VTX1800 Fuel Pressure Regulator

Posted by Bare | Last Updated March 15, 2015

With the recent outbreak of fuel pressure regulator (FPR) failures on the early model (02-04) VTX 1800’s, I decided to throw this together and expand a little bit on the problem. This problem only occurs on VTX 1800 models with the internal fuel pump that resides inside the gas tank. This typically means 02-04 1800 models and a mix of the 05’s. If there is any confusion look between the cylinders on the left side of the bike. If you have a coolant reservoir there, then you have an external fuel pump and none of this applies to you.

Biglry from the California VTX Riders addressed this problem years ago here. You’ll recognize some of the pictures in this article from that link, they’re here courtesy of Biglry. This tech article is intended to expand upon what Biglry has already written on this subject.

Let’s start by explaining where the fuel pressure regulator is, what it does, and how it works. Look under the tank between the cylinders on the left side of the bike and you’ll see what’s in the top picture to the right.

The VTX fuel pump pushes fuel through the high pressure line and into the fuel rail at a little more than 50 PSI. Depending on the engine’s fuel needs this pressure will fluctuate. It is the FPR’s primary job to stabilize the fuel pressure and prevent these fluctuations. This is accomplished by a spring loaded diaphram inside the FPR (see bottom pic to the right). When the fuel pressure in the rail exceeds 50 PSI it pushes against this diaphragm (in the direction of the arrow) opening a valve that allows fuel into the return line and back into the tank, therefore reducing pressure in the fuel rail.

It is important that the pressure in the fuel rail remain as consistent as possible since there is no sensor to provide feedback to the computer. The computer must be able to assume consistent pressure in order to calculate injector pulses and the like so everything runs as efficiently as possible. The design of the FPR also allows it to function as an emissions control device via the use of the vacuum connection. During deceleration the increased vacuum pulls the FPR diaphragm valve wide open (in the direction of the arrow) to reduce pressure in the fuel rail. The reduction in pressure means less fuel gets injected during deceleration and therefore less emissions.

Signs that you may have a bad fuel pressure regulator:

  • Decreased fuel mileage
  • Rough running engine or an engine that won’t hold a steady idle
  • Liquid fuel dripping from the throttle body/intake
  • Strong raw fuel smell and/or thick black smoke coming from the exhaust
  • In a very bad FPR failure you can actually have liquid gas dripping out of your exhaust

Tests to check if you have a bad fuel pressure regulator:

  • Remove FPR vacuum hose, if liquid fuel drips out the FPR is bad
  • Remove FPR vacuum hose. Hold your finger over the nipple where the vacuum line was and turn the key on (with the kill switch in the on position) so you can hear the fuel pump prime. If the FPR is bad liquid fuel will come out of the vacuum nipple when the pump primes the fuel rail

Replacement:
If you determine the FPR is bad then order a new one from Honda (OEM# 16740-MCH-013). A brand new FPR comes with a new O-ring so there is no need to order that separately. The FPR does come shipped with a small rubber plug to protect it and hold the O-ring in place so don’t expect the O-ring to be floating around in the parts bag.

Required tools/Materials

  • New Honda fuel pressure regulator OEM #16740-MCH-013
  • 1/4 drive ratchet and 10mm socket OR
  • 3/8 drive ratchet, universal joint, 6″ (or more) extension, and 10mm socket
  • Pliers
  • Flathead screwdriver (optional)
  • a rag to catch a small amount of spilled gas

When you have the new FPR in hand head out to the bike with your tools. Pull the vacuum hose off the top of the FPR. Use the pliers to open and slide the spring clamp down the fuel return line and then remove the fuel return line. Sometimes a light twist with pliers or a flathead screwdriver between the FPR and fuel line will help break the line loose. Now use your ratchet and 10mm socket (and u-joint and extension if necessary) to break both 10mm bolts loose before removing them entirely. The picture at the right of an FPR and fuel rail removed from the bike may help you see where the “hidden” bolt is located if you have trouble finding it. Once the bolts are both out remove the FPR making sure you remove it’s o-ring at the same time. It will pop right off but sometimes needs a tap if it’s stuck to the rail. Pop open the new FPR, remove the little rubber plug, make sure the new o-ring is properly in place and bolt it back on. If you have trouble getting the O-ring to stay in it’s groove use a tiny drop of grease to “glue” it in place. Obviously you can’t pinch or damage that O-ring or you’ll be leaking fuel all over! Snug the 10mm bolts down but don’t overdo it – these are steel bolts in an aluminum rail! Re-attach the vacuum hose and fuel return line making sure you replace the spring clamp in the process. If the spring clamp gives you trouble just replace it with a screw type clamp (like I did in the picture at the top of the page.

Now fire the bike up and see if your problems are fixed. If they are then it’s time to change the oil in the bike. This is absolutely imperative and an often overlooked step. When the FPR goes bad it allows the vacuum line to siphon raw fuel directly into the throttle body. This floods the engine with so much gas that it washes the cylinder walls and slips past the piston rings down into the oil sump. This dilutes your oil with gas reducing it’s viscosity which severely inhibits it’s ability to lubricate your motor. In turn, as this oil/gas mix gets pumped through the bike by the oil pump it washes out any grease or lubrication that is in the bearings throughout the motor. Ignoring this simple step can result in fixing the FPR problem but still doing significant damage to your motor.

After changing your oil you should also check your intake housing. If too much gas gets into your oil not only does it dilute, but it overfills the oil sump. Since part of what the crankcase breather vents is the sump, extra oil/gas can be blown out of the motor through the crankcase breather which vents into the intake. In very advanced FPR failures I have found a half a quart of oil/gas sloshing around inside the intake housing!

That’s it – you’re done – congratulations!

2 Responses to “VTX1800 Fuel Pressure Regulator”

  1. john toth says:

    Very good instructions…Pix helped a lot. I did it under 30 min and took my time. I only removed the seat to see better.

    THX.

    John

  2. Docc says:

    Yes Docc is still alive LOL. Another excellent write up thanks to Biglry and you..
    I just did major service and replaced regulator at 70K miles.. Slowed done a lot after back issues,,mostly in my Hot Rods..now.. Still love the X.and my other bikes..

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