Quote:
Originally Posted by ngoma
Isn't a pressure gauge (and a way to plumb it in before the OUT bolt restrictor orifice) required to reset the internal pressure to spec?
IIRC, it's the IP internal pressure (that this PRV manages) that controls the IP dynamic timing advance.
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True for sure. Ideally on a calibration bench I suppose.
But if the valve is completely sitting in pieces and doing nothing at all, at least reassembling it is better than nothing I think. Then it can at least have some regulating effect on internal pressure. If the spring and piston are just floating around loose down there in the well then the pressure has to be way off.
In truth I have never known this to happen on any VE pump EXCEPT in TDI engines where for some reason it happens all the time. Maybe the combination of more severe engine vibration and higher pump pressures in those conspires to pull the valves apart more there. But I believe it's theoretically possible in any pump like this. Something basic like a clogged filter still seems far more likely as a cause for driveability symptoms though.
On TDI engines I have always figured you can more or less get away with just slapping that regulator valve back together if it pops apart and not worrying too much about calibration, since they have their feedback timing control capability meaning that the mechanical systems (regulated by internal pressure) only have to get the timing curve reasonably close, then the computer can do the rest. Similar to how they are much more forgiving of sloppily set static injection timing as well. If it gets out of range then a fault code will sound the alarm, too, so there are guardrails to ensure you got it where it needed to be and it generally seems to work out no problem. In short they make it easier to cheat and get away with it.
You're right that conversely with these fully mechanical engines, none of that happens, so like with the pump timing, the pressure curve does need to be dead on and maybe set with a gauge. I hadn't really thought that through until you pointed it out.