Nissan GU Patrol Fuel Pressure Valve

It certainly seems that everything has to always come in threes. No sooner had I fixed the belt tensioner and the exhaust manifold gasket than another problem arose. Late last year I did an oil and filter change and at the same time decided to change the fuel filter as well. The Nissan Patrol genuine fuel filter isn’t an inexpensive item lately, though it’s supposed to last around 40,000km (with good quality fuel). But for some reason while searching for filters online, I ended up buying a non-genuine fuel filter that after some searching appeared to be a reputable brand. That was a mistake. After fitting the filter, everything appeared to be fine until I started smelling diesel and, on inspection, noticed diesel around the top of the filter and some stains under the wheel arch. The stain was fairly mild at first, but within a week had increased substantially.

Aftermarket Fuel Filter Leak

Aftermarket Fuel Filter Leak

So I assumed that I hadn’t tightened the clamps quite well enough and gave each one some further tightening. The clamps on the return lines were more difficult to tighten, as I was concerned about breaking the plastic pipes. I wiped away all the diesel and thought everything was now sweet, but then I smelled diesel once again and this time I saw lot of of diesel staining under the wheel arch. So I bought some new clamps, as the ones I used were somewhat old, but that didn’t change things at all. Clearly the fuel filter wasn’t up to specifications and it was time I replaced it with a genuine one. The leaking was coming from the black, plastic, return-line tubes and when compared to the genuine, the aftermarket one wasn’t quite the same. The factory hoses were slightly too large for the lines and when the clamps were tightened, the clamps just didn’t do what was required to hold the lower fuel pressure in the return line. As the fuel leak increased, I decided to buy a genuine filter and, after installing the genuine fuel filter, the third problem arose.

Aftermarket Fuel Filter

Aftermarket Fuel Filter

Aftermarket Fuel Filter Leak

Aftermarket Fuel Filter Leak

Aftermarket Fuel Filter Leak

Aftermarket Fuel Filter Leak

Having a lift pump in the Patrol, a newer version that works a lot better than the one that failed, makes a big difference when changing fuel filters, as the fuel is easily pumped into the filter for priming. So after the pump was primed, I started the Patrol to make sure that everything was working. The engine started and then promptly stopped and wouldn’t start again. It cranked over fine, but nothing else would happen. I then noticed that the fuel pressure reading on my Scangauge showed nearly zero pressure, that wasn’t good. So I had no alternative than to remove the intercooler and have a look at the fuel rail. I undid the banjo bolt that allows the fuel pressure relief valve to vent, as well as allowing excess fuel for the injectors to return to the fuel tank. When I did this, fuel came out of the fuel rail, quite a lot in fact, so it was clear that the fuel pressure regulator valve had failed. The fuel pressure regulator is nothing more than a spring loaded valve that when the spring pressure is exceeded, the valve will open. Over time the spring tension will weaken and the valve will release sooner until it fails completely.

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

I was surprised that the fuel pressure regulator valve had lasted this long, as I’ve had a piggy-back computer chip in the Patrol since new and that raises the fuel rail pressure, which aids in providing more power and torque. Pretty much everyone who does such a modification, when the regulated fuel pressure is reached, experiences the fuel rail pressure relief valve opening which causes engine stall. That this had happened immediately after I’d changed the fuel filter was purely a coincidence, but I had been given a warning for a week or so, as when I started the Patrol in the mornings, there’d be a momentary hesitation in the engine after it started, but then immediately ran normally. I think that hesitation was an indication that the relief valve was about to retire. So, the obvious choice was to replace the relief valve, but I was hesitant because I’d read so many stories of the valve always leaking as it requires a lot of torque to seat the valve.

Nissan Patrol CRD Fuel Pressure Relief Valve- (source: Amazon)

Nissan Patrol CRD Fuel Pressure Relief Valve- (source: Amazon)

I pondered this for a short while and thought that, given that I’ve already increased the fuel rail pressure to a level that finally caused the relief valve to fail, why not block it off completely. Now some do this by putting in a blanking plate inside the fuel rail before the relief valve and my piggy back computer kit came with such a blanking plate, but that still meant removing the relief valve. Others replace the fuel pressure relief valve with a dummy valve that does much the same. Then, as I looked at the banjo bolt I had an idea. If I simply blocked off the fuel entry to the banjo bolt, I’d have the same effect as blocking the relief valve. And that’s exactly what I did. I found a suitable tap and grub screw and proceeded to modify the banjo bolt. This was a much easier task and it only took a short while to tap the hole, add some thread locker and screw in the grub screw. I didn’t tap all the way through the banjo bolt so that the grub screw would also seat at the end of the hole.

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

Fuel Pressure Rail Bleed-Off Banjo Bolt

After re-installing the banjo bolt and other bits, I started the engine once again and it fired up right away. I let it run for a while and then switched it off. I repeated this a couple of times and everything was working as it should. So after a number of days driving the Patrol, all seems good. It’s now been several weeks since the fix and there are no more fuel leaks. The Patrol also starts first go and I even seem to have better performance than before. The latter may well be true, as the relief valve may have been opening very slightly, before it fully failed, losing some fuel pressure but not enough to notice. And that, I hope, is the last of it.

Leave a Reply

Your email address will not be published. Required fields are marked *