35 is doable, IMO/IME. 40 - good luck, I really hope you make it..

Your comment regarding injectors being set to put less fuel in cannot work, IMO. The way to do this is your right foot. A mass with a given aerodynamics, rolling resistance and mass needs a certain amount of power to maintain a specific speed. That's that. An engine is going to take as much heat (fuel producing work) as it can up to the limits of fuel and airflow. Artificially reducing fuel flow isn't going to help that.

The name of the game is efficiency, in terms of your driving habits and the powerplant and related parts. Injector pressure is an interesting one. Pressurizing the fuel takes work - it is parasitic to the efficiency and operation of the engine. Meanwhile, optimum fuel atomization and combustion is key. Assuming the ip wears evenly, it is then a matter of injecting at the right point in the cycle with tue right pressure to atomize properly. Id venture to guess that the optimum point is the opening preside being the same as the pumped pressure at the point when injection is at the optimum point in the cylinder stroke to maximize power. Going too high may only delay injection, may not atomize any better, be more stressful on the parts, and offer no viable benefits. I'd bet that Bosch knows how their pumps operate with age and what their injectors really need to optimize properly. I'd guess they aren't setting the number in a vacuum - doubtful it is that tough or any extra work to set them higher...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

You may have been mislead by my last post, if you did not read my earlier posts. I am talking about 40 MPG on the highway, and I am probably at 33-35 MPG, maybe more, right now. With a blocked fuel screen, major sludge in the fuel tank, bad wheel bearings, bad front end with wheels noticeably leaning in, I got 30 MPG driving the car home from Miami to Chicago area. I flushed the tank and lines (changed all filters) and did a purge which has done wonders. My prefilter turned black in only a couple hundred miles.

I looked at the links that you provided and I am going to study them further, but I am not seeing the spring you mention on the epc drawings, attached.

I have a 1983 240D. I assume that where the clear line is attached to the pump is the location of the spring, based on the posts you referred to. The bolt(s) are shown on the NO SPRING drawing. You also mentioned on your posts that not all pumps had springs. On my drawing with two bolts, it could be that one bolt (fitting inside the other) allows for some form of adjustment????????? (parts 125 and 107)

Any thoughts on this? Do I have the wrong spot? I am assuming that some cars have a spring where washer, part 164, leads into the pump (CLEAR LINE) image. You in chicago area? have a lift? beer in the fridge? a barco lounger, so I can watch in comfort?

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I am not a mechanic, but common sense and analysis can go a long way.

Perhaps, Bosch uses this 1450 PSI setting because they believe that a 30 year old engine is optimized with this setting. On the other hand, if an engine has had its rings replaced or was well maintained, it could have like new (or near) compression.

I am also interested in seeing how many knowledgeable comments come back on this last post. It could be that the questions I am asking are above all of us, and I need to rattle Mercedes a little.

I think it depends on how extreme you want to go, how you define "highway driving" and how many modifications you want to make.

You can reduce drag incrementally by doing things like removing the hood star (is that heresy?), the passenger side mirror (it was an option anyway), installing euro headlights (less turbulence with the flat lens), maybe even installing different style wiper blades - or removing the passenger side one.

Do you use A/C? If not, remove the compressor and reduce weight and drag. Does your alternator have two belts? Get rid of one.

If you track your mileage closely and can estimate your travel distance, then do what the airlines do and put only enough fuel plus a minimum reserve for your trip. You don't need to carry the extra weight.

Skinnier tires at higher pressures will have less drag and less rolling resistance. Taller tires will affect the effective gear ratio and let you travel further with lower rpms, but getting to speed will take longer so you'll be applying an accelleration force longer. There may be a sweet spot for optimum mpg. Changing the rear differential is an option.

What are the prevailing wind conditions in your area? Maybe driving in the morning with calmer winds may help or waiting for the tailwind (I'm not kidding, I did say "how extreme...").

One more question: what's your real goal? Do you want the maximum mpg, minimum fuel used, or minimum cost per mile? Max mpg may cause you to select routes and behaviors that cause you to use more fuel (e.g. selecting a longer route over a highway vice a shorter route over surface streets or driving further for cheaper fuel, then loading up with extra jerry cans and hauling extra weight unnecesarily.)

You may want to look at hypermiler forums since they're dedicate to fractions of mpg gains.

I'd say itis more complex than compression - rather wear on components, seals, etc. Timing chain stretch for example can misalign things and create the scenario for things to be off by some amount, causing a less optimal/efficient operational situation.

Remember, the compression is key to making heat to cause combustion - there is no spark to induce a flame front. So the need is enough and consistent enough compression to generate heat and have a suitable combustion environment, plus fuel injected with enough pressure that the nozzles can atomize sufficiently into the prechambers. Then it is a matter of good flame front and rapid combustion at the right point in the stroke to maximize power - thus giving you as much work as is thermodynamically possible for the amount of fuel you injected.

Everything has to be correct, optimal, for max efficiency. I'd want to start with the fueling system to make sure timing, pressure, flow, injectors, etc are all OK. If you're really big on this, I'd builds pop tester and check the difference in pattern and optimization at different pressures. To doug right requires a lot of $$$ equipment, but toucan likely do a cursory analysis...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

What I am striving to accomplish is to achieve 40 MPG by having a well tuned basically stock 1983 240D. Can I reach it? I don't know. I just know that my 1980 300D did 38 MPG on a straight highway drive. And, if anything, I will be adding weight to my 240D, as silence is golden.

The variables, at this point, are:

Injectors- Monark or Bosch nozzles, and the pressure at which they POP. I know the Mercedes specs for a new system is to have them POP at 1675-1775 PSI. I know that I have a tight engine, and am hoping that I find the compression to be well over 300 PSI. If I decide to buy injectors, I can get them set to whatever I want. I have seen the Bosch spray pattern, and it is relatively narrow. Monark has a wider dispersal pattern, and I have seen some good people say that they are they best. Right now I don't even know the condition of mine. At some point, I may be interested in rebuilding my injectors, but right now, I have too much to do. Here is a hydraulic pump that I saw that looks suitable for the task at a reasonable price: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230532393255&ssPageName=STRK:MEWAX:IT I don't believe Peachparts offer this equipment, so I am hoping I don't whiz them off.

Injection Timing- I don't know enough about this, and want to understand more. I will not delve into this or even let a mechanic mess around with it until I know more.

Fuel Pressure Relief valve adjustment- I have seen a lot of threads and posts relating to this. I am not seeing this part on my epc drawings, although there may be some form of adjustment there. My car is running OK, but I would like to understand how fuel is delivered to the pump (I know the route, but that is it), and how pressure could affect the injection pump.

Timing chain- I have 140,000 miles on the car, and this should be OK, but will look at it when I do the valves.

Valve Adjustment- I had someone tell me, oh, don't worry about that. Valves have an enormous amount of impact on fuel efficiency and the health of these engines. Too tight and you break something. Too loose and your burn something. Bad valve adjustment, sooner or later, is going to affect the whole engine, and the amount of crud that builds up in them, and the amount of crud that attaches itself to rings causing blowby and other problems.

ELSE?-

I have good "comfort" tires on the car, and I certainly don't want to start pulling mirrors and putting air dams on the body.

I fully believe that a 240D with really good compression can get 40 MPG on a roadtrip. If mine doesn't, it is my belief that it will be close.

I have good "comfort" tires on the car, and I certainly don't want to start pulling mirrors and putting air dams on the body.

One other thought. This is a high torque engine, and frankly, I wish there was a five speed automatic transmission out there for the car. I like the engine in my near 30 year old benz better than the new 1980 300D that I had. My car, clearly has the power to push at 60 and 70 MPH, at a lower RPM (don't ask me to pass a semi on a two lane). Got a 5 speed for me with paddle shifters?

The engine and fuel related items above, and anything similar that affects engine output and MPG is what I am interested in improving and learning more about. I also don't want to screw up the works either, as there is a lot of bad info out there.

Have a nice weekend.....maybe go to Indy. I think a nice 240D would make a great pace car, maybe with a couple of nice American flags on the front bumpers.

Rick

Adding weight??!? You're going against physics.

140k, what stretch on the TC? The question is where wrt TDC onthe stroke is the absolute thermodynamically optimum injection point, then how does that compare to where MB recommends on a spec engine, and then how far off the TC stretch takes you. Then, look into if just the ip should be timed or if The TC needs to be offset to optimize all conditions.

Don't forget low rolling resistance tires, oil, ATF and diff oil viscosity optimization, etc.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

If it came to just physics and weight, I should probably have someone else drive the car since they likely weigh less than me. The added weight relates to my second goal, and that is to sound insulate where it makes sense to do so. I am missing the sound blanket on the underside of the hood, plus I want to add more insulation where I can. 50-100 lbs. only adds 1.25% to 2.5% more weight, which is a sacrifice I want to make.

Please confirm that you are implying that the timing chain should be OK? I would think that it was OK, also.

What I am beginning to think I should do is start with a valve adjustment.

Step 2, if the valves were far off prior to doing Step 1, I would repeat the valve adjustment after 500 miles.

Step 3, check the compression in all cylinders as well as take a look at the injectors.

Step 4, replace the injectors if any are bad or so-so when examining the injectors in step 3. That will give me time to learn more about the injectors to decide whether to go with the Monarks, and what pressure to set them to pop given my compression.

Step 5, find a hopefully "qualified" technician to adjust the injection timing. I would have to see what a dealer would charge, and whether I am comfortable with the technician.

Thank you.

It may be a sacrifice you are willing to make, but you need to realize that that sacrifice is going the OPPOSITE direction from your attempt at 40 MPG. Nothing wrong with that, 38 or 39 MPG is a great number for a 30yo car with 1970's technology that is comfortable, safe and simple... Just remember that more mass requires more power to move down the road at some speed.

IMO, your approach should be to get the engine as close to factory spec, and then see if there are incremental improvements that can enhance the effect of the fuel you use, getting max power from each gram of fuel injected.

Your plan:

"What I am beginning to think I should do is start with a valve adjustment."

Agree. This is always a very important maintenance item and should always be the first step in baselining the engine state.

"Step 2, if the valves were far off prior to doing Step 1, I would repeat the valve adjustment after 500 miles."

Your time is effectively free, so go for it. Id think that if you brought it properly back into check and consistency, then there shouldnt be a big variation. Some mention turning the engine over a few times to make sure everything is OK and settled, then check the measurements one more time before closing up... Perhaps that would be smarter/easier... Your call.

"Step 3, check the compression in all cylinders as well as take a look at the injectors. "

Agree. Once the valves are all correct, check the compression for consistency and hopefully a high level. If it is not that high, I suppose youll have a harder time to begin with, but to what extent I cannot say.


"Step 4, replace the injectors if any are bad or so-so when examining the injectors in step 3. That will give me time to learn more about the injectors to decide whether to go with the Monarks, and what pressure to set them to pop given my compression."

Not sure I agree here. Not sure that any visual examination or approach to see if they are bad will be telling unless something is way off. The key is to make pop pressure consistent and make sure that they are clean, balanced and spraying nice. Some say that Monark nozzles give a better pattern. THat may or may not be the case, and any evidence may well be anecdotal. That said, atomization pattern optimization may have been performed and enhanced since it was done on w123 injectors in the late 1970s or so. As far as pressure goes, again, Im not sure what youre getting for going higher pressure. The key is to get the fuel to come out in an optimized pattern with minimal effort. The question becomes what happens if the pressure is set higher than required to obtain the designed pattern? I assume it will come out at higher velocity, which may be a good or a bad thing. Not sure what the theory is on this. My initial reasoning is to set it to the spec that MB states is correct (if a range is given, set it in the middle of the range). Higher pressures may well cause more wear on the moving parts, and for what? The benefit would be if and only if higher pressure decreases the fuel droplet size. Otherwise no gain IMO.

"Step 5, find a hopefully "qualified" technician to adjust the injection timing. I would have to see what a dealer would charge, and whether I am comfortable with the technician."

Agree that this should be done to set the conditions to all be correct. There is an optimum point where injection should occur. As I understand it, sometimes the injection position (at least for ga$$ers) is not absolutely the optimum position for burn/power. I assume this is either for emissions/NOx, or some sort of lean/overtemp protection. So the question is if the start of delivery position that MB recommends ( BTDC) is thermodynamically optimum or else what is? I believe that the other engines have other injection positions - like the turbo and non-turbo versions... In your quest for optimum MPGs, the thing to figure out is if there can be some improvement on the position that MB recommends. I dont have the answer to that...

Regarding your TC, I can't state whether it is OK or not. Ive had TCs that have just a few degrees of wear at >200k miles, so the question is what the maintenance profile was and the amount of stretch on the chain. Then the question is if the TC stretch takes the injection position to a more "optimal" position or worse off. The first key is to get the reading of the stretch. I'd do it with a dial gauge the correct way if youre really serious... Though the lineup on the cam tower may tell you enough...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

According to this experiment http://www.scipub.org/fulltext/ajas/ajas53197-202.pdf
it seems that increased pressure increases power and increases fuel consumption

JHZR2, 1-3, OK. On 4, direct examination of an injector can tell you one thing, I believe, that is if the nozzle needle is worn out. Injectors are basically flat on the end of the nozzle needle, and if the needle is worn, it may even have a sharp edge, which would likely cause a dispersal pattern problem. See blowup of the end of the nozzle needle to the right of the injector in the attachment. If they are worn, there is no added need for me to spend $70-80 for test equipment.

The specified compression value, as MB calls it, should be between 348 and 435 PSI. Minimum stated is 261 PSI. Mercedes also likes the variation between cylinders not to exceed 43.5 PSI (all for a 1983, 240D). I don't have any clue what you do if the variation is greater than 43.5 PSI. So, to summarize.

COMPRESSION SPEC 348-435 PSI
POP pressure 1,675-1,775 about

I agree with you, that the logical approach would be to keep all to spec. How about this?

MEDIAN COMPRESSION (new) 391.5 PSI
MEDIAN POP PSI (new) 1,725

1,725 / 391.5 = 4.41 times

POP is 4.41 times compression on a new car

261 minimum compression / 1450 min. POP = 5.5

I was hoping to see more continuity here, but if my compression is, say 348 PSI, then it would seem to make sense of setting the POP to 1675-1700 PSI.

If compression was a little less, set POP a little less.

The one thing that makes no sense is why Bosch would set their rebuilds to POP at 1450, which is the minimum standard for Mercedes.

As for the timing chain, do you know if the timing chain, as it wears, advances the timing or retards it? It would seem to retard it somewhat if the chain stretches. If it retards it, that would appear to be a negative, if timing was earlier to 26 degrees BTDC. I thought I read somewhere that you might want to advance timing to 26 BTDC on an older car (?), where a new 240D is set at 24 BTDC. If stretching took it to less than 26 degrees BTDC, that would probably be out of spec.

WOODBOAT3 ----------that is interesting info. The four cylinder they tested was, perhaps, a VW, newer technology. I wonder, however, if they have reached the point of diminishing returns, at least for now. In other words, a 240D pressure tops at 1,775 PSI, which is 122 bar, and the newer engine with the best mileage at 180 bar, it seems that VW made this engine to MAX OUT at 200 bar for performance, and not mileage. Put another way, going beyond 200 bar may have diminishing returns for power (and, based on the graphs, diminishing returns for mileage at 180) for this type of engine, and current technology.

I don't know if this is the correct conclusion, but maybe the lines drawn in the study are closer together in our 30 year olds, making the difference in MPG, minimal. I wonder if that is why Bosch is using a POP of only 1,450.

Rick

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My primary issue is that I do not believe that pop pressure has anything to do with compression. I do not believe that there is a real correlation. It is almost the same as saying that the pressure in your A/C system is related to your engine compression. It just doesnt relate.

Maybe Im way off, but the two are only sort-of related.

Injector pressure is the requisite amount of force to eject a specific amount of fuel out in a spray pattern with some maximum fuel droplet size (smaller is better). The real question is what is the net effect of any additional pressure beyond that which gives you the optimized atomization pattern... does it:

Decrease fuel droplet size? (good)

Come out faster (maybe good, maybe bad)

Cause more drag on the engine because of excess work on the IP (bad)

Cause more wear on moving parts (bad)

IMO, if you cannot create finer fuel droplets (atomization) by going higher pressure, then there is no benefit to going higher pressure. The question is what is the delta P between combustion chamber pressure and fuel pressure to get optimum atomization. If you know your compression, then you know what it is. Youre likely on the right track with your multiplier... The question is what is the right value?

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

There may be a correlation between POP pressure and compression, there may not be. There must be some connection between POP pressure and compression. You state so in the second half of your sentence, second paragraph. We have two junior engineers at work here.

If you increase compression, you probably need to increase your POP pressure to overcome the increase. Seemingly enough said. This conversation, now, reminds me of something which I think is helpful. A couple of years ago I saw this, and it makes a lot of sense. Increase the turbulence when fuel enters the chamber, and you increase the horsepower and fuel mileage.

Read this: http://mgccars.com/groove_101.htm To me, this is strong annecdotal evidence that turbulence and dispersal are a good thing.

This basically is the theory behind the Dodge Ram engines, which create a swirling motion before ignition. There are two things happening. You are increasing turbulence, but you are also increasing the dispersal of the fuel. You, probably, know flour can explode. Reminds me of high school chemistry class. You put a rubber hose into the bottom of a tin can with a lid. You put a rubber bulb on the end of the hose to create a puff of air. You put a candle in the middle of the can, and you put a little flour in and around the hose inside the can, you light the candle and put the lid on. Squeeze the bulb, and kaboom, the lid flies about 6 feet in the air. A grove in the head of a 240D may or may not do anything, but I think superior dispersal is what is needed.

Remembering all of this makes me want to use the Monark nozzles. The spray pattern of the Bosch nozzle is a narrow pulse into the center of the chamber. Old science. The Monark pattern is broader based and probably 2-3 times wider. That action over Bosch, would seemingly increase turbulence somewhat over the Bosch nozzle set at a low spec POP. No more fuel used, just superior dispersal. Grain elevators would not explode if there wasn't good dispersal.

So, you say, decrease fuel droplet size (good). Agreed, but I also think dispersal is just as important.

Come out faster? Doesn't matter. If the fuel ignites sooner, timing can be adjusted. If a new car is 24 BTDC, are you not experimenting somewhat on a 30 year old car when it comes to timing? I have read that 26 BTDC might be better on these older engines. Is that not a result of experimenting, and perhaps the need to compensate for a stretched timing chain?

As long as the POP pressure is kept within the design perameters of 1675-1775 PSI (or less), the IP should be able to handle it.

Right now, my compression is what it is, and the car seems fine. The three most important things to me to avoid damaging the engine are:

Unbalanced compression. First would be to determine that the compression in all four cylinders are reasonably balanced, and what the compression is in each cylinder. If they are not balanced, I have read of a way to bump up the compression in a cylinder that is weak. If they are not balanced, I am not inclined to mess around with the engine any further. Just drive. In the alternative, 2-3 valve adjustments with diesel purge may help the balance. Balanced compression seems to be the first requirement before making other modifications (different fuel injectors, and then setting timing based on this change).

All cylinders should fire within 2 degrees of their intended timing. This is determined with the timing drip test on my car. I still don't understand this thoroughly, but suffice it to say, I guess the needed correction would be to rebuild the IP if this was off. I need to look at this further, but valve adjustments are prerequisite. I went looking for this in my prior post, but I put forth stupidity in my second paragraph where I suggested I had no clue how to remedy a cylinder that had lower compression.

If there was one thing to pick to avoid, it would be early detonation, as in timing too far advanced. That would seem to wear an engine faster than about anything other than putting a ball bearing in each cylinder.

I need to adjust the valves once, twice or thrice and then see what the compression is on each cylinder.

Thanks

I think that because higher pressure also correlated to higher horsepower and higher fuel usage that one can assume higher pressure in our MB diesels with monark injectors would increase power and fuel usage as well. If a car is struggling to maintain speed this may have a net effect of better fuel economy. With diesels more fuel=more power so you can assume hiher pop pressure gives more fuel per squirt. So if it were my car I would shoot for somewhere in the middle of MBs recommendation to get a balance of fuel usage and power

Woodboat, I believe that the link you posted on 5-29-11 says otherwise. The 4 cyclinder diesel tested was probably a Volkswagen Jetta TDI or the like. VW, likely, has increased compression and POP pressure and mileage increased as well as a power increase over recent years. Now, this test, completed by this man, says they maxed out to the point that power is at the max at a slight cost to fuel usage. This does not apply to our cars as we are not pushing the envelope like they are.

Right now, we are not remotely thinking of increasing compression, but going with what we have, and working with it.

The Monark nozzles are a newer technology, and they have nozzles designed for these cars. The nozzles have better dispersal than Bosch, so I would expect better power, greater efficiency, and therefore better or equal mileage, with nothing sacrificed.

Until I know what compression all four of the cylinders are achieving, it doesn't make sense to me to settle for an average or median. If the engine compression is at the low end of a new engine, that is where my POP pressure will be. When Bosch puts out a product at the low end of specs, they are only thinking of avoiding problems for themselves, and not getting the best performance out of my engine as it stands today.

As I said earlier, I know I have good compression. What I don't know is exactly what it is, and whether the variance between the cylinders is within specs. Keep in mind, lack of valve jobs can cause buildup of carbon on the rings, putting the variances between cylinders out of spec. And just as that happens, a good valve job can help burn off that carbon and put the car back into spec with regards to the compression variance between cylinders. Once that is at its best, it is time to make other decisions.

At this point, I can complete three valve adjustments and unlimited compression checks (no, I am not going to do unlimited anything) with the only cost being my time. Call me, weekend warrior Mercedes mechanic. My car runs well now, and it starts easily. It can do that and still need a valve adjustment. CALL ME NURSE NANCY, as that is what I am trying to do, nurse this car back to good health.

I hope to live a long life and be buried in this car, so if it takes another year to do this, it will hopefully be worth the effort.