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

[VikingTrad3r]

Hi Everyone. I've owned my zr1 for just over a year now and i've sold my other c4's off. Finally getting to enjoy some serious alone time with it. Intoxicated by the LT5.

ive got an issue here is the best description i can muster:

during deceleration, while passing down around 3000 rpm....if i begin to lay into the throttle again as it is passing through the 3000 rpm range....the car falls on its face, it doesn't die, it just feels like its not getting enough gas quick enough to accelerate...then it 'catches', bucks once or twice and then takes off.

i have the haibec chip and my secondaries are wired open.

the car pulls just fine up over 7000 rpm.

secondary fuel pump? it happens right at 2900-3300 rpm range....if i lay into the throttloe again as its dropping down through it.

due to it being very predictable and happening every single time i do that, i thought maybe a coil or something

[Ccmano]

Does it show any codes?
Did this happen immediately after putting in the chip and wiring the secondaries?
What is the static voltage at the throttle position sensor? Should be 0.54volts
What else has been done to the engine?
H
:cheers:

[VikingTrad3r]

Hi Hans, thanks for replying . To be honest im not sure if it was occurring before or after the haibec/secondary wiring. I never noticed it before the chip install. But i also did the chip install pretty quickly after acquiring the car.

no other mods.

Will check tps for voltage at 0 and full and look for dead spots.

Will look for the schraeder for fuel pressure testing as well and will see whats happening during the bucking.

[Ccmano]

Other than the mods, have you done any other maintenance or parts replacement? Definitely check for codes.
H
:cheers:

[VikingTrad3r]

i?ll pull out my paperclip but i know im not seeing the light flashing or staying on while driving.

[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.)

:happy1: More on this after I get the new O2s.

[Ccmano]

I have my secondaries deleted, Dominic and I did the tune (mostly Dom) and I don?t have this issue. I do remember that during the tuning process we had a transient on throttle stumble we had to tune out. I believe it had to do with the Acceleration enrichment (AE) settings. Dom should be able to tell us.
H
:cheers:

[VikingTrad3r]

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.)

:happy1: More on this after I get the new O2s.

Hi Paul and thank you for listing your symptoms.

Sound exactly the same except for mine is up near 3000 rpm.

it does feel like a fueling issue.

[VikingTrad3r]

here is another thread discussing this issue

paul did you try installing new o2 sensors?

http://www.zr1.net/forum/showthread.php?t=23806&page=4

[XfireZ51]

In Full Power mode, the ECM enables the SPT to open at a proscribed TPS%. It opens the SPT first, then consecutively turns ON the Secondary Injectors. There is a delay there of about .3 sec to allow throttles to open in the stock calibration.
In decel mode, the Injector pulse is reduced significantly or shutoff completely (DFCO) leaning AF. When u hit the pedal again, there is a momentary delay before proper AF mixture gets to the cylinders. It typically requires a larger, quicker, pumpshot (AE), especially since the secondary runner is open, to overcome and is based on the change in MAP created by the accelerator movement.

[VikingTrad3r]

paul, did u install new o2 sensors? change?


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.)

:happy1: More on this after I get the new O2s.

[XfireZ51]

In both cases, a datalog would be very helpful. :neutral:

[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 (http://r.tapatalk.com/byo?rid=90383)

[Paul Workman]

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.