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Testing control pressure 400i fuel system

1792 Views 3 Replies 0 Participants Last post by  David Feinberg
This car has a balance line ru

This car has a balance line running between the WURs. Whats up with that? My question is how do I get a good control pressure reading? Should I isolate each side in my control pressure testing? Dose anyone know a good reason why Ferrari did this. Seems like problems on one side would certanly affect the other. }
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As the CIS system is


As the CIS system is pressure-based, the balance tube makes sense to equalize side to side pressures. It's a clever way to "match" pressures on two regulators....hence matching pressure to the fuel distributors.

The down side, as you have diagnostics. To determine accurate system and control pressures, disconnect/block the crossover tube.

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Thanks David I isolated the WU

Thanks David I isolated the WURs and ran control
pressure test.Left side Cold control 2.2bar Warm
4.1bar Right side 2.3 and 4.2 respectively. I also
teed into the intake at the WUR intake tap.I dont have
2 gages so I had to check them one at a time with
engine at normal operating temp.At idle no accesories
on.Left 11 inches Right 15. Then I dropped the trans
into gear left 6 inches right 8. I have checked gas
readings post cats and Dialed them in on each side to
about 1.0 co and about 100ppm hc. My problem is a very
rough idle only when cold and occasional intake
backfire only when cold. That disappears when the
engine is fully warm. Base idle is about 1000rpm. Yet
often when the engine is fully warm and i drop the car
in gear holding the brake and the idle drops low and
occasionally dies or seems to lose one side. Picking
up quickly if I return to park. I have checked the
brake booster for vac leaks none found. Warm this car
runs great. When I first started i did correct an
intake leak but havent found any others. Does any one
see problems with these readings? Or any advice on
what to test next? Thanks Sean>
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At first pass, the pr


At first pass, the problem appears to be side to side the vacuum readings are significantly different, based on your readings.

I am not familar with the balance process on the 400i, though I suspect it is very similar to setting up a BBi. Once side to side balance is achieved, you'll need to go thru the mixture setting process again, as one affects the other.

I would be interested in knowing what the HC/CO readings are...pre-cat, as this may help in the diagnostic process.

1st step-Side to side balance
CIS pressures look good...

Check the archives for an article about BBi FI set-up procedures..

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