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  #1  
Old 02-27-2018, 01:40 PM
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Voltage drop during hard stop

Hi guys,

I have 2003 4.4 and I am experiencing voltage dropping during hard stop. However due to the voltage dropped I sometime experience transmission slippage/bang from down shift and also upshift. For example while driving at around 40 - 50 mph and need to slow down to take the right turn without complete stop after quick braking then accelerate I sometime get transmission downshift from 4-3 problem. I also notice that the voltage drop bellow 13 v and sometime down to 12 v in the ODB and INPA while I am experiencing the transmission slippage/bang symptom. I also get the error code from transmission indicating battery is at 12.12 volt.

New battery put in a few days ago. At idling I am reading about 13.6 to 13.8 volt in the ODB. Freeway getting 14 v. If I turn on my heater and light it will drop and fluctuate between 13.6 to 13.8.

Autozone and Oreily tested the alternator while on the car, without load test it is good. With all light on, ac on max, audio on max, wiper on, the voltage bouncing around in the upper 12 v and lower 13 v and fail on the voltage regulator test.

I need and suggestions before I replace the alternator as it is water cool.
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  #2  
Old 02-27-2018, 03:00 PM
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You really have to DRIVE the car to get the voltage up to speed........like 50 miles at least.
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  #3  
Old 02-27-2018, 03:24 PM
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I have checked the B+ on the alternator and it look fine no corrode and it is pretty tight to the alternator.

Anyone know all of the ground point locations on this car? I wanted to make sure no corrosion and they all tight.
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Old 02-27-2018, 09:41 PM
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I've recently heard of problems from the main engine ground. Track that down it will mess with both starting and charging. Dips in voltage can get all types of trouble including trans failsafe


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Old 02-27-2018, 10:52 PM
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Quote:
Originally Posted by andrewwynn View Post
I've recently heard of problems from the main engine ground. Track that down it will mess with both starting and charging. Dips in voltage can get all types of trouble including trans failsafe


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Did you mean engine ground to the body chasis? I have been googling but haven't find where it is located. I hate to take out the aluminum plate unless I know that it is somewhere underneath.

Anyone one have any clue?
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Old 02-28-2018, 02:04 AM
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Good news and bad news.

I believe you can determine if the ground strap/s are the problem.

Measure the voltage from the block to chassis with the engine running. It should be under 0.5v. If you have more especially if over 1v, the cable/s are shot.

There are 2-3 cables: bare ground straps (Earth strap) and an alternator ground cable.

The bad news: have to remove the skid plate to replace.

One is apparently under the ac compressor I've not located the other on the E53/M54 (my engine).

Measure the voltage to determine if the cable is bad. You can use a jumper cable to ground the block and if the problems fade you've found the problem


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Old 02-28-2018, 09:31 AM
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Quote:
Originally Posted by andrewwynn View Post
Good news and bad news.

I believe you can determine if the ground strap/s are the problem.

Measure the voltage from the block to chassis with the engine running. It should be under 0.5v. If you have more especially if over 1v, the cable/s are shot.

There are 2-3 cables: bare ground straps (Earth strap) and an alternator ground cable.

The bad news: have to remove the skid plate to replace.

One is apparently under the ac compressor I've not located the other on the E53/M54 (my engine).

Measure the voltage to determine if the cable is bad. You can use a jumper cable to ground the block and if the problems fade you've found the problem


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I have checked the negative voltage drop yesterday while car off and running. However the temperature in the garage is around 45 degree.
1. Off = 0.00 V which
2. Running = 0.03 V which is 30 ish milivolt


I might going to take it out for 20 - 30 mins drive to warm up and check it later when I have time. Worst case I will drop the pan and check for the ground straps.
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Old 02-28-2018, 10:45 AM
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Not an obvious cause 30mV is as good as it gets. Could be a loose connection that only is a problem when shaken though.

I've seen cases where the strap was put in the wrong place or one was missing. The M54 has a negative alternator cable and an Earth strap on the parts list but sadly didn't show where they actually go.


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Old 02-28-2018, 10:56 AM
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Quote:
Originally Posted by bugbyte View Post
on, the voltage bouncing around in the upper 12 v and lower 13 v and fail on the voltage regulator test.



I need and suggestions before I replace the alternator as it is water cool.

Not sure how I missed this but the alternator should hold Rick steady voltage any load and any speed. The biggest instant load you can apply is probably the rear defrost with seat heaters.

If you are able to get sub 13v at idle not moving measure the vDrop from engine to chassis and see if you can measure any voltage drop on the ground.

Then using OBD measure the vBat and see if you can get it to hiccup with a throttle off with heavy load (wipers and defrost/seat should do it) if you can get a voltage drop of more than 0.4-0.5v from that test the voltage regulator is not doing its job.

I've recently removed and replaced an alternator on an M62 very similar it was way easier than the air cooled one on my M54 other than the annoyance of course of having to drain the coolant. Either case have to remove the fan.

I've never taken apart the water cooled models to figure out what it takes to replace the brushes and slip rings but it saved me almost $300 to refurbish mine vs replace it
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Old 02-28-2018, 11:25 AM
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Quote:
Originally Posted by andrewwynn View Post
Not sure how I missed this but the alternator should hold Rick steady voltage any load and any speed. The biggest instant load you can apply is probably the rear defrost with seat heaters.

If you are able to get sub 13v at idle not moving measure the vDrop from engine to chassis and see if you can measure any voltage drop on the ground.

Then using OBD measure the vBat and see if you can get it to hiccup with a throttle off with heavy load (wipers and defrost/seat should do it) if you can get a voltage drop of more than 0.4-0.5v from that test the voltage regulator is not doing its job.

I've recently removed and replaced an alternator on an M62 very similar it was way easier than the air cooled one on my M54 other than the annoyance of course of having to drain the coolant. Either case have to remove the fan.

I've never taken apart the water cooled models to figure out what it takes to replace the brushes and slip rings but it saved me almost $300 to refurbish mine vs replace it
I will do another load test with heated seats on and rear defroster. For some reason when I did the load test before I didn't think of the heated seat and the rear defroster. I have the re-manufacture alternator sitting on the shelve ready when I am sure that the alternator can't handle the load. I would said if all the load is on it should be getting around 13.5 V or more. If not the battery will never get enough charge.
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