Voltage regulator - Coil ?

[3D914]

At Daves suggestion, I decided to run the Ignition Troubleshooting tests to see if they could be a factor in my bucking/surging problem.

I did ithe first test where you measure the voltage at the coil plus terminal. Instead of 12+v I got 10.5v.

Does this indicate that the voltage regulator is faulty, or does the voltage for the coil bypass the regulator?

Or does it indicate something else?
(yeah - time for a new car!)

Fun fun, fun!

[John Rogers]

That voltage is too low I believe. It should be 12 to 12.5 volts and the source is the ignition switch (switched 12 volts). The low voltage indicates possible dirty contacts or wire connections and will result in reduced voltage to the spark plugs. Good luck

[Dave at Pelican Parts]

I vote for dirty or corroded connections. If the engine was not running, then the voltage regulator doesn't do anything to the system voltage. If the engine was running, check the voltage across the battery terminals--should be over 13 and under 15.5.

Trace the wiring diagram for your car, and clean all of the connections from the battery to the coil. Contact cleaner (e.g., Radio Shack TV Tuner Cleaner) and a wire brush are your friends in this.

--DD

[3D914]

Thanks guys,

I'm going to make a jumper wire to go from the battery terminal to the coil + to see if this impacts the bucking/surging problem I'm having.

The car is running, and voltage at idle - 3000rpm is a steady 12.5v - measured at batt terminals.

From what I can see from the wiring diagrams I'll have to clean just about every connection in the car to get from the battery positive terminal back to the coil. But hey, that's what we love about old cars - right?

Tell me again - why am I doing this?

John: Are the contacts at the ignition swith something that can be accessed externally, or are their internal contacts that need to be checked as well?

[jkeyzer]

When you measure the voltage at the coil, what's the voltage directly across the battery? You won't see anything higher than that anywhere with the engine not running.

[Dave at Pelican Parts]

He said it was 12.5V -- which is too low. A "full" battery should read ~12.65V, and the charging system should put out between 13 and 14.5V. At least, if the engine is over 2000 RPM, it should!

--DD

[3D914]

So Dave,

I know I have to track down the voltage loss from batt + to the coil. But about the low 12.5v charging value - is the alternator the only factor here or is the voltage reg, or both?

I suppose there's a PP article on the charging system right?

TIA,

[Dave at Pelican Parts]

Yup, there is!

Low charging system voltage could be the alernator, or the regulator, or the wires, or some other part of the circuit...

--DD

[pbanders]

Low system voltage is a known cause of erratic FI performance, and it isn't great for the ignition, either.

[3D914]

Well, I found that the low voltage is not the cause of the surging/bucking in this case.

OK, I tried a VR that is bridged to allow alternator full capability, but all I got was 12.5v still. So I will be looking into getting my spare alternator rebuilt or finding a new one - whichever.

The reason for the surging/bucking ended up being the tri-ground at the case. Even though it static tested OK, because of its location, I couldn't see that the nut on the other side had worked loose in less than 200 mi of driving. The whole thing was vibrating at RPM's - causing intermittent Injector connections.

So another problem solved, and two more discovered. I've replaced the injector points that needed it, and will now get to the alternator. Plus all the connections in the engine bay and ignition switch are nice and clean.

Thanks again,

[Dave at Pelican Parts]

You are talking about the voltage at the battery posts, right? Not the clamps that hold the wires onto the posts, but the posts themselves?

If you measure anything but the battery posts, you are adding places for voltage drop to occur. Dirty connections are the primary cause of that.

Check the battery as well. It could be low on water, if it is not one of the sealed types.

--DD

[3D914]

Dave,

Yes - volt measured at the posts (even though all connections have been cleaned). The battery is just slightly over one year old and is an Optima, so no water-level to check here.

I've picked up a rebuilt alternator at BAP imports, but they wanted $60 for the $12 voltage reg - no fr#!*#&ing way! Once they're both installed I'll be monitoring the charging volt. If the battery doesn't respond, I'll look into replacing it (on warranty of course) as well.

Thanks,