Timing adjustment methods - Page 17 - PeachParts Mercedes-Benz Forum

funola · #**241** 02-28-2011, 08:18 PM

I found that there was a 0.09 volt difference if I used the cigarette lighter tray as a ground. That's why I ran 2 wires with alligator clips from the engine compartment to the interior, so I can have a dedicated ground at the glow plug to avoid ground loop induced voltages.

The glow plugs put out negative voltages (with respect to ground). The more negative the numbers, the hotter it is.

Engine off DVM reads 0.0 volts

idle @ 60C coolant DVM reads - 0.008 V

idle @ 82C coolant -0.009 V

60 mph cruise on theflat -0.015 V
70 mph cruise on the flat -0.017

80 mph throttle floored on slight iuphill -0.022 V. That's the highest I could get it (speeding ticket concern)

I will keep monitoring the voltages under various driving conditions to get a better feel in its behavior.

I will also rig a 5 position rotary switch so I can read the other glow plugs one at a time.

Above voltages are on WVO. It'd be interesting to switch to diesel while cruising and see if the voltage changes. .

funola · #**242** 02-28-2011, 09:25 PM

I accidentally deleted my last post while editing it. If anyone has it can you pm it so I don't have to rewrite it?

Stretch · #**243** 03-01-2011, 04:08 AM

Quote:

Originally Posted by funola

I accidentally deleted my last post while editing it. If anyone has it can you pm it so I don't have to rewrite it?

Ask a moderator to help - I guess the deleted post would exist somewhere.

I'm interested to see what you measured

whunter · #**244** 03-01-2011, 05:58 PM

Quote:

Originally Posted by funola

I accidentally deleted my last post while editing it. If anyone has it can you pm it so I don't have to rewrite it?

Done.

layback40 · #**245** 03-01-2011, 08:44 PM

Interesting data funola.
It would be interesting to compare it with EGT at the same time.
I cant see that you could time the car with it though.
If you ever find a long up hill stretch that you can use full throttle at about 50mph for about 5 minutes the result would give you when you have max EGT.

leathermang · #**246** 03-01-2011, 10:18 PM

Quote:

Originally Posted by layback40

.....I cant see that you could time the car with it though.....

True, and has been said many times in this thread many ways... but has not slowed anyone down yet.... LOL

Stretch · #**247** 03-02-2011, 05:27 AM

I'm glad the deleted post is back - keep up the good work funola...

With these tiny voltages though an amplifier would be handy to notice smaller differences if there were any. I don't suppose you've got a digital voltmeter with a graphing function?

funola · #**248** 03-02-2011, 11:01 AM

Quote:

Originally Posted by Army

I'm glad the deleted post is back - keep up the good work funola...

With these tiny voltages though an amplifier would be handy to notice smaller differences if there were any. I don't suppose you've got a digital voltmeter with a graphing function?

Amplifier? Did you mean a DVM with higher resolution? My DVM goes to 3 decimal places (milli-volt), a DVM good to 4 or 5 decimal places will see smaller differences. No graphing function on mine.

I'll be taking an 80 mile drive today and will collect more data.

leathermang · #**249** 03-02-2011, 01:04 PM

" Higher resolution " ????
no offense...but this will be the classic case of ' garbage in , garbage out ' IF you use it for 'analysis'.....
Any heat the glowplugs are subjected to is MUDDIED ( read AVERAGED ) by its physical location.... not to mention that they are not constructed ( read maximized ) for this function... did you see Whunter's post by any chance ?

Stretch · #**250** 03-02-2011, 02:06 PM

Quote:

Originally Posted by funola

Amplifier? Did you mean a DVM with higher resolution? My DVM goes to 3 decimal places (milli-volt), a DVM good to 4 or 5 decimal places will see smaller differences. No graphing function on mine.

I'll be taking an 80 mile drive today and will collect more data.

No I'm not talking about trying to "zoom in"... that is difficult in practice.

You are measuring really small voltages that happen to change by really small amounts. If you amplify the signal by 100 times or even 500 times then you can see the changes more clearly. You can also come up with a value for the signal to noise ratio - which will give you an impression of the reliability of the measurement.

funola · #**251** 03-02-2011, 06:53 PM

Quote:

Originally Posted by Army

No I'm not talking about trying to "zoom in"... that is difficult in practice.

You are measuring really small voltages that happen to change by really small amounts. If you amplify the signal by 100 times or even 500 times then you can see the changes more clearly. You can also come up with a value for the signal to noise ratio - which will give you an impression of the reliability of the measurement.

The glow plug is a very low impedance device. Even though the voltage output is very low, noise is not an issue as long as you have good connections from the DVM direct to the glow plug electrode and ground (no ground loops). The readings on the DVM are very steady and do not jump around. If noise was an issue, I would expect erratic readings

During the 90 mile drive, I got out at fuel stations to switch to the other glow plugs. They all responded similarly, i.e. more engine load, more voltage. Highest voltage was -0.022 volts.

I do not have a 5 position rotary switch wired up yet, so these are readings of 5 glow plugs at idle only:

#1 -0.008 V
#2 -0.012 V
#3 -0.007 V
#4 -0.009 V
#5 -0.006 V

Note that #2 and #5 are at opposite extremes. I will be swapping them with #1,3,4 to see if it follows the glow plugs or cylinders.

What I have observed thus far is that glow plug voltage outputs are predictable and repeatable, and move in direct correspondence to engine loading.

whunter · #**252** 03-03-2011, 12:23 AM

Quote:

Originally Posted by funola

The glow plug is a very low impedance device. Even though the voltage output is very low, noise is not an issue as long as you have good connections from the DVM direct to the glow plug electrode and ground (no ground loops). The readings on the DVM are very steady and do not jump around. If noise was an issue, I would expect erratic readings

During the 90 mile drive, I got out at fuel stations to switch to the other glow plugs. They all responded similarly, i.e. more engine load, more voltage. Highest voltage was -0.022 volts.

I do not have a 5 position rotary switch wired up yet, so these are readings of 5 glow plugs at idle only:

#1 -0.008 V
#2 -0.012 V
#3 -0.007 V
#4 -0.009 V
#5 -0.006 V

Note that #2 and #5 are at opposite extremes. I will be swapping them with #1,3,4 to see if it follows the glow plugs or cylinders.

What I have observed thus far is that glow plug voltage outputs are predictable and repeatable, and move in direct correspondence to engine loading.

If this data where to be believed?
I would suspect head gasket issues on this engine.

Stretch · #**253** 03-03-2011, 04:04 AM

Quote:

Originally Posted by funola

The glow plug is a very low impedance device. Even though the voltage output is very low, noise is not an issue as long as you have good connections from the DVM direct to the glow plug electrode and ground (no ground loops). The readings on the DVM are very steady and do not jump around. If noise was an issue, I would expect erratic readings

...

I'm guessing steady readings on your voltmeter are probably more to do with the dynamics of the voltmeter rather than the output from the glow plug. As for your comment about noise - I don't go along with that - sorry (but I see little point in butting heads over it!)

So keep up the good work. You are more than a few steps ahead of me on this project - I'm still scrabbling around in the ditch trying to get some equipment...