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iamchappy's Avatar
 
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Intermittent start issues, Alternator?

I have been having intermittent start issues this month in my 914 turbo, the Alternator has been making a gravelly sound on start up but goes away when warmed up, the charge light stays on until the rpms reach 3000 under load the volt meter shows that it is charging then at 14.5.

I have been driving the car wired as is for several years without an electrical glitch.

Now I have noticed my tach jumping around sometimes when idling. Now my oil pressure gauge is pegged at the top.

Yesterday the fuel pump didn't get power for awhile, then it did.

I have the fuel pump wired to run when the ignition is turned on.

Here are the start symptoms:

Engine starts right up but will kill after a minute or so, may startup again several times and kill the same way.

May start up and not kill and is drivable.

Most of the time except for yesterday, the fuel pump still runs and is delivering 100lbs
of fuel pressure.

Definitely electrical ignition cutout when it kills.

Starter turns over fine

Battery Optima yellow top fully charged

MSD btm electronic ignition unit installed. Blaster coils.
All grounds pristine.

Dont know the age or condition of the Alternator other than it is internally regulated.

Local mechanic claims the the Alternator could not cause these symptoms, but i am
skeptical.

If i replace the Alternator any suggestions, New or rebuilt, Paris Rhone, Bosch, or Velo.
Prices i find range from 125 to 250 for rebuilts.

Possible causes---- Ignition switch, Alternator ?????


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914 6 Turbo twinplug 3.12
87 924S
Lexus SC400
Lexus LS400

Last edited by iamchappy; 11-03-2009 at 12:45 PM..
Old 11-03-2009, 07:47 AM
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I'm having similar symptoms...

1. On initial startup my voltage remains 12.25V until I rev the engine to about 3K, then, 14.4V

2. Occasionally, when the voltage is 12.25V at startup, my tachometer reads exactly 2X the actual rpm's. So, at 1,500 actual idle, the tach is reading 3K ?? then, when I rev to 3k [6k indicated], the voltage goes up and the tach becomes accurate, again.

3. Once I get the voltage up, I don't experience these problems again, as long as the car remains running. As soon as i turn off engine and restart, I have the same problem again. However, when the engine is fully warm, it's very easy to get the voltage back to 14.4V [just a tap of the accelerator will do].

This has been going on for a couple of months... It really isn't a problem to deal with [because it's very predictable], just worried that "whatever it is" could leave me stranded????

Anyone else experience this??? - - - Oh, my alternator is new [3K miles]....

Thanks
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.

Last edited by mooney265; 11-03-2009 at 03:35 PM..
Old 11-03-2009, 03:33 PM
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I would tend to agree with your mechanic's assessment. A failing alternator, assuming your battery is fully charged, could not cause these symptoms.

I don't know the 914 at all. However, what you are describing sounds like poor grounding to the chassis. I would check your grounds... from battery to chassis and from engine to chassis. Considering where you live, it is fairly common for ground strap connections to become corroded and no longer functional.

Typically, any time you have erratic functioning of electrical accessories, the culprit is a poor ground... assuming constant power supply to the fuse panel. This is what I would suggest you spend some diagnostic time.

It is not unusual for alternators of your vintage to require the engine to be revved up a bit before it will excite and begin to charge.

Hope this helps,
Dave
Old 11-03-2009, 03:56 PM
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By the way... you can test this with an ohm meter. With one probe on your battery's negative post, you should be able to put the other probe on any exposed metal surface throughout the body of the car and get a very low reading (less than .5 ohms). If you do not get this type of result, your ground is not adequate.

Dave
Old 11-03-2009, 04:01 PM
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Dave, thanks for your response but my ground connections and connectors are truly pristine. My car is a ground up restoration and has only seen a few baths since it's rebirth. Careful attention was taken to all of the grounds and wiring when it was assembled.
914 and the 911 electrical are very much the same they even share the same color codes on the wiring. Somewhere a short of some kind is bleeding into the system but why all of a sudden, i know the Alternator does not sound normal on start up so i suspected it, and the ignition switch has been used for over 35 years so that too may be where to look.
I cant get to the Alternator in my 914 as easy as you can in the 911's so just looking for advice. i will test the ohms to see what i come up with.

Here are some pictures of the not working so good - 914











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Lexus LS400
Old 11-03-2009, 04:31 PM
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I see the problem. Your ground is missing off the battery! JK.

Take a look at the large red wire on the Pos lug at the starter. That wire goes from the alternator to the battery. I had fits trying to find out my intermittent running and after replacing the alternator, found the nut holding that wire was loose. Tightened it up and all was good.
Old 11-03-2009, 04:53 PM
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BTW, your 914 looks beautiful, and turbo to boot! Out of curiosity, how do you get good airflow to your intercooler?

If you are very confident in your grounds, I think your ignition switch thought is a good one. Somewhere, you're getting intermittent electrical performance. The battery really functions as a capacitor once the engine has been started. If it is charged, the alternator really can't have anything to do with the types of symptoms you are experiencing... assuming you have a correctly functioning path between the battery and your fuse block (and good grounds).

As Rocket pointed out, that lug can be a problem on any car. Despite your restoration, it is possible for the cable ends to get corroded, leading to this type of problem. Pulling them and doing some Dremel cleanup on the ends, the lug/washer/nut can sometimes cure weird electrical issues.

If it were me, I'd be using "clean" power to the fuse block... jumper wires from the battery... to see if these issues went away. If they did, I'd follow up by removing the jumper wire for the ground to see if the symptoms returned. If not, I'd replace the ground jumper and remove the hot jumper... again to see if the issues returned. I believe you have either the ground or the hot failing, and this way you could determine which one.

Unfortunately, electrical issues are often a process of elimination.

I hope you keep us posted on what you find.

Dave
Old 11-03-2009, 09:32 PM
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Dave, i am going to sit down and go through the process of elimination. Because the
problem is intermittent it would be easier to solve if it flat out stopped working.

Air comes in through duct in the rear spoiler and air is pulled through the intercooler via
two-7" electric fans
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914 6 Turbo twinplug 3.12
87 924S
Lexus SC400
Lexus LS400
Old 11-04-2009, 05:54 AM
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That is really nice ride... well done. That thing must flat out fly.

Good luck
Old 11-04-2009, 07:31 AM
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After spending the day checking over everything behind the gauges, fuse box, relay board i finally found the bad wire that was intermittently causing the ignition loss, switched power lead connector going to the MSD. Picked up a new oil pressure sender and now all is well.
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914 6 Turbo twinplug 3.12
87 924S
Lexus SC400
Lexus LS400
Old 11-06-2009, 05:51 PM
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Congrats... glad to hear it. I only wish you could take me for a spin in that thing... it looks like a ton of fun.
Old 11-06-2009, 06:36 PM
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