L-Jet going full Rich on Deceleration Options

[Brian Fuerbach]

1974 1.8 with L- jet. Been playing with a wide band air fuel meter and noticed that when I lift the throttle the AFR goes to max value on the gauge. I thought it was supposed to go lean. I checked the throttle position switch and it checks out fine. Going to check the wiring harness next.

What else should I check? Decel valve?

[wonkipop]

i did a bit more reading.

because i was interested in the way that d jet has a fixed fuel pressure regulator but L jet has the vacuum adjusted regulator. i know the D jet injector is adjustable with the nut, but its a set and forget job. ie a static adjustment.

what L jet is doing is trying always to keep fuel pressure equal to manifold pressure in relative terms. when manifold pressure drops, (vacuum at idle or throttle close) it lowers the fuel pressure so that in relative terms it stays the same. injector delivers the same amount of fuel against the same relative pressure for certain time opening of injector.

there are more involved things it does too, which are to do with damping but thats beyond the simple principle. (and i got lost reading that).

i wonder if the fuel pressure regulator is not functioning properly when activated by vacuum. maybe an old stiff membrane? and fuel pressure is staying at 35 psi rather than dropping to 28 psi. i read they can fail in this way, not just by rupturing the membrane. back when the cars were newer it was rare for this kind of failure it seems.
but the cars are getting older.

i wonder if that could be doing anything as you come off throttle causing more fuel to dump in through injectors.

its just a thought.

you can do the test on the pressure regulator very easily to check the two values.
the procedure is in the factory manual.