An Electrical problem ?

[mbbnyc]

Ok, here is a problem that has been plaguing my 911 for over a year now. I have had it at some very qualified mechanics and they have not been able to figure it out.

It is a problem that comes and goes and of course I can't get it to happen in front of anyone who knows more about engines than me or even in front of a video camera for that matter. It can be a simple annoyance all the way to making the car undrivable. It seems to come and go at random. When I go to start the car I never know which car I will get. It is a Jekll & Hyde situation.

First off the equipment. 84' Carrera stock 3.2 motor. Re-built when I got it. I have put 20k on it so far.

Now the symptoms, The engine will lose power, the tach will start to come down then all of a sudden it will "catch" and go back up to normal. There will be an audable "clicking" sound from behind the dash. Like around the oil temp guage area. This is all during idling

When driving it will lose power and then "catch" making the car jump like a "new to stick" driver is driving. It kind of violently jerks. Sometimes during these bad moments the car will stall and will not restart.

None of this happens at speeds above 40 MPH

I recently had the ignition switch replaced when we thought it was that, we also replaced the hazzad switch as well. It worked fine for 6 months then Blam ! It was back. There goes $600

When the car is having a good day, It runs perfectly. All speeds and is a joy to drive. I drove it today for an hour and it was fine, I ran it through a range of speeds and revs on the tach with no problems at all not even a blink. If I start it tomorrow I have no idea what I will get.

I don't know if it is Electrical that seems to make the most sense. It occured to me that since it comes and goes and since I hear a click from behind the dash could it be two wires from one of the gauges touching each other ?

Please any suggestions will help, I love this car and really want to drive her more. I am so sick of having this problem.

[RFM]

Usually on 3.2 Carrera, the DME relay near the control box under the seat will go bad, in second place check the crankshaft sensor *** well.

[mbbnyc]

Thanks, I know it's not the DME relay. I forgot to mention I have replaced that. I will check the crankshaft sensor. But if it were that would it still make that "click" sound every time it happens from behind the dash ?

[mbbnyc]

I have just looked at the all of the connections and they are all clean and fitted tight. No corrosion at all. I am Not sure it is that, How could I test that further ? Thanks by the way for the help

[wvicary]

The engine speed sensors are a good place to start but can be difficult to reproduce the faults, if they are original just replace them as a matter of course. I would first change out the ignition coil and ignition control module. The coil can internally and intermittently short and overload the control module causing the primary ignition signal to drop out.

[RFM]

Make sure that the fuse terminals are clean and free of corrosion, in the front and the rear, check/swap out the fuel pump relay. I assume there are no traces of a kill switch/power interrupter switch, which was installed and removed poorly in the past. The best thing is to check (measurements) what's happen, the moment the problem occurs.

[Skip]

Not sure whether or not the issue could be related to the electrical portion of the ignition switch. You mentioned having changed the ignition switch (was that the hardware / key side or the electrical rear portion? I have recently replaced the key side, and realized that the electrical portion was loose as well, which would not allow the Acc posn to be accessed at all times. Once replaced, the problem disappeared - perhaps another option ($130 roughly I think).

Skip

[snbush67]

A common fault for electrical problems is corroded grond straps and connections. This is an easy and cheap fix, just remove the old ground strap , clean the connection areas, and put on the new straps.

Shane