Contents Under PressureThe last article got so long I decided to move the rest of the Pressure Side discussions to a write-up of their own. There really isn't a lot left to cover as these issues are pretty rare, but they are worth mentioning, nonetheless. The first piece I will address is the possible causes for TOO MUCH FUEL PRESSURE (adjusting the regulator down does not reduce the pressure). After that I've got a brief note on boost reference port usage.

Other Pressure Side Problems Causing Too Much Pressure : Remember that pressure is a function of flow and restriction, and that if you have enough flow from your pump, and a properly working regulator to create the restriction, you will be able to set the pressure where you need it. So what then must be the cause of "too much pressure"? The natural reaction is that it must be the regulator, because any time the pressure isn't where you want it, the regulator must be at fault...right? While this is certainly possible, I pretty much addressed how often it is actually NOT the regulator in my previous article (Stop Blaming The Regulator). Let's look at the common causes of excessive pressure.

Return Blockage : This is the most likely and common cause of excessive pressure. In a nutshell, ANYTHING that restricts or blocks the return line after the regulator "becomes the regulator". If the fuel tank gets dropped and during reinstallation the return hose gets pinched between the tank and the frame, that pinch point becomes the regulator. If some totally unrelated component gets installed and happens to pinch the return line, same thing. The easy way to check this is a modified "bucket test". This time you want to disconnect your return line as close to the bottom port of the regulator as possible, and make a test return hose that just dumps into a bucket. If you bypass the entire return line to a bucket and the pressure drops and you can once again adjust it with the regulator, there is some kind of restriction in your installed return line. 99% of the time you will find your problem in the return line. Read on if this does not fix your problem.

Loose Diaphragm Ball : This particular problem was a manufacturing defect that ended up only affecting a handful of Fuelab regulators that made it to customers (a few years ago, none since). I only mention it here because "anything is possible". Should the above test not resolve a high pressure situation, take the regulator apart and examine the ball on the bottom side of the diaphragm. The ball should NOT be able to move or roll around under your finger (Fuelab regulator, can't speak for others). If you can roll the ball around or visually see it move, you need to replace the diaphragm. What is believed to be happening if the ball can move, is that fuel pressure would push the ball toward the seat and the diaphragm up away from the ball, causing the regulator to NOT relieve enough fuel back to the tank. When the diaphragm was replaced with a new unit where the ball was firmly attached, the ball and diaphragm would lift off the seat together and properly relieve fuel to the tank. Again, this has not happened in several years as Fuelab changed their Quality Control procedures to prevent it.

Too Much Pump / Not Enough Regulator : With pressure regulation, you need enough flow along with the restriction of the regulator to make pressure, and you need the return port to be able to relieve enough fuel flow to keep the pressure from being too high. If the pump flow exceeds the flow capability of the return port, you will have a situation where you can't adjust the pressure down below a certain point. This situation would be rare in all but the craziest of builds. The regulator that we supply in our kits is capable of enough return flow for any of the commonly used Powerstroke pump systems. If your HP needs require such a massive pump, you may need to look at other regulator options from Fuelab that have a higher return flow capability, or possibly look at using a pump with speed control capability, or dual pumps where the second pump only runs under Wide Open Throttle. We would be happy to discuss your needs if you fall into this category.

Take note of what ALL of the above situations have in common...in every single case the return (from regulator to tank) could not move enough fuel to properly manage the fuel pressure. In every single case, the pressure is high because something is reducing the flow of fuel back to the tank. In a way, they are all the exact same problem, just presenting themselves in different ways.

The Boost Reference Port and Why We Do NOT Use It : Over the years we have been asked why we don't use the "Boost Reference Port" (brass nipple on the regulator) for its intended purpose. The answer is two-fold and simple. First, we are only managing "Fuel Delivery Pressure" with these fuel systems. Unlike a gasoline vehicle with injectors that spray fuel at "fuel system pressure", 7.3L and 6.0L Powerstrokes have the added layer of the high pressure oil system and the actions of an intensifier piston in the injectors. Increasing fuel supply pressure on a HEUI Powerstroke does NOT increase the fuel pressure at the nozzle, it just makes the pump work harder. This makes increasing fuel system pressure via the use of the boost reference port a complete waste of wear and tear on the fuel pump.

Additionally, if you consider the fact that diesel engines are throttled on FUEL instead of AIR, and the fact that 7.3L and 6.0L Powerstrokes don't have a throttle blade that opens and closes with pedal input, you will see that connecting the boost reference port to the intake tract is potentially dangerous in the event of a fuel pressure regulator diaphragm failure. Though it wouldn't be getting sprayed into the cylinders at the correct time and as a high pressure mist through a nozzle, a diaphragm failure with boost reference connected would result in additional "uncontrollable" fuel being dumped into the intake, and could lead to a runaway situation. Yes, you can kill the ignition, which would kill the electric supply pump and should stop the additional fuel from dumping into the intake, but is that really an experience you want to risk having? Strictly Diesel will never recommend the use of a boost reference connection in one of these trucks.

My next articles will be a short look at our custom fuel pump harnesses (94-97 "OBS" and "Universal") and how to determine if you have a wiring harness issue.


Author: Dennis Schroeder - Co-Owner of Strictly Diesel


Dennis has been Designing, Building and Supporting Aftermarket Fuel Systems for 7.3L and 6.0L Powerstrokes since 2001.