough and then die so it may not be the same problem.
Good Luck

Jim Garfield · 01-30-2007, 09:51 AM

I recently had the same thing happen to me. I found that the speed and reference sensor wires had badly deteriorated insulation and when I touched it big pieces fell off leaving the metal sheathing exposed. I changed these out thinking that I had found the problem, only to find that when the car ran for 5 minutes it happened again. Turns out it was the CHT sensor that had failed. Mine was the old one wire and I replaced it with the updated two wire version.

Thanks to Chris Bennet who helped to narrow my search.

An easy way to find out if it's the CHT sensor is to make a loop with a paper clip and put both ends into the plug (it's the top one with the white wire) when the car is warm but not starting. If it starts up and runs, it's a faulty CHT sensor. All three of these wires are mounted in a bracket under the heater blower.

88911coupe · 01-30-2007, 10:52 AM

Jim,
Just out of curiousity would that work to test is a CHT sensor is causing a poor running condition? I've got a new one from our host but I'd like to do some sort of test to find out for sure if the one in there now is actually faulty. How should a warmed up 3.2 run if the CHT sensor is bypassed as you instruct?

MOMO3.2 · 01-30-2007, 11:47 AM

mambodave: Thank you. That was the first thing I checked. It has plenty of petrol.

Jim: Thank you. I will run the paper clip test if the new plugs, rotor, and cap don't fix things.

A sincere thank you to everyone that has given me advice. I hope I won't need too much more...

I will post when I have problem solved.

Mike

JTL · JTL's Garage

I would check the flywheel sensors if there is no spark.

jt
-84 targa

moochie · 01-30-2007, 04:28 PM

Bad Coil?

Zeke · 01-30-2007, 05:10 PM

Please report the find when you get there. From my reading, the head temp sensor is a likely culprit. Now, we have to carry a paper clip and know how to use it. Oh, not the way of the 70's.

Lorenfb · 07:02 PM

If it's really a no-spark case, then it's a waste of time to check the CHT.
Verify the no-start by pulling the coil wire to dirtributor. Then check the
key inputs.

Check here for more info:

www.systemsc.com/diagnostic.htm

The diagnostic procedure should take about 15 minutes:

1. check for powers/grounds
2. 2 pickup sensors
3. coil pulse

Ned nyna 11 · 01-30-2007, 06:46 PM

The tech article on Carrera starting problems is the place to start.

Jim Garfield · 04:15 AM

Quote:

Originally posted by 88911coupe
Jim,
Just out of curiousity would that work to test is a CHT sensor is causing a poor running condition? I've got a new one from our host but I'd like to do some sort of test to find out for sure if the one in there now is actually faulty. How should a warmed up 3.2 run if the CHT sensor is bypassed as you instruct?

Buck,
On my car the problem manifested itself when the car warmed up. It would diesel, backfire, stall, and not restart until it sat for a while. When the car was in this condition (warm and not starting) I jumped the CHT sensor connector (on the harness side of the bracket) with a paper clip and it started right up and ran. I now carry a paper clip in my tool kit so that I can limp home if this ever happens again. Chris Bennet also mentions a resistor that you can pick up at Radio Shack that would work better if you were stranded far from home until you could change the sensor. Do a search with his name and you'll probably find the thread.

Lorenfb · 01-31-2007, 05:02 AM

Using the same logic (as some are suggesting) that the CHT could be the source
of a no spark condition then:

1. check the fuel level
2. check the alternator belt tension
3. check the throttle switches
4. replace the air filter
5. check the fuel pressure

Just to be on the safe side, one might also check the tire pressures, i.e. They all may
have different pressures. Someone posted this before when his car had a no spark
condition.

Jim Garfield · 01-31-2007, 05:24 AM

Some things never change eh Loren? If you noticed he said that he wasn't sure that he was checking for plug spark correctly. So I would say that it's not a given that that is the problem. And.... it's very easy to check the CHT wire.

In another post on this topic you held forth that the CHT sensor would not cause a no start condition, you were absolutely wrong about that so get off your high horse.

Lorenfb · 05:35 AM

"In another post on this topic you held forth that the CHT sensor would not cause a no start condition"

It will ALWAYS start but:

1. If CHT is open, it will eventually (fairly quickly) flood the engine.
2. If CHT is shorted (rarely happens) or the wrong value, it will cause a cold hard start.

No "coin flipping" nor "dart throwing", i.e. the shotgun approach, allowed when troubleshooting.
It's costly and ineffective!