Archived aternator switching on and off under load

[cblend]

2004.5 w NV5600 Highway driving, noticed AC blowing warm air. Checked gages - voltmeter at 12.2 (battery voltage). turned off AC, no change then raced up to 85 mph and alternator kicked on, read normal 14.2-5 volts. lasted 5 minutes or so (no AC) then kicked off again. Stopped and replaced alternator from NAPA. Ok for short while then back again. Stopped at dealer in Springfield MO - alternator checked good on bench, batteries OK. They said alternator not receiving (turn on signal from PCM) ordered and waited 2 days for new one. All ran good sitting in shop, got on highway and it started again. Read some forums, removed, cleaned and replaced battery connectors. No change. Made it to dealer in OK (headed to home in Tucson). replaced alternator again, new batteries. now no voltage, no AC, no fuel pump. Will try cold start on monday morning while monitoring alternator and battery voltage (heat related problem) (removed and tested battery temp sensor - ok) Head scratcher for me and tech. Chasing ghosts. HELP Charlie stranded in Oklahoma City bleeding $$

 

[AH64ID]

I would be inspecting the wiring harness that runs the control wires to the alternator and AC. There have been known issues with it, and something a dealer should know about.

 

[cblend]

I would be inspecting the wiring harness that runs the control wires to the alternator and AC. There have been known issues with it, and something a dealer should know about.

Thanks. Will do it in the morning when I get access to it at dealer.

 

[MichaelOverfield]

Did I read it correctly, you replaced the PCM and Alternator? If so it almost has to be a wiring harness/connection issue. Perhaps the PCM replacement made an intermittent connection a no connection, and if so I'd look really close at the connector to the PCM (ECU).

 

[cblend]

Did I read it correctly, you replaced the PCM and Alternator? If so it almost has to be a wiring harness/connection issue. Perhaps the PCM replacement made an intermittent connection a no connection, and if so I'd look really close at the connector to the PCM (ECU).

will pull them off and clean them to see if it helps. thanks

 

[Missouri Mule]

Not sure how low the evr (electronic voltage regulator) will tell the alternator how many volts are needed. But the battery temp sensor (under driver's side batter tray) sends temperature readings and (in 12/ 24 ? valves) the asd relay sends line voltage to the evr which determines the output of the alternator.
The colder the batteries are the more volts the alt puts out, the hotter the battery is the less volts the alternator puts out, once again the evr determines this.
( When start in cold weather it mite be putting out 14.5 volts but when it's warm (especially running down a highway you mite put or 13 or less volts.)
AC compressor could of been acting up or the engine fan(as in electric fan clutch could of been acting up.






The fan clutch wires are known to get messed up. (of course a dishonest dealer rather charge you for a pcm then a fan clutch).
Check fuses /relays in power distribution center/or what ever they call it on the 3rd gen. Another words the alternator/charging system had nothing to do with your ac blowing warm and ac system had nothing to do with voltage running low.

 

[Missouri Mule]

Also something else to check is your belt (fan/serpentine). It mite be doing OK at idle and slow speeds but at highway speeds with when ac compressor kicks in it could be slipping which could cause alternator not put out enough juice or ac not blowing cold air.
Re read the bottom of your post. Is tach working? On the 12 valves when the ac,alt tach was not working it was the engine speed sensor. You would have cam position sensor and maybe crank position sensor.
Your ecm should run the lift/fuel pump. Does your year truck have pcm and ecm, I take it does if it was replaced. Also some ac info the blend door on third generations were known to break.

 

[Missouri Mule]

Also something else to check is your belt (fan/serpentine). It mite be doing OK at idle and slow speeds but at highway speeds with when ac compressor kicks in it could be slipping which could cause alternator not put out enough juice or ac not blowing cold air.
Re read the bottom of your post. Is tach working? On the 12 valves when the ac,alt tach was not working it was the engine speed sensor. You would have cam position sensor and maybe crank position sensor.
Your ecm should run the lift/fuel pump. Does your year truck have pcm and ecm, I take it does if it was replaced.

 

[cblend]

Also something else to check is your belt (fan/serpentine). It mite be doing OK at idle and slow speeds but at highway speeds with when ac compressor kicks in it could be slipping which could cause alternator not put out enough juice or ac not blowing cold air.
Re read the bottom of your post. Is tach working? On the 12 valves when the ac,alt tach was not working it was the engine speed sensor. You would have cam position sensor and maybe crank position sensor.
Your ecm should run the lift/fuel pump. Does your year truck have pcm and ecm, I take it does if it was replaced.

thanks for the ideas. i'm off to dealership to check on the truck. tach was working, no instrument problems other than voltmeter reading. going to double check battery temp sensor too. thanks again for ideas. will post when I get more info.

 

[cerberusiam]

PCM\ECM is all integrated, did they actually replace the ECU? Was it a new one? If you are loosing functionality either the ECU is bad, mis-programmed, or there is a problem on the data bus. First thing to disconnect is the fan to see if it is shorting and causing problems.
With fully charged batteries you should see 14.2 -14.5 volts constant, that is normal. It sounds like you have had the misfortune of getting involved with parts changes not mechanics and all they are doing is throwing parts at it.

 

[cblend]

PCM\ECM is all integrated, did they actually replace the ECU? Was it a new one? If you are loosing functionality either the ECU is bad, mis-programmed, or there is a problem on the data bus. First thing to disconnect is the fan to see if it is shorting and causing problems.
With fully charged batteries you should see 14.2 -14.5 volts constant, that is normal. It sounds like you have had the misfortune of getting involved with parts changes not mechanics and all they are doing is throwing parts at it.

a whole day of trouble shooting wires, connections, relays, fuses and grounds was fruitless - until a tech leaned in to compartment and tapped the "new" ecu on the side. voltage went up (alternator kicked on), AC come on etc. lasted a few minutes the volts dropped off again. another love tap and back again. Dealer replacing ecu tomorrow!!! fingers crossed. thanks everyone for the ideas and support. will let you know how it goes tomorrow night. charlie

 

[MichaelOverfield]

a whole day of trouble shooting wires, connections, relays, fuses and grounds was fruitless - until a tech leaned in to compartment and tapped the "new" ecu on the side. voltage went up (alternator kicked on), AC come on etc. lasted a few minutes the volts dropped off again. another love tap and back again. Dealer replacing ecu tomorrow!!! fingers crossed. thanks everyone for the ideas and support. will let you know how it goes tomorrow night. charlie

Sounds like a connection problem inside the ECU. It's solid state components in there that should not be affected by mechanical agitation. Good to see you appear have progress toward a lasting repair.

 

[cblend]

Sounds like a connection problem inside the ECU. It's solid state components in there that should not be affected by mechanical agitation. Good to see you appear have progress toward a lasting repair.[/QUOTE

New ecu worked fine in shop. Everything ok till test drive. Alternator kicked off after 2 miles. Got back to dealer, couple love taps on ecu and alternator started back charging. UGH. testing ecu connections. How could driving affect this?

 

[BigPapa]

Something in your connector or harness. Cummins offers terminal repair kits.

 

[cblend]

Something in your connector or harness. Cummins offers terminal repair kits.

rewired a new ground from both fenders, firewall, ecu, alternator and batteries. works ok now. made it home to AZ and will search out a permanent solution in my own driveway. Thanks everyone for all you help. No longer stranded. Whew.

 

[MichaelOverfield]

rewired a new ground from both fenders, firewall, ecu, alternator and batteries. works ok now. made it home to AZ and will search out a permanent solution in my own driveway. Thanks everyone for all you help. No longer stranded. Whew.

Great to hear, so after all that appears to have been a wiring issue, a bad ground at that. Many years ago now I had a base model 1997 Dodge Pickup that while still under warranty had intermittent Engine cut out, first they could not find an issue, to do something they tightened the Battery connections (not it).. next time I limped in while it was acting up, they find a bad ground in the wiring harness, their "fix" was a rather obvious external to the harness alternate ground using RED wire, that was apparently OK with Chysler as well. Shortly after that "repair" the ECU dies completely.. when ordering a replacement they discover the original was the wrong one! That year they had a 3.9 V6 and a 4.0 straight 6, apparently it had the straight 6 ECU from the factory. It was a mess. I didn't think I'd ever buy another Chrysler product after that debacle, but have since had another lemon by GM, then the horrible experience with VW.. they all have such potential it seems.