My slow to start 87 190D 5speed first cold morning start... - PeachParts Mercedes-Benz Forum

vstech · #1 10-05-2014, 11:52 AM

Ok. I've been slack doing maintenance on her since I acquired the car...

I think 3 gps are burned out, the glow light stays on for several minutes, and randomly turns on during the drive.

If I wait a full 45 seconds before starting the car, it catches ok, but nowhere nearly as quick as my turbo cars.

I'd like it if an explanation of the light in the 87 glow system could be described.

I know I need to pull the plugs, or at least ohm them out... It's on my REALLLLLLLLY LONG LIST...

Thanks everybody.

mannys9130 · #2 10-05-2014, 02:06 PM

From my understanding:
87 2.5 turbo got the afterglow relay.

The relay looks at #1 plug's resistance and if it's wonky the glow plug light will come on and stay on AFTER starting to notify you that there is an issue. The light won't come on at all if you have no power to the relay (80 amp fuse).

There's more to it than that though. I just don't know much more at the moment.

Mxfrank · #3 10-05-2014, 02:26 PM

You have bad glow plugs, simple as that. The usual symptom is that the light doesn't come on when you turn the key, but comes on after you've been driving awhile. Yours is a little odd, but still consistent with bad plugs. On the 2.5 Turbo, it's all but impossible to do the glow plugs without removing the intake manifold...I'm sure others will describe some weird feat of mechanical legerdemain, but removing the manifold is the way I do it.

Mxfrank · #4 10-05-2014, 02:39 PM

Quote:

Originally Posted by mannys9130

The relay looks at #1 plug's resistance and if it's wonky the glow plug light will come on and stay on AFTER starting to notify you that there is an issue. .

Not exactly. The current flowing through the #1 plug is compared to the total current flowing through 2-5. If the ratio isn't 1:4, then the indicator light is turned off during the preglow cycle, but will come on later.

The result is very wonky, because the way that current is measured is with two coils on either side of a magnetic switch. One coil has 4 times the number of windings on the other, and is counterwound. These coils supply power to the plugs. When ratio of the currents is exactly 1:4, the magnetic fields created by current flowing through the coils are equal and opposite, and the magnetic switch isn't activated. So odd situations can occur when more than one plug is bad, or when the resistances aren't all in spec. My policy is to replace all the plugs whenever the lights go nuts.

Stretch · #5 10-05-2014, 02:44 PM

Here's the FSM chapter containing the operation and testing

http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/60010.pdf

vstech · #6 10-05-2014, 09:09 PM

Quote:

Originally Posted by Stretch

Here's the FSM chapter containing the operation and testing

http://www.startekinfo.com/StarTek/outside/11832/Resources/201Create/PDF/60010.pdf

My iPad gives me the site maintenance message with that link...

Shortsguy1 · #7 10-05-2014, 11:26 PM

Stretch's link worked for me on a PC using Firefox. Surprisingly, I normally cannot use Firefox reliably to access the startekinfo FSM .pdfs. I typically have to use Chrome, which is not my normal browser. Anyway, my point of all this is to say that you probably need to try on a pc or with a different browser.

Stretch · #8 10-06-2014, 08:54 AM

Indeed - I get straight to it with that link too.

If it still doesn't work try going to the start page

www.startekinfo.com

Then pick MB workshop resources

Then CD/DVD

Then find the W201 FSM

Then OM601 section

Then Engine electrical

jsain86 · #9 10-11-2014, 02:00 AM

Did you check the tire pressure?

Mölyapina · #10 10-11-2014, 09:50 AM

Out of curiosity, how do you think tire pressure is related to hard cold starts?

vstech · #11 10-11-2014, 11:42 AM

Quote:

Originally Posted by jsain86

Did you check the tire pressure?

Heh, the web is tricky with posts going In The wrong place isn't it...

jay_bob · #12 10-11-2014, 12:57 PM

Quote:

Originally Posted by Mxfrank

Not exactly. The current flowing through the #1 plug is compared to the total current flowing through 2-5. If the ratio isn't 1:4, then the indicator light is turned off during the preglow cycle, but will come on later.

The result is very wonky, because the way that current is measured is with two coils on either side of a magnetic switch. One coil has 4 times the number of windings on the other, and is counterwound. These coils supply power to the plugs. When ratio of the currents is exactly 1:4, the magnetic fields created by current flowing through the coils are equal and opposite, and the magnetic switch isn't activated. So odd situations can occur when more than one plug is bad, or when the resistances aren't all in spec. My policy is to replace all the plugs whenever the lights go nuts.

Mr. MxFrank has it right. It is a current balance relay. There are cases where you can lose more than one plug but the relay will not catch it.

Best thing to do here is go ahead and do a full plug replacement since you don't know the history. Time to bite the bullet and pull the manifold. Yes someone will chime in and say you don't need to do that, but on a 60x you pretty much have to, unless you like having to contort yourself to get around all the obstructions. And unless you happen to have the perfect length tools to get in there, and be able to rotate them through a useful fraction of the circle, without hitting anything down there.

You can of course try the simple ohm test from the connector. But the only thing I trust in that regard is if I get a high reading then it has definitely failed. Low resistance won't tell you anything. The element could be shorted halfway along the length, which would pass the ohms test, but won't get hot where it counts, at the tip.

You can pull them and do the jumper cable and vice trick, but you've already got them out by that point, so I would go ahead and put in new ones on principle. Unless you just wanted to confirm that glow plugs was the problem, and not something more serious like low compression, the vice trick is a waste of time in my book.

mannys9130 · #13 10-11-2014, 01:13 PM

Quote:

Originally Posted by Mxfrank

Not exactly. The current flowing through the #1 plug is compared to the total current flowing through 2-5. If the ratio isn't 1:4, then the indicator light is turned off during the preglow cycle, but will come on later.

The result is very wonky, because the way that current is measured is with two coils on either side of a magnetic switch. One coil has 4 times the number of windings on the other, and is counterwound. These coils supply power to the plugs. When ratio of the currents is exactly 1:4, the magnetic fields created by current flowing through the coils are equal and opposite, and the magnetic switch isn't activated. So odd situations can occur when more than one plug is bad, or when the resistances aren't all in spec. My policy is to replace all the plugs whenever the lights go nuts.

I knew it! It looks at current. That makes much more sense now that I think about it.

Mxfrank · #14 10-11-2014, 07:48 PM

Quote:

Originally Posted by mannys9130

I knew it! It looks at current. That makes much more sense now that I think about it.

If it's any consolation, measuring resistance or current get you to the same place, thanks to Ohm's law. It would have been simpler to test resistance, but this way the relay can cost three times as much.