1987 911 Turbo " shuts down"

transadapt · 08-07-2011, 09:32 AM

Hi.. Any help offered will be much appreciated...

this is the first time i have done this i hope all in posting works out..

I plan to take car to a qualified mechanic in the Seattle area... Just was wondering what might be the problem... The car has just over 55k miles... always had recommended services.. John Walker did last major service (15 K service) at 45k... So please rule out all basic problems (plugs, rotor, wires)...

the problem:

I was driving car on Saturday (running strong / solid idle "no missing") I was down town on 1st Ave idling at red light car shut down (no sputtering) just like a light switch being turned off... i checked engine compartment area for anything obvious.. All looked perfect... got back in started perfectly (1st try)... idled perfect... drove back to West Seattle ran strong... after about 7 miles of driving... i was sitting at 4way stop and it shut down again... but this time will an added "very loud" back fire a fraction of a second after engine shut down.... the only thing i did different this day was that i filled the gas tank 3 hours earlier (that morning)...

ischmitz · ischmitz's Garage

When the car shuts don don't even turn the ignition off. Instead, open the engine compartment and listen to the CDI box. It should make a whining noise. Try and keep the pitch and noise in mind.

Then power-cycle the ignition and don't crank. Listen again to the CDI box. If the whine is a distinctive lower note and louder than before you have identified a bad CDI box as the issue.

The Bosch box can latch up under temperature and that is what makes the engine momentarily shut down. Once you let the box cool down it'll work agian until it gets hot. Then the cycle repeats.

Ingo

spuggy · 08-07-2011, 03:06 PM

Quote:

Originally Posted by ischmitz

The Bosch box can latch up under temperature

And a 930 engine bay can get pretty darned hot once ambient temps rise. Oil temps on my 930 get hotter idling in traffic than they do under full boost on the track...

equality72521 · 08-07-2011, 05:09 PM

They yellow fuel pump relay does exactly that when it fails.

transadapt · 08-13-2011, 01:33 PM

thanks for the feed back.. i very much appreciate it.. I plan to drive the car around the neighborhood (not far from home) tomorrow and see if it shuts down again.. then i will listen to CDI box (after market unit Perma Tune)... I have idled car two different times in my driveway for 15 to 20 minutes (perfect idle) as always... perfect 900 to 1000 rpm... one strange thing i did notice the tachometer would bounce between 1000 and 1500 even though engine idle (sound) was consistent to normal stable idle... then if i turned on car head lights the tachometer would jump + 500 then when turned off lights -500 very strange.. thanks again for feed back you guys are great...

RSTarga · 08-13-2011, 02:00 PM

bad ground or bad alternator make the needle bouncing effect.

transadapt · 08-13-2011, 02:02 PM

I will check/replace the yellow fuel pump relay immediately... thank you..

transadapt · 08-13-2011, 02:59 PM

thanks for all the input.. if the time ever comes that any of you ever find yourself in the Seattle Area.. please contact me.. I will buy you a beer..

spuggy · 08-13-2011, 03:12 PM

Quote:

Originally Posted by RSTarga

bad ground or bad alternator make the needle bouncing effect.

Yes, and also check the voltage regulator output - anything over 14V at the battery terminals is too high.

If your battery isn't vented outside the car and your voltage is too high - look for where the sulphuric acid mist settled and neutralise it with baking soda...

dshepp806 · dshepp806's Garage

For sure, alt/VR thing going on...or one crappy ground. Let's get some voltages?

BEST!

Doyle

transadapt · 08-13-2011, 06:16 PM

engine off battery voltage 12.32v engine cold running 14.19v after engine warmed up 14.09 .. I will go tracking down "crappy ground" connections in the engine compartment.. I am assuming it must be there.. no one has ever cut or spliced into wires up in nose of car or under dash... is there any chance this bad ground and tachometer problem could be causing the engine shut down? it has only happen twice to the car same day within 10 miles / 20 minutes of traffic driving... both times idling at different intersections.. thanks...

MT930 · 08-13-2011, 08:02 PM

Quote:

Originally Posted by equality72521

They yellow fuel pump relay does exactly that when it fails.

Yep ! I would check that first.

I had a sticky over boost switch that would do the same thing. Stop fuel.

toms930 · toms930's Garage

Ingo - I have a similar "lock-up" condition within my 6 pin CDI as you've described in this and another thread.

What electrical components internal to the CDI have you seen that are suspect in producing this condition?

Thanks!

Quote:

Originally Posted by ischmitz

The Bosch CDI unit can go bad where it "locks up" and stops producing sparks under temperature stress. Once you turn the ignition to OFF it resets the box and it will work again for some period of time before the cycle repeats. The effect is strongly temperature-dependent.

To test whether lock-up is your problem do this: Once the car shuts down DO NOT turn off the igntion. Open the engine lid and listen to the whine of the CDI box and memorize its tone. Then turn the ignition to OFF and back to ON without starting the engine. If the whine now sounds different (lower pitch and louder) you have identified a lock-up condition.

If the whine sounds about the same after the power-cycling it confirms that lock-up is not your source of the problem.

Cheers,
Ingo

88911coupe · 02-12-2012, 04:19 PM

Buddy of mine had the exact same symptoms on his '88 930, turned out to be related to an alarm on the car. After carefully removing the alarm by a qualified mechanic no problems.

mikemdd · 02-13-2012, 09:18 AM

One of the fuel pumps. I had this exact thing happen to my 930. I was driving along and it just shut down. I think there is a minimal pressure required and when the pump get's weak, it shuts down. No sputter, no warning. I did get it to start, then it would shut off again. Replaced one of the fuel pumps and all was well.

toms930 · toms930's Garage

Thanks for the input!

Alarm system, Fuel pump and the Yellow Overboost relay are on the check list.

- Fuel pumps checked ok' after I jumpered 87 & 87A on the overboost relay socket.
- I have pwr (12.7 V) to pin 15 on the CDI.
- The CDI box whines with a faint very high pitch.
- Checked the primary and secondary coil resistance (within spec @0.7 Ohms / 680 Ohms )

Still no spark as checked with a spark plug grounded to the engine case.

- Pulled the CDI box and checked the capacitance value of Capacitor C8 that feeds the primary winding on the coil. C8 should be 1.4 uF, when checked found to be 0.15 nF. This may explain why the CDI box got very hot.

I'll order the recommended replacement film capacitor from Digi-Key. I'll replace the Cap and take it from there.

Thanks for the help!

Tom

john walker's workshop · 02-13-2012, 04:19 PM

the yellow relays can have cracked solder joints as well as the relay under the left seat, which will shut off the pumps. loose connections at either of the two red relays up front or at the fuel pump fuse. black permatunes do not whine. they do fail, but usually don't fix themselves. the delayed ignition relay behind the defroster relay on the rear panel transfers 12V to the ugnition unit and they fail. check for 12V at the ignition unit plug at the red wire, key on.

toms930 · toms930's Garage

My 930 is running again!

Replacement of the 1.4 uF Capacitor (C8) in the Bosch CDI box did the trick.

Thanks for the help!

Tom