This is kind of long so bear with me...

I have a 1984 240D that I picked up earlier this year. The car is in great shape and only has ~157K on it. However there was some vibration (shaking) at idle but once the car comes off idle everything smooths out. So I did the usual things... Adjusted the valves, replaced the motor mounts - still shaking...
From research I had done on this site and others I figured it was either a bad injector or low compression in one cylinder. I installed four reman/balanced injectors from ebay. This seemed to make the vibration/shaking worse, so I thought compression would be the issue... Well I checked the compression today and all cylinders are in the 375-400 PSI range.

Does anyone have any ideas on what else I can look at? The car runs great otherwise, starts right up and has all the power you would expect from a 32 year old 240D haha.

Thanks in advance,

Alex

A common suggestion (and it does help) is to run a couple of cans of Diesel Purge through to clean any sort of built up gunk out of the injection pump. Always a good place to start and sometimes that's all it takes.

Getting more advanced, you may have low fuel supply pressure or the timing could be slightly off (usually due to timing chain stretch). Try the Diesel Purge first and see if that helps. If it does, great. If not, it's time to check the timing chain stretch and see how many degrees off you are.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Diseasel300, thanks for the insight.

Low fuel supply pressure is one I had not thought of. Do you know what the pressure should be?

I did the diesel purge and both fuel filters, no noticeable effect on the performance. I checked the chain stretch as well, it was within tolerance.

Alex

I would re-check the valve adjustment. It's very easy to mess up the adjustment, because of the clumsy way you must maneuver the wrenches. Ask me how I know?

Get the engine to operating temperature. Take a hand temperature reader. All the glow plugs should be running at about the same temperature.

Another way is to read the milli volts from each glow plug to the engine ground. Again on a good running engine they should be somewhat similar. Although old glow plugs may generate different voltages. You have to use the engine itself for ground remember. You are looking for any cylinder with a substantial difference either in temperature or voltage.

Either of the above methods can help in many cases but not all. At least you do not have the really bad issue of low compression on one cylinder. So things are not really too bad. If you post the results I and others can make suggestions. I was also thinking the idle speed may just be too low. Or the injection pump may be advanced too far.

Thanks for all the replies. I will check these items out and post the results.

The consensus seems to be roughly 9-15PSI of fuel pressure at the inlet to the injection pump. You'll have to get a spare banjo bolt and tap it for a pressure gauge to test it.

Another thought occurs...you said you got reman injectors for the engine. They're the 115 bar version for the N/A engines and not the 135 bar version for turbo engines right? If you have the wrong injector installed, the timing will be very late and will result in low power and poor idle. Just thinking out loud.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I got to take a look at the 240D today. Here are the readings I got on the glow plugs, engine running at operating temp.

#1 - 162*F
#2 - 155*F
#3 - 150*F
#4 - 180*F

All glow plugs were reading 6.7-6.9mV to engine ground.

What can you guys glean from these numbers? Maybe #4 is running a little lean?

Thanks for your help,

Alex

No one has any insight into these numbers? Are they within tolerance?

Barry is the only person I've ever seen mention using mV readings to the engine block or using an infrared gun. Been done on several threads, but I'm not so sure it's actually useful.

The "eye" on an infrared gun is roughly the size of a half-dollar at a 1 foot distance, so a lot of things can fool it into giving a false reading. It is also reading the head temp, which is balanced by the coolant and thermal conduction from the other cylinders. The glow plugs are NOT an RTD thermocouple. They're not designed to measure temperature of anything, I'd imagine if you swapped them around to different cylinders you'd get different results. They're designed to get hot within a tolerance with power applied to them, and that's really it.

If your compression numbers are good, your fuel supply pressure is good (has this been checked yet?), your injectors are all balanced and have the right pop pressure (these are 115 bar injectors for N/A diesel right?), then you might check the rack damper. My SDL doesn't have a rack damper since it uses a different pump so I can't give you detailed instructions, but there are other threads on this forum that deal with it's adjustment. If only the idle is rough and the engine is smooth throughout the rest of it's operating range, it very well could be your culprit.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I am an awful speller; be warned.
Not everyone subscribes to the mili volt method and there is nothing in any Manual to support your readings.

However, what is going on is you are using the Glow Plugs as a thermocouple and the electrical reading is supposed to reflect the combustion temp.

So you are using your electrical reading to make a comparison. In your case they don't seem to vary much which is a good thing.

If it turned out one of the cylinders was extremely different then you would need to swap that Glow Plug with one from another cylinder and re- take your readings to determine if it is the Plug or a colder cylinder that was causing the varience.

Concerning you issue what rpm do you have at idle set at? If it is too low the engine will vibrate. On mine on the upper Radiator Cross Member there is a sticker that has the normal idle speed range.

On the back rear of the Fuel Injection Pump Body on the Engine side of the Fuel Injection Pump is a Fuel Return Line with what appears to be a Banjo Blot. That is actually the Fuel Pressure Relief/Overflow Valve.
If you have the type you can take apart you can do that (don't loose the Ball Bearing or Spring inside) and Stretch the Spring back to a free length of 27mm and re-assemble it. And see if that helps.

If you have an MW Fuel Injection Pump there is some articles in other forums like Benzworld where you need to take the back plate off of the Governor and there is another adjustment inside.
While they listed it as another idle ajustment I suspect what it is; is the adjustment that determins the sensitivity of the Governors response. I don't no what Bosch calls it but with other Fuel Injection Pumps it is called Governor Droop.

The other member mentioned re-checking the valve adjustment. The rason for that is if it had not previously been done for a long time crud builds up on the face and seat of the Valves. You adjust them and after some time that crud comes off and your valve clearances can now be different.

None of the above stuff costs much.

Repair Links Fast navigation Fast navigation Do It Yourself Links

__________________
84 300D, 82 Volvo 244Gl Diesel

If you up your idle to where it does not shake.... what RPM is that ?
Until you know that... and compare to what it is supposed to idle at.... you may not be dealing with a problem...

__________________
1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

As mentioned the milli volt method is not popular. What your numbers do suggest is all cylinders are firing to some reasonable extent. If you have one cylinder just barely firing you should have had an even worse separation of the voltages.

As mentioned to get good accuracy either means using a new set of glow plugs from the same production batch. Or swapping your used glow plugs to see just how they track from cylinder to cylinder. Making one the standard refferance.

Sorry to be so late in posting back.

My thoughts remain the same. Using the milli volt method with great care is an alternative way to identify things over just guessing. It is a time spent versus buying non required parts. Or actual location of the fault if it is elusive. The glow plug is not a thermocouple but does give an accurate indication by comparison from cylinder to cylinder if you are willing to put in all the effort required.

Actually your voltage numbers where far closer to what one would expect with a used set of glow plugs. Here is the hard part. It is an assumption only that the plugs are acting close to a new set or having been moved around to verify the results. Assumptions are dangerous.

Still if we base them on what you obtained. The injection pump is probably fine and the injectors as well. The overall voltages are a little higher than what is usually found. This could be the hot idle is faster or the injection pump timing is slightly advanced. Or the glow plugs you have are from a batch that is generating a little more voltage from the dissimilar metals.

The manufactures of the glow plugs have no intent to make a set of glow plugs with the exact consistency of metals involved from batch to batch. Yet based on what you have presented voltage wise I probably would check the injection pump timing. I am far from certain it is a little too far advanced but it might be.

What I would do for certain is make sure you have say 15 to 19 pounds of fuel pressure present in the base of the injection pump. Low fuel pressure there can present some idle problems as well. Or more correctly the idle is usually smoother and better at those pressures I mention if the present pressure is too low.

Now I will go into unexplored territory. I have had a suspicion that when the fuel pressure is really low. You may or may or may not see a higher voltage on the number one glow plug. . You presented none. At highways speeds though I suspect the voltage of the number one cylinder will be higher than the others. My belief remains that at low fuel pressure the number one cylinder works harder.

As another general rule milli volts greater than 1/2 of a milli volt differance verified by swapping glow plugs or using one as a standard are worth looking into. At about that much voltage difference some of us humans start to notice things. At a 1 to 2 milli volt difference or greater generally really pronounced differences are observed.

The readings by actual temperature of the hand held reader you might try moving it closer to the glow plug. They are not what is to be expected from the very limited exposure to others using the temperature sensor.

The dot indicated the target area but as mentioned the actual cone that reads the temperature may be much larger. You want to read the glow plug only if you can.

From what I remember the last gentleman using this had three plugs reading almost the same temperature. One was at block temperature and it was his dead cylinder. The others where about fifty degrees higher than the low one. Between 180 and 190 if I remember.

To me assuming the engine was at operational temperature number four is the only one that is in the proper operational temperature area. That I would have expected to see from all of them.

It seems that when the average engine is at about 80 degrees celcius the readings at the dead cylinders glow plug where about 150 degrees F. So the results from this test where not consistant with what the milli volts indicated. Try to get closer to the plugs when reading if possible.

It may also be possible I suppose that your reading cone is just too wide. Yet at the same time that number four glow plug temperature reading seemed about right.

Temperature of around 180 at hot idle is what seems about normal from others. The reading of temperatures of the glow plugs is a pretty recent development.

Get your temperature reader closer if possible. As mentioned the actual reading cone may expand seriouisly with distance. A dead cylinder is about 150 in those test conditions normally.

The 240ds with manual transmissions are my favorite versions of the 123s. Under some operational situations like some women. You almost cannot live with them. Yet you cannot shoot them either.