Ferrari 412 /CIS Injection Experts Opinion Needed - Low Power/Weak

You should certainly measure the cold and warm control pressures to make sure that they are in spec. Mechanical drag in the Plunger and/or Plunger mechanics could cause a similar symptom -- does the airflow flap (and Plunger) move very easily (and return to the rest position) when there is no fuel pressure at all?

 

As soon as you mentioned timing chain I am concerned about camshaft timing. What is your engine vacuum at idle? Low vacuum equals low airflow which equals low movement of the plunger which may act like a fuel issue.
Outside of that as mentioned above you should recheck ignition timing and advance. Then monitor your supply fuel pressure and the control fuel pressure and ensure they are in specifications.

 

You could use the port of the air-bypass that is just the closest port to the metering plate. All the other ports are somehow afected by the air bypass.

You shoul check the bypass properly closes as it is meant to create a "vacuum leak" when descelerating. Also the vacuum amplifier (the disc) if the auto transmission could play havoc with vacuum.

There are however some variation between 400 and 412, I do not remember wheter it's the high idle or the bypass that are different.

 

In my experience the warm up regulator is the most problematic part in a CIS system. When I saw the distributors had been done I guess I just assumed the regulators had too. I have sent regulators by themselves often but never a distributor without the regulator. Id send them off to CIS Flowtech in Alabama. I have been very pleased with his work.
And if he is not the one who rebuilt the distributors I'd send them too.

 

Why don't you measure the control pressure and the regulated fuel supply pressure when the fuel pump is running? The control pressure is a fairly significant pressure so the sensor plate should be fairly hard to move when the control pressure is applied versus having no control pressure present at all. (But having good, smooth, easy sensor plate motion when the control pressure is zero is a good thing.)

Also your comment about being able to blow thru the return line seems odd. The return line from the WUR back to the tank passes thru a valve in the fuel pressure regulator section (that should be closed when the fuel pump is not running -- this keeps the residual fuel pressure at about the 3 bar of the Accumulator at engine shut off). Are you blowing into the fuel return line leaving the WUR or the fuel return line leaving the fuel pressure regulator section?

 

That's always best.

If you mean hose #33 here = that's good and normal:

https://www.ferrariparts.co.uk/Diagram/Ferrari/412/011-Fuel-Injection-System-Fuel-Distributors--Lines

 

Yes, the larger port connects to the control pressure volume of the system.

No, but there is a disc valve between the large port and the small port that continually "leaks" fuel back to the tank via the hose on the small port. This is how the pressure in the control pressure volume is set to be below the regulated supply pressure. When the disc valve in the WUR is more closed (cold or more intake vacuum) = less fuel leaks back to the tank = the control pressure is higher = the plunger deflects less = slits more closed for the same intake airflow = more lean, and, likewise, when the disc valve is more open (warm or less intake vacuum) = more fuel leaks back to the tank = the control pressure is lower = the plunger deflects more = slits more open for the same intake airflow = more rich. I don't have any 412 documentation, but there is a good figure of the style of WUR used on your 412 on page D13 of the Mondial8/QV WSM 281/83 (and although your 412 has an updraft airflow metering unit, the Mondial8/QV WSM 281/83 information would still be a good reference for how your K-Jet without Lambda system works IMO):

https://www.dropbox.com/s/z99soo68ny9n2qa/Mondial8qv_workshop_281-83.pdf?dl=0

 

High control pressure, means the Wur is clogged: normaly the wur does let escape some system pressure (control pressure = system pressure - whatever the wur leaks out).

I would suspsect the mesh screenS (there are3?) were clogged. I did clean mines with a few drops of MEK (o-rings removed!).

As steve said, testing pressure is straightforward: just install a K-JET gauge between the distributor and the WUR. If you close the valve of the gauge, no gazoline can reach the wur, si no pressure leak, so what you see inbthe gauge is system pressure, then open the valve and check the control pressure.

When I service the WUR I Just try to avoid messing with the bottom part that contains the WOT enrichment mechanism. That's a part that does not see gazoline, and the membrane is hard to source.

As for the o-ring of the disk, I did replace it with a green one (from an AC shop), works quite well. These are supposed to contain viton and fluorine so can handle agressive gazoline blends.

 

Changing the or-ring slightly modify pressure, but not on the scale you describe. The disc is countering quite a few forces while regulating the pressure: the pressure of the o-ring, the pressure of the bi-metal strip (cold start adjustment with a heating element), the pressure of the "sombrero hat" that is adjusted by vacuum, and the fuel pressure itself. The later being the most important part.

No clear idea for the o-ring size: I had an assortment of green air-conditioning o-rings from Summit Racing. This was a kit meant for Air-conditioning fittings. The full set was a few bucks, one size was a perfect fit.

 

Very common.

On CIS a pressure test should always be first diagnostic step if fuel system is suspect.

Also correct calibration of regulator is essential especially on cars with 2 systems.

 

Except that this is the opposite of what you got...

Weak o-ring reduces the control pressure, i.e makes it easier for the distributor disk to move. In your case your disk was stuck due to excess of control pressure. (The control pressure is what allows the distributor disk to hold against the airflow).

A thicker o-ring does let escape more gazoline through the WUR, but this is no big deal as this can easily be compensated with the CO screw or you can knock the wur barrel that is pressed fit in the wur case. (The big barrel with the two inlet and outlet ports) (small barrel only allows to tweak cold pressure)