Lay it on me

Hello lamby. You need a digital multi meter with a milli volt scale (cheap is fine)......Attach the positive lead to the bolt head on the glow plug bar where the large wire coming from the glow plug relays attach and the negative to the Block....not the battery ground...............extend the leads with jumpers so you can have the meter inside the cab to a place that you can safely see while driving.........

I am not going to tell you what the readings should be at this point, all I want you to do is see that the readings are very responsive to your driving conditions...............

Make notes of the readings when at the following conditions:

30 seconds after you start the engine and at idle rpm....

go for a drive (about 10 miles) and note the highest reading you get ...............

during your drive find a stretch of highway that is very flat and note the reading at 45 MPH while in fourth gear.........

play with it.......see how the readings change with rpm, going up a hill and down a hill or when you see smoke from the tail pipe........notice any relationships to the readings and driving conditions.........

when you return home, note the reading at idle........

I need to know what fuel you are using during the test and if the engine is turbo...........

feel free to call me if you have a question, but I want you then to post on open forum what your question was and my reply........<img src="/forums/images/graemlins/patriot.gif" alt="" />

regards,
crossbones
919 698 6613

This is a very interesting discussion. If you do experiment with this, please post the results.

Crossbones, am I way off-base here or are you basically using the glow plugs to measure (and log) something similar to EGT? It seems the data could be used in the same way EGT data is, as far as determining proper fuel delivery and timing.

Hello acy76. You are on target......I am utilizing the "Seabeck Effect" of the glow plugs to give me a temperature relationship inside the cylinder.........IMVHO it is many times more accurate than using exhaust temperatures........and ten times faster responce time in real time.................

You will see this method used to control diesel timing more accurately in the next few years..............

regards,
crossbones

Easy 'nuff. As soon as I have a moment, I'll toss one on there. Well, a moment when it's not pooring down rain--doing all my work in the driveway. Garage is too full of parts <img src="/forums/images/graemlins/wink.gif" alt="" />

Will report back on the forum.

First let me say, Crossbones, you were right about it being responsive. The multimeter shows the millivolts running all over the place--go up a slight hill and the reading changes. Hit the fuel pedal, and the reading changes. Very very responsive.

Now for some results:

First phase of glowing--5 volts running up to over 6.
2nd phase (after the light goes out) -- runs up to 7.3 volts

After turning the key, the reading is 7.5 mV, but over the next 30 seconds it drops down to about 3.5 mV.

After the engine warms up, the idle reading is 2.1 to 2.4 mV at 730 RPM.

Driving down the road in 3rd at about 35 mph, reads 3.5 mV.

Driving down the road in 4th at about 45, reads 5.6 mV. But keep in mind, I've got 3.73 gears, and 31 inch tires. RPM's in 4th at 45 are a bit low (2000-2100) and my engine sounds much better at 2400. If I move up to 2400 rmp in 4th, it reads more like 5.3 mV.

In fact, I noticed that lugging the engine down gave the highest numbers. On the freeway, uphill, 4th gear, 50 mph, 2100ish rmp gave me 6.7--the highest reading I saw.

Most of the time, it hung down around 3.3-4.4 ish mV. When I ran it up over 3000 rpm the reading would go up to 6mV.

As I mentioned before, lugging it down, in any gear, would cause the reading to go up as well--between 6 and 6.7 as noted.

The lowest reading I saw was 2.1 while going downhill slowly. Saw 2.4 while going downhill at more like 45 mph.


Diagnosis, Doctor? <img src="/forums/images/graemlins/wink.gif" alt="" />

Hello lamby. First, let me say that the reading of 7.3 volts on cut off of the glow plugs "may indicate" you have a weak glow plug which can cause higher readings.......If a weak glow plug is not the case then..........Diagnosis: you have a good running engine.......power is down some......fuel mileage is down some.......you have typical diesel smoke under light load............Prognosis: with a little work you can most likely improve the performance a good bit....

The milli volt readings are giving you a temperature relationship in the cylinder of how well it is burning the fuel.........now what is so very important to note here is that to get the most efficiency in a diesel is to control the temperature.....not to low or to high, but just "right"................

Your idle rpm should be a min of 800.........I prefer 1000........

The first simple test is to test the function of the "cold start devise". The CSD advances the timing for start up.....this is done after the engine is hot (best)............start the engine without much gas.....allow the readings to settle down to the lowest reading (note the reading).........now rev the engine up to about 2500 rpm a couple of times.........this should cancel the CSD.........the readings at idle now should be lower than the previous reading at idle....

Your gear ratio and tire size could be a major factor here with the road readings, so lets look at the idle readings for now...........your readings of 2.1 to 2.4 are very close to what I like to see..............I look for them to be 1.5 to 2.....

I would prefer for you to test each glow plug before making any changes..........the engine has to be hot to do this, the bar that connects all four glow plugs has to be removed and the glow plug relays disconnected.........you test the readings of each glow plug and note the readings at idle and driving conditions...........what you are looking for is a glow plug with higher readings than the other three.......................if this is found, then exchange the glow plug with the highest readings with the cylinder with the lowest readings...............test the readings again...................if the very same cylinder is now still showing the highest readings then this cylinders valve lash, injector and compression may have issues................if it turns out it is the glow plug itself is giving the higher reading, then it should be replaced...................pay close attention to the road readings.............

By any chance do you have a set of about 28" tires that you could put of the rear for a test??

A little fun until you have time for the above test.................

notice on a low grade hill when the readings start rising the effects of giving it more fuel.........now let up ever so slightly and see what happens..................keep watch in the mirror for smoke........

now find a high grade hill and on the down side let completely off the gas and drag the engine, down shift to keep rpms above 2000.......after a few times doing this, how does it effect your over all readings..................

on level road at even speed, let off on the gas,........does the readings blip up and then go down or do they instantly go down............................

are your readings a little different when you have a full tank of fuel verses about out...................

your engine can tell you what it needs for performance.........if you are will to listen to it...................

You may find this thread interesting:
http://www.isuzupup.com/forum/viewtopic.php?t=945
regards,
crossbones

Howdy Crossbones,

I will try these additional test as soon as I get the chance. Pretty packed schedule for a bit here, but I ought to be able to do most of these (except removing glow-plug bar) without tools and during normal driving trips--as long as I don't mind confusing the heck out of anybody following me <img src="/forums/images/graemlins/wink.gif" alt="" />

Why do you like the idle up around 1000?

I might be able to come up with some 28" tires, but that's going to take even longer before I can do the tests. How important is it? Even with the 28 inch tires, my gearing will be off.....

For your full versus almost empty fuel tank question--these little postal jeeps only came with a 10 gallon tank. It would make a much bigger difference in terms of weight if I brought along a passenger to watch and record the numbers for me

For a junkyard motor, I've had my socks impressed right off of me <img src="/forums/images/graemlins/wink.gif" alt="" />

Hello lamby. I have found on my engines that the timing "dances" a lot less at 1000 than 800 and I get a smoother running engine,,,better oil pressure and as I run "alternative" fuels it just does better......

The reason for the 28" tires was to try to see what effects your gear ratio is having on the engine........I have been thinking on how to take the effect of the gear ratio "out" of the reading and I "think" I know how to do it..........

As you continue seeing your readings under different conditions you will be able to tell a difference with and without a passenger.....they are that sensitive.............the beauty of the method is you can set the timing for your average load conditions.........

I am going to give you a little more information on the readings..........but you Must remember that you can not use the readings Until you have tested the glow plugs as I have described to make timing changes..............

High readings indicate a problem......it can be the glow plug, injectors, carbon in the injector port of the head, timing or fuel...........

It is important to note that a glow plug can work (glow) fine and still produce a high reading.........but for our purpose we need all four to be as "balanced" to each other as much as possible.............


readings at or over 10 milli volts will soon burn out the glow plugs..........

reading at or over 8 milli volts needs attention (low power, smokes bad)

readings at 6 to 8...power is down some and smokes under moderate load

readings at 4 to 6...power improvements noticeable and smoke limit is much better...........

readings between 3 to 4 indicate that a change in timing may be all that is needed to "dress" out the engine.........provided the fuel quanity screw has not been messed with........

our target is 2 to 2.5 at about 45-50 MPH , in fourth gear on level ground...............

Changing the timing is the very last thing to change..............

These are just guide line numbers........we are more concerned with the relationship of getting the readings as low as possible with more power before making a timing change...............<img src="/forums/images/graemlins/kewl.gif" alt="" />

regards,
crossbones

Sorry to jump in again, I'm following this with interest:

Crossbones, are these target values going to be the same regardless of engine design or are they specific to the C223 being discussed here?

If they relate to combustion temperature, I would assume they are fairly standard - however, different glow plugs (e.g., Ford vs. Isuzu) may give different readings, so perhaps it is engine-specific.