CUCV alternator symptoms, diagnosis and fix.

[niferous]

OK sorry it's taken me so long to check and get back. I measured my wires and here is what I got.

Red wires with key off - Driver side: 12.5
Passenger side: 24.5

Brown wire with key on - Driver side: 3.5
Passenger side: 13.5

So should I assume something is wrong somewhere in that wire? Are there any common problem spots? Also just in case it matters I just left the plugs plugged into the alternator and stabbed through the cable. Then just wrapped where stabbed in some electrical tape. I doubt it would hurt anything to leave them unwrapped but I had some handy so I went ahead. Plus I'll know where there is a hole in the future should I need to test again.

 

[johnsr]

my m1028 was doing the same as yours. i had bouth alts tested one good, one bad. replased the bad one. after checking the system, and Warthog's help, i found a bad fusable link going to the ground stud on the back of alt 2.

 

[Barrman]

You need to unplug the plug from the alternator. The purpose of testing with it un plugged is to determine if the problem is with the alternator or with the truck. That 3.5 volts could be from a short in the alternator or a broken wire on the truck. We don't know which at this point.

Yes, just wrapping that up will reduce the chance of it shorting on something in the future.

If you put the ground for your DVOM on the negative for the battery the alternator serves, all your readings will be 12 volt scale. This might be a help when you are comparing numbers.

 

[niferous]

OK I pulled the plugs off today and here are the readings I got.

Red Wire Driver: 11.6
Red Wire Passenger: 24.3

Brown Wire Driver: 8.7
Brown Wire Passenger: 20.9

I also went ahead and tested the batteries. I got these readings when I tested positive to negative post.

Front Battery: 11.7
Rear Battery:12.7

Just for reference I got the batteries tested overnight at Advanced about two weeks ago and they tested out fine. He said they were a little low but not enough to make them fail.

Ideas? Also to all you CUCV electrical gurus THANKS!

 

[Warthog]

OK I pulled the plugs off today and here are the readings I got.

Red Wire Driver: 11.6
Red Wire Passenger: 24.3

Brown Wire Driver: 8.7
Brown Wire Passenger: 20.9

I also went ahead and tested the batteries. I got these readings when I tested positive to negative post.

Front Battery: 11.7
Rear Battery:12.7

Just for reference I got the batteries tested overnight at Advanced about two weeks ago and they tested out fine. He said they were a little low but not enough to make them fail.

Ideas? Also to all you CUCV electrical gurus THANKS!

Is the reading from the brown wire with the key on of key off?

1st you need to charge both batteries. They should both be in the 12.5~12.7 range.

It also sounds like you have some dirty contacts some where. The 8.7 voltage is too low. It should be the same voltage as the front battery itself. In this case 11.7v.

How did the two plugs look? Really dirty? If so use some electrical contact cleaner and a small cardboard nailfile to clean them.

When was the last time you removed the insturment cluster and cleaned all the contacts?

Warthog

 

[niferous]

The key was on when I tested the brown wires with the key in the on position.

The contacts were very very dirty and I just went to the local NAPA and got some lectra clean so I'll be going and cleaning those as soon as I get done typing this. The instrument was cleaned less than a year ago. However I didn't clean the contacts for the voltmeter. I will do that now too.

Both batteries are consistently low. The front more than the rear is usually low. Maybe I can replace the front and see if that helps. Later on I'll get the rear.

 

[niferous]

Ok went out and cleaned out the plugs and then I went ahead and switched out my glow plug control card since I knew the used one I had in there was no good. Well I got the plugs good and clean and picked out some of the crud with a pick. Then I let the lectra clean dry off and I plugged them back in.

Well I plugged them back in and then went to try and start the truck. By the way even with the low volt gauge it's been starting and running just fine. Well the volt gauge was reading lower than normal and while I was waiting for the "WAIT" light to turn off something under my hood sounded like a jet engine spooling up and then made kind of a grinding noise. My volt gauge at this point was all the way down in the brown. SOOO I took investigated and it was coming from my glow plug relay on the fire wall. Anyone ever had that happen? Maybe it's due to the low batteries? I'm charging them right now and will let everyone know if that changes anything.

 

[Barrman]

You have several problems not really related to each other happening at the same time. Glow plug card issues, glow plug relay issues and then the charging system issues which cause your low batteries.

Theory wise, your volt meter being lower meant all or at least more of your glow plugs were on and heating when they haven't been in the past because of the bad card. Maybe the card was bad because of a short at the relay? Have you swapped out the relay for one that is actually good?

Either go ahead and fix the relay or just pull the card and let that system/ problem sit un used and un fixed for now.

Getting back to the charging system which is what this thread is supposed to be about. Once you have 12.4-12.7 volts on each battery with it just sitting. Then, unplug the plugs at the alternators and do the checks again with the key on and key off. Try grounding to the battery the alternator charges so you are not getting a system wide voltage. You just want the voltage for that part of the system. Let us know what you find.

 

[niferous]

OK I charged both batteries overnight and went and got a new multimeter since the testing ends on mine were starting to look bad. After charging the batteries, cleaning up the connections, and tightening the belt on the driver's side alternator I got:

Front Battery: 12.5
Rear Battery: 12.5

With key off -
Driver's red: 12.54
Pass Red: 25

With key on and glow plug card removed -
Driver brown: 12.0
Pass Brown: 24.3

So everything looked good but I wanted to check the alternators. I reinstalled the glow plug card and let the plugs cycles. No crazy noise from the glow plug relay this time. The engine cranked right up but the belts gave some whining. I think I need to tighten up my power steering belt but that's a different story. Anyhow at first the volt gauge read in the yellow, then slightly in the green, then it went up past the little white tick mark (picture attached).

I went ahead and tested my alternators and I have attached a picture of what I got for those results with the corresponding point on the alternator that I tested it at.

 

[Warthog]

Sounds like you have fixed the problem. The voltages you got at the excitor plug are good, so the interior wiring is fine. The alternators haven't worked in a while so after a short time they woke up. Keep an eye on everything and run it for awhile.

Good job.

So the solution to this issue was to clean the electrical connectors on the two pin excitor plug. With 25+ years of dirt, grime and who knows what else the alternator was not getting the 12v required to "excite" the windings.

You might also want to put some di-electric grease on the plug to keep the connection clean and dry.

 

[Barrman]

Yep, everything seems to be working good. The volt meter will be right at the yellow/green line or a little below at start up cold because the glow plugs stay on for 5-30 seconds after start up depening on how cold the engine is. Then, you will hear the glow plug relay kick off and the needle will jump up to where your picture shows. Running down the road for several hours with nothing on will also have the gauge coming down to just over the + sign as the batteries get charged up. You seem to be describing a perfectly operating system.

If you want to freak yourself out, leave the heater blower fan on high when you turn off the truck. The fan winding down will send voltage to the GEN 1 light causing the light to come on with the key off and then dim with the slowing down fan. I hadn't turned on my fan except to verify it worked since I owned the truck until Tuesday night. It took me a second to realize what had happened.

 

[jooakes]

were do you get your rebuild kits from? I checked napa they don't have them. and are they both the same driver side and pass side?

 

[Warthog]

Stock alternators are the same on the left and rright.

Here is one place I buy my rebuild kits.

http://www.aspwholesale.com/index.php?act=viewProd&productId=5137

A local repair shop can order them also

Delco 27 SI ,Type 100, 100 amp

 

[jooakes]

thank you looks like what i need

 

[Disciple]

Hey guys, I've been having similar problems, been going down the list of things to check as well. I will be cleaning my contacts at the alternators today too, but just curious if it's possible to get the white plugs anywhere other than cutting them from a junker truck? Mine are really dirty and the tops are melted. I'm wondering if this could be the beginning of all my recent frustrations.

Thanks!

 

[Warthog]

Any autoparts store has them. Around $5. Standard GM alternator plug.

The colors of the wires will be different, usually red and white.

I have been preaching since my intruduction to the CUCV world......CLEAN all the connections and the majority of your electrical problems will be solved.

With the Deuce, 5-ton and M715s the connections are usually sealed and aren't an issue.

 

[cfish]

Wow, I just went to school. Thanks guys this was informative beyond compare. Just absorbed a great deal of important info. Thanks.

 

[Warthog]

Here is an update for alternator parts:

Spring Hill Auto Electric has changed thier name to Alternator & Starter Parts Wholesale. Thier old website no longer works.

The new website is www.aspwholesale.com

And the Alternator kit is:

High output Alternators - Alternator Parts - Starter Parts - Repair Kits - DELCO 27SI HEAVY DUTY REPAIR KIT

Also www.CUCVElectric.com ( a SS Vendor) has info on rebuilding alternators. He is not selling any parts at the moment. Hopefully again sometime.

 

[jholler]

...should I need a come-along to pull the plug on the #1gen, or am I not holding my mouth just right? That thing does NOT want to come out!

 

[Warthog]

There is a tab on the plug that keeps it in place.

Added a picture of a plug that has been replaced.