TDi injection pump tuning - Defender Source
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  #1  
Old September 29th, 2016, 01:53 PM
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Craig Spaeth
93 RRC LWB 300TDI
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TDi injection pump tuning

An upfront disclaimer I am by no means an expert on this, but some ideas I have learned while fumbling my way through the injection pump on my 300 Tdi in my RRC and the one in my Dad's Disco 1.

I am just going to talk about the adjustments and give two links to how to adjust each one.


I am only addressing the 3 adjustments accessed through the cover on the side of the pump. The outside screw under the outside press in cover is the amount of fuel that is added from off idle before there is any boost. This screw really helps driving off from a stop. It does not have a huge effect on EGT temps, but will put out a fair amount of black smoke and waste fuel if turned up too far. I turned this down until it was painful to pull away and then slowly brought it back until the drivability was there, with as little fuel as possible.

The star wheel adjusts how much fuel is supplied as the boost comes up. You turn the star clockwise to loosen the spring tension which will supply more fuel at lower boost levels. Counter clockwise takes more boost pressure to start adding in more fuel. Getting this setting right REALLY helps overall drivability. Don't be afraid to really dial this in. As with all of these adjustments mark your starting point so you can go back if you need to. People talk about adjusting this in full or half turns, but even after you get in the ballpark 1/4 turns can make a difference in the midrange feel. This adjustment can do more to EGT temps but not quite as much as the diaphragm adjustments. I would not do ANY of these adjustments without an EGT gauge as you can cause critical damage.

Lastly is the rotating of the diaphragm. This adds fuel throughout the whole range and especially at full throttle. This adjustment can greatly affect your EGT with very little movement, 1/4 turn or so can put you over the line. This also means that if you are having problems with EGT's you can move this setting back 1/4 turn at a time until you don't need to watch your EGT's as closely.

On my truck I turned the star wheel clockwise to bring in some more fuel earlier in the midrange, but this made my full throttle fueling too much so I backed it off slightly. The first time I tackled these adjustments I played briefly with them and let it go at that. The more successful time I set up a loop by my house with a good climb and some starts and stops so I could really get an idea of what each setting was doing. I did probably 6-8 loops with making small adjustments each time and really dialing in how it drove. I was doing 1/4 turns on the star wheel at the end and rotating the diaphragm by as little as 1/8 of an inch to get the max EGT set where I was comfortable with it. I really tried to think about each adjustment and how they interact.

I applied this method to my Dad's truck as well and it really brought that motor alive as well. It isn't so much a huge improvement in power as much as a HUGE improvement in drivability.

Be careful as these can melt down your engine. This is my experience, strictly related in case it can help someone. I take no responsibility for your results. If anyone see some advice here that is directly wrong please feel free to correct it, you will not hurt my feelings. I am pretty new at figuring this out.

These are two of the links I utilized for helping me through this.

How To Increase The Performance Of Your 200/300tdi - Land Rover Technical Archive - LR4x4 - The Land Rover Forum

TDI Fuel Pump Tweaking - with pictures

Oh yeah, I guess there is an overall fuel screw on the back of the pump that has a lock ring on it. I did not touch this screw. I didn't want to mess with a Dremel tool to remove the lock collar and several sites recommended not getting into this adjustment.

Hope some of this helps someone.
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  #2  
Old September 29th, 2016, 10:20 PM
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Carl Jonsson
1995 NAS D90 #219
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Great write up Craig. It might be worthwhile to mention that the diaphragm adjustment does not work in the same way as the star wheel. If you turn the diaphragm past 6 o'clock you're essentially just past 12 o'clock if that makes any sense. To my understanding it is symmetrical so once you go past 6 o'clock you start over. Is this direct? When looking at the asymmetrical tip on the end of the pin that the diaphragm is attached to you understand what I'm talking about.
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Old September 30th, 2016, 12:12 AM
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Craig Spaeth
93 RRC LWB 300TDI
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Join Date: Sep 2011
Location: White Salmon, WA USA
Posts: 92
Yes, Carl, that is an important point. The diaphragm adjustment is a pin that rides on an eccentric end of the diaphragm shaft. The first time I played with it I kind of looked at it, but this time by working out each adjustment on it's own I was able to really see the effect it had. as well as understand it better.

If you turn the diaphragm past 180 you are starting over in where the pin rides. I was really surprised how small of a turn would make a difference to the EGT's. Hopefully that makes sense.
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