volt gauge issue...fuel pump buzz

[LummoxPG]

Hi All...ok...here goes...I have an 88 ROW S4...I have had trouble with my temp and fuel gauge reading inaccurately but the other day my normally reliable volt gauge suddenly jumped up to 16 plus and stayed there...so being a cautious person I parked the car removed the positive and negative cables put my volt meter on the terminals and it reads at approx. 12.4...so not a bad thing...then I hook the battery again and turned the car on and the volt gauge reads at just over 14...of course...not the 13 it had normally read but not the 16 I had experienced just minutes earlier...so I put the voltmeter back on and it reads approx. 13.6...again not a bad thing...hmmm so I don't drive the car for a few days and continue to check with volt meter. At first my first thought would have been that either the regulator has had it or the volt gauge has joined the fuel and temp gauge and decided to give up the ghost. Today I drove the car for a few kilometers...say 15...the volt gauge doesn't read above 14 but not the 13 I consider normal...fine. Then tonight I fire up the car and I hear this awful buzzing come from the rear of the car...hmmm... I get out and it seems to be coming from underneath...odd thinks I...I just changed the fuel pump 500 kilometers ago...could it be going...nah it's a new bosch part...right...the odd part is that the pump does not make this buzzing with key turned all the way right just prior to turning it over, but damn its loud with the car started...so ...could this buzzing from the fuel pump be an isolated yet coincidental thing or is it related to my possible electrical problem...and where to start...open to suggestions. thanks

[Danglerb]

Don't trust the pod gauges. Buzz more likely mechanical than electrical, but can't be good.

Voltage that is real and above 14.5 sounds like the regulator, hard to imagine its anything else unless the meter reading was bad. Too much potential damage if it goes wacko long, I would replace it and/or test at least asap.

[stepson]

With an '88, do you have an internal fuel pump? If so, your internal pump may be non-functional, which is forcing your external pump to work harder by drawing fuel past the locked up pump vanes in the non-working internal pump. That can cause the noise you are hearing.

[LummoxPG]

Yeah, I have had this plus 14.5 volt reading on the pod gauge 3 or 4 times now, sometimes the gauge fluctuates and other times it comes down to 13 and other times it stays pinned at 16. But I have yet to get a reading on my volt meter ( at the battery ) that is higher than 13.85 with the engine running. I need to catch the pod gauge at 15-16 when parked so I can test it. As to the fuel pump...I do not believe that the 88 ROW has the in tank fuel pump but I could be wrong. However, I have not run the tank below a quarter, I have not changed fuel from the 94 octane that "Olga" prefers, and it has not been hot enough, nor have I run it long enough to heat the fuel.

[Danglerb]

Its about $500 to have the brain rebuilt, how many times do you plan to roll the dice?

Have you ever replaced the battery ground strap?

[LummoxPG]

Well Dangler since you put it that way...928 Motorsports has a 200 amp alternator...you think that would be wise update. I have never replaced the ground strap...this one looks pretty minty...but better safe than sorry and the forty bucks is less painful than the alternative...i'll get on that right away. The 88 does have a fuel sending unit at the tank...that must be the internal pump and they are only 130 dollars or so...guess i'll get one of those too.

[stepson]

Originally Posted by LummoxPG

The 88 does have a fuel sending unit at the tank...that must be the internal pump and they are only 130 dollars or so...guess i'll get one of those too.

No. The fuel sending unit is at the top of the fuel tank. The internal pump would be at the bottom of the tank tucked in the tank behind the external pump. Every 928 has an extra set of wires for an internal pump, but only certain years' wires are hooked into an internal pump. The MY 928s that do not have an internal pump just have the wires taped up behind the external pump. Look to see if your extra wires are hooked up to terminals and not just taped up.

[harborman]

Those ground straps might look fine but not inside the crimp ends. I pulled mine apart and all kinds of powder dust was inside the crimp end where the wing nut is. One way to tell, put your volt meter across the battery, then from battery + to the wing nut and see if any voltage drop.

[LummoxPG]

Harborman - Thanks for the tip. I did as you suggested, and the voltmeter read 12.38 on both readings...so no need for a new ground strap me thinks.

Stepson - Interesting...I'll take the pump shroud off when I get another day off...in truth I cannot remember if there were extra wires behind the external pump so I'll find out whether these were hooked up or not...the curious thing is that I can't find anywhere online that advertises an internal pump for a 88 s4...but it raises the question...do non internal pump cars require a different external pump from cars with the internal pump hooked up.

[Danglerb]

I tend to favor stock alternators, fewer issues.

To see if a ground strap is flaky you need to have some current flowing through it, not static with nothing running. Headlights might be sufficient with motor off to check the strap. I would do some wiggling on it too during the measurement.

[LummoxPG]

Dangler - Thanks...That's a good thought I'll try the volt meter with the head lights on...by stock alternator do you mean a Porsche part or any oem that is 115 amps...I'll admit that I have had my concerns about installing a 200 amp alternator.

[Danglerb]

Factory part, but need not be sourced from Porsche. Some have had good luck using a modern alternator, but many have issues with proper cooling like the factory units use.

200 amps is the claimed max output, working properly there is no difference in voltage, except voltage doesn't drop under a very high load.

[LummoxPG]

ok so I used my volt meter on the battery at the positive terminal and the negative terminal at the wing nut again...this time with the lights on, and the volt meter read 11.26...although it also read that at both the positive and negative terminal with the lights on...with the lights on it reads 12.36 amps.

[harborman]

Originally Posted by Danglerb

I tend to favor stock alternators, fewer issues.

To see if a ground strap is flaky you need to have some current flowing through it, not static with nothing running. Headlights might be sufficient with motor off to check the strap. I would do some wiggling on it too during the measurement.

Yes, best to have some load while measuring any voltage drop. Mine was so bad I was getting .8 Volt drop on that cable with no load.

[harborman]

Originally Posted by LummoxPG

ok so I used my volt meter on the battery at the positive terminal and the negative terminal at the wing nut again...this time with the lights on, and the volt meter read 11.26...although it also read that at both the positive and negative terminal with the lights on...with the lights on it reads 12.36 amps.

Bypass the braided ground strap with a good jumper cable and take another reading.

[LummoxPG]

Thanks Harborman. Ok so I did bypass the braided ground with a jumper cable and no change on the volt meter from the ground strap... I did restart the car today and the volt gauge on the pod read 15 plus, so I quickly put the voltmeter back on at the battery and it read 12.67. So I am thinking that the volt gauge on the pod is lying to me...the curious thing is that the last time I started the car the fuel pump made a pronounced buzzing which did not stop,this time this fuel pump was quiet...so I have resolved to replace a number of relays as a first step ie. LH, EZK, and the fuel pump relay, the next step will be to take the car in to the shop and have the alternator tested... I may just order a new rebuilt alternator, keep the original and put the regulator I just bought into it as a back up for the future...

[LummoxPG]

Decided I'd better just do it and ordered LH,EZK, and fuel pump relays as well as a rebuilt Bosche alternator and ground strap from International.

[stepson]

Originally Posted by LummoxPG

the next step will be to take the car in to the shop and have the alternator tested... I may just order a new rebuilt alternator, keep the original and put the regulator I just bought into it as a back up for the future...

Just start the car, put the positive lead of a multimeter on the jump start post and the negative lead on a good ground. That should tell you what volts/amps your alternator is producing, right?

[LummoxPG]

Stepson - true, it should...that's a good point... I'll test that tomorrow...thanks...Oh BTY I have pulled the fuel pump shroud and confirmed that the 88 ROW does not have an internal fuel pump so I'm not sure what caused the pronounced buzzing in the fuel pump that time...it hasn't done it since so perhaps it was not a mechanical issue, kinda hoping that replacing the fuel pump relay is a good preventative measure. I have already ordered the alternator so I'll put it in, and in truth I don't mind having a backup...so I will replace the regulator in the original and that will give me a solid replacement should I need it. Up here in the Great White North we only have a limited driving season so I'm anxious to get Olga on the road...meaning I'm feeling I should just get it all done ASAP.

[LummoxPG]

Stepson- multimeter gives no reading at all at the jump start post and a good ground with the engine running.