9two8

During a journey today, what I can only describe as a complete shutdown for about 2 seconds happened, during a gear change 3rd to 2nd then accelerate bam ! ,2 seconds, then all was fine., Felt like someone put the brakes on . I think also all instruments went out, but can,t be 100% sure. After that happened the car drove great again with no more issues? Previously when starting out and with the engine relatively cold I noticed the red warning light between the rev counter and speedo flickered very slightly, the oblong one with exclamation mark on it., first time for that, then after a few more seconds it went out and never came back on again.
Have to ad that the car was running first class during these events, however when it momentarily shut down I was already heading for the grass verge thinking this is it, breakdown time !

This time last year the throttle body and plenum were all refurbished along with spark plugs, dist cap, leads, "beru", vac hoses etc, and since that the car runs real good, even the air-con is almost blowing ice cubes, guess there,s always something..., any help/advice really appreciated

WallyP

Lots of possible problems, but a loss of power to the ignition circuit is one thing to consider. Worn switch, loose connection, broken wire...

An intermittent problem can be really frustrating to find and fix.

MainePorsche

Yep. This would be number 1 on my differential.
Also you may want to check veracity of your power harness connections at the starter, alternator, and at hot post by 13 pin connector. I had a similar complete electrical cut off after I fabricated new power harness for split seconds - I had to redo a connection and never had an issue since.

Fr8trplt

When I first purchased my 85 928S, I had an intermittent shutdown issue as well. At first it would just quit, loss all electrics and engine shutdown. Ran perfect right until it quit. Happenened under all conditions, idle, accel, study highway. After replacing numerous, ignition, electrical parts, etc $$$, it turned out to be the electrical switch behind the ignition switch. If that has not been replaced and/or you or the previous owners hung large key rings from the ignition key, I'd replace it. Not a huge job, if I remember correctly. Good luck.

9two8

The ignition switch did occur to me vaguely, but hoped it was not that, Iv,e owned the car 24 years and it has,nt been replaced, and getting on in years I,m not so flexible when it comes down to lying on my back with head under dash.
Thank you for the advice everyone

murray928

Same thing was happening to me, occasionally at first, then intermittently on a daily basis. A new ignition switch cured the problem. Porsche part no. 964 613 012 00.

GregBBRD

Most common, by far, is a loose connection on the supplemental red wires at the battery. I'd check there, first.

Also check the connections for the big red wires at the top of the relay board.

Ignition switches are very robust and we replace very few of these. A quick test is to gently wiggle the key around in the "run position" with the vehicle running.....looking for a "dead spot" on the contacts of the switch.

gb

gb

9two8

.., thanks for the part number John, hope I don,t need it ?

Greg .., when you say supplemental red wires, on my car there,s only the red positive lead on the + battery post ? or am I missing something ?
Thank,s

fraggle

replacing the ignition switch is actually a pretty easy job once you pull the pod off. I can probably do one in a little more than an hour.

9two8

Guess I,ll start with easy stuff first, about 12 years ago I fitted a "kill switch" on the front of the tool tray which had the desired effect, ie no more flat battery.,, maybe it,s time for a check on those connection points, battery leads as well.

Jetdriver69

My 82 with an L Jet had the same symptoms at exactly 4000 rpms.

Turned out the AFM had an excessively worn resistance track and the wiper arm lost contact with the resistance material in this rpm range.

I bent the wiper arm per the AFM refurb youtube video and haven't had the issue since.

But I am seriously considering getting a rebuilt AFM as this fix is only temporary and the AFM is 33 years old.

They can had for about $300 and then you get the core charge returned.

9two8

Took apart my "kill switch" and cleaned the connections,and re-made them just to be sure, also removed battery leads cleaned them and split the sheath on the negative lead just to check for corrosion.., put it all back together , started the car and tried "wiggling" the ignition key while the car was running just to see if I could induce a shut down, no amount of wiggling would stop the engine ?

Just in case I ordered part No 964 613 012 00 ignition switch, Is there a how to on here re fitting a new switch, is it possible to replace it without taking the pod apart ? love to think so, as I have had it out twice in my ownership to replace odometer gear wheel and a break in the circuit board...., and did,nt like it much!

Fogey1

Add "fatter than Falstaff" and you've described me. If I have a job under the dash I'm going to remove the seat for a flatter lie down and more wiggle room - on one of those closed-cell foot saver pads with my feet up in the rear seats. I have them already to use as kneelers. In- and particularly e-gress will be neither fetching nor dignified but I'm too old to care.

Someone on the forum, or list, long ago described using a board between a milk crate and the rocker panel as an external support to allow one to get one's head and shoulders into the car at floor level without being as supple as a swami. I can see it being of assistance prone, supine and even seated.

Have fun.

ww