easiest way to diagnose glow plug system - video - PeachParts Mercedes-Benz Forum

funola · #1 02-08-2009, 01:03 PM

With the cold weather, I see a lot of people here are having glow plug system problems. Take a look at this video.

It shows a starter/ generator ammeter placed on the battery cable negative (breaking the connection to put this ammeter in series is not required) and a glow cycle without starting engine. The black pointer (piece of tape) on the ammeter was placed there when 5 known working glow plugs was installed. Per the ammeter (generator) scale. it is approx 35 amps at the marker. When I experience a hard start condition, I just place the ammeter on the negative terminal, turn the key on to the glow position, and watch the meter. If it reads up to the marker, all is fine. If it reads 28 amps, 1 glow plug is bad, 21 amps 2 glow plugs are bad and so on. If it does not register at all, it is likely the glow plug controller's fault. To check which glow plug is bad, place the ammeter on the wire to each glow plug.

What do you think? Easy?

Jeremy5848 · #2 02-08-2009, 01:08 PM

Nice. Where did you get the inductive ammeter? Looks like a useful tool – why don't I have one?

Edit: SNAP-ON P/N MT1009, $65 a pair direct from Snap-On. (one for charging-level current, 0-100 Amps, one for starter-level currents, 0-600 Amps) Perhaps less expensive elsewhere.

Jeremy

funola · #3 02-08-2009, 01:24 PM

I've had it for many years and can't remember where I got it. Mine is made by Black Hawk. Maybe JC Whitney before chapter 11? Try them, or NAPA, Summit Racing, Harbor Freight, Ebay? I'm suree you can find it for less. It couldn't have been more then $10 back then.

funola · #4 02-09-2009, 02:16 PM

Very few places seem to sell these type of inductive DC ammeters. SnapOn does carry a set of 2 for $65

http://buy1.snapon.com/catalog/item.asp?search=true&item_ID=11307&PartNo=MT1009&group_id=1477&supersede=&store=snapon-store&tool=all

After some searching, I found this company Hoytmeter.com that still make them.

http://www.hoytmeter.com/products/products.php?catid=53&subcat1id=67

Model 663 75/0/75 Amps $24.38 seems to be the best choice for the Mercedes. You can also use it on any wire with DC current flowing through it, such as alternator, headlights etc.

DieselAddict · #5 02-09-2009, 03:06 PM

I don't think this will work if one or more of your glow plugs has a short circuit. I prefer my cold/hot glow test where I read the resistance of each glow plug through the relay connector, once before glowing and once immediately after glowing. I have yet to hear of a better method.

kerry · #6 02-09-2009, 04:36 PM

I have an inductive ammeter that I probably purchased for around $4 30 years ago, probably at JC Whitney.

winmutt · #7 02-09-2009, 05:17 PM

ps FSM states 50AMPS, is one of yours bad or the meter just off?

kerry · #8 02-09-2009, 05:22 PM

Does a voltmeter plugged into the cigarette lighter give a similar set of indications based on the drop in voltage of the battery?

funola · #9 02-09-2009, 06:37 PM

I can't see how a glow plug can develop a short circuit. Open circuit, yes. Short? Very unlikely. I can see maybe if you left a wrench on the glow plug lead shorting it to ground, in which case the strip fuse will blow immediately. The problem with measuring glow plug resistance is that it is very difficult to measure it accurately due to lts low resistance, in the order of 1.2 to 1.5 ohms. Your run of the mill DVM will not do the job. High heat in the glow plug causes expansion/ contraction in the connections of the heater wire, which could give you erroneous readings in a flaky glow plug. Measuring current is the best way. Inductive ammeters don't 't lie. It works on the principle that a wire carrying a current through it will have a magnetic field around it proportional to the current. Try it, you will like it.

Quote:

Originally Posted by DieselAddict

I don't think this will work if one or more of your glow plugs has a short circuit. I prefer my cold/hot glow test where I read the resistance of each glow plug through the relay connector, once before glowing and once immediately after glowing. I have yet to hear of a better method.

funola · #10 02-09-2009, 06:41 PM

That's inflation for you. I probably got mine from JCW also. They don't carry it anymore. Neither does NAPA, Advance, Autozone. The SnapOn unit is made by Hoytmeter per the sales guy I spoke to.

Quote:

Originally Posted by kerry

Does a voltmeter plugged into the cigarette lighter give a similar set of indications based on the drop in voltage of the battery?

argus445 · #11 02-09-2009, 07:10 PM

How many amps does the starter normally draw i'm thinking getting one for testing starter as well. Is the normal draw from the starter around 200 amps?

kerry · #12 02-09-2009, 07:22 PM

My device has two separate scales and two separate locations on the back for laying it on the wire. One is for starters and one is for 'generators' (that tells you how old it is). I think the two scales are from 0-200 and 0-80.
Also written on the back is Patent applied for. Guess that did not pan out.

funola · #13 02-09-2009, 09:19 PM

Good question. I don't know what the absolute accuracy these induction ammeters are capable of. My guess is they are not all that great. They works by proximity to the wire and the placement (distance) of the meter from the wire has an effect on the reading. I was using the generator scale slot on the fat battery cable, which did not fit all the way in the slot, and that may have caused the reading to be lower. I can try it at the glow plug controller feed wire (thinner) to see if the reading go up closer to 50 amps. I could also have a less than perfect ground affecting the reading. What's important is that I calibrated the meter with 5 good glow plugs at the battery cable and as long as I use the meter at the same spot for diagnosing burned out glow plugs, I'm ok

Quote:

Originally Posted by winmutt

ps FSM states 50AMPS, is one of yours bad or the meter just off?

funola · #14 02-09-2009, 09:26 PM

Their SG-1 has dual scales for starter and generator. The starter wire slot puts the meter further away from the wire than the generator wire slot.

Dual Starter Generator Current Indicator
Dual Starter Generator Current Indicator features dual ranges of 75/0/75 Amps DC and 600/0/600 Amps DC. Tester is utilized on any 6, 12, 24 or 36 volt DC electrical system for any vehicle.

Quote:

Originally Posted by argus445

How many amps does the starter normally draw i'm thinking getting one for testing starter as well. Is the normal draw from the starter around 200 amps?

funola · #15 02-09-2009, 09:32 PM

I have dual starter/generator scales on mine also. 750-0750 and 75-0-75
I cut the aluminum starter slot off on mine since it gets in the way of the generator slot wire placement.

Quote:

Originally Posted by kerry

My device has two separate scales and two separate locations on the back for laying it on the wire. One is for starters and one is for 'generators' (that tells you how old it is). I think the two scales are from 0-200 and 0-80.
Also written on the back is Patent applied for. Guess that did not pan out.