So here are the stats:

Battery Only - 12.8V

Engine Running 1000 rpm 13.3V

Engine Running 1000rpm Headlight switch on 12.5V

High Beam on the rpm's drop and hunts - forgot to measure voltage

So here are my questions:
1) I have a hard time believing the extra load from the high beam is bogging down the motor. Is the extra alternator mechanical load really that much or is the high beam draining from the ignition system causing erratic idle?

2) Is 13.3V (no lights on) low? Should I be closer to 14V? Is this possibly more a alternator or voltage regulator issue?

I've read some of the threads and I think my grounds are good. The VR case to ground bolt reads 0.4 ohms. This is a new assembly car so I wire brushed all the ground stud landings (of course they can still be an issue). The transmission to chassis strap is in place.

This is a D-jet car if it makes a difference.

Are you getting these readings from the built-in voltage gauge in the center console? If so, that's normal due to where it's power is sourced from. I joke that is a secondary blinker/brake light indicator.

I should of mentioned these readings are from the battery terminals with a DVM.

Assuming with engine off? Resting voltage should be 12.6V.

If you just started it, then 13.3V isn't bad as the alternator is working hard to recharge the battery after starting. If running for a while, it seems a bit low. What is the voltage at 2k RPM?

Need to know what the voltage is at 2k RPM. 1K RPM is marginal for the alternator to keep up.

The voltage must be lower than 12.5V if it affects the FI.

The electrical load shouldn't bog the motor down that much. It will slow a bit but shouldn't be much. What size engine?

Measuring resistance under 1 ohm is very difficult. Sometimes you can have 0.4 ohm just touching the probes together. It's best to measure voltages when running to get an idea of the health of the wiring and connections.


Several things can be at fault including the VR, engine grounding, contact resistance of the battery terminals.

With engine running, lights on, measure:

1) Battery POS stud to its connector. You should measure zero volts.
2) Battery NEG stud (not its connector) to chassis ground. You should measure zero volts.

1) and 2) will test the battery connection to the electrical system.

On the VR connector on the relay board, measure:
3) D+ to chassis ground (not the engine). You should measure 14V.
4) D- to chassis ground (not the engine). You should measure zero volts.
5) DF to chassis ground (not the engine). You should measure 5-9V.

3-5 will test the VR and the grounding of the engine to the chassis. Let us know what you find.

- You're right. 12.8V right after I shut off the engine. Before first start I get 12.6V.

- At 1600 RPM I get 13.6V engine on lights off.

- At 1600 rpm Headlights on I get 13.16V, Headlight and highbeam 13.04V

- Is 12.5V required for FI or ignition or both?

- This is a 2056cc with Elgin 330-1 cam, everything else stock.


The update from above was prior to your post so it was done at warm-up idle other wise I would have measured at 2K rpm as suggested.

How does one measure 3)-5). Do I run the engine without the VR?

I also measured voltage at the + coil and they all measure 0.7~0.9V lower than at the battery connector (+) given above. Is that a typical voltage difference between coil and battery?

Another point worth mentioning is I am using a small battery. It is only 22AH. I have no problems cranking and starting with this battery so I didn't think it was an issue, but I'm starting to learn the battery is required as a buffer to maintain electrical power including current through the alternator.

Thanks

On my 914, the voltage at the battery stays constant at around 14V w/headlights on or off.

I don't know how much voltage FI needs before dropping out. It would be nice to know what voltage was happening when the FI started skipping.

Leave the VR in. The measurements will check the VR, the alternator, and the engine/alternator grounding. Just jam the DMM probe into the connector from the alternator at the relay board. You'll be testing each one to chassis so just measure and record all 3 voltages.

Probably not bad. The path that voltage took was from the battery through the ignition switch back to the relay board then over to the coil.


I don't have any experience with small batteries like yours.

Good resource material, bookmarked.
Sorry for slight hi-jack

Test 1 & 2 measure 0V. With lights on I'm getting D- .08V, D+ 13.3V, DF 5.5V. I have a couple of spare VR and got about the same results with both. With the lights off DF drops to about 3.6V. I also rechecked the transmission to chassis strap. The alternator to chassis shows good continuity too.

Okay a bit of an update. The above was at 1600rpm. Drove around and the motor finally warmed up and settled at 1000 rpm. So now I'm getting D+ 13.7, DF 6.5V, D- -0.12 lights off. Lights on D+ 13.2V, DF 8V fluctuating, D- -0.21.

Both VR are about the same with one reading about 0.2V higher on D+. Also the higher reading VR DF fluctuated up to 12V.

I forgot to drop my brake so the light was flashing the whole time.

D- at 0.08V is good. This also tests the transmission strap in action.

DF will go up and down as more or less alternator action is needed.

Was D+ at 13.3V done at 1k RPM with lights on?

I should have mentioned to measure the battery voltage at the POS connector to chassis at the time you measured D+.

Two other tests to try:

1) Remove the VR and short D+ to DF and start the engine. You should see 16+ V at the battery. Do not run like this very long as it is not good for the battery. Also the connector and wires from the alternator should remain in place so the GEN light is still in the circuit to bootstrap the alternator.

2) With VR in the circuit, try another battery if you have one handy.

A question about the battery: Was this issue happening before the battery was installed?

The 13.3 was at 1000rpm lights on. I went to remeasure and I got D+ 13.1V and Batt+ 12.8V with lights on. Lights off I got D+ 13.6V, Batt+ 13.5V.

Based on previous test I think the 13.3 vs 13.1 at D+ is using 2 different VR's.

Is it a problem that D- is negative? I do have the negative probe on chassis and positive probe on D-. I also misreported. The D- is -0.21 with lights, -.08 no lights.

I shorted D+ and Df and got 17.8V at the battery.

I've only run this car with this 12V, 22ah battery. It's was not running prior to me stripping and reassembling.

Unfortunately to test with a larger battery I'd have to buy one which I'd gladly do if all these tests say both VR and alternator are likely good.

The D+ to DF shorting giving 17.8V at the battery indicates your alternator is ok and if requested by the VR, can put out good voltage. This seemingly points back to the VR. The VR should raise DF until the output voltage D+ (with respect to D-) is 14V.

D- being negative is expected. See the diagram below. Battery charging current and vehicle loading like lights and ignition are sourced from the B+ lead of the alternator. So in the diagram, the alternator current is flowing upwards out of B+ which means it is flowing upward at the ground connection of the alternator.

The ground symbol below the alternator represents the chassis. The short wire from the ground symbol to the alternator represents the resistance of the transmission strap and its connections, the transmission to engine connection, the engine to fan shroud connection (the alternator connects to the shroud), and finally the shroud to alternator body connection. Any resistance in this path with current flowing upward will cause a negative voltage at the body of the alternator.

Zach (VaccaRabite) had a lot of trouble with this connection losing 1.6-1.7V. Yours is losing 0.21V. That doesn't seem bad. After Zach put a dedicated cable from the alternator body to the chassis stud behind the relay board he saw a voltage drop of 0.17V. Here's a link to Zach's thread:

The alternator replacement thread, Fixed!

I have no experience with the small battery you have so I can't say if it is the culprit. That's why I suggest dropping in a different battery. I wouldn't go out and buy one though unless you wanted to replace the small battery.

If the battery could be eliminated from issues, it would seem the VR is running low. I hesitate to replace components before determining which component is bad. One could buy a lot of items before stepping on the real issue.

Thanks @Spoke for taking time out from Thanksgiving and helping. I see your point about figuring out what's wrong prior to replacing parts, but at some point I'm going to have to go with the trial and error method.

As mentioned before I have 3 VR's. I took my best VR which gave me D+ of 13.8V/13.4V lights off/lights on respectively and decided to drive around and see how it performed. After returning home I retook measurements and got D+ of 13V/12.6V. The VR felt warm so I put a TC on it and got 125F. Ambient is in the mid high 60's here today. Is 125F normal or hot?

I saw in a previous post that you used a Duralast from Autozone. I was wondering for those who have used this VR if a special mount has to be fabricated or will it fit in the space of the stock unit?

http://www.914world.com/bbs2/index.php?sho...97516&st=20

About the Duralast VR, I have one in my car. Bought it locally when the current VR was misbehaving. It dropped right in. The voltage is 14V above idle. At idle the voltage varies from 13-14V as the alternator is not spinning fast enough to generate the energy needed to maintain 14V.

Not sure about the temperature rise of the VR. I've never checked mine but others have said their VR runs warm.

You've tried several VRs with the similar results. You know the alternator can output significant voltage during the DF shorted to D+ test.

The one thing I can think of that would cause a good VR not to give 14V output is if the armature in the alternator is very low impedance. This means to pull up DF might take a lot of current. If the VR has to supply a lot of current to the armature, it would run hot. If the VR cannot supply the current needed to drive the armature, you would get less output voltage, DF may not be so high in voltage, and the VR would get hot. This is just a theory.

An interesting test of the current draw of the armature is the DF shorted to D+ test using the ammeter part of your DMM to check armature current and short DF to D+ at the same time. Put the DMM on the AMPERES or 10A setting and see what the armature pulls. I've never done it so I don't know what current is normal

The least expensive item is the VR. Rock Auto has some for $25. If you throw in a new VR and the battery voltage doesn't get higher, then likely it isn't the VR.

If you do check voltages again, measure D+ to chassis and battery POS to chassis during the same test. They should be within 0.5V or so from each other. This would check the alternator diodes.

Brought my spare alternator to get rebuilt and asked about the smaller battery. They told me the car runs off the battery so running a smaller battery could be an issue. While he was rebuilding the alternator I ordered a group 34R Bosch AGM. I couldn't find a group 42 AGM.

So seeing that a battery is easier to swap than an alternator I tried the new battery today. Charging is better. At 1000 rpm I get D+ 14.08V, 13.9V, 13.88V for no lights, head lights, and high beam, but the car still idle hunts with the lights on. I measured the amps across the fuse box and got about 3 amps/headlight and 4.5 amps/high beam which I've read to be normal current draw.

My questions:
1) Based on the above was the small battery the culprit and I just have an idle tuning issue now?

2) Is it the alternator putting more than normal load on the engine to power the lights? So a bad alternator?

3) If I swap alternators do I have to remove the harness with the old alternator or is it possible to remove the back plate and leave the harness in place for the new alternator?

4) I've read group 34's will fit, mine doesn't. It's a tad too wide (which I can live with) but it's too tall with the rain tray in place. The (+) post interferes with the rain tray. Is it just me or is this a problem for everyone using a group 34 battery? I believe someone in the past replaced the battery tray so maybe it's in the wrong place, but visually it looks correct.

Thanks.