falling on its face while decellerating when i lay the throttle on again approx 3000r

[VikingTrad3r]

paul, did u install new o2 sensors? change?

Originally Posted by Paul Workman

Same exact issue here: 1) Secondaries deleted.

Just spoke to Marc and there is no solid answer (yet) to the issue, EXCEPT possibly changing to a different set of O2 sensors (quicker to react).

I concur with his characterization of the problem:

1) secondaries deleted,
2) deceleration between ~ 1400-2000 rpm
3) stutter/lurch when back on throttle*
4) does not happen when decel below 1400 rpm (e.g., urban type driving)

The cure is a work in progress, according to Marc. Doesn't do it all the time, just a nuisance but seems more often when decelerating from high speed, w/ or w/o clutch engaged. (And, from personal experience, hot/humid days or at high (mountainous) altitudes it occurs more often)

Marc just gave me an O2 part to try (I'd rather not say in case it isn't a cure) and to get back to him if it affects this issue. (The issue is worse on the 93-95 MY cars, Marc says. However, my wife's 91 cammed ZR-1, also with SPTs deleted does NOT display the problem that I'm aware of.)

More on this after I get the new O2s.

[XfireZ51]

In both cases, a datalog would be very helpful.

[Mikey]

Maybe not exactly the same but some similarities to an issue I experience in colder weather.

http://www.zr1.net/forum/showthread.php?t=32599

[Great White]

I'm still having a very similar issue that I haven't been able to figure out either. My car has the Haibeck 500hp package. Still has secondaries but he set it to default in full power mode. (I never switch it to "normal.") On my car there's no particular RPM that the stumble occurs at, it's just after decel it stumbles when I'm getting back on the accelerator.

If you give it WOT after decel it'll clear up real quick (as opposed to easing back into the throttle) so I think it may actually be too rich. (Just speculation.) If it was too lean, I figured it would just fall on its face for a split second.

It's very inconsistent. It almost feels like the car is "loading up" under decel, then clears out when back on throttle.


Edit: I just remembered- I have replaced my O2 sensors in an attempt to correct this issue; the car has always done it since I first bought it. Changing the O2 sensors didn't help at all. I believe the ones in the car now are Denso.

I don't recall what kind I removed; but I think I still have them. I do remember reading through the old service records on my car there was a rich fuel issue that a local Chevy dealer tried to correct with new O2 sensors. I believe those are the same sensors I replaced.

Sent from my BBF100-2 using ZR-1 Net Registry mobile app

[Paul Workman]

Originally Posted by VikingTrad3r

paul, did u install new o2 sensors? change?

Yes, I did. And, I can say that the issue (after some months now) is reduced by ~80%? However, some tweaking by Dominic to the AE file might clear the rest up. YMMV!

PS: Now living in Missouri, where "Alcohol Free" is posted on all the stations pumps (at least around me). I haven't driven enough after just moving here from "FBI LAND" to assess the difference (if any). But, I'll keep a eye on it.

P.