Archived Alt guage dead, slight burning smell.

[jchapin]

Hi All,

Apologize up front for long wordy post but throwing out all I currently know...

Was able to park truck at local mechanic (who has decent reputation), but otherwise disabled until we discover fix.

Symptoms: Drove 5-minutes out of driveway (~25 degrees F local temps) last night and at stop sign, detected a faint (not strong) burning smell (defroster on medium). Thought it could be coming from car in front so I pulled out and drove 1-2 miles, then "Check Gauges" idiot light illuminated with the Alt/Bat gauge dropping pretty much dead. Pulled off into parking lot, opened hood and could slightly smell the same burning scent as before. It was dark and unfortunately my toolbox with flashlight was left in garage (of course... ) so I could not pinpoint where smell came from. Shut down, checked P-Codes which revealed a P-1682. Don't have device to check ECM codes (... time to purchase a scan tool). Took the walk of shame home... Came back 2hrs later, cranked over easy enough with alt/bat gauge reading 10-12, no idiot light however alt/bat gauge climbed near 14 then would drop down to 10, then climb up again, and repeat. At drop there would be brief dimming of interior lights. Decided to drive to local mechanics lot (better than a public lot) 1-2 miles towards home. While driving there I got same symptoms as original (slight burn smell, idiot light, dropped alt/bat gauge). Parked and checked under hood: no detectable smoke/smell, alternator was spinning (to rule out frozen alt pulley). While I generally plug in heater block on evenings, I always cycle grid heaters 1-2 times before cold starts.

Relevent Info: 2001 ETH/DEE, Original Alternator, 140K miles, Edge EZ, FASS 95/95, AFE, 4" full exhaust. New pair of Die Hard Platinum batteries (2 months old). Original Heater Grid Relays.

Diagnosis: My first guess is the alternator. Adding the FASS & Edge may or may not have bumped up the demands (I added them last Spring) but this Fall my 3 y/o Autozone batteries died. (forget name brand, but they were cheap replacement to get me out of a dead-battery spot (originals)). I ordered a Mean Green Alternator when replacing batteries 2-months ago, but it took them 6 weeks to deliver. So I have it and will install it today. But, I don't want to be throwing parts at it before nailing down the real problem. I am still wondering about that smell. Will bad alternators make a burning smell?? There's also possibility of an electrical short somewhere. My TDR searches revealed Heater Grid Relay problems that threw similar symptoms. I checked Heater Grid last night after a few hours shutdown and it didn't appear any warmer to touch than rest of engine. This morning I checked alt/bat gauge and it was still at about 10-11.

So that's where I'm at. Unfortunately I had to get to work, so will let the local mechanic have a look (they are not known for diesel work, but do a good job on everything else), and I gave them the new alternator to install (might as well).

Does anybody have anything else I could have checked out while in shop?

Many thanks, again sorry for long post. VR/Jack

 

[JApol]

Good morning
I would not worry about the lights dimming when you are at a stop when its cold. The grid heaters pull a lot of amps and will dim all your lights when they turn on.

I am not 100% about your alternator but if its the original it probably is bad.

 

[JLandry]

Jack,



If it's not the alternator, then it'll likely be either a wiring problem or the PCM. The PCM regulates the alternator's output and has been known to fail internally. If it does turn out to be the PCM, you have the option of replacing it or just rewiring the charging system with a separate voltage regulator (thus bypassing the PCM).



Good luck,



John L.

 

[jchapin]

Good morning

I would not worry about the lights dimming when you are at a stop when its cold. The grid heaters pull a lot of amps and will dim all your lights when they turn on.



I am not 100% about your alternator but if its the original it probably is bad.

Thanks for the help!



The light-dimming symptom was only happening parked at idle in conjunction with the alt/bat gauge climbing up near 14, then dropping down below 10, then climbing up again and repeating. Gauge would climb up, lights would suddenly dim, then gauge would drop down as lights brightened, then repeat. (ie: gauge was actively moving up and down as I watched it). Cheers.

 

[jchapin]

Jack,

If it's not the alternator, then it'll likely be either a wiring problem or the PCM. The PCM regulates the alternator's output and has been known to fail internally. If it does turn out to be the PCM, you have the option of replacing it or just rewiring the charging system with a separate voltage regulator (thus bypassing the PCM).

Good luck,

John L.

Thanks, John.
The smell of something burning has me thinking a short somewhere or some other wiring issue. Sure, I have the new MeanGreen Alt to throw at it, but again I'm unsure if it is that's true problem. Understand I could rewire as you stated for good or until I find a PCM <$500. 00 (if it's the PCM)

Unfortunately I'm electrically-challenged for these problems, but the good thing is it forces me to learn more...

Thanks again. -Jack

 

[Mishkaya]

My guess is you do have a short somewhere that probably killed the alternator. Did you check to see if the main 140 Amp fuse is still intact or not? I would be reluctant to replace the alternator until the short has been found. Of course it could be the PCM that caused the Alt failure, but it is relatively uncommon in later trucks.

Good luck.

 

[jchapin]

My guess is you do have a short somewhere that probably killed the alternator. Did you check to see if the main 140 Amp fuse is still intact or not? I would be reluctant to replace the alternator until the short has been found. Of course it could be the PCM that caused the Alt failure, but it is relatively uncommon in later trucks.
Good luck.

No, didn't check the main fuse. I am also reluctant to replace alt without further investigation, especially if doing so endangers the new alt. The MeanGreen Alt wasn't cheap.

Any suggestions on where I can go to learn how to chase down (or rule out) a possible short?

Many thanks, -Jack

 

[JLandry]

Any suggestions on where I can go to learn how to chase down (or rule out) a possible short?

Jack,



Before you spend a lot of time checking the wiring, you first might want to have the OEM alternator tested at your favorite local chain auto parts store. That's the fastest way to find out if there's anything wrong with it. If it tests fine, then you'll know the problem lies elsewhere and can go ahead and spend more time on it.



To check the wiring, start by doing the following:

1. Disconnect the negative battery cable from both batteries.

2. Pull the 140 amp GEN fuse in the PDC.

3. Pull the TRANSMISSION CONTROL RELAY located in the PDC.

4. Disconnect the connectors on the back of the alternator.

5. Disconnect PCM connector 2 (the one in the middle).

6. Disconnect PCM connector 3 (the one on the end furthest from the driver).​

Next, using a Ohmmeter check for continuity (a complete circuit) between the following points and a good chassis ground. You SHOULD NOT find a complete circuit with any of these or you have a short and will have to fix it.

1. The positive battery cable/post.

2. Both sides of the 140 amp GEN fuse socket.

3. The end of the heavy 4 ga output wire which was connected to the back of the alternator.

4. Terminal 1 (field wire) of the 2-pin connector at the alternator.

5. Terminal 2 (source wire) of the 2-pin connector at the alternator.

6. Pin 10 of PCM connector 2.

7. Pin 25 of PCM connector 3.​

Next, check for continuity between the following pairs of points. You SHOULD have a complete circuit for each. Any open circuit means you have a break in the wiring.

1. Positive battery cable/post and one side of the 140 amp GEN fuse socket in the PDC.

2. The end of the heavy 4 ga output wire which was connected to the back of the alternator and one side of the 140 amp GEN fuse socket in the PDC.

3. Terminal 1 of the 2-pin connector at the alternator and pin 10 of PCM connector 2.

4. Terminal 2 of the 2-pin connector at the alternator and pin 25 of PCM connector 3.​

Best regards,



John L.

 

[GAmes]

Thanks for the help!



The light-dimming symptom was only happening parked at idle in conjunction with the alt/bat gauge climbing up near 14, then dropping down below 10, then climbing up again and repeating. Gauge would climb up, lights would suddenly dim, then gauge would drop down as lights brightened, then repeat. (ie: gauge was actively moving up and down as I watched it). Cheers.

That is the way it is supposed to work. It is normal grid heater cycling. I think that one or both of the grid heater relays is sticking closed after a few cycles. It could be a PCM problem as well. The PCM sends a ground signal to the relays, the hot side is hot all the time. I would rule out the alternator because once it fails it won't give you 14 volts between cycles. I have my relays wired to a toggle switch and bypassed the PCM. If I forget to turn the grid heaters off, or hit the toggle switch by mistake, the high amperage draw will kick the alternator off line after a few miles. That requires me to shut the engine off for a few seconds and restarting it. The PCM (which is also the voltage regulator) resets and all is good. I recommend you disconnect the grid heater relay's signal wires and maybe even the large wires to the grid heaters and troubleshoot from there.

 

[jchapin]

Everybody,

Thank you VERY much for your time and insightful help. I have much to learn on this electric system and really appreciate your help.

As stated, I left it at local mechanics while I went to work. He ran a test on the charging system and the alternator failed. Cause (test-machine definition) was bad diodes and low charging volts. This is what the Snap-On D-Tac Plus machine printed out (Batteries & Starter good). Therefore he replaced alt with the new one I had already purchased. Unfortunately he did not run any more tests on the PCM/ECM looking for codes and since he had to pull the cables from batteries while replacing alternator, the memory cleared.

I took it for a test run for about 8 miles and didn't experience any issues; the alt/bat gauge stayed pegged just above 12 while driving. I'm still wary that the root problem could still be somewhere else (hopefully to no detriment of new Alt), and will continue to troubleshoot using the directives provided above. Tomorrow I will test more (Thanks, John, for the above test sequences).

However, for all practical purposes, the truck is back in service. Not with full confidence, but enough to be out of the disabled category. Therefore if there are any moderators reading this, please move this thread to a more appropriate category so to free up resources for more urgent 911 problems.

Again, thank you all very much I am extremely grateful for your kind help. You Rock!

VR/Jack

 

[Sticks]

Don't sweat it. If the Alt tested bad (140k miles) then it is a done deal. I think the only thing on these trucks that were designed to last over 100k miles is the engine core (block, crank, pistons, etc... )

If you are concerned about the amperage draw, have your buddy do a load test on your truck to see what it is actually pulling with everything on (lights, engine, wipers, radio... ) you will be surprised how much fluff room you have even with an OEM alternator.