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1986 Corona with EFI mysterious electrical problems

Posted by john999 (My Page) on
Wed, Jan 16, 13 at 22:23

First the battery kept going flat, and so I had that replaced.

Immediately the "generator" light went on and I kept using it until it ran down the (new) battery shortly afterwards.

I have replaced the alternator and now it runs out of puff, like its going to stall (automatic) when I press down the accelerator. It seems like it it won't advance the timing properly. I suspect the transistor block for the electronic ignition.

I've buried a couple of cars that did this ; they would keep burning out electrical components (like battery, alternator, iginition coil, leads, spark plugs, transistor blocks, distributor reluctor, dash dials, fuel sender etc).

I suspect its resistance building in the wiring harness and dropping voltage, driving up the voltage and burning out components. The cars have always been 25+ years old.

I was wondering if anyone else has experienced this and knows what it is and how to fix it ?


Follow-Up Postings:

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RE: 1986 Corona with EFI mysterious electrical problems

You do have an electrical problem. You will need a wiring diagram for tracing circuits and to aid diagnostics. If you don't have this, you are probing in the dark. Also, you need some basic measuring tools like a multimeter, etc.

your first symptom pointed to a failed charging system. Get that sorted out and then see if there are other misbehavors.

You replaced the alternator. Was it the right one? The output control of alternators come in two flavors: On many modern systems, the voltage regualtor is built into the alternator, but on old systems, the voltage control may be external and mounted at a locattion away from the alternator.

The voltage control adjusts the rotor current and controls the output. A sense wire may run from the battery terminal or a terminal on the starter where the heavy battery cable is. The alternator's output tries to maintain a given voltage seen by the sense wire. The alternator voltage can go high if the power circuit between the alternator and battery is cruddy - has high resistance. One cause is poor conduction between the connectors of the battery cable and the cable wire. A battery connector can appear physically secure on the cable and yet have a poor connection. On many battery cables, the battery conector is made of lead or lead alloy and corrosion between the lead and copper wire may produce a resitive connection. The cure: replace the cable.

This is not the only place that can cause charging problems or high voltage. I mentioned this one as an example, and because the battery cable connectors are often overlooked.


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RE: 1986 Corona with EFI mysterious electrical problems

Sorry about the late reply. After posting this I drove the car and it was fine, must have been just a flattish battery. Then I forgot about it.

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Anyway I was thinking more in general terms, ie what is it that causes a car to "die" with seeming electrical problems. People restore old cars and they replace the entire wiring harness but is there anything specifically that dies ?


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RE: 1986 Corona with EFI mysterious electrical problems

Yes, old cars can and do 'just die' for many reasons. Two major trouble areas are fuel feed and ignition. The next trouble maker is idle control. Engine valves and compression also can contribute. Vacuum sensors and controls create their share of problems. Exhaust gas recirculator valves lead a harsh life and do fail.

Other fanthom (random) causes are hair pullers. I hate chasing these because they are so hard to find. For example: I once owned a 1949 Plymouth with a straight 6 engine. It ran ok most of the time until it developed a bad habit of quitting without a warning. Sometimes, it would restart and get me home without another incident. However, it could not be trusted for any sizeable distance from home. I looked the distributor over many times and found nothing wrong. The clue came when I realized that the ignition quit when hitting a jarring bump in the road.

This time, I removed the distributor to get a good look at it and found the problem. It was a chaffed wire under the vacuum advance plate. This wire fed the points. It was bent such that it occasionally rubbed against the plate until a bare conductor was showing through. When this wire touched the plate, it shorted the points and stopped the ignition. After the engine stopped, the vacuum advance plate rotated back to its start position and often moved the wire away - the engine would restart.

The solution was easy: replace the wire (with one having more than 7 strands) and positioning it so that it did not rub on anything while allowing for full rotation of the point plate plate. By the time I found and fixed the problem, I was getting another car.

Why more than 7 strands? Copper is notorious for fatigue breakage. Flex a solid copper wire often enough, even while keeping it within its elastic range, and it will crack and break. Copper has poor fatige resistance. Replacing a single strand wire with a 19 strand wire having the same cross section area makes the lead far more flexible and greatly reduces bending stress.


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