jwillman

I had a previous post about low idle once my car was hot with high outside air temps. I also noticed my fuel pump was noisier than when the car was started and cold / cooler.

Yyesterday after a 40 mile drive the idle was agin low and a bit irratic, 5-600 RPM and I also noticed the fuel pump a bit noiser. As I increased rpm in nuetral the speed sound from the pump also increased.

I assume the pump should run at a set RPM from a nominal to max voltage range. Is that correct? If so it would lead me to think I have a voltage issue to the pump or a pump issue when hot.

Thoughts?

kevinlieb

Well just drive the car with a voltmeter attached. Perhaps to the cigarette lighter plug. If voltage is increasing with RPM your alternator or voltage regulator on the alternator is bad (if don't know if it is one piece on this car).

WallyP

Yes, sounds like voltage is low. Not unusual with a really low idle, especially if you have aux fan and/or AC running.

First check is to make sure that the alternator belt is tight. Next is to clean all battery cables and ground straps/cables.

Podguy

Third throw away the Porsche alternator and replace it with a Delco.

The bearings wear in the pumps or get dirty with gas varnish. First get some Berryman's B12 gas treatment and run it through with a fresh tank. This will clean the pumps and injectors. On the second tank use a pint of Miracle Mystery Oil. It will help with the cleaning and add some lubrication. This will quite the pumps down.

A consistent voltage from the Delco alternator - especially at low idle speed will improve a lot of the electrics on the car. There is a speed cut off where the regulator will cause the voltage to drop. The cut off on the Delco is at a much lower RPM than the porsche unit.

The ground by the rear taillight controls the fuel pump. You should consider cleaning it.

jwillman

Drove car today with a digital VM connected to the battery and run up to the front.

Voltage starts out at 13.8 after cold start at idle. Once car warms up volatage is solid 13.4ish at any rpm above 1200 but drops to mid 12's at idle and down to 12.2ish with AC operating. I did convert to electric cooling fans so I have that extra draw once engine is up to temp. Thats the only change over stock electrics in the car.

Eagle Auto electronics sells a bosch rebuilt upgraded to 120 AMPS on ebay for $110. I like the idea of more amps given I am running the electric fans. Is that a viable option over the Delco?

Podguy

Screw the Bosch and get a Chevy Delco. You will get more amps and longer live. Rock auto had them for $76 a while back when I got mine. We put one of Erik's car and never had a single issue. The Bosch is still vulnerable to water when going through the a puddle. I lost a Bosch this way. The 86/87 Camero V6 is the one to get. Any parts store will have them in stock.

jwillman

Thanks Dan.

Did you do anything for cooling? I have read both opinions that it still needs cooling and that it is not required.

depami

Never heard of this.

Please elaborate.

Thanks

Podguy

Jim,

Erik is running one down in Austin TX. That should be hot enough. And considering Erik he has not been babying the car.

You will need to buy a pigtail and a new belt. The pulley off the Porsche alternator will fit on the Delco. The mounting bracket on the delco is thinner and needs a couple of washers behind the bracket to shim it out. Other than that it is basically a bolt up. I am putting one on my 78. I have had all kinds of alternator problems with varying voltage, a jumping gauge and not enough current to run the A/C on high or the A/C with the headlights.

Podguy

Denney,

An alternator puts out alternating current. The Porsche runs on DC. An alternator requires a field current to generate current. Generally an automotive alternator generates more than 12 volts. If the field is disconnected the alternator can run away and generate unlimited voltage - well not unlimited but enough to burn things up.

A generator on the other hand as found on older cars generates DC current which is what the car uses. The only regulation needed on a DC generater is to turn the thing off when the battery is fully charged. A field is also used to control output on the generator.

There is a cut off point where a geneator does not generate current is failry high. This is why on older cars the generator light would often come on at idle. The alternator cures this as it will continue to generate current at a much lower RPM. This is because the alternator can generate a much higher voltage and then be divided down to get current output at very low RPM. To do this requires some diodes to rectify the AC to DC the car can use. Fortunately electronics are far easier to control than relays for current and voltage regulation.

I hope this is the answer to the question you had. My take on Delco is that is a far better design than the Bosch or the Paris Rhone. It is more common, cheaper and more reliable. Many manufacturers make the same unit. For a little more you can even get one that is polished or chromed.

jwillman

I have searched the big 3 neighborhood parts dealers and not found an "AC Delco" brand listed online. All three carry a couple of different branded alternators. Do I want / need the AC Delco brand or is AC delco design CS130 by other manufactures also fine? I have seen a few claiming 105 amps at a higher cost versus 100 amps for most of the rest. Worth the premium?

Thanks for all the insight!

Podguy

I got mine on sale at Rock Auto with a close out and no core for $75. Erik bought his at NAPA. NAPA has a repution for having higher quality parts.