frequency valve, 200tq '89 MC2

[Orin Eman]

> 
> > This is a multi-part message in MIME format.
> 
> It shouldn't be.  Somehow got past my MIME message filter.
> 
> > Checking the car I noticed that FV buzzes not constantly but =
> > periodically (on idle), with 1-2 seconds breaks when it is silent.  On =
> > my 200tq '89 MC1 it buzzes constantly. Is it normal on MC2 (MAC-14)?  At =
> > output test FV  sounds ok.
> 
> No, it's not normal.  I suspect it's running all the time and struggling
> with cavitation _most_ of the time - the quiet periods are when it's
> not having trouble.  You'd need to attach a fuel pressure gauge to the
> system pressure to be sure.  First suggestion is to check the fuel pump
> screen and remove it if it's clogged with brown stuff.

I've seen this when someone has messed with the mixture screw and
set it way rich.  I think the valve fails to open when the duty
cycle drops down to 5%.

The two cases can be distinguished by hooking up a duty cycle meter.

If the duty cycle is going down to 5%, you have to work out why.
Just using the mixture screw to bring it back up may be masking
the real problem.

Orin.