Gen 2 Very dim. Relay?

[scottladdy]

So after the above post where I was throwing in with the the guys who have an indicated problem but nothing serious happening...... I got to work yesterday like normal and when I went to leave the front battery was dead. The truck started instantly with a little battery booster and then did the same routine with the clunk under the hood and the bat/gen gauge jumping up and down.

Does anyone one have any input on this? It would be very helpful to know if this is a relay problem or a gen problem. I suppose in the end I should just do it all and go on with my life but unlike most of you fine people I dont have a safe full of cash in the shop just waiting to do a ground up restoration on the truck.

Separate issues until you diagnose each system and prove they are correlated.

Glow plug system in afterglow is most likely the cause of the voltmeter/relay behavior. This is normal. Antennaclimber made a great video on this which can also be found on YouTube.

As far as your dead battery, you need to check the battery and the charging system. Follow the diagnostic routines in the TM's.

Please let us know what you find.

 

[bshupe]

Thanks Scott. That is surprising that the glow plug circuit would cause such a drop on the gauge. Would the "Wait" light not energize if the glow plug circuit is on? It has been in the 20-30s here the last week or two so perhaps that is why the glow plug circuit is coming back on after starting in the morning. Perhaps if my batteries are in good condition but the alt is not charging then the load from what you are calling afterglow would be pulling down the volt gauge and I am just not reading it correctly? I had always presumed that if the volt gauge is up in the green the system is charging but it sounds like that might not be correct with what I am learning now.

Like many sad people, I was never in the military so I am not actually very good at interpreting the TMs although I do have them and I do try. A member here was even nice enough to pass along the TM and diagrams for the 1031 system. I will revisit the TM and I also am trying to work through the Gen2 sticky on SS to diag the gen2 diode. It would appear that I am fortunate to have a gen2 light that works and comes on when the key is on and then goes out when the engine starts although occasionally after a little goose on the accelerator.

The batteries are both brand new. I have considered installing a disconnect at the main battery ground and throwing it when I park to keep the batteries from being drawn down but that is just a bandaid.

Thanks for your input scottladdy. I am hoping to have some time to look at this in the next couple of days and will follow up here.

 

[scottladdy]

The glow plugs are a fairly heavy drain. Check this video out: http://youtu.be/MTkOl947aTk (Thanks again to Antennaclimber)

Automotive electrical and charging systems can be daunting until you understand them. The CUCV's hybridized 12/24 volt system adds some additional potential for confusion until you get familiar with it.

To keep things somewhat simple, electrical loads in a vehicle periodically exceed the capability of the charging system. In these cases the batteries act as a sort of buffer, helping to smooth out the load.

Now consider your specific situation. It is Winter and cold. You have just put an initial drain on your batteries by running a longer GP cycle (until wait light goes out) and then start a cold diesel engine. It is often stated that running the starter is the single biggest load you can place on your batteries. And, your batteries are cold as well, which reduces their output. All of this happens before your alternators are spinning and charging.

So, now your engine is running and the GP's cycle on. You hear the clunk of the relay which completes the circuit through your GP's to provide that afterglow heat to help warm up your engine (and reduce emissions). That additional drain can show up on your voltmeter. Now, we also know your front battery has been compromised. It is either on it's way out or not getting charged (or a combination).

I intentionally simplified some of the explanations here.

Take your time and follow the steps in the TM's. They are logically laid out, and intended to eliminate the most likely causes first and to help narrow down to the root cause of your issue(s). Some people print the pages out and mark them up as they go. Use highlighters, especially on the schematics (The wiring diagrams near the end of the TM's).

Most of what you will be dealing with is direct current. Just think of the electricity kind of like water flowing through a copper pipe. It helps to view the flow starting at the positive post of your battery. But, unlike water which will flow out of a broken pipe, the electricity must flow back to the negative post of the battery or nothing happens. You also need to know that your front battery's negative post is connected directly to "ground", which is your truck body/frame, the engine block, etc.

So, again, go step by step, tell us what you did and what you found. If you get stuck, just ask. We all started out not knowing this stuff.

Simple stuff first, you can get your drivers side alternator tested (which feeds your front battery) free at most local parts monkey stores. You can also get your battery tested. I would consider starting with these items.

Other suggestions most welcome.

 

[biggestc69]

Just for the record its still does it. Just on faintley. You'd miss it if you werent looking for it. But the multimeter says its good to go and the voltmeter's in the green so. Replaced batteries, belts, bulb's, sockets, the alternator cleaned all connections several times and still same result. I'm kinda a perfectionist on the truck, its my baby so for the first several months it was nails on a chalkboard driving at night and just barley seeing it lit up. Now I check it when I'm driving occasionally like with all the gauges but I've gotten to the point where this one has beat me. And as long as its working I've finally accepted that I'm just gonna have to live with the quirks of a 29 year old truck. Bshupe, good luck with your electrical gremlins. Electrical, not my strong point either and its not on most of the CUCV's either. But once you figure out your wiring schematics and get used to standing on your head under the dash and trying to read a multimeter or finding a ground for a test light with a flashlight in your mouth as you go from wire to wire you'll do well with the truck. I drove one an M1031 in Iraq and the only problem it gave us electrically was the starter relaly stuck in downtown Baghdad right after the Thunder Runs that 3rd ID did. Not a place you wanna break down. If you havent done that I would make it top priority, before you have no wiring harness to troubleshoot. Then do what scottladdy said and load test the batteries, mighta got a lemon and get the alternator tested. Grounds are important too so make sure they get hit with a wire brush or wire wheel on a drill is how I like doing it. If you need help with the TM's I'm not the best and after 10 + years I was a little rusty, and I'm now scholar on them now but I'm sure we can get you headed down the right path. Just a lot of little steps and things to check out before replacing big ticket items.

 

[scottladdy]

Just for the record its still does it. Just on faintley. You'd miss it if you werent looking for it. But the multimeter says its good to go and the voltmeter's in the green so ...

I've seen this issue with a high resistance short of the stator windings in the alternator. You would not see it if tested with a light. You must check it with a good meter (no HF freebies for this job).

 

[bshupe]

@scottladdy - Thanks for the great info and encouragement, and for the video. I will dig in and see if I can track down the problem.

As for the electricity part, I have worked on cars since I was 12 including building/installing high-powered A/V systems. I also was an industrial electrician in a previous career working with motor control systems that ranged from power supplies putting out negative and positive DC voltages all the way up to 480V three phase frequency drives for large manufacturing plants and robotic assembly lines. I think I have a mental block more than anything with the CUCV because it's old, dirty, very difficult to access and has components that dont often make sense to me from the electrical engineering aspect of it. Its hard for me to get deep into the logic of a circuit if I dont have some idea of what they were thinking about when it was originally conceived. Even a poorly designed circuit can be pretty easily gone through if you have the back story.

Brand new batteries in the truck BTW. When this problem first started I had the OEM 6T batts tested and the front one was shot. At $400 a copy I opted to replace both with the standard GM spec batteries for the truck. That seemed to cure the problem I was having with the battery going flat but now Im thinking that was just the first part of the problem. In a way, I guess I followed the TM troubleshooting guide instinctively.

 

[bshupe]

OK, so now that I had a minute to watch the supercalofagiouslyexpalidiouslylyoisis video on the glow plug system I think I likely have a much simpler problem of an intermittent drain on the front battery. From what the video showed everything on the glow plug side of my rig does exactly what he showed and the sound of the relay opening and closing is exactly what I hear and it makes perfect sense that the volt meter would show that load turning off and on.

I have had alts go bad in the past and provide a short to ground draining the battery in a car but as previously noted, this is not generally an intermittent condition. Either the diode is shorted or its not. This leads me to the sum of all fears that I have a short somewhere under the hood. I will start with the wiring on the back of the gens cleaning it up and checking for voltage etc. on the battery and exciter wire and follow up. Why dont these things happen in the summer when its 65 degrees out?

Thanks again for all the help and encouragement!

 

[bshupe]

By the way, who is working on vids like that for all the other systems on the truck? Where can I send my donation to the cause?

 

[biggestc69]

I've seen this issue with a high resistance short of the stator windings in the alternator. You would not see it if tested with a light. You must check it with a good meter (no HF freebies for this job).

Scott, would a two different snap on multimeters and a bench test at a reputable shop be good enough to meet your "good meter" standard?

 

[doghead]

Spend $80 and rebuild both of your alts.

You cannot diagnose electronics by sounds.

Use a meter. Every single component can be tested (except the GP controller card.

Troubleshooting is covered in very easy to follow format in the -20TM.

 

[scottladdy]

Scott, would a two different snap on multimeters and a bench test at a reputable shop be good enough to meet your "good meter" standard?

I can't speak to the meters, but Snap On has a good reputation. The situation I am describing was only found on a complete tear down of the alternator where the stator was explicitly checked for shorts. As I said, it was a very high resistance short, so your meter needs to be able to detect it. A bench test of this very same alternator indicated all was OK. I am sure it was going to be just a matter of time before the insulation broke down sufficiently to cause a dead short.

Stator replaced, and the issue went away. This was after a rebuild, which as Eric suggests is a great recommendation

The charging circuit is fairly straightforward. Take a good look at the manual for the 27si (attached), especially starting on page 2. You will see that there are very few things that can be the root cause of your issue. Delco Remy provided a good description of the regulating circuit and the fact that it is cycled several times a second. An imbalance caused by the high resistance short I describe can easily cause a low current to flow through that light bulb.

I would trust your initial gut on this that something isn't right. Keep plugging, and let us know what else you find.

Most importantly, thank you for your service biggestc69. I can't imagine what it was like to have your ride quit like that on you under the conditions you were in.

View attachment cucvdelco.pdf

 

[j.cherry377]

to diagnose this circuit, try unplugging the connector that takes the signal from the alternator to the dashpanel, if the light is still on with the key on and engine running , the problem is in the harness or the circuit board on the back of the gauge set. If the light stays dimly lit only while plugged into the alternator, the circuit is being completed through that point. With the gauge panel out inside on the left there is a ground connection, remove that terminal block, using a wire brush clean the metal behind it and brush the grounding block that was held on with the screw. Replace the grounding lug that plugs onto this point or clean with wire brush and use OX-GUARD anti oxidant compound. Cleaning all the grounds should be performed like this, this will eliminate a lot of the weird glowing from lights throughout the vehicle. Most of the time the dim glow is because there is a bad or missing ground and some other circuit is grounding through whichever lamp is glowing to complete the circuit.

Verify using an ohm meter that the ground connection on the circuit board has less than 1 ohm of resistance to the ground on the sheet metal. Also check from this ground to the negative post on the battery on the DC 0-2 volt scale, there should be less than .1 volt across the two grounds. If higher, check the neg to frame cable and clean both ends and the jumper cable from the battery neg to the vehicle sheet metal jumper should be checked for integrity, often they are corroded through from acid fumes and just hanging there and not really providing a good ground reference to the sheet metal.

Also use OX-Guard on the fuses blade in the fuse block and battery terminals themselves. Anyplace where wires are attached to terminals should be cleaned and have the ox-guard treatment

 

[cpf240]

Maybe swap alts to see if the problem follows the alt?

 

[SFC Deal]

I've got the same issue with my 85 M1009. The Gen 1 light stays on with a low glow when running. I don't even notice it in the day time. I've had both batteries load tested & are good, and all belts are tight but NOT new. Could this low glow just be a gremlin & nothing to worry about?

 

[cpf240]

Gen 1 shares the heater blower circuit, so check out the heater blower motor, switch, resistor, connections, etc.

 

[SFC Deal]

Gen 1 shares the heater blower circuit, so check out the heater blower motor, switch, resistor, connections, etc.

My heater blower works great on all 3 setting.

 

[Gripy]

OP, The glow plugs coming on and off could mean that your some of your GP's are fried. Are they still 24v or have you done the resistor by-pass. The GP control card will do that to prevent the other GP's from burning out too quickly.

 

[SFC Deal]

OP, The glow plugs coming on and off could mean that your some of your GP's are fried. Are they still 24v or have you done the resistor by-pass. The GP control card will do that to prevent the other GP's from burning out too quickly.

I've had the glow plugs all tested & were good. How do you check the glow plug card?

 

[Warthog]

I've had the glow plugs all tested & were good. How do you check the glow plug card?

First you need to follow the step-by-step procedure in the TM 9-2320-289-20 tech manual. Electrical troubleshooting, section 2-15. It makes sure the wiring is working correctly. There is no "test" for the controller. Just how it "should" work. The GP Theory sticky has a great video that explains how the system should work.

 

[SFC Deal]

First you need to follow the step-by-step procedure in the TM 9-2320-289-20 tech manual. Electrical troubleshooting, section 2-15. It makes sure the wiring is working correctly. There is no "test" for the controller. Just how it "should" work. The GP Theory sticky has a great video that explains how the system should work.

Thanks for the help.