International T444E in a 3400 transit bus. Fixed a lot of problems in the fuel system, now she runs great. However, in the course of the fixes, I added a simple aftermarket fuel pressure gauge before the mechanical pump, and I noticed when running the needle jumps up and down rapidly (it’s periodic, not random, though-- in other words, the average and the peaks look stable, it’s not just jumping around completely wildly). The gauge gives a steady reading when the engine is not running (when pressurized by the aftermarket electric lift pump), and I’ve used this model gauge before on other kinds of engines and never seen this behavior.
This looks like the “water hammer” effect to me (though obviously with fuel instead of water). Is this normal for these engines? Makes sense it might be, with a such a reciprocating-style mechanical fuel pump as the T444E has, but I would expect the regulator at the end of the system to smooth this out, and/or the fact that the mechanical pump is two-stage. Could something be wrong with either of those? I know in other kinds of systems, like plumbing, severe water hammer can lead to serious rapid wear and failure of parts, but can’t say I know much about the T444E fuel injection system, as I haven’t seen anything quite like it. It’s pretty different from even the Ford Powerstroke 7.3L it’s patterned after.
Also, I noticed there’s a proper high-pressure tap for testing the fuel injection system pressure. It’s a Schrader valve, so it looks like I could just hook a regular old tire gauge up to it, but since it’s fuel instead of air, I wasn’t sure if this would either damage the tire gauge, or give a false misleading reading. Are you supposed to use a tire gauge? If not, what should I be using and where do I get it?
Sorry for all the questions, but my auto parts store knows nothing about these and has no Haynes manual or anything like that, and information online seems to be piecemeal at best…