Molly

In my 86.. the voltage gauge reads about 13 usually but every few minutes there is a very loud hum from the right rear - I assume fuel pump. It strains very hard for about 10 seconds, then goes back to normal, which is silentand working fine. The car has no apparent fueling issue and starts and runs decently all the time. When it strains, the voltage gauge goes straight to the red. All the way to the top of the gauge. The car does not stumble or anything else during these events. I do hear a significant whine through the stereo during the event. It's a small head unit with no amps and just two door speakers, and it has zero whine any other time. I don't know a lot about electricals.. but it seems that if something is running extras hard sometimes, then the voltage would drop like when other things run such as the windows, lights, not skyrocket. Thanks as always.

bw993

Your electrical problem sounds unusual. If it is the fuel pump, I would check the ground and power connections at the fuel pump to make sure you have good current continuity. The wires to the pump are somewhat light in gauge, so any poor connection will result in the pump seeing lower voltage, which results in higher current draw.

divil

Could it be the voltage regulator in the alternator? There really isn't anything the fuel pump can do that could cause the voltage to go so high. If the pump were to somehow slip, it would draw less current, and you might see the voltage go up *slightly* (though probably not), but the regulator should be limiting it to somewhere around 14v, even with no load. Plus, you would also have poor fuel delivery in that case. On the other hand, if the voltage from the alternator goes up a lot, the fuel pump will speed up and that could explain the noise - but it would not cause a fuel delivery issue because the pressure is regulated at the rail.

Molly

So maybe the voltage is going up and that is causing the pump to make more noise, rather than the other way around like I assumed.

Droops83

Exactly. Sounds like a classic case of overcharging due to a failing voltage regulator. Overcharging will cause all kinds of weird electrical issues, and it is usually intermittent at first. Check your charging system or have it checked out by a qualified shop. Double check your battery to ensure that it is not boiling over and causing corrosive damage to the battery compartment.

It would also be wise to check all of your electrical connections between the battery, starter, and alternator, both power and ground. Of course the voltage regulator can and will fail on its own, but loose, dirty, and/or corroded wires and connections will result in the alternator working overtime to maintain battery voltage, thus causing charging system failure.

Not so. According to Ohm's law, the opposite is true. High resistance in a circuit will always result in lower current draw. It will, however, generate a lot of heat that can burn contacts and melt things. In extreme cases, fire can result. But the current and voltage will ALWAYS be lower.

Molly

Problem solved... the FPR (stock) was bad and causing some flow issues in the fuel loop, and causing the pump to have to work super hard, causing massive voltage spikes. Replaced FPR and has not done it since ; ) Thanks

PorscheFanatic202

Interesting find. I wouldn't have guessed that. What made you think fuel pressure regulator and how did you test it and rule out the damper? Fuel pressure test? Congrats on fixing it!

Molly

Nope... problem not solved.

I thought of the FPR because when it fails it might cause some straining in the fuel pump since the fuel pump is next behind it in the line of fuel flow and pressure. And I refreshed my motor including a new FPR and the problem was gone for a bit. But that was just coincidence as the problem is back now with a vengeance.

Follow on thread: https://rennlist.com/forums/944-turb...-part-2-a.html