Front Engine P337H has low MP after start

[weebyf15]

I have 1979 P337H with american aviation intercoolers. Suddenly out of nowhere when I started it the other day the front engine manifold pressure was reading down at 15 inches rather than 30 or so I usually see. After starting the rear the front stayed at 15 while the rear held 30 as expected. As I advance power on the front engine the MP decreases an inch or two. When I feather the prop or bring the engine near cut off the MP increases a bit. The turbo is working fine and I don't believe it should be a factor while on the ground anyhow. I swapped the inputs to the MP gauge and the problem was the same on the (now) rear reading as well. Therefore I think the gauge has nothing to do with this. What could cause a vacuum to be created on the intake manifold of my front engine. I assume some sort of restriction is happening somewhere.
Any help would be greatly appreciated.

Brad

[n86121]

On the turbo models there are three easily interchanged fittings on the firewall.

1. Manifold pressure to the MP gauge
Reads MP pressure, ideally.

2. Turbo outlet pressure
Goes to the backside of the fuel pressure indicators - accurate at altitude

My rear was connected instead to fuel flow gauge.
At idle, as intake pressure goes down (vacuum)
the fuel flow (pressure gauge) went up.

3. Fuel injection for cold starts
The little pressure thingy you push squirts fuel into intake
That one goes right to the manifold where the two pipes come together

Its easy to swap those out, and odd things happen.

A. To confirm the injection line, disconnect and press the thingy.
If wet, that one goes to middle of the intakes.

B. To confirm turbo line, just follow it back. Can't remember, but was self apparent.

C. To confirm MP, make sure that line goes to where you want MP takeoff.

[weebyf15]

Thanks for the info. I don't believe I have any of those problems. I say that only because it had always worked fine and no maintenance was done between when it used to work to when I started having this problem. Correct me if I'm wrong but appears all these suggestions imply a mis-rigging of some sort.
Brad

[n86121]

If fuel flow restricted...?

As engine spools up fuel flow increases, obviously.

As turbo kicks even, maybe sucking Fuel pump can’t deliver?

[weebyf15]

Now that's something I had not thought of, Thanks
Brad