low charge voltage at startup - PeachParts Mercedes-Benz Forum

thayer · #1 11-29-2010, 10:13 AM

83 300sd.

Ok, so I've been working on getting my charging system up to snuff. I have found 3 little issues that I have cleared up.

I messed up the wiring when I installed an aftermarket fuse block for the climate control. That has been corrected. 8 volts inital charging up to 11 volts

I pulled the fuse from the bass amp and electric remote entry.
11 volts up to 11.5.

So now , after I start the car, I am still only getting 11.5 volts at idle until I get going. After I drive a few miles, I check again...13.8 to 14.1 at idle.

My only thought is that my glow plugs were upgraded to the stay on for 30 seconds to a minute regardless of whether the engine is running or not.

How would you check that? Any other ideas?

PS. With the car off, recconect the battery. Car takes .58 amps for 5 seconds...then drops and stays at .13 amps. I assumed thats my aftermarket radio sleep booting.

vstech · #2 11-29-2010, 10:15 AM

you could pull the harness to the glow plugs and see if the voltage stays up.
I've seen starters cause this issue also...

tangofox007 · #3 11-29-2010, 10:21 AM

Quote:

Originally Posted by thayer

My only thought is that my glow plugs were upgraded to the stay on for 30 seconds to a minute regardless of whether the engine is running or not.

What is the brand of your preglow timer?

Quote:

Originally Posted by thayer

How would you check that?

Bump the starter, leave the key in the run position, then listen for the relay to click open. That could take up to three minutes to occur.

thayer · #4 11-29-2010, 10:51 AM

I just looked at the box that the fuse and plugs are mounted on for the glow plugs. Its A Bosch. Gludenfloutsnerberger. and a bunch of numbers.

After driving for an hour and then sitting for 2 hours...my battery is giving off 12.3 volts. Probably needs to be replaced.

thayer · #5 11-29-2010, 10:52 AM

Quote:

Originally Posted by tangofox007

What is the brand of your preglow timer?

Bump the starter, leave the key in the run position, then listen for the relay to click open. That could take up to three minutes to occur.

which relay am I listening for? When I turn the key to position 2 (run) the plugs stay on for approximately 30 seconds before turning off. I haven't tried to bump the starter, I'll do that tonight.

vstech · #6 11-29-2010, 10:57 AM

this is worrysome.
if the relay is clicking off at the 30ish second mark, it's likely not an afterglow timer.
it COULD be a standard relay that's had the purple wire cut to give a moderate afterglow effect, but unless the wire is cut under the cover, it's hard to tell.
you could wire in a lightbulb connected to one of the glow plugs so you could tell when they are getting power.

Diesel911 · #7 11-29-2010, 12:47 PM

After you run the Car and the Engine is up to operateing temp try restarting the car without using the Glow Plugs and see what the Battery voltage is when it starts to charge. If it is still low you most likely are haveing no issues with the Glow Plug Relay.

Try this both with and without using the Glow Plugs. Connect your Voltmeter to the Battery and start the Engine and see how low the voltage goes during starting.

I would think that if when not using the Glow Plugs the Voltage drops low during starting the Battery is on the last legs.

You could also simply pull the Battery and have it Load Tested at Autozone or some other place where they do it free. The Battery needs to be fully charged before the test.

tangofox007 · #8 11-29-2010, 01:04 PM

Quote:

Originally Posted by vstech

this is worrysome.
if the relay is clicking off at the 30ish second mark, it's likely not an afterglow timer.

That isn't true. "Afterglow" is not actuated unless a start is attempted. (That would be the reason that I recommended engaging the starter briefly.)

Quote:

Originally Posted by thayer

which relay am I listening for?

The one in the preglow timer assembly, on the inside left fender.

thayer · #9 11-29-2010, 01:58 PM

I took the car to advance to and had them run there battery and load test...they said the battery was fine. But they also said I needed a new alternator.

From what my DMM is telling me...the alternator is great and the battery is dying.

A start is tough on a battery...I bought it in 09, but it has been deep cycled many times due to my charging issue. I'll run the no glow start test and see if the voltage still drops.

Could be plugs...but its probably the battery.

tangofox007 · #10 11-29-2010, 02:19 PM

Quote:

Originally Posted by thayer

But they also said I needed a new alternator.

If they checked the alternator while afterglow was running, it could look that way. Your report of approx 14 volts at idle suggests otherwise.

pawoSD · #11 11-29-2010, 04:01 PM

The afterglow bosch relays run for about 2.5-3 mins after starting. With a 65A alternator this will keep voltage low for a couple minutes at first. I have an 80A unit on my car so it is less noticeable.

vstech · #12 11-29-2010, 04:44 PM

I think Kent has an 90 amp there. not 100% on that.
it's simple for a test of the relay though. start the car, notice the voltage, then unplug the glow harness. if the volts immediately go up. pow problem is found. if volts do NOT go up, then it's someplace else.

Quirky Mercy · #13 11-29-2010, 11:07 PM

Is it normal for the glow plugs to be on for 30 sec.? Mine are only on 10-12 sec.

vstech · #14 11-29-2010, 11:12 PM

your glow plugs are on for either 35 seconds, or as long as you wait before you try to start the car, up to 35 seconds.
the light is meaningless.

funola · #15 11-29-2010, 11:47 PM

Quote:

Originally Posted by thayer

83 300sd.

Ok, so I've been working on getting my charging system up to snuff. I have found 3 little issues that I have cleared up.

I messed up the wiring when I installed an aftermarket fuse block for the climate control. That has been corrected. 8 volts inital charging up to 11 volts

I pulled the fuse from the bass amp and electric remote entry.
11 volts up to 11.5.

So now , after I start the car, I am still only getting 11.5 volts at idle until I get going. After I drive a few miles, I check again...13.8 to 14.1 at idle.

My only thought is that my glow plugs were upgraded to the stay on for 30 seconds to a minute regardless of whether the engine is running or not.

How would you check that? Any other ideas?

PS. With the car off, recconect the battery. Car takes .58 amps for 5 seconds...then drops and stays at .13 amps. I assumed thats my aftermarket radio sleep booting.

What's your idle RPM? Try raising it to 750. Are the alternator belts tight? Connections clean at the alternator (especially the plug)? Take it out and clean the contacts. Voltage regulator brushes worn? These items can affect idle alternator voltage.