1986 Fiero SE 2.8L V6 Notchback
Hello

As of about summertime I have been having this weird problem. Whenever The battery is anything but 100% charged up (as in if it sits for two weeks, untouched) I have this issue where the speakers have a pulsing thump to them when the key is in the 'run' position but the engine isn't running. When this situation is happening and I go to start the engine, the started is very slow and the voltage drops significantly and the engine barely gets going. However; if the car was just running (battery all charged up from alternator), none of these problems exists and it starts up just fine. I do not think this is the battery because I have swapped out the battery twice with brand new, charged up batteries since the problem has existed. This problem happens more frequently when it's cold outside. I have changed two of the fusible links in the back battery area with fuses of 30A each, but they have been in place and working before this problem was happening.
Here is a video of the situation. The Speakers thump like a heartbeat, but I can turn on the radio and sound comes out just fine, with the thumping in the background.

Video for Electrical Problem

I need to get this problem resolved once and for all, because my dad and I changed the distributor O-Ring this weekend and I haven't been able to get the car to start, so fixing this issue must come before I start trying to diagnose that,

Thank you

OKay so i Hooked up jumper cables to the Nissan Quest and to the fiero right at the battery terminals and let the quest run for a while. Now it cranks just fine with 13.5V reading at the battery, however the tach doesn't move at all. I head here: Cranks But No start that is should be reading at around 300rmp while cranking.

Now I do have the A and B pins shorted because I'm trying to get this thing started to do some timing, after replacing that Distributor O-ring. I replaced the ICM with an ACDelco replacement and it made no difference. Spark plug wires are brand new, cap and rotor are 6 months old. I also tried starting it with the pedal to the floor to see if it was flooded, but no difference, idk if the computer pins need to not be shorted out for that to work.

quote Originally posted by jschmidt95: …....Whenever The battery is anything but 100% charged up (as in if it sits for two weeks, untouched) I have this issue where the speakers have a pulsing thump to them when the key is in the 'run' position but the engine isn't running. When this situation is happening and I go to start the engine, the started is very slow and the voltage drops significantly and the engine barely gets going.

I would ignore the “thump” for now and treat it like there is something slowly draining the battery. Disconnect the + terminal of the battery and put an amp meter between it and the cable. If the meter shows more of drain that you would get from a clock or whatever else a fiero powers when it turned off (someone else will have to chime in if you need a number), start pulling fuses one at a time till the meter reading drops. Look for a problem on that circuit, probably a high ohm short. -Paul

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1988 Fiero Formula 25k miles, garaged since 1988

quote Originally posted by jschmidt95: .........Now it cranks just fine with 13.5V reading at the battery, however the tach doesn't move at all. I head here: Cranks But No start that is should be reading at around 300rmp while cranking.

Check my post on that thread if you haven't already. -Paul

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1988 Fiero Formula 25k miles, garaged since 1988

quote Originally posted by jschmidt95: I also tried starting it with the pedal to the floor to see if it was flooded, but no difference, idk if the computer pins need to not be shorted out for that to work.

That should work in normal driving mode. -Paul

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1988 Fiero Formula 25k miles, garaged since 1988

sweet. I'm going to check for one of those parasitic draws over the weekend