Well my 240D glow plugs failed this morning - Page 2 - PeachParts Mercedes-Benz Forum

Zacharias · #16 02-22-2015, 02:41 PM

Quote:

Originally Posted by funola

Why is the engine block not a good ground? It is where the glow plugs are grounded so it better be a good ground.

Good question. I tried using the block when I measured mine and got strange readings.

When I asked for advice here, I was told that only reliable ground was the negative cable. By several respondents.

When using a multimeter or test light on other cars I have always used the engine, or something attached to it, as a ground.

charmalu · #17 02-22-2015, 03:18 PM

Quote:

Originally Posted by BWhitmore

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I must have 30 of the things.....hey they give them away

Charlie

pj67coll · #18 02-22-2015, 05:07 PM

So I got the multimeter at HF and here's a pic of my relay.

I've measured 12.86 V across the battery terminals. 12.86 at the two screws that hold the fuse in. And 12.86 at the power terminal. Power connection. That's the large cable on the right. That cable does look a bit ratty though. Wondering if it may be the problem. But if so why would I be getting 12.86V when touching that silver metal goodie in the middle of it?

- Peter.

funola · #19 02-22-2015, 05:10 PM

Quote:

Originally Posted by Zacharias

Good question. I tried using the block when I measured mine and got strange readings.

When I asked for advice here, I was told that only reliable ground was the negative cable. By several respondents.

When using a multimeter or test light on other cars I have always used the engine, or something attached to it, as a ground.

You have to clean the corrosion off the engine ground point first by scraping or sharpen the probe to puncture through the corrosion to make a good ground connection.

funola · #20 02-22-2015, 05:36 PM

Quote:

Originally Posted by pj67coll

So I got the multimeter at HF and here's a pic of my relay.

I've measured 12.86 V across the battery terminals. 12.86 at the two screws that hold the fuse in. And 12.86 at the power terminal. Power connection. That's the large cable on the right. That cable does look a bit ratty though. Wondering if it may be the problem. But if so why would I be getting 12.86V when touching that silver metal goodie in the middle of it?

- Peter.

That silver strip is the fuse. It is always hot. It looks like somebody messed with the wiring and spliced into the power feed stud.

pj67coll · #21 02-22-2015, 06:17 PM

Quote:

Originally Posted by funola

That silver strip is the fuse. It is always hot. It looks like somebody messed with the wiring and spliced into the power feed stud.

Yes. I think work has been done on the glow plugs in the past. In addition to the power feed there seems to be some soldering or something on one of the plug leads itself.

Well. I think I'm done for today. I have a massive aura in my vision and can hardly see to type. Migrane coming on. I'll have to resume the troubleshooting tomorrow.

- Peter.

pj67coll · #22 02-22-2015, 10:01 PM

Well. Turns out the migrane I thought I was getting was just a tiny one so. I continued checking on some stuff. I got readings of between 2 and 4 ohms fluctuating at the plugs with the ignition off. Not sure if I was making a good enough contact on the plug wires though.

I decided to see what readings I'd get when the key was in position II. In other words when the glow plugs should be on. I was getting just under 12 V in the switch and the power connection but while I was measuring it at the power lead I head the relay click. I double checked and sure enough after about 15 seconds of the glow cycle the relay clicks again.

I couldn't hear this from with the car as my blower fan will not switch off and drowns out the sound of the relay clicking from within the car.

So could it be that the relay is working but the bulb in the instrument cluster is not?

- Peter.

Carpenterman · #23 02-22-2015, 10:18 PM

Regarding your blower fan not turning off, try a hard bang on the side of the console near the climate control. I think the relay for the fan gets stuck closed. Probably from a fan drawing too much current and fusing the contacts.

Worked for me.

pj67coll · #24 02-23-2015, 12:28 AM

Quote:

Originally Posted by Carpenterman

Regarding your blower fan not turning off, try a hard bang on the side of the console near the climate control. I think the relay for the fan gets stuck closed. Probably from a fan drawing too much current and fusing the contacts.

Worked for me.

I have the 240D manual climate control with the large center switch for the blower fan. I don't think that's the same as you are describing if your referring to one of the cars in your sig?

- Peter.

BillGrissom · #25 02-23-2015, 12:59 AM

The other measurement you can make is w/ red probe on glow plug and blk probe on ground, w/ plug in and "glow on", see if you get ~12 V across each glow plug. You only have ~20 sec each time. That is the best way to judge that your car is doing its job supplying them.

The prior test was of each glow plug itself. Putting 12 V on a failed glow plug doesn't help.

The very best test is with the injectors (and heat shields) out, to view each glow plug tip and see it glowing orange. Do that whenever you remove the injectors, but not just to test glow plugs. People have found some to glow in the middle, instead of the tip, which you wouldn't know otherwise.

Re ground, I usually use the fuel filter mount since close, but last time I got less resistance using the power steering pump. That matters more for the ohms test, not the volts test. Funola is correct that the head is theoretically ideal, but might be harder to get good electrical contact. Could even touch the threads of the glowplug if you can get 2 hands in there. I don't fuss about the readings. A bad plug is infinity. Found one last time I did it a week ago, and guess what - a Bosch again.

Re the GP relay box, I was going to swap the one out in my 1985 today, but I couldn't find the spare box I had set aside. It is getting tricky to get the GP lamp, and usually (always?) when I don't get the lamp it truly is hard to start. It could be the key switch is going since seems I must get it in just the right spot to get the lamp, but swapping the GP box is much easier than the key switch (3 dang screws are hard to get at).

vstech · #26 02-23-2015, 06:18 AM

That cable connector in your relay wiring is pitiful... I strongly recommend you follow the soldered wire and figure where it goes, and I recommend you replace the main lead all the way back to the battery if you don't have enough slack to properly replace the end.

pj67coll · #27 02-23-2015, 08:13 AM

Quote:

Originally Posted by BillGrissom

The other measurement you can make is w/ red probe on glow plug and blk probe on ground, w/ plug in and "glow on", see if you get ~12 V across each glow plug. You only have ~20 sec each time. That is the best way to judge that your car is doing its job supplying them.

I'll check that when I get home from work this afternoon.

Quote:

Re ground, I usually use the fuel filter mount since close, but last time I got less resistance using the power steering pump. That matters more for the ohms test, not the volts test.

Good info, thanks. I've been using the fuel filler mount for ground as well.

- Peter.

pj67coll · #28 02-23-2015, 08:14 AM

Quote:

Originally Posted by vstech

That cable connector in your relay wiring is pitiful... I strongly recommend you follow the soldered wire and figure where it goes, and I recommend you replace the main lead all the way back to the battery if you don't have enough slack to properly replace the end.

For that I'd have to cut open the wiring harness would I not?

- Peter.

toomany MBZ · #29 02-23-2015, 08:22 AM

The ohm readings can be taken without power applied, 2-4 is high, you're looking for less than 1.

I use the plug, it's numbered and the bolt for the relay.

pj67coll · #30 02-23-2015, 08:35 AM

Quote:

Originally Posted by toomany MBZ

The ohm readings can be taken without power applied, 2-4 is high, you're looking for less than 1.

I use the plug, it's numbered and the bolt for the relay.

Ah I see. I was actually putting the red tip on the plugs themselves. I'll try using your method and see what happens.

- Peter.