“No-Start” Something Other Than Glow Plug-Related? - Page 2 - PeachParts Mercedes-Benz Forum

wcmartin75 · #16 07-13-2010, 05:33 PM

SUBJECT: “Glow Plug PROBLEM SOLVED, Wagon Up and Running”

1982 300 TD (Turbodiesel Wagon)

After considering all the good and thoughtful advice you all provided, I decided to heed the advice of those who counseled me to “work the problem, first”. If the 80A Strip Fuse was blowing, then concentrate, first, on solving that problem (and ignore any other possible problems until after solving that one)!

The Glow Plug “GP”) testing methodologies recommended on many websites and forums are based upon GP resistance, in Ohms. Based upon that methodology, I did not have an obviously bad GP (not open or infinite!), as the readings, reported elsewhere in this thread, indicate.

Because I did not have a high comfort level working with battery-size currents, I decided to use my relatively small shop Battery Charger (“BC”) which puts out 8 Amps, has a built-in Ammeter, and is protected by an internal circuit breaker.

Both to remove the wiring harness from my experiment as a variable, and to protect it from current, I removed the 8 mm nut from each of the five GPs and then removed the wires coming from the large connector in the GP Relay. The GPs were to be tested in the cylinder head, however.

To test my experiment methodology, I removed No. 1 GP from the cylinder head and laid it down on the concrete driveway. I hooked up the Negative of the BC to the body of the GP, and the Positive to the threaded end of the GP. I plugged the BC into the extension cord, and watched as the element of the GP first smoked, and then grew a bright red. After 40 seconds or so, I unplugged the BC and allowed the GP to cool. When it was cooled, I reinstalled it into the cylinder head.

For the next stage of my experiment, I knew I wanted a good ground, so I took the negative cable of my shop jumper cables and hooked it to the battery ground. I was not looking to get battery power, just the good ground provided by the battery negative. I hooked the negative lead of my BC to the other end of the grounded jumper cable coming from the battery.

To review, I now had each of the five GPs isolated in the cylinder head with no wires connected to them. I knew No. 1 GP was good outside of the cylinder head, but just for good measure I tested it again in the head. I connected the positive lead of my BC, and then plugged the BC into the extension cord. The Ammeter pegged itself at 8Amps and held steady. After about 40 seconds, I unplugged the BC. No 1 GP checks out as good.

I moved to No. 2 GP, connected the positive lead of the BC, and plugged the BC into the extension cord. The Ammeter pegged itself at 8 Amps FOR ABOUT FOUR SECONDS, then the circuit breaker in the BC made a relatively loud noise as it tripped, and the Ammeter went to zero. I unplugged the BC and waited several minutes for everything to cool down and for the circuit breaker to reset itself. For the second try, to reproduce the experiment, the same exact thing happened: 8 Amps for about four seconds, and then dead short.

GPs No. 3-5 tested good, exactly like GP No. 1.

Next, I connected the wires coming from the Glow Plug Relay to GPs 1, 3, 4, and 5, only. I left No. 2 unconnected. After replacing the 80 A fuse in the Glow Plug Relay and making sure the large and small connectors were connected, I turned the ignition, watched as the GP light lit up, and cranked the engine which caught quickly and started up!

Sometime later, I removed the new GP Relay and reinstalled the old relay I had replaced with the new one. After installing a new 80A Strip Fuse, the old GP Relay lit the lamp in the instrument cluster, started the engine, and now does not blow the Strip Fuse. It seems to be just fine!

I will now proceed to replace all the GPs (believe it or not, I think the Beru s are all original) and ream out the precombustion chambers before installing the new GPs. I have quite a lot of carbon in there! Can anyone suggest where I could find an image of the section, shape of the precombustion chamber so I would have a better idea of where I should try to remove the carbon from?

What I learned, of course, is that that you can have a GP that tests just fine using the resistance method, but will quickly short out as it begins to draw current! By the way, I think several “experts” on this website said as much.

Thank you all so much for your thoughts.

-Bill

Rick Miley · #17 07-13-2010, 05:40 PM

Quote:

Originally Posted by wcmartin75

“work the problem, first”. If the 80A Strip Fuse was blowing, then concentrate, first, on solving that problem (and ignore any other possible problems until after solving that one)

I'm vilified! err, vindicated! Well, something with a v.

Anyway, glad to hear that you got it running. I think it was P.E.Haiges who said many years ago that the definitive test was to take a glowplug out and put voltage across it so you can see it heat up.

Now we can continue with the discussion of why your engine didn't start when it was warm but had no glow. Have you adjusted the valves yet?

wcmartin75 · #18 07-14-2010, 04:55 PM

SUBJECT: “Glow Plug PROBLEM SOLVED, Wagon Up and Running”

1982 300 TD (Turbodiesel Wagon)

After considering all the good and thoughtful advice you all provided, I decided to heed the advice of those who counseled me to “work the problem, first”. If the 80A Strip Fuse was blowing, then concentrate, first, on solving that problem (and ignore any other possible problems until after solving that one)!

The Glow Plug “GP”) testing methodologies recommended on many websites and forums are based upon GP resistance, in Ohms. Based upon that methodology, I did not have an obviously bad GP (not open or infinite!), as the readings, reported elsewhere in this thread, indicate.

Because I did not have a high comfort level working with battery-size currents, I decided to use my relatively small shop Battery Charger (“BC”) which puts out 8 Amps, has a built-in Ammeter, and is protected by an internal circuit breaker.

Both to remove the wiring harness from my experiment as a variable, and to protect it from current, I removed the 8 mm nut from each of the five GPs and then removed the wires coming from the large connector in the GP Relay. The GPs were to be tested in the cylinder head, however.

To test my experiment methodology, I removed No. 1 GP from the cylinder head and laid it down on the concrete driveway. I hooked up the Negative of the BC to the body of the GP, and the Positive to the threaded end of the GP. I plugged the BC into the extension cord, and watched as the element of the GP first smoked, and then grew a bright red. After 40 seconds or so, I unplugged the BC and allowed the GP to cool. When it was cooled, I reinstalled it into the cylinder head.

For the next stage of my experiment, I knew I wanted a good ground, so I took the negative cable of my shop jumper cables and hooked it to the battery ground. I was not looking to get battery power, just the good ground provided by the battery negative. I hooked the negative lead of my BC to the other end of the grounded jumper cable coming from the battery.

To review, I now had each of the five GPs isolated in the cylinder head with no wires connected to them. I knew No. 1 GP was good outside of the cylinder head, but just for good measure I tested it again in the head. I connected the positive lead of my BC, and then plugged the BC into the extension cord. The Ammeter pegged itself at 8Amps and held steady. After about 40 seconds, I unplugged the BC. No 1 GP checks out as good.

I moved to No. 2 GP, connected the positive lead of the BC, and plugged the BC into the extension cord. The Ammeter pegged itself at 8 Amps FOR ABOUT FOUR SECONDS, then the circuit breaker in the BC made a relatively loud noise as it tripped, and the Ammeter went to zero. I unplugged the BC and waited several minutes for everything to cool down and for the circuit breaker to reset itself. For the second try, to reproduce the experiment, the same exact thing happened: 8 Amps for about four seconds, and then dead short.

GPs No. 3-5 tested good, exactly like GP No. 1.

Next, I connected the wires coming from the Glow Plug Relay to GPs 1, 3, 4, and 5, only. I left No. 2 unconnected. After replacing the 80 A fuse in the Glow Plug Relay and making sure the large and small connectors were connected, I turned the ignition, watched as the GP light lit up, and cranked the engine which caught quickly and started up!

Sometime later, I removed the new GP Relay and reinstalled the old relay I had replaced with the new one. After installing a new 80A Strip Fuse, the old GP Relay lit the lamp in the instrument cluster, started the engine, and now does not blow the Strip Fuse. It seems to be just fine!

I will now proceed to replace all the GPs (believe it or not, I think the Beru s are all original) and ream out the precombustion chambers before installing the new GPs. I have quite a lot of carbon in there! Can anyone suggest where I could find an image of the section, shape of the precombustion chamber so I would have a better idea of where I should try to remove the carbon from?

What I learned, of course, is that that you can have a GP that tests just fine using the resistance method, but will quickly short out as it begins to draw current! By the way, I think several “experts” on this website said as much.

Thank you all so much for your thoughts.

-Bill

wcmartin75 · #19 07-14-2010, 05:02 PM

No, Rick, I have not adjusted the valves yet. First, I'm going to get all new Beru Glow Plugs installed AFTER I spend some time removing/reaming the carbon material out of the precombustion chambers.

I think the Glow Plugs were/are original; 28 years?? I'm replacing the Beru that are coming out with new, identical Beru

leathermang · #20 07-14-2010, 05:07 PM

Be sure to read the threads about that reaming...

many people assume that you can just use the engine to blow out any carbon which might not have been captured on your heavy greased threads or vanes of the reamer...
but that is not the case.... since half the time your piston is sucking. and if you do not pull the precombustion chamber in this process ... then the potential for where that loose carbon will GET STUCK is the precombustion chamber holes... radial tiny holes which are the essence of your whole diesel physics.... I think there are 7 of them on most of our engines... like many things they did change some things about them....like the size on the ' uprated' engines...
And if you take out the precombustion chambers remember this part is critical...
take out the glow plugs,
take out the precombustion chambers,
put the precombustion chambers back in,
put the glow plugs back in.

VERY IMPORTANT CONCEPT.... otherwise you cause real damage when you shear off the end of the glow plug while moving the precombustion chamber.... LOL

kerry · #21 07-14-2010, 05:23 PM

Since you have all the glow plugs out, I'd do a compression test. It would only take about 20 minutes and could give you some useful information.

barry123400 · #22 07-14-2010, 05:35 PM

If you take that glow plug that the charger fed it's maximum output into before the thermal breaker tripped. I hope you will find that it has a dead short.

You can compare it to one of the new plugs. The difference ohm wise between a dead short and normal is not a lot on our meters but it should show. There would be a time delay with your 8 amp charger under overload until the thermal breaker tripped remember. The gauge would show its maximum amps as the output until then. The amperage output would be developed over the hook up wires only.

A glow plug that develops a short after heating is difficult to rationalise. Plus we would have to reconsider changing our advice to others if this is so. It could also be a one in a million type of thing.

Can you recheck it with an ohmeter? About one to two ohms resistance showing would mean we will have to change guidance a little. Dead short and the status quo remains.

I am pretty sure you are well aware that to establish where zero ohms is on your meter just short the two leads together on the lowest ohm scale and observe what the meter indicates.

The glow plug has to indicate exactly the same to be considered shorted. Now if you used an analogue meter all bets about any usable accuracy at these low value ohm readings will be off.

Rick Miley · #23 07-14-2010, 05:50 PM

Quote:

Originally Posted by leathermang

Be sure to read the threads about that reaming...

many people assume that you can just use the engine to blow out any carbon which might not have been captured on your heavy greased threads or vanes of the reamer...
but that is not the case.... since half the time your piston is sucking.

OK, I read a few threads on reaming and didn't find a "procedure." So I went to your beloved FSM and it says this:

Quote:

Removal

1 Unscrew all nuts, remove connecting line, connection insulators and conductors

2 Unscrew glow plugs with box wrench

Installation

3 Prior to installing glow plugs, clean glow plug channels and bores in prechambers with reamer. For this purpose, fill flutes of reamer with grease and ream glow plug channels.
Note: In the course of time, oil carbon will settle in glow plug channels. This may result in a ground connection of glow plugs.

4 After reaming glow plug channels, crank engine several times with starter motor, so that the residue is blown out of combustion chamber.

5 Install glow plugs, connect to conductors, connect connection cable and attach with nuts.

7 Check glow plugs for function.

Hmmm, I wonder what step 6 was.

Anyway, the folks who wrote the book said to crank the engine. Would you like to recommend an alternate way to remove the carbon? Vacuum cleaner perhaps? Or is removing the prechamber the only way?

leathermang · #24 07-14-2010, 06:54 PM

Yes, vacuum cleaner...
NOT pressurized air... as that can do the same thing... force any loose carbon into places it should not be.
But I have long advocated taking out the precombustion chamber and inspecting ( pentle often missing so fuel is not being dispersed properly ) and cleaning it.. ( not my labor, easy to recommend others do it ...LOL ) because it is the heart of the whole mechanism... and if any of the ' bottleneck' holes have obstructions you are going to get less power and fuel efficiency....

( of course I got these ideas from the FSM.... but those that know me could guess that ).

Rick Miley · #25 07-14-2010, 07:02 PM

Oh boy! So now he has to get the pin wrench for the prechamber collars, the prechamber puller, new fuel return line because the old ones will fall apart when he pulls them off the injectors, and a set of injector heat shields.

Right - easy for you to recommend to someone else.

I assume you have the prechamber tools and use them like R Leo uses his spring compressor. Just for the fun of it.

A vacuum cleaner is sounding better and better here.