[v8volvo]

I wanted to share this since it's funny we were just talking about it here recently.

I haven't seen one of these pressure relief valves fall apart in years, but recently I noticed the TDI engine in my Toyota pickup truck was running a little funny, seemed to be smoking more at high RPM and driveability was a little less smooth, just generally seemed off.

After checking other more common causes first (fuel filter, air filter, in-tank fuel lift pump in the particular case of this vehicle), I pulled the pressure relief valve out. The pictures attached show what I found. That's the valve body empty, with the spring, piston, and retainer all having fallen out of it and floating around loose in the well. I had to fish them out with a (clean!!) magnet and put the valve back together. I put on new O-rings too for good luck.

Again for some reason this seems to be a commonly seen problem on TDI engines with the VE pump, yet does not seem to happen to the injection pumps on the older IDI Volvo engines nearly as often. Hard to understand why. Maybe differences in severity or type of vibration, since the vibration is both different in character and also generally far more pronounced on the 4-cylinder direct injection engines than on the comparatively glass-smooth IDI 6-cylinder D24/T. Maybe something about the way the TDI vibrates happens to be a natural frequency for the parts of the valve, and slowly over time the retainer gets pounded out?

Anyway, just a curiosity, and maybe something to check on a D24/T every once in a while if ever chasing a driveability issue where looking at the other usual causes doesn't seem to be giving any progress. I had not checked the valve on this IP yet and had been meaning to anyway, so this was good timing. After putting it back together it runs quite a bit better than it has in a while, so the valve may have been working its way apart for some time.