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Old 10-04-2008, 11:02 PM
barry123400 barry123400 is offline
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
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Yes it has to be you must have changed the element loading amount. This causes the opening pressure of the injector to be hit much earlier. Thats the new torque with the advanced timing. Or perhaps it's the equal loading lessening the imbalanced firing in the engine creating the additional torque. All cylinders are generally contributing more equally. Also possible is a combined effect.

I am pretty sure a new spring is minimal cost and precalibrated if available. Unfortunatly because of manufacturing tollerences you may have to get a complete replacement pre calibrated relief valve. In my opinion otherwise you have to have a look at your holding pressure with an accurate pressure gauge.

The question that is lurking in my mind right now. How many pumps have been replaced or rebuilt for a rough idle and or poor fuel milage that just had a seriously tired relief valve? An external pump part that is easy to check and change if required.

Still good for general knowedge you went there. From now on I will check my pressure on any car I feel the milage is substandard or idle is rough. It cannot hurt and I could even learn something. On cars at the top milage for type. I kind of know that pressure will already be about fourteen pounds I think.

I guess the item you really brought to life for me was how detrimental unequal element fueling would obviously impact milage. The engine in my opinion would be dumping much more fuel in some cylinders than others especially because it was unbalanced. Or in the unbalance state the problem was constantly changing to some degree. The loss of engine efficiency could be twenty five percent or so I imagine fairly easily. Or the rolled back timing effect might cause the milage drop. Even a combination perhaps.

All of a sudden the guys reporting better fuel milage after changing fuel filters may be making some sense. Again I never doubted their statements before I just was not cognizant of how that senario could be occuring.


Another one of my by now notorious thoughs. If the residual pressure were really low say the relief valve was stucjk open. I suspect you might have a terrible rough idle. To find out how it would be I think I will remove the relief valve or take out the spring and see just how the engine runs when I get a little time. I am aware the timing will also be a little retarded as well. Still the increased disparity of fuel amounts in the elements should easily overcome that. I never remember anyone suggesting that this be considered on a rough idle and/or running complaint. It has always been grouped in with air perhaps if anything.

Once again if this results in the reasons being found on the milage discrepancies between otherwise identical cars. Cervan you will have made one of the major site accomplishments so far in my opinion. This milage discrepancy problem has occupied my mind for a long time with the 240ds especially. Yet I was and have been unable to develop a sound theory of why.

Cervan what you might have proved in my opinion already. Amount of element loading is directly dependant of fuel pressure in the pump. This by your timing advance alone. There are many solid indications that quality therfore consistancy of all loading of the elements is also highly dependant on this operating residual pressure as well. If it is off so will a few other things be as well.

It will still be awhile until a percentage of the relief valves that are way off calibration with age emerges. There may be virtially none or quite a few. Time will tell and our knowledge about injection and lift pumps increases a little more.

Paragraphs added on today with some modification of the above.

As I was driving last night it occured to me that a possible reason the milage was worse with a poor flowing fuel filter. This has been reported too many times on site not to be true. Also it would have to be quite a drop for site members to have noticed it after changing out the fuel filter. I know I mentioned it earlier a little but it's importance is worth thinking seriously about . As my thoughts evolve I will modify present statements and insert information that may help others rationalise or recall issues from the past that tie in well.

I hate a wild goose chase in general yet suspicious things need examined. My own drive or compulsion is still this milage discrepancy thing. I know it is generally not a combined problem defect. The difference seems clear cut enough it is one item causitive in my opinion. There has been no basic pre chamber or head design rehash with these engines. In a gas engine if what I am observing was occuring the combustion chamber for design differences is the first place I would look. There just is no difference there on these engines.


It might effectivly roll the timing back a long ways. Or that and the unequal loading component of the elements if present. If this is so there is justification to change that filter out on a lessning miles per gallon basis rather than just waiting until it obstructs so bad you have to change it.

I personally ignore frequency of spark plug changing for example and change the spark plugs out if milage sags or car is starting harder. There are too many variables to give specific milage intervals. Some spark plugs will need changed out for example before the recommended milage interval but the majority seem to easily go much further in my experience. This type of possibly abstract reasoning just might apply to the fuel filters.

The manufacturer cannot control actual field conditions so he generalises with a safety margin with his recommendations. Again just my opinions. I think load of dirty fuel for example might do it. The car would still run decently yet your milage per gallon is comprimised. Now if you combne this with a weak regulator spring if they indeed change their calibration with time and use you are never going to see good fuel milage. This has all yet to be proven. Parts of it already seem to be.

Cervan. It is possioble to find how far your timing is advanced in my opinion by the milli volt method. Or a magnetic pulse type device if known to be accurate. Not worth the effort and you do not want to be there anyways.

Part of my intensity with the milli volt attempt to time these engines was it averages all the lurking variences in an old engine that an owner is not addressing. Or he cannot locate and finds the best available timing for an individual engine. The pulse device cannot do this and the manufactures timing recommendation is based on everything in good/excellent condition. Unfortunatly the stiffness in the injector lines make this approach not practical on these engines in my opinion. It cannot even be used to indicate you have underlying problems by indicating the peak efficiency point is well removed from the factory recommended timing.

Those stubborn hard injector lines negate any such effort. Perhaps yet in the future some practical way will be found to verify the factory recommended timing position is right for your individual engine with this method. The present methods do not even allow for the fuel we use today with lower celane numbers. This applies for instance to changing timing requirements mind any wear or defects.

From my past experience on volkswagon timing too far advanced can possibly loosen up the harmonic balancer. Your new hardness to start is possibly an effect of considerable timing advance. This whole senario may not be the best. I would just try to make sure the relief valve is calibrated to whatever the manufacturer states and observe my milage.

You have no baseline on where it was prior to the spring stretch in my opinion. Still after everything is restored see if you are getting better milage in general. That might kind of prove the residual operating pressure was indeed low before. Or that you had about 14 lbs pressure prior to the adjustment. Thats if the current milage is the same after restoration if required. Also I would move my timing up two degrees that a lot of people have reported over the factory recommended setting. I have never heard any difficulty reported by doing this. It also sounds reasonable just by the ongoing changes such as celane ratings in our present fuels over the last twenty or so years since these cars were made alone.

The lowered celane values compared to europe are real by the way and it is starting to appear amight be the true cause of the 3.5 diesels going bad as the same block in europe with their higher celane rated fuel is holding up I am led to believe. How the lower celane value fuel is doing this is another issue. I see no issue then of boosting the celane with aditives on a 3.5. If this area sorts itself out perhaps they might be even be a safe buy at some time in the future.

Right now I would only take one home if close to free and in good condition. Thats just me though. I still feel it is almost criminal they left so little material between cylinders. Thin material is not only weaker but will distort or warp easier as well.

I visualise investigating over time observations of items or effects observed by members until the culprit for the milage discrepancy is found. I am out of ideals myself. So I just try to keep an open mind until an item like Cervans is posted. It almost has to be somewhere in the complete fuel system.

On the 240ds the discrepancy allowing for different drivers habits is still 15-25 percent overall. Why this percentage spread is not showing up on 300ds is beyond me.

Or is it a requirement to see thirty miles per gallon to have almost static compression greater than 400 lbs? One day a member getting 30 or low thirty plus miles per gallon with a 240d will report his static compression.

If you get through this you are older but not wiser. I still would like to see disscussion in this area increase.

Last edited by barry123400; 10-05-2008 at 01:48 PM.
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