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  #1  
Old 11-20-2011, 01:19 PM
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Injection Pump Timing and Crank Pulley Question

I'm well-experienced with working on diesels (particularly VWs) but not very well versed on some of the details of the Merz diesels. Sorry if this is long, but all the details I will post are pertinent to the bigger picture, IMO.

I am currently trying to get a friend's '81 300SD to run well. It currently takes A LOT of cranking to start and creates a big mosquito fogger smokescreen when it does. It generally runs somewhat poorly with too much smoke, somewhat lacking in power and has a bit of a miss. The glow plugs are all new bosch duraterms and are working properly. The compression has been tested and is good on all cylinders. The injectors have been tested and are all functioning properly. The air filter is in good shape and there intake tract is clear at least to the turbo. I don't think he's pulled off the turbo or intake manifold to check for any blockages but I doubt the problem lies there.

It gives all the impression of having the injection pump timing severely out.

He also has an '81 300TD that starts and runs well and I have an '82 300 TD that also starts and runs very well. I happen to have a diesel pulse adapter and strobe timing light which shows the exact time of the start of injection for a given cylinder while the vehicle is running. I figured it would be easy to check the timing on my good running '82 300TD and his good running '81 300TD and use those two specs to adjust the timing on his poorly running '81 300SD. Here's where the oddness starts... The pulse adapter on my good running '82 300TD shows the start of injection for #1 cylinder to be at 10° BTDC. The pulse adapter on his good running '81 300TD shows the timing for the #1 cylinder to be OFF THE SCALE. It shows that timing for the #2 cylinder is 42°BTDC. The pulse adapter shows the timing for his poorly running '81 300SD to be at 8° BTDC. The difference between 8° on his poorly running car and 10° on my good running car does not seem to me to be enough of a difference to account for the poor starting/running of his car. That coupled with the off-the-scale timing of his good running '81 300TD makes me think that the crank pulley must be incorrectly installed on two of the three vehicles. So my BIG question is:

Can the crank pulley be installed more than one way?

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  #2  
Old 11-20-2011, 02:12 PM
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Also, how can you confirm/find TDC aside from using the crank pulley and scale?
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  #3  
Old 11-20-2011, 04:02 PM
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Quote:
Originally Posted by libbybapa View Post
Can the crank pulley be installed more than one way?
The pulley can be installed six different ways. All of which is irrelevant; the markings are not on the pulley.

The crankshaft angle markings are on the balancing disc. Whether or not it can be installed 180 degrees in error is subject to much debate. Considering the effort involved to get one on right, I have never tried to put one on backwards just to see if it could be done.

Quote:
Originally Posted by libbybapa View Post
The pulse adapter on his good running '81 300TD shows the timing for the #1 cylinder to be OFF THE SCALE. It shows that timing for the #2 cylinder is 42°BTDC.
How does the device determine crankshaft angle for cylinders other than #1?

Last edited by tangofox007; 11-20-2011 at 04:18 PM.
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  #4  
Old 11-20-2011, 05:40 PM
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It uses a piezo pickup that clamps onto the injector line of the cylinder it is reading. To read the timing of a different cylinder, you swap the pickup to the other line.

The increase in pressure in the metal line causes a slight expansion of the line, that expansion squeezes the crystal in the piezo pickup. When the injection event starts, the metal line relaxes and so the pressure on the crystal is released and a pulse of electricity is generated. The pulse adapter converts that signal into a current similar to a typical ignition signal in a spark plug wire and so you can use a typical gasser strobe timing light to see the exact start of injection. Because it reads the actual injection event it is more accurate than mechanical methods of timing as those do not take into account the effect of varied injector pop pressure.

What is the firing order of the 617?
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  #5  
Old 11-20-2011, 05:48 PM
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Quote:
Originally Posted by libbybapa View Post
It uses a piezo pickup that clamps onto the injector line of the cylinder it is reading. To read the timing of a different cylinder, you swap the pickup to the other line.

The increase in pressure in the metal line causes a slight expansion of the line, that expansion squeezes the crystal in the piezo pickup. When the injection event starts, the metal line relaxes and so the pressure on the crystal is released and a pulse of electricity is generated. The pulse adapter converts that signal into a current similar to a typical ignition signal in a spark plug wire and so you can use a typical gasser strobe timing light to see the exact start of injection. Because it reads the actual injection event it is more accurate than mechanical methods of timing as those do not take into account the effect of varied injector pop pressure.
None of that explains how the crankshaft angle is obtained for cylinders other than #1. Is it calculated mathematically on the basis of the #1 angle?

Quote:
Originally Posted by libbybapa View Post

What is the firing order of the 617?
1-2-4-5-3
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  #6  
Old 11-20-2011, 06:30 PM
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Quote:
Originally Posted by tangofox007 View Post
None of that explains how the crankshaft angle is obtained for cylinders other than #1. Is it calculated mathematically on the basis of the #1 angle?
I don't actually understand what you are asking. Are you asking what the crank angle of the various other cylinders is? It's a 5 cylinder so I would assume the angles of the various crank throws would be 72° apart. Because the engine is a 4 stroke, the cylinders should fire 144° apart (360 x 2 = 720 / 5 = 144). The scale on the crank should represent the position of the crank relative TDC for the #1 cylinder. In my first post, when I described the timing of the injection of the #2 scale, it was relative to the timing scale and so, if the timing scale is correct, then it would be relative to TDC for #1 cylinder.

To reiterate, I have tested an '81 300TD that starts and runs very well and I have tested an '82 300 TD that starts and runs very well. The '81 shows injection for the #2 cylinder to occur at 42° BTDC and the '82 shows the injection for #1 to occur at 10° BTDC. Assuming 10° BTDC is a good timing spec for the actual start of injection, then the injection for #2 should occur at 134° ATDC (TDC for #1). Instead it is shown as 42° BTDC which is 176° off. I assume that the markings MUST be off by 180° and the timing of the two engines is off by 4°.

So, IMO, one mystery is solved, now to figure out why the '81 300SD runs like crap...
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  #7  
Old 11-20-2011, 06:56 PM
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Quote:
Originally Posted by libbybapa View Post
In my first post, when I described the timing of the injection of the #2 scale, it was relative to the timing scale and so, if the timing scale is correct, then it would be relative to TDC for #1 cylinder.
That clears things up.

Lining up the camshaft index marks should tell you quickly if the balancing disc is upside down.
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  #8  
Old 11-20-2011, 07:16 PM
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Once, a long time ago, on a VW diesel, I timed the injection pump to the crank properly but didn't check the cam to see what position it was in. It turned out was one complete revolution of the crank off relative to the cam. The result was that the pump timing was one crank revolution off or put the other way, the pump was 180° out. The engine ran VERY similar to how my friend's '81 300SD runs. It was very hard to start, lots of cranking. When it did start it smoked a lot until it warmed up and it was a bit down on power.

Is it possible that a previous owner or mechanic installed the injection pump 180° out? How does the Merz pump interface with the timing chain?
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  #9  
Old 11-20-2011, 07:33 PM
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Quote:
Originally Posted by libbybapa View Post

Is it possible that a previous owner or mechanic installed the injection pump 180° out? How does the Merz pump interface with the timing chain?
If that was the only problem, you would still get a good reading for the crankshaft angle. It would just be reletive to TDC on the exhaust stroke. It would not be "off the scale."
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  #10  
Old 11-20-2011, 09:16 PM
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We are talking about three different cars. The two 300TDs both run well, but one of those shows its timing to be 180° out. The third car, a 300SD, shows correct timing with strobe, but starts and runs like crap. I've probably added to the confusion discussing all three cars, but the whole discrepancy was perplexing.

Is it possible for the injection pump to index to the timing chain 180° out?
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  #11  
Old 11-20-2011, 10:20 PM
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Not sure about 180 deg but mine ran at 24 deg off

87 TDT black smoke all the time

Andrew the IP timing is not very difficult to check in the usual way. My 87 smoked unbelievable when the IP timing was off by 24 deg. Reset the timing and it was like night and day, started and ran beautiful strong and smooth, the timing chain had been installed wrong. I still cant believe the PO was driving it that way. Although it may be interesting to use various electronic gizmos to test things, the eyeball is more reliable. I suggest checking the old fashioned way. When you have established the correct timing you can check with your strobe device to get an equivalent calibration for next time. Cheers Dan
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  #12  
Old 11-21-2011, 07:58 AM
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I already have a baseline timing spec from a properly running Merz for the strobe timing system. The thing that was hanging me up was that one other car that ran well did not have the correct timing according to the scale on it's engine (180° out) and another one that ran like crap DID show the correct timing on the scale. I currently assume that the one that runs like crap is timed one crank revolution out of time. It certainly runs like that and if that were the case, the timing would appear correct according to the crank scale. Only from looking at the cam at the same time would the issue become apparent. I will open the valve cover and check today.
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  #13  
Old 11-21-2011, 08:41 AM
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Quote:
Originally Posted by libbybapa View Post
Is it possible for the injection pump to index to the timing chain 180° out?
Sure. That is precisely what would occur if the crankshaft was positioned relative to the exhaust stroke, rather than the compression stroke, when installing the IP. But 180 off at the IP is 360 off at the crankshaft, which woud result in an apparently "normal" reading at the crankshaft, but it would be relative to TDC on the wrong stroke. It would not be "off the scale."
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  #14  
Old 11-21-2011, 08:44 AM
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Quote:
Originally Posted by tangofox007 View Post
But 180 off at the IP is 360 off at the crankshaft, which woud result in an apparently "normal" reading at the crankshaft, but it would be relative to TDC on the wrong stroke. It would not be "off the scale."
Right, which is exactly what is happening on the car that runs like crap. It shows the correct timing spec (or at least close enough to run well), on the scale at 8° BTDC. Thanks.
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  #15  
Old 11-21-2011, 09:00 AM
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Quote:
Originally Posted by libbybapa View Post
Right, which is exactly what is happening on the car that runs like crap. It shows the correct timing spec (or at least close enough to run well), on the scale at 8° BTDC. Thanks.
The proplem would be easy to identify using the drip method.

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