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Thanks, Roger and Jerry,
I'll have the tachs checked with one of those devices that counts the blades of the prop. Certainly worth checking.
Honestly, I don't think it's the gauges. I synch the props by ear, and when they're in synch the RPMs read the same, front and rear. If the gauges are the problem, both gauges must be wrong by the same amount, and that seems improbable.
And the problem is not just underboost of the rear engine, it's also frequent bootstrapping. The rear engine power won't stay set for more than a few minutes before, totally on its own, the RPM will either rise or fall and the MAP will follow suit.
Swapping parts is a great idea, but on our weird bird the front and rear turbo plumbing is different. I've just replaced the rear turbo, so there's no point in swapping turbos. I'll look into the practicality of swapping the intercoolers.
Elsewhere on other threads, I've seen reference to leaking fuel strainer gaskets introducing air into the fuel and causing engine surging and/or underperformance. Ditto, reference to malfunctioning fuel tank vents and/or filler cap vents. Could one of those cause the underperformance and bootstrapping of the the rear engine?
And I continue to wonder about possbile leaks in the air reference lines that, as I understand matters, tell the fuel pump how much output is needed.
There's something wrong somewhere, and it has eluded the best mechanics I can find. I just know it's some darned thing we're overlooking. Wish I were an A&P and AI, maybe I could solve the problem on my own!
Thanks for your concern.
GJ Humphrey
N3CU
Concord, NH
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