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Old 10-06-2008, 09:23 PM
barry123400 barry123400 is offline
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
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Originally Posted by Cervan View Post
Well after i stretched the spring i also retarded the timing as much as i could to try and alleiviate some of the knocking. But i couldnt retard it enough to stop all of it. My milage was about 25-30 around town. Im going to de-stretch the spring a little bit and see how that changes everything.
My guess and it is only a guess is that your 240d was close to a top milage example before the spring stretch. I have never heard of one exceeding 32 mpg on long highway cruises. Exception being ebay of course. So your old calibration of that spring was about right or fairly close in my opinion. I Think this area needs investigation on any 240d standard getting less than about 27 mpg on the highway being driven in a reasonable fashion keeping up with traffic.

Now the five cylinders are a little trickier. They too can be deficient in milage but not so noticeable. So it is more subjective. At present. Suspicion should occur if you feel yours is substandard to the top 20 percent of your type examples.

The best approach is to read the residual pump pressure. If low I suspect in every case that they are returned to what they should be the engine will have more accurate timeing when the engine is running if the drip method was used. In fact if you find you have to restore the original pressure your timing with the engine running will match the drip method that was used to set it better again. Restoration of proper pressure also gets rid of the retarded timing effect inherent with low residual pressure I suspect.

Another important consideration is a ragged idle. This might indicate low pressure in the pump and unequal element loading . These cars are now so old deteriouration of something like relief springs is not unreasonable on some of them. You have to make sure the filters are not bad enough to limit pressure in the pump when reading. We know from others low pressure in the injection pump from poor filter flow hurts milage. Too many cases reported to dispute. I am at last almost certain the cause is now established.

If your milage is high average for type you can almost assume the pressure is about right. Rather than running out and stretching spring people with low mpg examples might read the pressure in their pumps. If lower than what it should be then adjust or replace the relief valve. First make sure the lift pump can reach past the required pressure perhaps by a quick pinch off test once the meter is installed. Volume flow to maintain pressure is another consideration. The filters have to be eliminated as a causitive as well. Restricted flow can result in low final pressures.

One last important item. It is apparent and was suspected an effective timing change does take place with different relief pressures or pump residual pressures if you preffer. I think the swing is substantual. This can be graphed with the milli volt method if bosh does not already have that. The tremendous increase in power these gentleman are feeling is the heavily advanced timing over their pre spring stretch timing.

The best and safest approach is to have the residual pressure at the high end of the original tollerance by bosh. If yours was substandard to that you will certainly feel an improvement. Especially in milage I hope. At this point we should establish the manufactures original intention and if he modified this value over the production time run. I suspect they did not.

If absolutly nothing else the method of insuring reasonable accurate running timing by pre checking the residual pressure of the pump is no longer much in question. If thaty pressure is off much you can drip time until the cows come home and the running timing will still be wrong. The relief valve in almost if not all cases of change will weaken with time. I have this gut feeling bosh wanted it really close to design requirements. A pound off might be 1-2 degrees of engine timing.

Last edited by barry123400; 10-06-2008 at 10:21 PM.
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