Yes the fuel pressure should be checked by a gauge. You want between 11 and twenty pounds at idle. For example your increasing the spring length might have pushed a sub standard condition still lower. Thinking the lift pump perhaps. It has to work a little harder now. It might not be up to it and has fallen a little further back pressurewise.

A quick scan of the glow plug voltages might indicate a sub standard element in the injection pump once you are sure your operating fuel pressure is in the normal range. Something is unbalancing your running engine to the extent of really hurting the fuel milage. When it's as bad as yours there should be a positive indicator somewhere.

Consider making the gauge a permanent installation when it does arrive. The small area of the factory fuel filter alone means you should change it out as you start to see your injection pump pressure drop below the minumin. Also any kind of permanent or semi permanent installation means you can check for feed pressure under load at speed.

This is not your problem at present I believe. Just important to make sure feed pressure is properly present before fixating more on that injection pump. I would always take the time to verify it is the injectionm pump before changing it out. It of course can be the pump.

Received my gauge from HF, picked up some rigid tubing and constructed my lift pump pressure tester. Now prior to testing i did stretch the pressure relief valve spring from 21mm to 26mm as other have done, but my only results were a slightly rougher start - engine shake still there. Idle pressure measured between lift pump and spin-on filter 19 - 20 psi, up to 25 - 26 psi @ 3/4 throttle.

Used different pressure relief spring, measuring 20mm, and tested. Idle pressure @ 15-16psi with 19-20psi at 3/4 throttle, engine starting normal, shake still there.

What's next? Do i attempt to adjust pump by hand similar to what Cervan did http://www.youtube.com/watch?v=FBtI3UdFi4Q or Barry123400 millivolt method?

The only other option i see is pull the IP and take it to a Bosch shop for bench calibration.

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1985 300D, 250k
1980 300SD, 180K

Okay your base pressure is obviously good. Was normal at idle all along before stretching the spring apparently. Now is the time to take a digital voltmeter and read the individual glow plug milli volts at warm idle.

Since your glow plugs are fairly recent you are hoping to find one cylinder with a much different milli volt reading than the others. The worst possible senario is that the readings are all over the place. Unlikely but possible. Remember to ground the meters negative lead on the head. This eliminates the ground legs picking up noise and affecting the readings. It is important.

If you post your results I will try to keep returning to your thread regularily. The next step if you find only one cylinder with unusual readings is to swap the glow plug with its neighbouring glow plug and examine all those voltages again.

If they are still the same we are down to the troublesome cylinder. Depending if it is higher or lower milli volt wise will determine the next step. Remember that you from this point on have nothing to lose as the pump is substandard and you will have proven that soon if so. You of course will also swap two injectors just in case and read the milli volts again. I know the injectors were balanced so they are probably good. I just do not want to see an injection pump element modified to cover up another fault.

You would always be able to return to your past rough idle situation if you just record accuratly the readings as you go from step to step. It is a little tedious but cost effective to use this approach in my mind. You cannot basically land up worse off either.

With your poor fuel milage alone I think you are going to find something. Lets hope sometime in the past a previous owner or garage messed up the calibration of the number one element somehow when timing the engine. That is the easiest possibility to rectify.

Basically what you will have proved is if the injector pump is not correct one way or another. If it turns out the pump is indeed the problem it might be corrected at home.

Remember that there were no basic failures to fix the problems dealt with previously. The posters did not have the advantage of recent glow plugs in the majority. Or injectors that had been reciently balanced either. Those important preliminary areas have been covered by you increasing the chances of easier success.

Back then as well I was not aware of the poor milage caused by low injection base fuel pressure and its contribution to poor idles on some engines. So I reciently decided the base pressure must be known before moving forward.

Otherwise elements might land up being adjusted to overcome underfuelling on some of them in certain cases and the idle at the end of everything still would not be ideal.

My other feeling is these old indirect injection engines are not quite as fussy in the injection sequence timing as originally suspected. If the sequential timing of the elements is in the ball park all will be well in most cases. Of course the closer the better yet still not totally critical. Something has to be quite a way off to cause noticable symptoms.

I do not think you will regret getting into this. Also if succesful you will find many other areas that can be dealt with by application of this method if they arise at some later date.

Of course every advance has a price. Since I am a slow thinker it takes time. For example I have wondered if all the injector lines are the same temperature?

On a normal engine I would expect so. On an engine with a marginal element that is not compressing the same quantity of fuel it might be different. Cheap temperature scanners are now starting to become common. . Their accuracy is not a real issue as like certain other things it is just a comparison reading that is desired.

I simply need a cheap method to determine if an element was delivering a sub normal amount of fuel. Or one line was running at an elevated temperature indicating something else. Unfortunatly I am not sure if the line temperature would be swung enough to indicate these things. I am always on the lookout for easy methods to indicate an injection pump is not normal.

There has to be no feeling quite like sending an injection pump out. Getting it back and installed with the same symptoms present. I would tend to feel it was a thousand dollars basically spent for absolutly nothing. There is always a possibility of problems with substituting used pumps as well. Especially as these series of cars get older and older.

Just a note to be sure & measure pressure (Between Filter Output & IP input)....

Record readings on level road at 20 mph intervals up to Hwy speed....

This is where I was getting a big drop even with a recent new filter....

Looks like the old fuel I had was plugging the new spin-on faster than I thought....

This was showing up after I had restored good lift pump pressure....

Just to rule this out as a possibility....then follow the Barry1234000 milivolt tests for more info....

These tests will let you know before you try to change the IP element fueling...(last resort)...

Many IP's are rebuilt with no real improvements noticed after all those bucks.....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)

I have been looking at the pics and it looks to me like the Test Guage was connected between the Spin On/Secondary filter and the Fuel Lift/Supply Pump. Taking the pressure of ther Fuel going into the filter.
If this is the case a plugged Filter would give you a high pressure reading.

I would take the pressure with the Test Gauge between the outlet of the Spin On/Secondary filter and the IP. This will tell you the pressure that the IP is getting; which I believe is also related to the pressure the Overflow Valve is set to.
If the pressure here was low I would change the Spin On filter and re-test to see if the pressure goes up.

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84 300D, 82 Volvo 244Gl Diesel

Yellit is quite right. Althouigh I would deffer the road load pressure test until after the idle is dealt with. We were concerned at present that enough base pressure existed at idle to go further. You dealt with that and proved it was.

Once idle is dealt with yes a road test under load for proper base pressure is always going to be a good thing. It just tends to keep everything at the most efficient level possible for good fuel milage. Possibly more power as well would go hand in hand.

I believe at this stage the elements load up in a fashion at speed that keeps the intended injection pump timing properly advanced on all elements in comparison to what a drip test indicated.

Low fuel base pressure tends to retard the effective timing at speed it seems. Or some form of an imbalance occurs to some unknown extent at this point.

So power balance is lost and milage goes down. It wil probably be awhile till whatever is really happening is known for sure.

As a somewhat unrelated topic. I feel that reading the temperature of the injection lines would produce almost nothing of usable value and is a dead end. I just thought it through This morning. It was reaching too far.

Yet there is always another avenue it seems. Another obscure thought was a fluid presure valve that controlls an almost instantainious on/off switch on the number one injector return line. That should be able to feed a strobe light easily. There has to be a strong pressure pulse as soon as the return portion of the injector opens. It would just be inserted on the return nipple of the injector for timing purposes. I guess you would have to temporarily block the other nipple as well. That pulse has got to be strong, tangable and not subject to many factors if the injector is good. What do you think yellit?

A lot of thoughts and ideals are not really practical. If enough are projected someone at some point will come up with something really usable by either combing items or picking up a tangent otherwise not previously considered.

It is my opinion that we have to keep looking for means that work to simplify service on these engines at home. In retrospect it was not that long ago even I tried to find fault with using the milli volt method or even thought it would find any application. Mind proving it even worked at all. I think for about the first month I could not get past why it was not used for some forms of service a long time ago. I really thought I must be missing something.

Yellit and Diesel911 - Good point! I have replaced the spin-on filter 2 or 3 times in the 1.5 years i've owned her, but your observation of Lift pump pressure reading location makes since. Though i'm sure after replacing the spin-on, pre-filter and tank strainer, i believe the fuel system is clean and unobstructed, changing location removes the 1% chance some other issue popped up.

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1985 300D, 250k
1980 300SD, 180K