Well at least one believer now. If or as soon as you establish miles per gallon post. Take into consideration if you are driving the car a little harder as more power is available or just about the same when you had lesser power. post everything.

If you establish you are getting more than 29 mpg and driving harder than you used to. Get your pressure read at the pump. Come to think of it if you are getting more than 29 miles per gallon driving as you always did still read the pressure.

I warned you from my prior experiences not theory you can go too far with this. If so it may cost you severly. Invest the fuel savings at the end of this tank on a pressure gauge and fitting or fittings is smart money. In your case they have almost already been paid for in fuel savings.

I am well aware when you have accomplished this much you never want to go back. At worse you might have to only lose a small amount. Maybe nothing. The gauge will tell. Believe it or not you might even be below the top threshold limit. So more power and mpg would be available with no risk.

There is a remote possibility fuel milage may be safley pushed even higher than what you are seeing. It is only a possibility and intense instructions would have to be followed to get there. I hate current retoric but it would be possibly a win win situation. Or a win neutral result. More power on demand with the same high fuel milage you get when the pressure in that pump is set to requirements.

Or if really fortunate and I am missing something more of both with little or no risk to the engine. Right now since you do not know the actual pump pressure there can be risk. You actually have to get a gauge on there or might really regret you did not at some point. Not optional in my opinion.

What has happened to your car does not suprise me at all. It may have suprised others though. If you examine your first post and my reply thread you will notice I described three things that I believe you have experienced. There is a reason for that. Now did you get the 320 miles on your car out on the highway? City driving? Or a combination? if the last give estimated percentages. Give any other details you can think of as well. The 300d is a heavy car.

Smart advice. My 30psi gauge cost $11 from a local hydraulic shop.

Which is why I'm installing a gauge before I even touch my stock spring.

Would it be too much to ask you to post pics of your gauge setup?

__________________
Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles

My driving is very mixed on this tank i would say 70% highway with some rush hr. driving and at speeds from 70 to 75 mph.

When I get it installed I'll post plenty of pictures.

Thanks for the post. Just assures me you are not at 29 mpg or a higher area with just mostly around town driving. As I earlier stated that 300sd is a heavy car.

Forced induction's post will be very interesting. I believe he will be quite objective. Posting his initial pressure and any boost he dials in if he feels the room is there. The effect of that dial in if done is where my own interest is, He will actually be the first person on site to read his original operating pressure I think. Plus move to the high normal setting.

I am hoping the found pressure is a little low with an aged spring in there for starters. That may indicate the majority of 123 cars are possibly simular.

One area the service manual did not stress in my opinion. A tired spring might not compress or sag with time. Instead it could loose its actual design tension. Removed from the relief valve it might still present with the right length. Load it or make it work and it is substandard under dynamic or loaded operating conditions compared to a new one.

Can a loaded spring in a changing enviroment have a finite lifespan? This spring is almost totally protected from corrosion by oil. The temperature swings it tollerates are not too high.
Other factors can certainly impact like time/use /fatigue /temper /cycle issues. Almost certainly one or more of these will have impacted some if not the majority of springs by now to some extent. I am almost counting on it.

Working cycles as old as they are now are in the millions perhaps. So fatigue may be the most probable senario. . The deterioration if present would have developed quite gradual I imagine if it occured. . So slow the deterioration was not noticed. Even the fuel milage slipped away very gradually.

The service manual indicates that even when these cars were a lot newer some springs may have needed restretched to original length so there had to be some issues. The majority of those manuals with this information were printed in 1985 or earlier I think.

Besides the safety issues this kind of questionable logic means you should read the actual pressure with a gauge just not pull the spring and measure length. I know this might be a long shot to some yet possible to me anyways.

I also have a site friend that is on the issue this weekend as well. I will try to entice him to post if he does not. Like Forced Induction his posts will be credable. We have worked issues before together. Im fact he helped prove some hypothisis on another item. His contribution at that time was important.

At least I never suggested strapping magnets to fuel lines. Maybe next time. I also still like my fuel molecules in a chaotic state. I would not know what to do with them if otherwise.

Can someone post a pic of where is this Pressure relief valve located please... I too want good mpg !!!

__________________
Current Garage
2008 Mercedes GL320 CDI 188k mi Repair/Work in progress
1994 S350 160k mi Garage Queen & prepping for repairs
2005 E320 CDI 203k mi Healthy & Daily Driver
1994 S350 357k mi Retried as parts car
1984 300TD 214k mi Blown OM617 Poss OM603 Swap??

Sold
1987 300SDL 200K+
1994 S320 181K mi
2008 E320 Bluetec 127k mi
1999 S420 130K mi
1980 240D 360k mi
15+ Others that has come, stay and gone

GONE, BUT NOT FORGOTTEN
1995 E320 SE 220k mi
1984 300SD 350k mi

Some more meat on the bones has just been posted to me by my site friend. I have also asked him to post on site if he wishes. He is a member. Between ourselves we seem to feed each other ideals when colaborating. I certainly want nor desire any credit for someone elses serious contributions. He is already on the move.

His critical examination this evening has shown there are deposits on the seat and ball. Plus associated crud present. Looks like rust on the ball he states. I think it is ring shaped. That means it would match the spring and is irrelavant if so. The bottom line is this relief valve on his 240d injection pump may not totally seal. The initial pressures he will post I hope are before he cleans or repairs the relief valve.

Unless the lift pump supplies very heavily the injection pump will possibly not even reach design pressure even if the spring is good. There is also a chance the seat/ ball is worn out somewhat or unable to totally seat even if the crud was not present. So crud and wear might be present. He also has measured all the dimentional details of the spring. His spring is 20.5 mm and the coil diameter and coil spring thickness etc. Are recorded. This may be useful to find a common replacement source at some time.

I will not post the list of details on the spring as it is not that important to our quest right now. . It may have experienced millions of cycles over the years. I have not done the numbers but everytime the lift pump cycles the spring moves as well at the same time regulating the more fixed pressure and moderating the pulse present simultainiously.

So the whole relief valve should now undergo an examination as well as the spring issue if the presure is substandard.

Simple test just blow into the assembly. Hook a plastic or rubber hose to the barb where the return line attaches. The harder you blow the tighter the seal if all is well. Hopefully yours is cleaner than his. Do not count on it though.

Certainly if the relief valve is basically not capable of sealing it might be a problem. One possible effect for example. In the morning you start to crank your engine. Residual pressure level is not built up quickly in the pump at cranking rpms. Engine will not get enough fuel to fire off easily.

There should still be some residual pressure left in the pump if the return valve seals properly and the return check valve in the lift pump is tight. No leaks present anywhere between the two either. I guess with a gauge installed permanantly you would see this. Car may start easier as well.

May be the reason or at least a contributor to why some exampes will start at far lower temperatures than others . One engine is getting good clean inputs of fuel to the cylinders and the other is not. Usually blamed on compression or electrical. The signifigance of this nickle and dime type component seems to be increasing.

Fuel pressure relief valve adjustment
Fuel pressure relief valve adjustment

I don't see how this can possibly help MPG.

Remember you do not just freehand adjust the pressure relief valve spring. That can actually destroy an engine. Yes thats one way it will deliver better fuel milage for sure. I personally can almost gaurantee it. Your first consideration is exactly what is your present mpg and model of car. There are many things that influence miles per gallon.

The correct proceedure is to check the pressure present in the pump. If it is substandard move it to a point in the approved range by the manufacturer for your type pump. Maybe this is what you intended to do. If not leave the relief valve alone unless you are a real knowledgeable person about engines and effects.

This takes a pressure gauge installed to see what is initially present for pressure. There is no percentage even looking if your car already gets pretty good milage for its type. You cannot elevate the milage beyond the highest honestly reported milage per gallon basically no matter what you do. For that kind of milage everything else has to be in good shape as well. For instance injectors have to be in top condition for just one item alone. I fixated on the 240d standards as they seemed for some reason to have the greater problems milage wise between different cars..

It was not being caused by a combination of effects that are basically maintenance items. Or any one known item. . Actually the cause was unknown as far as I am aware. I probably have two years invested in watching for an item. This area just turned out to be the best possibility so far.

There is nothing wrong with going into this area responsibly. To try it quick and dirty can really cost you your engine. It is easier for me to explain this than tell you what are the probable damages later. They are so serious I cannot soft soap them. For all possible purposes engine destruction results in several ways. Not can result. Get that set too far ahead and you will experience it first hand.

Remember I am the guy that ran purposly advanced volkswagon diesels and have repaired the resultant problems. I knew they would probably arise going in and did not mind the risk. In my case it was part of learning on purpose. All I suggest is continue to read the thread and decide if you want to try it in a proper fashion as more people post the results if any of proper proceedure. Far better to get some miles per gallon rather than no miles per gallon.

Sorry guys ive been really busy last night i took apart all injectors cleaned them, and cleaned the inside of the combustion chamber best i could (a little bit of carbon build up on the prechamber balls). I also adjusted the cam phasing for each cylinder and the results are astounding, all the way to high rpm's the engine just soars But the trade off is at idle i have a small ammount of white smoke from the exhaust. Maybie this is because my thermostat is bad and not allowing the engine to get to 84c (it hovers at about 75) Or its injecting more fuel than the engine can burn at idle, Or its none of those and its just condensation. Ill take a few videos tommarow of the before 0-60, the without 0-60 and the after 0-60.

__________________
Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac?

As long as they would add one additional commandment for you to keep thy religion to thyself.
George Carlin (Wonder where he is now..)

1981 240d (engine donor 1983 240d) recently rebuilt engine hurray! - No more.. fought a tree and the tree won.

pearl black 1983 240d 4speed (Converted!@$$%) atleast the tranny was rebuilt.

Before and after mileage?

How about your 0-60 time?

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

My car has the hot idle shakes so I wanted to check the spring length to see if it was way off in order to decide if it was worth the effort to engineer a fuel pressure gauge setup. Today I pulled the relief valve out and it does not have a plug on the end that can be unscrewed to get at the spring. Instead it has a ball plugged in the end and the housing peened over. It is very similar to how oil passages are plugged in transmissions. I can only guess that when the PO had a rebuilt injection pump installed the pressure relief valve had been replaced with a new one as part of the rebuild process. While I feel better that the valve is fairly new (probably about 50K miles) I still have hot idle shakes so I'm go to have to hook up a fuel pressure gauge anyway. If the pressure is low I guess I'll find a used one and adjust it.

can't tell exact MPG because i fill up at work off the truck but i used to go 200 miles on a half tank and now i go 300

That does sound like a cats whisker of an improvement. A little math. Not reliable at all though. About 200 miles on 8 gallons is around 25 mpg. 300miles on eight gallons is about 37 miles per gallon. This is not possible and the error is completely reasonable as the indicated half tank use is too loose a refference. A natural understandable error.

The suspected improvement is greater than I would like to see though. Trust me and get a gauge on the pump. See if pulling it back somewhat is indicated. A lot of people reading this will find it hard to even relate to and sorry if a little bit of the power has to go as well. I have a formula in my head to keep some of the power and some of the increased milage. That has to be left till later.

Yellit as mentioned before will be on the move. He is teed in at the point between the fuel filter and the injection pump. The best place possible in my opinion as well. His first experiment as he has two gauges is to indicate the detrimental effects of pressure drop with a well used fuel filter and change it out and duplicate. This immediately clued a slow learner like me in that a new fuel filter should be installed before pumps are set to the high allowable limit. Otherwise when you change your fuel filter or filters later you will be above the allowable range.

This freebasing of presures also goes beyond my original ideal of restoring lost fuel milage that disturbed me for a long time. Funny though if those injector lines had not been so stiff we would have stumbled on the corelation of timing problems. It would have been quite noticable some if not the majority of pumps in operation were not following the static timing refferance with any accuracy at all in my opinion. That milli volt method was a curse on application to the 616 /617 pump. The accuracy was not suspect. Just the application. Some pumps other than mercedes are very easy to use it on.
To complicate this post at this stage would not be responsible or even sensible. Cervan is playing around in areas of the formula.

Yellit my site friend has already teed in a gauge and read the pressure on his 240d. Fluxating at 10-12 psi. Too low if the range is the same on a 240d natural aspired engine.

The pump he found the relief valve issues in was a spare that is not going to be run soon. Yellit is going to increase the pressure by restriction of the output of the pump on his running car gradually I hope. As soon as you start that another effect swings in. The residual pressure will tend towards the upper portion of the pulsation initially. Now it follows the average of the pulsation or lower in my opinion.

We do not know if the recommended range of 11-19 pounds applies to these natural aspired pumps as well. Anyone out there have the specs in their manuals for this n/a pump? The 617 non turbocharged pump should be simular in my opinion.

The sooner we know them the quicker yellit moves. As the revs come up the meter cannot fluxate quickly enough to indicate it so the needle steadies at about 1700 rpm totally. His is not a liquid filled gauge I beleive. This means there are no complications at all with metering the pressure.

Please do not follow Cervan without a lot of knowledge. The videos he is going to post are going to be unbelievable to most of you. I have been there with a different diesel engine. It too was unbelievable but I could not remain there long term. The fellow that thinks he has gotten about a 30 percent fuel milage increase is not off his stick either.

Back quite awhile ago when learning how to dynamically time pumps. The only way that it is really valid by the way. There were some amazing symptoms noticed. In away you kind of expect them to perhaps be there. When present though it is another complete story in itself.

As stated I already have a pretty good ideal of how Cervans 240d engine is going to sound. Most would say this cannot be but the video and related information should indicate otherwise. His 0-60 drop in seconds I could only speculate on. He is almost a gas car now though in performance if he is where I think he might be. If this does not keep people watching this thread and contributions increasing exponentially I will pack up my tent.

Again does anyone have the normal range of residual pump pressure in their literature? We cannot assume the 617 natural aspirated is in the same range as the 617 turbo pump as these pumps are known to be different. If nothing else this type of endevour removes some of the bordom of recent posts. It never hurts to throw a little spice in the mix sometimes.