Electrical - Fresh Insight Needed

[Copper]

77' - 318 - No aftermarket electrical BS, only very basic factory options.

There must be something I'm overlooking...

Problem: Electrical functions as expected at driving speeds. At idle (750rpm) the amp gauge reads as normal with everything off, but moves into the discharge side of the amp gauge with any draw whatsoever. Even the turn signals move the gauge over to the discharge side in time with a flash. The more items you turn on, the more noticable (slow operation, dim lights) the draw becomes and the further the needle moves into the discharge side of the gauge. No particular item (heater fan, lights, wipers) seems to be the obvious culprit. With everything on, the turns signals flash so slowly, I'd consider it a safety hazard. Give it just a little gas and everything speeds up, maybe even too fast. I'm guessing that's the increase in voltage as the battery recharges.

At the battery you get 14.75v at idle; 12.25 with everything on. You get the usual rise in voltage (16v but not up to 17v) and a gradual decrease after starting the engine. As I understand it, that is normal operation.

What I have done:

- Checked for shorts. I get a .01-.02v draw between the positive battery post and the positive cable when disconnected. I'm guessing that's not enough to cause my problem, maybe even normal. Feel free to correct me on that one.

- I replaced the voltage regulator and alternator - no effect.

- I checked for charging feedback between the negative battery post and the block,frame, radiator. None noted.

- I inspected all the wiring under the dash. Checked all connectors under the dash and at the firewall. Amazingly good condition; absolutely no sign of corrosion, heat damage, or dirt. Just the same, I cleaned them all with contact cleaner and coated everything with dielectric grease and reassembled them. No effect.

***Yes, I'm aware of the bias against amp gauges, and the recommended bypass procedure. I have a hard time believing it came from the factory as crap. It's been in there for 33 years. With regular inspection and maintenance, I don't see it as a ticking time bomb. I attribute the common complaints of fires, heat damage, burnt wiring/gauges and corrosion to poor user maintenance and the addition of unneeded overload of electrical accessories - not unreasonable design standards. I'd like to treat the ingrown toenail, not cut off the toe.

I'm leaning toward removing the alternator and voltmeter and taking them back to NAPA for testing.

Can you think of anything I'm missing?

Thanks for your help.

[DODGEBOYS]

12.25 under load is wrong / it should hold the 14.50 all day no matter what the load / of coarse you,ll get up and down spikes from turning stuff on and off but it should stabilize at the 14.50 always


have you chacked you bulk head connector for burning the MAIN positive wire

[Copper]

have you chacked you bulk head connector for burning the MAIN positive wire

"- I inspected all the wiring under the dash. Checked all connectors under the dash and at the firewall. Amazingly good condition; absolutely no sign of corrosion, heat damage, or dirt. Just the same, I cleaned them all with contact cleaner and coated everything with dielectric grease and reassembled them. No effect."

Absolutely no sign of a problem there. Clean as a whistle.


Increasing the RPMs does get it back up to 14.5v. It's as if the alternator does not put out enough amperage at low RPM, or something is inhibiting the of flow until you turn up the "pressure".

[n1265]

I have the same problem, but to a lesser extent. I have often wondered if the Pulley's were the right size....

[Copper]

I had the alternator and voltage regulator checked to eliminate the possibility I received a bad one. They are fine.

I double checked the bulkhead connectors. It's all in great condition.

[greg rider]

Here may be my dumb 2 cents but are your ground connections good? Make sure the engine ground is solid as this will cause all kind of stupid problems. If you have a bad ground it will backfeed through other circuits.

[74w300uteline]

gregs correct

Good clean solid grounds will eliminate all sorts of intermittent problems. I used to start trouble shooting, by throwing parts at the problems. that was getting expensive. A wise forum member, "Jimmy D" and others, suggested I start with clean ground connections. Good advise

[ddarnell]

Take the grounds off and clean them. Pulley size may be wrong, common with rebuilds. Belt tension has a surprising effect.........check that. The current path from the alternator to the battery is long and goes through the ammeter. When I pulled my factory meter out I found that the connections were burned. No doubt a high resistance connection. Combine that with a wire that should have been larger and you get quite a bit of voltage drop at the battery post. The factory did, in fact, manufacture crap. Like it or not it's not a good system, which is no doubt why they discontinued the ammeter in favor of a voltage meter. Once bypassed mine has maintained desired voltage
David

[Copper]

Grounds, grounds, grounds ...

Here may be my dumb 2 cents but are your ground connections good? Make sure the engine ground is solid as this will cause all kind of stupid problems. If you have a bad ground it will backfeed through other circuits.

Good clean solid grounds will eliminate all sorts of intermittent problems.

I checked for shorts, bad battery cables & grounds first. I went through the grounds again this afternoon. I wire brushed all the connectors washers and bolts, even ran a tap through the bolt holes. I'm confident it's not a ground problem.

I used to start trouble shooting, by throwing parts at the problems. that was getting expensive. A wise forum member, "Jimmy D" and others, suggested I start with clean ground connections. Good advise

The old alternator was actually still good, but it was noisy and didn't spin smoothly, so I replaced it anyway. I replaced the voltage regulator because I've learned the hard way that the old one often goes when you give it a new altrenator. It may be coincidence, but the method has some following.


It's got to be something just as simple.

Got any more ideas?

[Copper]

Hi David

Take the grounds off and clean them.

Done.

Pulley size may be wrong, common with rebuilds.

It's the same size as the old one. Then again, it had the same problem. Who knows how many alternators it has had. Does anyone know what size the factory original pulley was?

It's the same size as my 84'; it works fine. Is there a difference in the design?

Belt tension has a surprising effect.........check that.

No, that's not it.

The current path from the alternator to the battery is long and goes through the ammeter. When I pulled my factory meter out I found that the connections were burned. No doubt a high resistance connection. Combine that with a wire that should have been larger and you get quite a bit of voltage drop at the battery post.

I checked all the wiring in and out of the dash, including pulling the panel and checking the amp gauge. There are no signs of heat damage corrosion or loose connections.

I could check the voltage direct from the alternator and straight to the battery. Both sides of the bulkhead to the battery. I think that would identify if this is the issue?

The factory did, in fact, manufacture crap. Like it or not it's not a good system, which is no doubt why they discontinued the ammeter in favor of a voltage meter. Once bypassed mine has maintained desired voltage
David

Crap? I don't know. It's lasted a long time. Are you saying, it rolled out of the factory working this way? If not, then it must be repairable.

I do appreciate your opinion. Bypassing does seem to be the popular option. I'd like to exhaust all of the possibilities before I amputate.

Thanks for the ideas, it's helping me make sure I covered all the bases.

[KRB64]

Looks like we're fishing now...

Ground would have been my guess but that has been dismissed.

Using properly sized wire and clips you could start temporarily jumping to check things before amputation.

What about those danged ol fusible links? Can they partially burn out? Can they kinda work, just not real good? Or are they either all good or all bad? I don't know, but you can't tell by looking at the things all the time either...

[USN78W150]

charging

Is your idle speed set to factory specifications? I still think that your alternator is not putting out enough amps at idle. It is easy for some to blame the manufacturer when something goes wrong, calling it junk. No, it was not that way from the factory. The system is fine as designed. Ammeters are considered "hard to read" due to their frequent movements by the new generation of less educated drivers, so they put volt meters in instead. A voltmeter does not show if you are charging or not. How many dead batteries have we ALL seen that still read 12 or 13 volts, but won't run a domelight? My M885 is also 33 years old, and is perfect at all speeds, and under any conditions. The only ammeters I have seen fail on these trucks is on ones that have had aftermarket electrical modifications done by folks who laughingly call themselves "mechanics". They proceed to grossly hack in to the wiring in all the wrong locations to add accessories, creating a rolling fire hazard, to put it mildly. Have the alternator checked for amp output while it is in the truck, at curb idle speed.

[Copper]

Is your idle speed set to factory specifications?

Both my Chiltons, and my Hanes manual refuse to give a rpm setting specific to the model. They suggest referencing the emissions lable. If this vehicle every had one, it's long gone. This truck will idle at 500, I went with 750. I got the number from another reference for a 1960s pre emission 318 with AT.

Increasing the rpms does fix the problem, but I don't want to damage anything else. Does anyone have a shop manual that states the correct rpm for a non emission 77' D200 318 AT 2bbl?

I still think that your alternator is not putting out enough amps at idle.

I agree. I checked every leg of the charging circuit including straight from the alternator to the battery. The most difference I could find was less than half a volt.

I remeasured the pulley diameter and compared it to my 84. The new one has an OD of 3.00, the older one in my 84 is 2.75. If you do the math, thats almost a 10% loss in rpm at the alternator. Considering the climb of amperage to rpm ratio on the test card that came with the alternator, I'd suggest that is a very likely culprit.

Where could I get a different pulley? I'm thinking a 2.5 in would be perfect.

It is easy for some to blame the manufacturer when something goes wrong, calling it junk. No, it was not that way from the factory. The system is fine as designed. Ammeters are considered "hard to read" due to their frequent movements by the new generation of less educated drivers, so they put volt meters in instead. A voltmeter does not show if you are charging or not. How many dead batteries have we ALL seen that still read 12 or 13 volts, but won't run a domelight? My M885 is also 33 years old, and is perfect at all speeds, and under any conditions. The only ammeters I have seen fail on these trucks is on ones that have had aftermarket electrical modifications done by folks who laughingly call themselves "mechanics". They proceed to grossly hack in to the wiring in all the wrong locations to add accessories, creating a rolling fire hazard, to put it mildly.

I agree with you 100% on this one. To prove your point, my son and I ran all new wiring, one gauge larger through the firewall. I did not drill out the bulkhead, I simply removed the wires from the bulkhead connector (PITA) and routed new ones through a grommeted hole. All connections/splices were soldered. The realized difference was less than .2 volts. I'm sure, if there were damaged components from abuse or poor maintenance then there would be a notable difference. That was not the case here. Tomorrow, I'm putting it back the way it was.

Have the alternator checked for amp output while it is in the truck, at curb idle speed.

The best I could do is to get the auto parts store to check it for correct function. It's fine. He said if he knew how many rpms the alternator was running when my truck was at 750, he could check it. The number is irrelavant. Whatever it is, is not enough. I need more rpms at the alternator. It's just a question of how to achieve them.

[KRB64]

Both my Chiltons, and my Hanes manual refuse to give a rpm setting specific to the model. They suggest referencing the emissions lable. If this vehicle every had one, it's long gone. This truck will idle at 500, I went with 750. I got the number from another reference for a 1960s pre emission 318 with AT.
...

My Haynes says that in the absence of the engine compartment sticker to adjust idle to 750 rpms with tranny in nuetral or park.

[USN78W150]

alternator pulley

My alternator pulley on the M885 truck looks to be approximately 2.5 inches in diameter, if that. That would spin the alternator much faster than your 3 inch pulley does. I will try and get an exact measurement on it tomorrow.