1993 Buick Park Avenue Battery change then erratic behavior

Tiny
OSIDE JOHN
  • MEMBER
  • 1993 BUICK PARK AVENUE
  • 185,000 MILES
I changed the battery in my 1993 Buick Park Avenue. Now it behaves funny. It will start fine, then after a while it will exhibit the following behaviors:
the idle raises and become slightly irregular,
the fan comes on full force and will not turn off,
the anti-lock brake warning light comes on,
all of the gauges go nuts (volt meter shows 0 volts and the warning light comes on, the temperature gauge goes full hot and the warning light comes on, oil pressure gauge goes to zero, fuel gauge is unchanged but the low fuel light comes on)

After a while the car may start running smoothly again (low steady idle, all gauges showing normal.) Then it may start the erratic behavior again. If I turn off the car when it is running poorly there is a fifty-fifty chance it will start fine.

Since the volt meter showed a short I put a DVM on the battery to monitor it during this behavior. When the engine is running the battery shows a steady 13.5 V at all times (12.5 V when engine off) The DVM showed no AC component even when the car was running wacky.
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Wednesday, September 18th, 2013 AT 11:50 AM

4 Replies

Tiny
CARADIODOC
  • EXPERT
13.5 volts is too low. It must be between 13.75 and 14.75 volts. That little difference seems like nit-picking but it can be an indicator the generator has a bad diode. That will reduce its maximum output current to exactly one third of its rated value, and that's not enough to run the entire electrical system under all conditions.

GM has a very high failure rate on their generators since they were redesigned for the '87 model year. They develop huge voltage spikes that can destroy the internal diodes and voltage regulator, and can interfere with computer sensor signals. Anytime you have a failure, replace the battery unless it is less than about two years old. As they age they lose their ability to dampen and absorb those voltage spikes. Since you just did replace the battery, that suggests it was old enough to allow the voltage spikes to be a problem. To see if I'm right, have the charging system professionally load-tested for maximum output current and "ripple" voltage. Ripple voltage is the AC voltage you mentioned but that may not show up with a digital voltmeter at the battery now that it is new. Professional testers look at the rapid variations in output current as well as voltage at the battery.
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Wednesday, September 18th, 2013 AT 12:03 PM
Tiny
OSIDE JOHN
  • MEMBER
Thanks for the quick reply. After reading your post I went back and monitored the voltage while paying more attention. When it started it was at 14.6 V, but as the engine warmed I noticed dropping slowly. When it got down to 13.9 - 13.8 V ( after about five minutes) I figured I'd push it by turning on the air conditioning, Bingo! That did it. The voltage then stayed at 13.7-13.8 and I could induce the behavior by adding the air conditioner stress.

I'm prepared to replace the alternator. It will run me about $90. Do you think it is worth while to just go for that, or should I go through the other diagnostics. (Time is critical, I have to have the car reliable for the wife before I leave town Friday.)
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Wednesday, September 18th, 2013 AT 12:49 PM
Tiny
OSIDE JOHN
  • MEMBER
New alternator. Same problem.
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Wednesday, September 18th, 2013 AT 5:18 PM
Tiny
CARADIODOC
  • EXPERT
Sorry to leave you hanging for so long. Had to run out of town.

I'd still do the load-test to verify the new generator doesn't have a problem. As an alternative, you can also look for a high resistance connection between the generator output terminal and battery positive terminal. Turn on a lot of loads like head lights, heater fan, and the air conditioner, then measure the voltage at both places. The readings should be within a couple tenths of a volt.

If the problems occur with the air conditioner running but not with just the heater fan on, that would suggest a slipping drive belt although there should be a lot of squealing with that. The air conditioning system only draws a couple of amps more than the heater fan for the compressor clutch, so if that causes the symptoms, the compressor may be loading down the belt. Look for a spring-loaded tensioner pulley that is rusted tight and not putting enough tension on the belt. If you can see the belt slow down, look at the speed of the crankshaft pulley. It is not unheard of for the outer ring to break loose from the hub. If the pulley is cast as part of that ring, it can slip, although it usually falls off.

By the way, you said you replaced the battery but you didn't say if it was a new one. If you installed a used battery that is more than a couple of years old, the voltage spikes these generators produce are likely interfering with some sensor signals. You can verify that by unplugging the small connector at the back of the generator. If the problems clear up, suspect those voltage spikes.
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Wednesday, September 18th, 2013 AT 11:03 PM

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