Did a search and found some info but before I dive in and R/R the alternator I thought I would check other opinions.

2005 R52 with 83K miles replaced bad battery 3 days ago.

Symptoms,
When driving during the day with just radio the car runs fine, add the A/C and the engine will die with lights on the dash coming on. Put in neutral and engine will restart after I turn off the A/C.

***Update, engine does not actually stall, it looses power 15-20 mph, like limp mode***

At night I can only run the lights, even adding the radio will kill the engine. Sunday this happened and the CEL came on, it is now on when the engine is running. Drove home with lights on but nothing else, made it home home fine.

Will test Alt. output tomorrow and belt tension etc. just wondering if there was some weird electrical gremlin that I am not aware of.

BTW, where is the engine ground located at? I have never touched this car besides normal maintenance but have build plenty of rigs domestic and foreign.

PS don't have a code reader but read you can do it with the odometer? How do I do that??

TIA for ant suggestions and replies Tom

 

To me looks like your crank pulley went to sitts... Had the same issues but my car always went to limp mode with ac on and if run at wot. Pop the hood and start the engine without ac. Then let someone turn on ac button and inspect if the belt slips. And if that's the case do your self a favor and buy ati crank pulley from way.

 

That is what I am leaning towards now after more reading. The part that gets me is that it runs fine if I turn all electrical draws off (radio, A/C and lights) I can run the radio only or the lights only and be fine but not both. The A/C part makes sense but the radio doesn't draw that much power.

 

Second (third?) the crank pulley, but you may also be seeing an alternator on its last legs that is putting a lot of load on the crank pulley.

 

Look at the crank pulley....
A battery SHOULD provide extra power at low rpms I'd the electrical draw is too high....
Limp mode is caused by things other than a lack of electrical power usually...
Think if limp mode as the cars ecu saying "I give up" cause the numbers it is seeing don't make sense when trying to operate the motor....usually a slipping crank damper causes lots of lights...the sc suddenly is not running at the right speed...so the airflow numbers then the fuel number don't make sense to the ecu... especially if the damper is gripping and slipping...
The fact you say with the ac on and radio on it get worse is a bit if the tell...toy add load to the belt, and it slips more.

 

And you can't get gen 1 codes from the odometer...that's gen2+3

 

Thanks, I found my reader and of course got the P1688 so it is time ..........