I have been having lot's of fun in up-ing the fuel pressure by tweaking the IP fuel pressure relief valve in this thread and getting some positive results.

Fuel pressure.

I just made this adjustable pressure relief valve. On the right is the adjustment (a socket head cap screw), the blue nut is a nyloc lock nut, there's an o-ring to provide a positive seal. By turning the screw CW, fuel pressure is increased, CCW, pressure is decreased. I still have to test it to make sure it works well. I have confidence it will.

This poll is to see how many are interested in buying an adjustable fuel pressure relief valve and renting the test equipment to set the pressure. The test equipment will be a banjo bolt that has a quick disconnect fitting with a 6 ft nylon line to a pressure gauge so you can set the fuel pressure, like the setup in the thread I linked to above. There will be a core charge on your unmodified fuel pressure relief valve. I only have 3 of them currently and need your core so I can continue to make them. Price is TBD. I am just putting this poll out to see how much interest there is.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Clearly there is a need for a Fuel Pump Pressure test Kit.

However, I think the 2 way shipping charge needed to rent one could better be used to buy one or what you need to make one.

I am sure there are some who would like an adjustable Pressure Relief Valve.

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84 300D, 82 Volvo 244Gl Diesel

Maybe you cold factory preset them to the OEM pressure. People could then do their own extra adjustment. You should be able to give a starting point like say 3 turns out from the stop. There are probably some down sides to increasing the pressure by too much like diesel leakage into the oil.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

D911, good point about offering a fuel pressure test kit instead of rental with the 2 way shipping.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I could most definitely preset the pressure to whatever is desired.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I might be in but due to my current situation pricing would be the deciding factor.

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92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )

I know a free solution; stretch the spring to 27mm like the factory tells you to and be done with it for good.

Attached Thumbnails

 

Yes, except the spring will slowly give and the fuel pressure will slowly drop. Looks like there is not much interest. That is good actually because I don't have a lot of time for another project.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

For some odd reason people don't seem to be concerned about fuel pressure??!!

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1981 240D

Well if you get around to making one up for yourself. Throw one more together for me and pm me when done.

Possibly will be a requirement for balancing vo cars power strokes at some point. I do not use vo but will find a use for it another way.

I think it's the extra fuel milage and power that puts them off? The smoother idle as well perhaps? Might be the 10.00 or so cost of the fluid filled gauge holding them back. Or the effort to install it.

Also the unproven potential cause of the number one rod failure should not be ignored. .Even if this is thought just an outside chance . I think it almost compulsory to check pressure on the four cylinder 616 engines because of that issue.

By now at their age a percentage of lift pumps are defficent as well in pressure output. The system has just gotten old and tired. Yet cheap to restore as well if it is low pressure wise. More likely it is a diesel and if it runs it must be fine.

Seriously though I too find it strange more people have not checked the fuel supply area out better. Although quite a few have already. Just not mainstream yet. Those that go to 19 pounds are more than happy from their feedback every time.

When I say check it out I mean setting diesel fuelled examples to 19 pounds. There are no issues curently or in the future I feel at that pressure.

If you send your injection pump out for a rebuild it will come back set at nineteen pounds by many shops. So even if overall calibration was close enough when it went in it will still seem better.

I would be in if I could get an idea of a "Ballpark " cost. Or send me some complete info and I will see if it is something I can make.

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92 500E Silver 66k
82 Porsche 911SC 84K
68 Cadillac ( Gone Now )
03 Suburban Z71 200K
85 300SD 217k From Original Owner ( Dad )

From reading the posts on these "effects" it seems like they are completely anecdotal at best! Has there been any verifiable direct comparison "pre" vs. "post" data generated and shared for peer review?

Everyone really being serious has always quoted a change. Much depends of course what your original fuel pressure was.It is always hard to get believable accurate fuel milage numbers. So far no two cars have posted simular original existing fuel pressures. So no two cars will have the same exact gains at 19 pounds.

Now for the hard part. Since you have more power you have to disipline yourself to drive the car as it was before the power increase to get valid mpg comparisons. Most will drive into their new power to a certain extent I believe. This decreases the actual gain in mpg somewhat. Fixed cruise speed on the highway is probably the best comparison method. Did I mention the engines sound happier at speed as well has been reported.

If you consider what is actually occuring from say properly raising the pressure from 8 pounds to 19 pounds the answer is there. The principal point is all the cylinders then get a more equal charge of fuel with better timing. So the engine is far better power balanced. At low pressure there seem to be a few if not many undesirable conditions.

Some people will have to convince themselves over time. No body is trying to sell them something remember. Or try to consider it standard maintenance is another approach a doubter could consider. The manufacturer wants to see a minimum fuel pressure available. Too many cars are below their minumin requirements I suspect. They have just gotten old.

You could be the first to post extrememly accurate complete information. It does take some effort to gather it.

I had a chance to pressure test the adjustable pressure relief valve and it works like a charm! I'll shoot a video of it tomorrow and post.

Still have to install it and make sure the o-ring seal works otherwise all bets are off.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked