w123 engine mod - PeachParts Mercedes-Benz Forum

MBRO · #1 10-08-2007, 06:27 PM

Hello. This is a new thread started because the discussion derailed onto this topic on another thread.

Here is that thread:
Anyone ever thought of doing away with the precombustion chambers on a 5cyl 126 diese

The discussion started with the question if it is possible to convert the IDI (indirect diesel injection) engine to a DI (direct diesel inection) engine by removing the precombustion chamber. There were two answers for this question:

1. You can, but you will ruin your engine in seconds. So actually you can't.
2. If you want a DI engine under you w123 then buy a new MB DI engine and plant it under your hood and hope to behave

But another interesting question surfaced: Is it possible, and more is it useful in some way to remove the mechanical injection pump and install a common rail, computer controlled system for delivering the fuel? (the engine remains IDI, just the way it is timed and controlled changes from mechanical to electronic).

We agreed that such a system must be used by the person who built it or by someone who understand every detail about how it works. We also agreed that the cost of hardware is not extremely high (depending on what you compare it to). It should be around 1.5k to 2k $.

Another question was stated: "Again, what is the point? The already existing mechanical system does everything you are asking and it does it efficiently and reliably."

Well as I found out, maybe is efficient for others but for me it is not. After some calculations that I hope is correct I am doing about 18 mpg. (13 liters for 100 km).

I have to admit that I have the car for a short time (1 week) and it was a taxi before. The segments have been replaced by the former owner and I am sure that there is no damage to the pistons and / or cylinder head. But nothing else was adjusted on it. So as a advice from a fellow member as soon as I have some free time I will check the valves and replace the injector nozzles.

We also agreed that the electronic system (hardware) for the system I propose wouldn't be too expensive (in the range of 500$).

In this thread I will like to hear you opinions about if such a change is worth anything more than the satisfaction of the one who built it that it works (if it works).

Here is also the place to tell your average mpg, and ways to improve it.
Thank you for viewing / writing on this thread (my first) and I hope this will result in a constructive and, why not, fun conversation, without debates that are unnecessary.

#2 10-08-2007, 06:49 PM

OK, regarding your current mileage (18 mpg), which car are we talking about? Either way, that is much to low, both my 617 turbo and my 616 will get in the mid to high 20s without much effort. Some folks claim close to 30 mpg, but they work at it pretty hard.

What work have you done so far (valve adjustment, check IP timing)?

MBRO · #3 10-08-2007, 07:01 PM

I am talking both 240D (10 liters / 100 km) and 300TD ~ 18 mpg.
The 240D is my fathers, and it didn't see any care in two years

. And he doesn't like me to fiddle with it. That's the reason I bought mine

(i also have a Dacia 1300 and a VW trasporter t2b, but W123 was the car of my dream since I first saw one 17 years ago

)
The 300TD is mine only for a week. I didn't do anything yet. But the sure fact is that I intend to take care of it.
Could it be the quality of diesel fuel here?

MBRO · #4 10-08-2007, 07:05 PM

I don't know what to say. My friend's citroen BX from 1990 (which can hardly be considered a car compared with the w123) does something like 5 l/ 100km (about 47 mpg)

Ara T. · #5 10-08-2007, 07:51 PM

These diesels aren't terribly efficient. The engine is probably bigger than the one in the Citroen and also they could benefit from an overdrive gear in the transmission and a lockup torque converter. The citroen you are talking about has a 1.4 liter I believe. The W123s are pretty unaerodynamic too.

Obvious things are check your tire pressure, injection pump timing, valve clearance. And make sure your odometer is accurate, it is pretty common to have a crappy odometer on these cars.

In the city the best you will probably do is 24 mpg, though i never did better than 20-21.

No point in meddling around with complicated crap when you can just do what you can for the engine maintenance-wise, and then accept what you get. Doesn't make sense in spending thousands of dollars and a hundred hours of labor for a few mpg.

I was looking up a Citroen BX and there are a lot of trim differences but the Citroen is a lot more modern of a car than the W123. It has ABS, lower profile rubber on 16" rims, a lot less weight and therefore better handling. Im not sure if that;s the car you were talking about though since their badge nomenclature is kind of confusing.

Seem like a neat car.

#6 10-08-2007, 08:15 PM

Quote:

Originally Posted by MBRO

Well as I found out, maybe is efficient for others but for me it is not. After some calculations that I hope is correct I am doing about 18 mpg. (13 liters for 100 km).

18mpg is not at all normal. You are talking about changing how the engine operates when you should change your driving techniques or look for why the engine is working harder than it should to move the vehicle.

1 week isn't enough to get an accurate measurement anyways. It may just be a fluke.

gsxr · #7 10-08-2007, 09:01 PM

Over tens of thousands of miles, my OM617.952 (1984 300D, 123.133) averaged roughly 24mpg. That would be a 33% improvement over your current 18mpg. Other people have gotten the same model to 28-30mpg, although IMO anything over 28mpg is pretty rare territory for a 123. Regardless, it sounds like your car is definitely in need of some TLC. You need to start with all the things I mentioned in the other thread (cam timing, valve adjustment, IP timing, pop test injectors, clean filters, proper lubricants, etc) and also make sure the brakes are not dragging. The results will not be immediate, either. It can take some time. Finally, for the most accurate measurements of MPG, run every tank to the reserve light, and fill it up all the way, every time. Use those numbers to calculate MPG over a few thousand kilometers. I keep track of every tank in a spreadsheet, it makes it much easier.

siral3x · #8 10-08-2007, 09:06 PM

Quote:

Originally Posted by MBRO

Hello. This is a new thread started because the discussion derailed onto this topic on another thread.

Here is that thread:
Anyone ever thought of doing away with the precombustion chambers on a 5cyl 126 diese

The discussion started with the question if it is possible to convert the IDI (indirect diesel injection) engine to a DI (direct diesel inection) engine by removing the precombustion chamber. There were two answers for this question:

1. You can, but you will ruin your engine in seconds. So actually you can't.
2. If you want a DI engine under you w123 then buy a new MB DI engine and plant it under your hood and hope to behave

But another interesting question surfaced: Is it possible, and more is it useful in some way to remove the mechanical injection pump and install a common rail, computer controlled system for delivering the fuel? (the engine remains IDI, just the way it is timed and controlled changes from mechanical to electronic).

We agreed that such a system must be used by the person who built it or by someone who understand every detail about how it works. We also agreed that the cost of hardware is not extremely high (depending on what you compare it to). It should be around 1.5k to 2k $.

Another question was stated: "Again, what is the point? The already existing mechanical system does everything you are asking and it does it efficiently and reliably."

Well as I found out, maybe is efficient for others but for me it is not. After some calculations that I hope is correct I am doing about 18 mpg. (13 liters for 100 km).

I have to admit that I have the car for a short time (1 week) and it was a taxi before. The segments have been replaced by the former owner and I am sure that there is no damage to the pistons and / or cylinder head. But nothing else was adjusted on it. So as a advice from a fellow member as soon as I have some free time I will check the valves and replace the injector nozzles.

We also agreed that the electronic system (hardware) for the system I propose wouldn't be too expensive (in the range of 500$).

In this thread I will like to hear you opinions about if such a change is worth anything more than the satisfaction of the one who built it that it works (if it works).

Here is also the place to tell your average mpg, and ways to improve it.
Thank you for viewing / writing on this thread (my first) and I hope this will result in a constructive and, why not, fun conversation, without debates that are unnecessary.

Ha, I can't belive I would see romanians on this forum

Nice place to visit..Timisoara that is

HI there!!! Welcome aboard!
Rather then moding the old w123 diesel, just do an engine swap?Only the ECU, the common rail, and injectors will be WAY over $500!

jkoebel · #9 10-08-2007, 09:17 PM

Quote:

Originally Posted by ForcedInduction

18mpg is not at all normal. You are talking about changing how the engine operates when you should change your driving techniques or look for why the engine is working harder than it should be to move the vehicle.

1 week isn't enough to get an accurate measurement anyways. It may just be a fluke.

It's not? Hmm.

My 240D has been averaging ~17 mpg since I bought it, been through 15 tanks of gas so far.

#10 10-08-2007, 09:20 PM

Yes, less than 20mpg means there is a major problem or extreme operating environment.

pawoSD · #11 10-08-2007, 10:06 PM

My average is 24-25mpg now that I have new injector nozzles, before it was 22-23mpg...and sometimes 20-21 if I was a leadfoot more than usual.

Now its almost always 24.

Worst I ever got was 18.5 in the winter, mostly since I was rev'ing to get going in the snow so often during a week of bad weather....and spent a ton of time idling while cleaning off the car and waiting in backed up traffic.

My best ever was traveling across Michigan's Upper Peninsula at 60mph for 175 miles....got around 30.8mpg! I came close last summer by driving at 55 for over 250 miles....29.4mpg.

17 in general driving means you're either not burning it all, or even more likely if the car is running ok....you're just leaking it out somewhere!

Check all hoses and lines!

lutzTD · #12 10-08-2007, 10:13 PM

mine started out around 19, biggest boost in milage for me was turning the idle down to 500 and living with the shake i could get out with the damper. this and a valve adjustment, oil and filter change and proper tire pressure and mine has been getting 24-26 for a year. No a/c helps too I think. I will sacrifice a few MPG to get it working

Shawn D. · #13 10-09-2007, 09:33 AM

Quote:

Originally Posted by Craig

... both my 617 turbo and my 616 will get in the mid to high 20s without much effort. Some folks claim close to 30 mpg, but they work at it pretty hard.

I don't have to work very hard to get the 27.5 MPG my '84 300td is getting me -- that's the average over 41 tanks since I bought the car nearly a year ago. The worst I got was 24 MPG @ 80 MPH on the 550 mile trip home, and the best was 29 MPG over five tanks during the hottest Atlanta months (that's before I fixed the A/C). After fixing it, using A/C during the afternoon portion of my commute cost me 2-3 MPG overall.

Quote:

Originally Posted by jkoebel

My 240D has been averaging ~17 mpg since I bought it, been through 15 tanks of gas so far.

Slow and thirsty -- not a good combination! Something is definitely wrong there.

Rashakor · #14 04-22-2008, 10:38 AM

Let's bump this thread, because it may actually get to some interesting conclusions.
My experience with mileage is over 4 years with a 240D and a 300SD (W116). so I got both the OM616 and OM617 to comment on.
First on the 300SD. In always got around 21mpg city or highway, until i had to replace the windshield and had to remove all the aluminum trim around it. It took me several months to put the trim back (more because i am lazy than anything else). I actually gained 2mpg in the meantime... this suggest me than the aerodynamics of the car could use some help... I am not sure how to do that... but that is a starting point. I think a lot of the gaps in the car that generate wind and road noise could be a source of drag... So by fixing them you not only inprove your phonic comfort but also streamline the car (decrease cd).

Now on the 240D. Routinely got 24mpg for many months until I took the car for a break job. With nicely inflated tires (34psi) and brakes not dragging (just to think of all the fuel i could have saved!!!!) i was getting 27mpg.
Furthermore I found the fairly uncommon Aluminum Fuch rim in a pick and pull last year. at 13lb with the tire on it they are very light. The improvement is very slight but i get to slightly above 28mpg on almost all fill-ups.

As a conclusion for this is that mileage is greatly affected by small accumulative tuning factors so it is necessary to keep the vehicle in-tune to really get some of the mileage claimed.
26-30mpg should be normal on a OM616 equipped W123.
22-29mpg is what is expected from a OM617 turbo or not in a W123
you should be around 20-26mpg on a OM617turbo with a W116 or W126.

Now getting SIGNIFICANTLY beyond those numbers implies radical modifications and that is probably what this thread is about and wants to get to...

jkoebel · #15 04-22-2008, 10:48 AM

I feel a bit better, after a valve adjustment, fixing some other misc. related issues, my 240D is now in the low 20s -- a 5mpg improvement before, but still on the low side. I think new injectors, purge might help further.