Weird Distributor Blues

Discussion in '1994 - 1995 Specific Tech' started by Rob Ot, May 22, 2014.

  1. My car is fixed now so I am posting this to possibly help someone with the same issues. I always thought that when your PIP sensor (in the distributor) went bad that your car would not run at least till it cooled down again.

    Car is a 95 gt, 5 speed no mods to speak of. This car had a lot of little things wrong when I got it. Most annoying was this “stumble” that would happen intermittently. At first it was very hard to predict when it would happen. You would be driving along (no particular gear) and around 2 to 3000 rpm there would be a slight drop in rpm on the tach and the car would seem to slow down a little and then it would be ok. And yes there was the typical knocking under acceleration too.

    Last year the PIP sensor in the distributor failed by breaking apart so I replaced the distributor with a rebuilt one from car quest, not sure who made it, Cardone maybe? But while this did get the car back on the road the same occasional stumble was still there. There were no codes generated.

    After the distributor replacement almost every other likely part was either replaced or tested. Spark plugs, wires, coil, TFT ignition module, temperature sensors, fpr, thermostat, grounds, electrical connectors, fuel filter, pcv, lots more that I probably forgot. Nothing helped and as the weather warmed up in the springtime the problem got worse and would happen more often. I tried many different timing settings all the way back to TDC but the knock (and stumble) was always there when the engine warmed up.

    Another odd symptom was that sometimes during starting the engine would crank and not fire but if I released the key and tried a second time it would start immediately.

    And this was all with that “new” distributor.

    So at this point the symptoms were:

    Stumble when engine/underhood temperatures were warm/hot
    Pre-ignition knocking when warmed up.
    Starting trouble
    Tach needle dipping during the stumble

    What really made me try another distributor was how the tach acted, it would dip a little and then be ok when this stumble occurred. If the PIP was messing up when it got warm this would make sense. But I had always thought that when the PIP sensors fail from heat that the car would stop and not run again till things really cooled off.

    I had heard good things about the Rich Porter distributors, they are supposed to be “new” and were not expensive so I tried one. About $90 at O’Reilly’s.

    All is well now, stumble and knock is gone, I can time it to 8 BTDC and there is no knocking. I guess what people have said about some rebuilt distributors maybe just being cleaned up with the old PIP sensor is true. But I am really curious about how my PIP sensor failed. I had always thought that if they were on the way out that when they got hot the engine would just stop and you had to wait till it cooled down. This was not happening with mine, anyone else seen this sort of thing?
  2. A PIP failure isn't generally related to heat on the SNs. The TFI module on earlier Foxes attached to the distributor and were affected by heat. On the SNs they are on the inner fender under the air intake. This solved the heat issue. There are two parts to the PIP. One is the electrical sensor component and the other the physical vanes that break the sensor signal as the distributor rotates. Sometimes this assembly starts to come apart and the PIP signal become erratic. Generally as the PIP fails you will have a no spark then it will fire again. This will repeat until the time the sensor fails completely and at that point the engine will not fire at all. Quite often the there is no code thrown for the failure.
  3. yes that is what I had thought, that is why it took be months to figure out that it was the PIP/distributor that was bad. Even with the TFI over on the fender I did swap that out, did no good.

    The PIP in my old "Bad" distributor and the trigger wheel were in good visible condition. It would apparently perform perfectly when the distributor was cold but when it was hot it would start to mess up.

    I just thought that PIP failure would involve it not working at all when it was hot. Mine I guess would just drop a pulse every now and then making the computer go slightly nuts.