Cold start injection timing - PeachParts Mercedes-Benz Forum

gastropodus · #1 10-12-2010, 10:26 AM

Hi, my '79 240D is running really well... no REALLY well

... once it warms up, that is. Cold starts, like 45 degree mornings that we're currently having, it is balky and smokes a little. I recall that the previous owner, who generously could be called an idiot, told me that his diesel mechanic son "tuned it up" by advancing the injection timing. I'm sure that he did not follow any sort of factory service manual procedure, he just loosened the IP and moved it. Could advanced timing beyond factory spec lead to balky starts? And if I do it by the book to return timing to spec, will I lose the top end power that it seems to have? Actually, I wouldn't mind smoothing out the power band to distribute a little of the top end zoom to the bottom end.

Other facts: it's a four speed manual transmission, and the power is OK at the bottom of the gears, but really quite good from mid-gear to top of gear (say 2400 rpm to 3000 rpm). This makes it a little zoomy, which is OK, but it climbs highway hills like a rabbit (the animal, not the car!). I had MBI Motors check the compression when I bought it; the results were OK, but not great. The #1 cylinder was 280, and the others were 320 to 350. This was before I adjusted the valves, so if they did a warm engine test they should have gotten better (the valves were all way tight). If they did the compression test cold, well then those numbers are worst case.

Thanks, as always, for your advice.

Kurt

vstech · #2 10-12-2010, 10:29 AM

glow plugs?

gastropodus · #3 10-12-2010, 10:50 AM

I forgot to mention... tested and replaced the one bad glow plug. They are the pencil type, though I suspect that the engine originally had the loop style. Maybe I should just spend the other $45 to replace the other three.

Kurt

Diesel911 · #4 10-12-2010, 01:59 PM

Quote:

Originally Posted by gastropodus

I forgot to mention... tested and replaced the one bad glow plug. They are the pencil type, though I suspect that the engine originally had the loop style. Maybe I should just spend the other $45 to replace the other three.

Kurt

Are you useing only Diesel Fuel?

Why not just check the Glow Pluts with a Volt/Ohm Meter. If you live in the US Harbor Freight Stores sell them for $5 or less when on sale.

When was the last Valve Adjustment?

If the Timing is too advanced it can effect the Starting but that is also going to depend on how good your compression is.

Another issue is Camshaft Timing due to stretch and/or wear on the Timing Chain and Gears.

Low Engine Cranking speed is another issue that can make the Engine hard to start.

gastropodus · #5 10-12-2010, 03:26 PM

Yeah, I'm a diesel-only kind of guy. I don't trust B100, and buy B20 only if I have to. Adjusted the valves last week.

I used a volt-meter to judge the one bad glow plug; it was missing in action (open circuit) when in the engine, though it later showed 0.2 ohms while out of the car. I suppose I could remove all the glow plugs again, run the compression test, and put in all new glow plugs and see where that gets me.

Another possibility is the injectors; I could send them off to C Sean Watts for a rebuild.

I'll try and pay attention to the starter speed on the next spin. I don't recall it sounding slow, but then I'm not well calibrated.

I'm still curious about my original question: does advanced IP timing hurt cold starts?

Kurt

whunter · #6 10-12-2010, 03:49 PM

Quote:

Originally Posted by gastropodus

Hi, my '79 240D is running really well... no REALLY well

... once it warms up, that is. Cold starts, like 45 degree mornings that we're currently having, it is balky and smokes a little. I recall that the previous owner, who generously could be called an idiot, told me that his diesel mechanic son "tuned it up" by advancing the injection timing. I'm sure that he did not follow any sort of factory service manual procedure, he just loosened the IP and moved it. Could advanced timing beyond factory spec lead to balky starts? And if I do it by the book to return timing to spec, will I lose the top end power that it seems to have? Actually, I wouldn't mind smoothing out the power band to distribute a little of the top end zoom to the bottom end.

Other facts: it's a four speed manual transmission, and the power is OK at the bottom of the gears, but really quite good from mid-gear to top of gear (say 2400 rpm to 3000 rpm). This makes it a little zoomy, which is OK, but it climbs highway hills like a rabbit (the animal, not the car!). I had MBI Motors check the compression when I bought it; the results were OK, but not great. The #1 cylinder was 280, and the others were 320 to 350. This was before I adjusted the valves, so if they did a warm engine test they should have gotten better (the valves were all way tight). If they did the compression test cold, well then those numbers are worst case.

Thanks, as always, for your advice.

Kurt

End the doubt, check your timing.

Diesel Injection:
http://www.peachparts.com/shopforum/showthread.php?t=142405

Drip Timing Threads
http://www.peachparts.com/shopforum/showthread.php?t=197093

.

gastropodus · #7 10-24-2010, 08:17 PM

Quote:

Originally Posted by whunter

End the doubt, check your timing.

Well, whunter, you're right. I had to end the doubt, so I re-timed it. It was between 26 and 27 degrees BTDC, and I set on 24 degrees exactly. That in itself was a learning experience worthy of a separate post, full of 'Aha' moments to share. The end result: I bled the lines with DW's help (glow plugs off), then did a glow, turned the key, and... VROOM! Way, way better starting. The look on my wife's face was priceless: "I can't believe it, but apparently you know what you're doing." I haven't had a chance to put it out on the highway yet to check low and high end torque, but it sounds really good.

Between the total fuel system clean out, the valve adjustment, the re-timing, the Marvel Mystery Oil soak, the new glow plugs, dang this thing is like back from the dead.

Kurt

whunter · #8 10-25-2010, 12:18 AM

Quote:

Originally Posted by gastropodus

Well, whunter, you're right. I had to end the doubt, so I re-timed it. It was between 26 and 27 degrees BTDC, and I set on 24 degrees exactly. That in itself was a learning experience worthy of a separate post, full of 'Aha' moments to share. The end result: I bled the lines with DW's help (glow plugs off), then did a glow, turned the key, and... VROOM! Way, way better starting. The look on my wife's face was priceless: "I can't believe it, but apparently you know what you're doing." I haven't had a chance to put it out on the highway yet to check low and high end torque, but it sounds really good.

Between the total fuel system clean out, the valve adjustment, the re-timing, the Marvel Mystery Oil soak, the new glow plugs, dang this thing is like back from the dead.

Kurt

Happy to hear your wife survived the shock.

Brian Carlton · #9 10-25-2010, 12:25 AM

Quote:

Originally Posted by gastropodus

Well, whunter, you're right. I had to end the doubt, so I re-timed it. It was between 26 and 27 degrees BTDC, and I set on 24 degrees exactly. That in itself was a learning experience worthy of a separate post, full of 'Aha' moments to share. The end result: I bled the lines with DW's help (glow plugs off), then did a glow, turned the key, and... VROOM! Way, way better starting. The look on my wife's face was priceless: "I can't believe it, but apparently you know what you're doing." I haven't had a chance to put it out on the highway yet to check low and high end torque, but it sounds really good.

Between the total fuel system clean out, the valve adjustment, the re-timing, the Marvel Mystery Oil soak, the new glow plugs, dang this thing is like back from the dead.

Kurt

I really hate to spill cold water on such a marvelous performance, but it's impossible for three degrees to have a dramatic effect on cold starts. There were some folks who actually got the IP timing off by 180 degrees due to some wrong assumptions and the engine started and ran...........but, without any power and with considerable smoke.

Additionally, we checked about six vehicles at one of the GTG's with the pulse unit. They varied from 6 BTDC to 15 BTDC. Nobody made any mention of starting issues.

In conclusion, the engine is very tolerant of varying IP timing with the result being increased fuel consumption and/or lack of full available horsepower, but starting them isn't an issue.

gastropodus · #10 10-25-2010, 01:16 AM

You may be right, Brian, or maybe not. After reading your post I checked the temperature at mid-day: not quite as low as the mornings I was noticing really balky starting. But it still came to life in a way that I hadn't seen except during the summer. We're in the midst of a rainy period, so it may be a few days before temperatures dip back down into the low forties on a clear night.

There's a definite difference in the torque. Before, I used to characterize it as 'zoomy': pretty gutless in the low end of the power band, and then at a certain RPM it would take off. It now feels like some torque has shifted down in the power band, to where I notice it in the bottom end of the gears. I'm not sure that someone with an automatic transmission would notice it much, but with the manual transmission one really knows where the torque is and where it isn't.

What is the nominal timing when using a pulse unit, Brian?

Cheers,

Kurt

whunter · #11 10-25-2010, 03:20 AM

Quote:

Originally Posted by gastropodus

You may be right, Brian, or maybe not. After reading your post I checked the temperature at mid-day: not quite as low as the mornings I was noticing really balky starting. But it still came to life in a way that I hadn't seen except during the summer. We're in the midst of a rainy period, so it may be a few days before temperatures dip back down into the low forties on a clear night.

There's a definite difference in the torque. Before, I used to characterize it as 'zoomy': pretty gutless in the low end of the power band, and then at a certain RPM it would take off. It now feels like some torque has shifted down in the power band, to where I notice it in the bottom end of the gears. I'm not sure that someone with an automatic transmission would notice it much, but with the manual transmission one really knows where the torque is and where it isn't.

What is the nominal timing when using a pulse unit, Brian?

Cheers,

Kurt

What you did, in order of starting improvement:

#1. new glow plugs.

#2. valve adjustment.

#3. Fuel system clean out.

#4. Set injection timing.

#5. Marvel Mystery Oil soak.

What you did, in order of power/performance improvement:

#A. valve adjustment.

#B. Fuel system clean out.

#C. Set injection timing.

#D. Marvel Mystery Oil soak.

Wasted time/effort = zero..

Brian Carlton · #12 10-25-2010, 08:18 AM

Quote:

Originally Posted by gastropodus

You may be right, Brian, or maybe not. After reading your post I checked the temperature at mid-day: not quite as low as the mornings I was noticing really balky starting. But it still came to life in a way that I hadn't seen except during the summer. We're in the midst of a rainy period, so it may be a few days before temperatures dip back down into the low forties on a clear night.

There's a definite difference in the torque. Before, I used to characterize it as 'zoomy': pretty gutless in the low end of the power band, and then at a certain RPM it would take off. It now feels like some torque has shifted down in the power band, to where I notice it in the bottom end of the gears. I'm not sure that someone with an automatic transmission would notice it much, but with the manual transmission one really knows where the torque is and where it isn't.

What is the nominal timing when using a pulse unit, Brian?

Cheers,

Kurt

Well, you've done a bunch of things, all of which can affect the cold start capabilities...........so, we really cannot get a firm conclusion on it.

We found that the 617 has a nominal timing of 14BTDC with the pulse unit when the engine is set exactly at 15 ATDC using the A-B lights.

tangofox007 · #13 10-25-2010, 09:34 AM

Quote:

Originally Posted by Brian Carlton

In conclusion, the engine is very tolerant of varying IP timing with the result being increased fuel consumption and/or lack of full available horsepower, but starting them isn't an issue.

When I adjusted the IP timing on my'82 300D, the most noticeable affect was the decrease in cranking time required. The timing was advanced from 15 degrees BTDC to 24 degrees BTDC. The cranking time was reduced from a few seconds to almost nothing. The engine now starts almost instantaneously.

Quote:

Originally Posted by Brian Carlton

We found that the 617 has a nominal timing of 14BTDC with the pulse unit when the engine is set exactly at 15 ATDC using the A-B lights.

I think that I understand what you mean here, but I suspect that the propensity for misinterpretation is extremely high.

Brian Carlton · #14 10-25-2010, 09:50 AM

Quote:

Originally Posted by tangofox007

When I adjusted the IP timing on my'82 300D, the most noticeable affect was the decrease in cranking time required. The timing was advanced from 15 degrees BTDC to 24 degrees BTDC. The cranking time was reduced from a few seconds to almost nothing. The engine now starts almost instantaneously.

I think that I understand what you mean here, but I suspect that the propensity for misinterpretation is extremely high.

I'd agree that improving the timing from 9 degrees late will marginally assist the cold start time. However, reducing it by 3 degrees has to be considered negligible.

Yes, you're probably correct:

The method using the A-B lights has a reference point in the IP of 15 degrees AFTER top dead center. If set to this reference point, the IP timing is correct and will match the drip method when set properly at 24 degrees BEFORE top dead center.

When the engine is set perfectly, the pulse timing was confirmed at 14 degrees BEFORE top dead center.

Three different methods............three different figures...........exact same timing depending on the method utilized.