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93 PAU 90K miles, No Crank, No Start

GunnyP

A Regular
91
11
8
Cleveland, OH
Buick Ownership
Buick Park Ave Ultra 1993
She's been running like a charm but this morning wouldn't start. Turning the key brought only silence. Had replaced the starter solenoid two years back. Has 220Amp Alternator for 1000W inverter w/ several additional 00 gauge grounds to power laptop, 27" monitor and multiple harddrive NAS, deep cycle AGM battery for RV-Motel mode when on the road. Averaging under 3000 mile per year so monthly use CTEK charger to top off battery.

Anyway, DMV shows battery at 12.7V, 12.6V @ starter. When key engaged to start position, shows 12.1 at the ignition wire. At the battery posts when key is engaged there is only 0.2V drop in voltage.

I'm thinking this all means that there is no problem with the Starter Enable Relay, else there'd be no voltage at the ignition wire, right? So at this moment I'm pulling the starter to bench test.
Does this seem the right direction to take?
 

GunnyP

A Regular
91
11
8
Cleveland, OH
Buick Ownership
Buick Park Ave Ultra 1993
Well, pulled the starter for a bench test. Cabled up to a spare battery reading 12.3V with jumper cables then used alligator clips from positive battery post to the ignition wire on the starter and the gears extended and spun quite vigorously. So there's apparently nothing wrong with the starter.

Puzzling indeed!

Back to the drawing board...
 

GunnyP

A Regular
91
11
8
Cleveland, OH
Buick Ownership
Buick Park Ave Ultra 1993
Let's call it a lesson in not trusting the voltmeter to fully describe the condition of a battery.
Decided to use the recondition setting on CTEK Multi-US 7002 charger upon remembering there was snow on the ground during my last "monthly" top-off of the battery. This seems to have done the trick. The battery was at 12.81V and this time cranked easily.
Ordered a conductance battery tester which should arrive tomorrow so that I can check the actual cranking capacity of the battery before wrecking a day with unnecessary and fruitless diagnosis.
 

Alan 55

Buick Newbie
276
85
28
Florida
Buick Ownership
2001 Buick Park Avenue, previously owned 1997 Park Avenue
Let's call it a lesson in not trusting the voltmeter to fully describe the condition of a battery.
Decided to use the recondition setting on CTEK Multi-US 7002 charger upon remembering there was snow on the ground during my last "monthly" top-off of the battery. This seems to have done the trick. The battery was at 12.81V and this time cranked easily.
Ordered a conductance battery tester which should arrive tomorrow so that I can check the actual cranking capacity of the battery before wrecking a day with unnecessary and fruitless diagnosis.
Thanks for providing such detailed information. Glad that your vehicle is starting now.
______________________________
 

GunnyP

A Regular
91
11
8
Cleveland, OH
Buick Ownership
Buick Park Ave Ultra 1993
Thanks for providing such detailed information. Glad that your vehicle is starting now.
Thanks!

This Battery Clinic Playlist by a Mercedes-Benz technician was most helpful.

Received the conductance battery tester yesterday, a Konnwei KW600; very pleased so far. It showed that the old battery that I'd shelved as a spare after it repeatedly failed to start the car in Nov 2018 was only putting out 280 CCA of the rated 800 CCA after a recondition cycle. So it is dead and headed to recycle, although it did allow me to test the starter. The low reading means that the AGM deep-cycle must have been in even worse condition before reconditioning. Going to invest in a variable voltage bench power supply thingamajigger.

The AGM deep-cycle that powers the car now did pass the battery charge test, putting out 94% of the rated 880 CCA. The above playlist did alert me to added benefits of multiple reconditioning cycles so applying a second cycle now.

Clearly though, I don't drive sufficient mileage to keep the battery charged and also believe there is a parasitic drain that needs to be exterminated. Will begin weekly top-off charging since this low-amp charger can safely trickle charge the battery .
 
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