hey all,

My 82 just underwent an engine swap.

The engine donor wouldn't charge batteries, and had killed 2 batteries for the PO, so I swapped the alternator with a known good one from the original motor.

Have driven the vehicle now 6 or 7 days and 150 miles with all smiles. But, this morning, no start - dead battery. AAA jump started.

- charge light on dash never on during operation (but comes on normally at start-up)
- 12.60V charging voltage
- I swapped the regulator with a known good one. Same results.
- I read another thread here that a stuck GP relay can cause the symptoms.
- Removed the GP relay connector. Charging voltage now 13.4V
- then removed + lead from battery - 'unloaded' charging voltage now 14.4V
- plug the GP relay in and the then voltage drops to 12.6V (even after several minutes ,one after GP relay should be off)

- tested resistance of the glow plugs, seem to be OK (1.2ohms), but noticed inconsistent results with sometimes the plugs all showing a .2 ohm short to the engine block. need to re-verify

How could the glow plugs (pencil style) or wiring harness cause this issue? And why wouldn't it blow the strip fuse?

Any help much appreciated. I have a spare harness, but Id like to root cause it first.

Thanks,
dd

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Sounds like the GP relay is not opening. You should be able to hear it click on and then off (in about 45 seconds) if you do not start the engine.

... the GP fuse fails after a short, or wear, not just from time... actually, the GP's pull less amps the longer they are on... to a point, so the 80 amp fuse will likely handle extended glow times easily.

I've had GP controllers do weird things to the car's charging system, one even caused the starter to engage whenever it was in the Glow position...
if the harness out of the pic gets good charging, AFTER the 45 seconds have elapsed, you have a bad controller.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

With the glow plug connector attached, and the readings at 12.6V, put a voltmeter on the #1 glow plug. If you have 12V after the relay should have opened (35 seconds), replace the relay and the problem will be eliminated.

Just a friendly reminder. Do not disconnect the battery with an engine running. You will get away with it usually. Then one time you will not and the resultant repair cost may be very high.

These 123s are an old technology car but can still also suffer damage. It is just not as bad.

whats the risk? can the alternator not go from load to no load gracefully?

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

Glow plug relay was indeed broken and not turning off after 45 seconds.

Replaced and no problems thus far.

Will report back if anything else develops.

Thank you! Without the forum tip of looking at the relay Id be replacing an alternator and battery probably.

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

I was under this same impression until just recently. The prevailing and generally accepted knowledge is that you should NOT disconnect the battery terminals with the engine running. You are likely to blow a voltage regulator.

By the way, it does sound like something is wrong with your glowplug circuit. If the controller never shuts the glowplugs off then you probably would not have a reliable charging system.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)