From time to time I get some interesting private messages that start me thinking. The latest one was welcome and alerted me to the concept of proper drip timing.

The gentleman involved was asking about using the total average of milli volts combined as a guide to timing an engine. Replied that I think the drip method is better and more reliable at this point. I explained the milli volt approach is best left for trouble shooting at this time. It can excell at finding many things if conciencious application is observed.

Since we tend to believe if the number one element is properly drip timed. The sequential timing of all the following pump elements will be as close to proper or ideal as the manufacturer intended. I also agree that with a good injection pump this should be so.

Now if the base pressure in the injection pump is substandard all bets are off. The varying degree of unpredicatability present in element filling will have an effect on this sequential pump element timing to some extent. So the feed pressure present in the base of the injection pump should be checked as an integral part of the process.

My feeling at this time is about a three pound leeway below the old recommended pressure is about all the system will tolerate. Below that the effective timing between the elements is in a questionable range. The engine will still run fairly well but there may be problems present.

This leeway is based on the recomendation of no more than 19 pounds pressure should be present. Plus some pump rebuilders standards. The low pressures in many systems in operation are detremental to many things. I can even visualise a constant viariable problem between elements being present depending on different amounts of fuel being required at different loadings with substandard pressures.

The only way to verify the pressure is with a fluid dampened 0-30 pound gauge. Nineteen pounds seems to be the target to obtain if possible for good and allowable efficiency.

At some unknown lower pressure perhaps ten pounds serious effects may be underway. It is also very important to maintain a good usable operating pressure at highway cruise speeds as well. The fuel filters have to be clear enough to allow this. Otherwise they should be changed out.

I believe the recommended frequency of fuel filter changes by manufactures were though of as overdone. Reflecting on this generally without a pressure gauge permanently installed they may have just been trying to remain on the safer side of operating pressure paremeters.

If driven till the fuel filters actually blocked off enough to notice was far too little fuel pressure present in the injection pump base. Possibly for quite a time before becoming noticeable.

How often to change the Fuel Filters is dependant on the quality of the Fuel you get from the Pump and your willingness and/or skill at changing a Filter on the Road Side.

We have all read stories on this Forum of someone on an out-of-Town trip filling up with some bad Fuel and having the performance effected or even rendered un-drivable.

I buy 98% of my Diesel Fuel from the same Station sinc 1992 and seldom drive more than 20 miles from home. I have never had a Filter plug up on me and effect my performance.

The longest I have driven with the same Fuel filter on my Volvo Diesel for as long as 5 years with no ill effects.
It has only 1 Fuel Filter; but the Filter does have a Drain on it and during the 5 years I drained in one time that I can remember.

But, previously I had changed it ounce a year or ounce every 2 years but not because it was plugged up; just preventative maint.
I do not carry extra Filters in either of my Diesel Cars.

So Fuel Quality and willingness to deal with a Road Side Filter change will be the "Tail Wagging the Dog" so-to-speak.

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84 300D, 82 Volvo 244Gl Diesel

Where is the best place to tap in to measure fuel pressure? Pictures of a set up very helpful.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Anywhere between the secondary fuel filter and the injection pump. The neatest ideal so far was to drill and tap a bajo fitting.

As the filter becomes restrictive in service at some point the injection pump base pressure is going to start to fall. Far before any effect is noticeable to the driver the injection base pressure may have sagged well below the better operational pressure area. This condition might be present for months or years possibly.

I have suspected this possibility for a long time. In fact ever since some posters mentioned they had changed their secondary fuel filter and noticed increased fuel milage as an result.

If they changed the filter as part of preventative maintenance with no other noticeable effect present to indicate the need. Then the operational; pressure has obviously increased with the new filter.

Without a pressure gauge installed there is generally speaking no way to know when some restriction is growing in the supply system or the lift pump is gettting too weak to allow overflow from the injection pump. For the money a gauge costs and the small time required to install it.

The time perhaps has come to really consider it as a bellweather or monitor of the condition of the fuel supply. Far better than being stranded on the side of the highway someday.

Besides the lower fuel milage. The possibility of better balancing and sequential timing of the engine being present. If my speculation is also correct about the damage done to the first cylinder over time with the low pressure deficiency it is a really worthwhile addition to these 616 and 617 engines.

Once enough of these are installed troubleshooting the fuel system may decline as a need. Or become so much easier. The gauge should warn you of events well ahead of time in a lot of cases. If it even saved a few engines over the years from disaster it might be worthwile. On a 616 four cylider engine you really should know your operational fuel pressure. At least until low pressure is eliminated or established as the true cause of the number one cylinders excess loading and resultant excessive wearing rod bearings.

I know that I am still flogging a dead horse so to speak. Over time I have observed nothing to reduce the advisability of having a fuel pressure gauge installed. The pressure in the base of any injection pump on these older indirect diesels should be known.

Not the atitude taken that the car does not run too bad or pretty fair so I will ignore it. It is just wrong to expect thirty year old automotive systems to still be as they were new. Of course some will be but there is no sure way to know yours is without a test.

Between the secondary filter and the IP you are measuring lift pump pressure. Is that what you want? I thought it's internal IP pressure before the ball and spring check valve on the return banjo that we want?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The Pressure between the Secondary Filter/Spin-on Filter and where the Fuel goes into the Fuel Injection Pump House is controled by the Spring Check Valve; unless as Barry was saying the Filter is restricted.

If you were to install the Pressure Gauge between the Lift Pump and the Secondary/Spin-on Fuel Filter as your Filter becomes restricted your Fuel Pressure would go up but that full pressure will not be going into the Fuel Injection Pump.

If you want a real test of your Fuel Pressure you are best off changing the Filters before the test.
That way a restricted or Plugged Filter is not going to interfere with your reading.

In the Manual there is several test proceedures.

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84 300D, 82 Volvo 244Gl Diesel

Below is what I did to the Banjo Bolt of the Fuel Outlet on the Secondar/Spin-on Fuel Filter.
However, even with the Liquid Filled Gauge the needle still bounces. I think there is an need for some sort of restricted/orfice inside of the Fitting to further smooth things out. Or, maybe a small adjustable valve.

I am haveing some issues with my new computer. If you can or cannot view the thumbnail please let me know.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

How much bounce? Can you average it or is it too fast and too broad? I was wondering if a trapped air pocket device would be enough to help average it? Otherwise a small pinhole feed restriction might work as you suggest..

A solid line plug with a very small hole drilled through it perhaps. If it turns out some gauges bounce more than others we should find the reason. Basically all the gauges used are the approximate ten dollar fluid dampened chinese one I suspect. Actually appears to be fair quality and value for what it is.

It might be better yet to use an inline rotary electric pump rather than the lift pump- That lift pump is always going to cause some fluctuation of the pressure. Theoretically, that in and of itself could cause uneven fueling.

One of our Members did make a PVC Tubing Air Colum to stop the pulsating Gauge Needle. His comments may be in the DIY section some where.
They use a similar setup to stop the thumping (Watter Hammering) in you Water Pipes.

About 1.5 years ago I bought a lot of 3 Liquid Filled Gauges on eBay; and they are from China.

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84 300D, 82 Volvo 244Gl Diesel

The Electric Fuel Pumps that I have seen that can put out the pressure needed are over $100; and I do not know if they can out out the Volume.

The other issue is that there is a lot of violent Fuel movement inside of the Fuel Injection Pump Housing caused by the way the Plunger Elements work.
The Element Plungers always have a constant stroke and they always fill with the same amount of Fuel.
It is difficult to describein words how the Helix cut on the Pluger works but so I will not attempt that.
But, at idle most of the Fuel that went in to the Element is expelled back out of the same hole the Fuel went into.
While that amount of Fuel being expelled at Full Throttle is less the velocity of the Fuel shooting back out of the hole is much more.
On some Fuel Injection Pump Housinges they actuall put Steel Inserts opposite the what I will call the Fill hole on the Fuel element becaues it the velocity of the moving Fuel can erode a hole through the Aluminum Fuel Injection Pump Housing.

So even with an Electric Fuel Pump you will still have a lot of pulsation going on caused by expelled Fuel from the Elements.

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84 300D, 82 Volvo 244Gl Diesel

True, but that pulse is not timed to the inlet of another element, and it isn't a very large amount of fuel either. The lift pump, however, does send out a fairly large amount of fuel on each shot, and has the potential to increase the pressure to whichever element it's timed closest to, causing uneven filling and differences in timing/power output between cylinders. It's just a theory, though, I have no direct research to back this up.

The pulses are not timed to any other elements loading period perhaps. Yet at low injection pump base pressure the resultant longer lasting turbulance may have more of an effect.

By it's design I see a good lift pump with fairly tight internal valves having a design of least disturbance pulsewise to the fuel supply. If the internal valves are leaky enough the fuel pressure supply pressure gradient may become less constant through one cycle. More likely the pump will not maintain 30 pounds plus pressure though.

The lift pump repositions it's fuel pressure piston once every injection pump rotation. The simplest test to verify that excess internal leakage is not present is to close the return line on the injection pump off. Your pressure gauge should slam to thirty pounds. This indicates any leakage losses inside the pump are still acceptable. If lower than 30 pounds there is either an obstruction to flow somewhere or the pump needs a rebuild. A ten dollar kit and a little care should do it if it turns out to be the pump.

The actions ocuring inside the pump base are chaotic in my opinion. The pump is set up on a machine that allows for those chaotic events. The saving grace is they are repedative as well as seeming chaotic.

This is where the proper background fuel pressure of 15-19 pounds becomes so important. With all the interactions being present the pump was calibrated at a certain base pressure. Start dropping that base pressure and the chaotic events start to have more influence. Especially when the injection pumps base pressure becomes lower than the relief valves opening pressure.

With the change of the primary elements filling pressure. The effects are going to become abnormal or outside the injection pump manufacturers intent by design.

On a pump being fed the proper higher fuel pressure the relief valve is always open.In my opinion this allows the cigar hose to moderate some of the pulse effects. Or once again get the calibrated injection pump back into the operational parameters it was set up for.

Especially when the return fuel line in the tank is submerged in fuel. A lot of people believe the cigar hose is only a noise reduction device. I believe it has been proven otherwise. Also the cigar hose does reduce the noise component. In doing so it is tending to average the overall effect of the sharp pulses or excess turbulance downward I believe.

Fortunatly we have no real concerns here as long as the base presure in the injection pump is fed properly and the relief valve is calibrated to say 15-19 pounds with the upper side of the range being prefferable.

I also do not hear of cases where the cigar hose has gone hard with age. If you live in the south it may be otherwise. If you suspect your has check pliability or hardness against a new one. It can be the small details in any well designed system upsetting the applecart.

Fortunatly everything in that system of fuel supply is both managable and restorable to good condition at minumin cost and some effort. The vast majority of site members can manage this in my opinion. But you do need a 0-30 pound liquid filled gauge to verify it is where it should be and all is well.

The gauge mounted as a permanent item allows forward monitoring. Warning you in advance of deterioration of fuel filters and other things. This is worth serious consideration in my opinion.

Better fuel milage, smoother idle, and most importantly the survival of the number one rod bearing in the engine may depend on the proper base pressure in the injection pump being present.

Quite some time ago I felt a company that could build sophisticated aeroplane engines at one time. Would not leave an oiling issue unsolved for the length of run of both the 616 and 617 type engines. So until proven otherwise low fuel supply pressure feeds more fuel through the number one element or retards the timing of injectors past number one in comparison. This results in loading the number one cylinder with more work than the others. Over time this wears out the number one rod bearing first besides reducing overall power and fuel economy.

If what I believe to be true it is only good economic sense to pay attention to the fuel supply area. In a good percentage of cars it will be substandard. The added plus is the more you learn about this system the easier it is to keep it in good condition or troubleshoot it if it comes to it.

Who in there right mind wants to take their older cars to the average service garage in todays economy anyways. Brings a total new meaning of you get what you pay for. They got the pay for part of it right..

Thanks for idea and the pic! I made an adapter similar to yours and will be taking a fuel pressure reading when I get a chance.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked