Electrical Gremlins - small ones solved with one fix
03-08-2010, 10:53 PM
#1
Chronic Tool Dropper
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Electrical Gremlins - small ones solved with one fix
For a while I've been chasing a few gremlins. The dash computer would reset on start sometimes, on shutdown sometimes. Key to start would sometimes fail, but retry would cause a normal start. Door locks acted funny, where key in driver side would trigger lock solenoid to buzzing rather than locking, while pass side would not lock. Battery ran low enough to cause poor fuel pressure while driving that I had to stop the car. On ground lead removal and replace, then restart, the battery and FP were working fine. The ignition switch (close to 100k on the car...) seemed the obvious choice as the common element in some of these, so that was replaced a few weeks ago with no change to symptoms.
Evntually I just decided to get out the meter and start on primary wiring from the battery all the way to the CE panel. Battery disconnected, started with ohms for each section of the battery cable. Battery to starter OK. Starter to alternator 2 ohms. Starter to jump post has 2 ohms. Hmmm. This cable commons in a single connector at the alternator, one wire from starter and other to jump post, so this was a little wierd. Pulled the connection off the post on the alternator and cleaned it, reinstalled. Now 0 ohms, very strange since that connection is not in series with the circuit, but apparently flexing/restoring the cable was enough to 'cure' it, at least for a while. Cleaned and buffed all the connections at the jump post too for good measure. When done, almost zero ohms between jump post and battery positive. So far (fingers crossed behind back...) so good, and everything has worked as intended after several drives and starts/stops.
Lesson learned is that one problem often presents multiple symptoms, especially voltage drop issues from poor connections. The ohmmeter is a valuable tool, especially when equipped with a 20' long jumper with alligator clips on it. That 2 ohms of unexpected resistance caused voltage to drop, enough for the listed problems to show up, but once the car was running the alternator carried everything forward of the starter connection relatively fine. So location-location-location applies too. Doing the Wally List of electrical maintenance stuff is a Good Idea it turns out.
Evntually I just decided to get out the meter and start on primary wiring from the battery all the way to the CE panel. Battery disconnected, started with ohms for each section of the battery cable. Battery to starter OK. Starter to alternator 2 ohms. Starter to jump post has 2 ohms. Hmmm. This cable commons in a single connector at the alternator, one wire from starter and other to jump post, so this was a little wierd. Pulled the connection off the post on the alternator and cleaned it, reinstalled. Now 0 ohms, very strange since that connection is not in series with the circuit, but apparently flexing/restoring the cable was enough to 'cure' it, at least for a while. Cleaned and buffed all the connections at the jump post too for good measure. When done, almost zero ohms between jump post and battery positive. So far (fingers crossed behind back...) so good, and everything has worked as intended after several drives and starts/stops.
Lesson learned is that one problem often presents multiple symptoms, especially voltage drop issues from poor connections. The ohmmeter is a valuable tool, especially when equipped with a 20' long jumper with alligator clips on it. That 2 ohms of unexpected resistance caused voltage to drop, enough for the listed problems to show up, but once the car was running the alternator carried everything forward of the starter connection relatively fine. So location-location-location applies too. Doing the Wally List of electrical maintenance stuff is a Good Idea it turns out.
03-10-2010, 12:38 AM
#3
Rennlist Member
Good reminder to check the basics, Bob!
Malcolm, not much to it really, just the big connectors at the alt & starter, clean & treat with Stabilant(or your favorite stuff), same with the jump post. The plastic block that the jump post lives on may crack, couldn't hurt to have a spare on hand.
Malcolm, not much to it really, just the big connectors at the alt & starter, clean & treat with Stabilant(or your favorite stuff), same with the jump post. The plastic block that the jump post lives on may crack, couldn't hurt to have a spare on hand.
03-10-2010, 04:50 AM
#5
dr bob,
By the computer resetting on starting do you mean that the odometer "I " resets to zero or what happens?
I have a problem that I have lived with for 10 years in that every now and then the odometer resets to zero on start up and then resets every .2 0r .3 kilometres back to zero. If I change to odometer II it will do the same and if I change to the stopwatch it will not operate correctly. When I push the start button when the system is plyaing it can continuously reset or as now I cannot get it to operate. When odometre I, II and stopwatch (when partially working) sits in the background they work OK until brought up on the screen, then they all reset.
When the computer is playing up, I cannot reset the average fuel consumption to zero or reset the odometers to zero with the control lever.
I have changed the switch internals with the intensive washer switch, but the problem is evident the switch makes no difference. Some time when I really ensure that the pins in the plug are fully and tightly engaged the system will work, however the problem returns sometimes after a few months operation.
It maybe some resistance in the wiring from the battery as you describe and it maybe also be compounded when the battery is getting older and the resident voltage is down a little and on starting the voltage drops to around 10 volts. This maybe resetting the computer or confusing it.
When driving the alternator shows good voltage initially to 14.5 volts ( my car is fitted with the larger pulley , which IIRC was fitted to the 1990 models) and then settles back to around 13.5 volts when the voltage increases within the battery (back EMF).
Any thoughts, is it similar to your problem?
Thanks,
Tails 1990 928S4 Auto
By the computer resetting on starting do you mean that the odometer "I " resets to zero or what happens?
I have a problem that I have lived with for 10 years in that every now and then the odometer resets to zero on start up and then resets every .2 0r .3 kilometres back to zero. If I change to odometer II it will do the same and if I change to the stopwatch it will not operate correctly. When I push the start button when the system is plyaing it can continuously reset or as now I cannot get it to operate. When odometre I, II and stopwatch (when partially working) sits in the background they work OK until brought up on the screen, then they all reset.
When the computer is playing up, I cannot reset the average fuel consumption to zero or reset the odometers to zero with the control lever.
I have changed the switch internals with the intensive washer switch, but the problem is evident the switch makes no difference. Some time when I really ensure that the pins in the plug are fully and tightly engaged the system will work, however the problem returns sometimes after a few months operation.
It maybe some resistance in the wiring from the battery as you describe and it maybe also be compounded when the battery is getting older and the resident voltage is down a little and on starting the voltage drops to around 10 volts. This maybe resetting the computer or confusing it.
When driving the alternator shows good voltage initially to 14.5 volts ( my car is fitted with the larger pulley , which IIRC was fitted to the 1990 models) and then settles back to around 13.5 volts when the voltage increases within the battery (back EMF).
Any thoughts, is it similar to your problem?
Thanks,
Tails 1990 928S4 Auto
03-10-2010, 10:14 AM
#6
Rennlist Member
Bob, et al,
Earl Gillstrom and I have developed a habit of putting a drop of either "Corrosion Block" or "Corrosion X" on any connection we separate - before re-assembly. Earl's experience with either of these products on severely corroded marine connections has convinced us of their ability to maintain a no-resistance connection, and even to restore a good connection to something that is already corroded to the point of non-conductance.
Gary Knox
Earl Gillstrom and I have developed a habit of putting a drop of either "Corrosion Block" or "Corrosion X" on any connection we separate - before re-assembly. Earl's experience with either of these products on severely corroded marine connections has convinced us of their ability to maintain a no-resistance connection, and even to restore a good connection to something that is already corroded to the point of non-conductance.
Gary Knox
