Partial Acceleration Hesitation / Stumble
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Partial Acceleration Hesitation / Stumble
1990 M/T Vette, Procharger, Mini-Ram
On partial acceleration (from a dead stop or from off throttle cruising) it hesitates and stumbles as though it's going to fall on its face.
My wideband shows it spiking really lean (off the gauge 19+) when this happens. Sometimes I can muscle with additional throttle into a better A/F, but I don't particularly like doing this. I haven't taken it over 30mph or so.
Another note, the entire car runs a lot rougher and this is much more dramatic after the car warms up and enters closed loop. (in open loop, it's not nearly as bad)
I have a datamaster log of idling in open loop in garage and then driving around in closed loop a little bit.
Any ideas would be greatly appreciated.
On partial acceleration (from a dead stop or from off throttle cruising) it hesitates and stumbles as though it's going to fall on its face.
My wideband shows it spiking really lean (off the gauge 19+) when this happens. Sometimes I can muscle with additional throttle into a better A/F, but I don't particularly like doing this. I haven't taken it over 30mph or so.
Another note, the entire car runs a lot rougher and this is much more dramatic after the car warms up and enters closed loop. (in open loop, it's not nearly as bad)
I have a datamaster log of idling in open loop in garage and then driving around in closed loop a little bit.
Any ideas would be greatly appreciated.
Safety Car
Joined: Sep 2003
Posts: 3,599
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From: Orange County NY
St. Jude Donor '10-'11-'12-'13
That lean spike can be tuned out. It falls under the heading of "Acceleration Enrichment"; the engine needs additional fuel to compensate for the sudden increase of airflow when you whack the throttle. The Mini Ram certainly needs a good increase here (and I'm sure the Procharger isn't helping 
)
Are you tuning it yourself, or did you have someone tune it?
What does the A/F look like when you go from open loop to closed loop? I don't have any experience with super chargers (I'm sure they present some unique tuning challenges), but the O2 sensor could be picking up a vacuum leak or an exhaust leak, causing the engine to run rich in closed loop.
Engine specs would help, too - you can put them in your sig for referral.
)Are you tuning it yourself, or did you have someone tune it?
What does the A/F look like when you go from open loop to closed loop? I don't have any experience with super chargers (I'm sure they present some unique tuning challenges), but the O2 sensor could be picking up a vacuum leak or an exhaust leak, causing the engine to run rich in closed loop.
Engine specs would help, too - you can put them in your sig for referral.
Last edited by byebyeL98; Mar 26, 2007 at 01:06 PM.
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I'm working with a baseline ballpark tune from Avlon. I'll likely be updating the bin myself as necessary.
When I go from open to closed loop, that's when the problem emerges and I start to go lean.
Also, this is off the wall, but on C4 Action Center, someone mentioned that after their charcoal canister failed on them, they had similar issues. Does the sensor attached to the canister actually return information to the ECM that affects the tune?
I've supplied my specs in my sig now.
When I go from open to closed loop, that's when the problem emerges and I start to go lean.
Also, this is off the wall, but on C4 Action Center, someone mentioned that after their charcoal canister failed on them, they had similar issues. Does the sensor attached to the canister actually return information to the ECM that affects the tune?
I've supplied my specs in my sig now.
Safety Car
Joined: Sep 2003
Posts: 3,599
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From: Orange County NY
St. Jude Donor '10-'11-'12-'13
Funny - one of my older tunes was just the opposite - once in closed loop, A/E was decent. Open loop, it lean popped like hell.
The supercharger and the alcohol injection put it a little out of my league, but the principles are generally the same.
Are you certain it is being triggered by the open loop / closed loop switch and not engine temperature? What does your A/F reading look like during open loop vs closed loop? What do the BLMs look like?
On my '87, there is no sensor feeding the ECM from the charcoal canister that affects the tune. I'd bet the same holds true for your '90.
Are you getting an SES light? Any codes?
The supercharger and the alcohol injection put it a little out of my league, but the principles are generally the same.
Are you certain it is being triggered by the open loop / closed loop switch and not engine temperature? What does your A/F reading look like during open loop vs closed loop? What do the BLMs look like?
On my '87, there is no sensor feeding the ECM from the charcoal canister that affects the tune. I'd bet the same holds true for your '90.
Are you getting an SES light? Any codes?
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From: OKC OK
Assuming your main fuel table is tuned correctly, it needs more power valve and pump shot. It's in the software. Are you using a 2-bar tune, or just 1-bar? If it's 1-bar, you're never going to have the part throttle and low boost tuning right.
