Dead 1985 911 Carrera Elec. problems help!!!

[mackskibum]

Hi gang- Well here it is- murphy's law- finally pick up my freshly purchased 911 3.2, and I get about 50 miles and all hell breaks loose in the electrical system. Symptoms are as follows:

Car started and ran normally for about 40 mi. At that point it started intermittant I'll call it "stumbling". The further we went, the worse it got. If you kick in the clutch the engine would rev smoothly, and the would be smooth under load for a short distance. This continued at greater frequency until the car quit- had a loud pop, a little smoke from the dash vents, buzzers and warnings galore- seat belt warning, etc.

Coasted into a gas station, and the battery had boiled over, and was very hot (Voltage reg??) Now, the car cranks over, but will not start. Had to tow home, now sitting in my driveway.

I don't know where to begin the diagnosis with so much happening at once. Please help!!!

Thanks in advance!!!

[Wil Ferch]

First quick thought...hot battery.....boiled over?.....

Bad votage regulator..... I have a Tech article in the Pelican Tech Section on a self R&R.....posted in this forum too as a link....FWIW

- Wil

[ChrisBennet]

While you at it, pull the battery and rinse and wipe the area where the battery acid spilled with some baking soda and water. That battery is a killer. If you decide to replace it, there is a smaller one that will fit. Type 41?
-Chris

[wholberg]

A boiled battery has to be the voltage regulator. The stumbling sounds like the car was running too rich and the plugs were gradually fouling, maybe due to the fuel injection system getting more than 12V? The pop was a backfire, maybe? Unburned fuel in the exhaust igniting. I would start as such:

1. Pull the alternator and have it tested to see if it is working correctly. Replace if necessary.

2. Replace the voltage regulator at the very least.

3. Check all the fuses and make sure none of them are slightly melted. Replace any that look the least bit damaged.

4. Definitely pull everything out of the boot and wash it down with saturated sodium bicarbonate (baking soda) solution. Throw the carpet in the wash. To make saturated solution, buy a big box of baking soda and throw it in a bucket of water. Let the bucket sit for about an hour, while stirring it well every 5 - 10 minutes.

5. Carefully check the wiring harness where it is convenient looking for melted or burned insulation. If you find evidence of damage, replace the damaged wire, and consider replacing that section of the wiring harness.

6. Look at the insulation on the battery cables. If the insulation looks like it was subjected to high heat, replace the cable(s).

If you do all this and it still does not run, take it to a mechanic.

Best of Luck!!

[wholberg]

I forgot to add to pull the plugs and check them. If they are fouled, clean or replace.

[mackskibum]

Thanks gang. I was already onto the voltage regulator issue.

Wholberg, thanks for the reply. I haven't taken a vehicle to a mechanic in 15 yrs. so I'll have to figure this one out. Pop was definitely electrical, and was accompanied by smoke from the dash AC vents for about 5 seconds. The engine immediately died. I guess I will have to trace every circuit to see which is dead.

I will definitely baking soda the battery area- I have a '66 under restoration and am familiar with the damage from the acid.

I believe I am missing fuel or spark, both controlled by the DME. I guess that's where I have to start.

Any ideas where the smoke might have come from that came from the AC vents? AC was not on, nor was the fan.

Great ideas gang- thanks for the help.

[wholberg]

Good Luck.

The pop might have been the battery boiling. I have heard a similar description from people who had a battery "explode", which just tended to be the noise made by the cell covers when they were pushed out of the battery case by steam, or when the case split from vapor pressure.

Please post what you find, as we will all be interested.

W

[mackskibum]

OK I dug into this a bit. I started by checking the fuses, etc. I have power everywhere it is supposed to be at the fues block. If I am reading the wiring diagram correctly, I should have power at the DME relay on pin 30 all the time (I do). It also appears that I should have power on pin 86 with the ignition on. I have 12V at the connector at the fuse panel, but not at pin 86. Is this correct? If so, what route does the Black/red wire take to get to the DME relay?

Thanks again!!!

[wholberg]

Mack,

Any luck yet?

[mackskibum]

Thanks for the interest Wholberg!

Sor far: found bad voltage regulator, have replaced. Through lots of troubleshooting found that the car wouldn't start because of a burned up DME relay (the fule pump control side) and a burned up Anti theft module. I jumped around the anti theft, and jumpered the fule pump at the fuse panel, and I can get the car to run.

With the replaced regulator, the alternator is charging normally again. Also replaced the battery.

My concerns are this- Failed parts so far:

Voltage regulator
DME relay
Turn signal relay
Alarm module
clock

Non working parts awaiting diagnosis:

Speedo
Tach
Horn

Parts I'm concerned about:

DME brain
All related sensors.

I have no information how to troubleshoot these items- the pertinent pages from the manual are missing from Haynes and Alldata for the instrument cluster.

Thats the update- any suggestions?

[wholberg]

Sorry, I don't have any suggestions. With any luck, you will charge up the battery and it will run like brand new.

Keep us posted.

[jyl]

You say you can get the car to run. Does it run fine, or badly?

lorenfb, who posts here sometimes, seems to know about the DMEs - I think he repairs or sources them for a living, something like that. Here is a link to the troubleshooting flowchart on his website. http://www.systemsc.com/tshoot.htm

[mackskibum]

JYL. thanks for the reply. The car runs badly. I checked resistance across the coil, airflow sensor, cyl temp sensor, crank sensor- all within spec. I do not hae an oscilloscope to check the actual operation, although I am going to try to get my hands on one today. With all the other failed electronic devices, I am not sure how to dtermine if the tach and speedo are shot- I don't have a pinout, and the DME if it is functioning properly.

[mackskibum]

Update on the mess:

Electrical woes also took out:

Speedo
Tach

Also found 2 fouled plugs- part of the running issue, and one that was almost fouled- changed those- runs much better.

Jury still out on sensors and DME.

New relay comes tomorrow.