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?

[emerygt350]

Let's just blame autocorrect on all of that....

Really an interesting topic. I wonder if the afm shut off wasn't taking advantage of residual pressure. Sure the pump will stop when the afm closes but residual pressure will give another second of gas. If the engine is still running the afm will open again.

Just went for a little test run. Did the downhill drag (not intense, just normal kind of hill driving) and when I got to the bottom my idle was about 200 low. Engine was quite cool though. 186 head temps. It was hard to tell if I was fighting a computer induced rich condition rather than fouled plugs. The car ran fine beyond the low idle. By the time I got to the next stop sign and the temp came back up to 260ish, idle was back at 900.


I did notice that my vacuum on decel was 23. And that was not rpm dependent. If I was dragging down the hill at 4k rpms, the vacuum was the same as 1800 rpm.

In a 2.0 we have the mps measuring plenum vacuum for normal operating conditions (and at high vacuum fuel duration is cut) but we also have a more active tps, and one of its jobs is to tell the ecu to ignore the mps at closed throttle.

Need to get my new o2 sensor to play more with this... I just have to imagine that the engineers would have cut fuel almost completely during decel.