Car bucks at low RPMs
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From: Germantown, MD
Car bucks at low RPMs I've noticed that my car now bucks when cruising and my RPMs drop below 1K RPMs. I'm guessing this has something to do with the idle? The car is trying to maintain a certain RPM but doesn't realize the car is in gear and the momentum will keep it going. Is there a way to fix this with tuning? Or is this just the nature of the beast with a new cam?
Thanks,
Mike
Thanks,
Mike
Mine still bucked even after I did that. What has helped the most so far was doing some mafless tuning and smoothing out the ve table in that range. It's like 90% gone and I think I can get rid of it completely by messing with timing.
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From: Germantown, MD
I don't think so, although I don't know what the computer is doing. But I have in-car wideband and can hit boost easily with less than 50% throttle. At low throttle boost I notice my wideband bouncing like it were still in closed loop.
What does the VE table control? I'd look at Edit, but right now I'm caught up in the XP/SP2/AMD processor problem. So perhaps someone could explain how the ve table would help this problem.
Mike
What does the VE table control? I'd look at Edit, but right now I'm caught up in the XP/SP2/AMD processor problem. So perhaps someone could explain how the ve table would help this problem.
Mike
Last edited by buschman; Oct 28, 2004 at 11:26 PM.
You are talking about bucking at around 1000 rpms, i bet you don't build boost there. You could unplug your maf, start scanning and then go chugging around the parking lot at 1000 rpm while you let your ltrims update. That is better than just multiplying by 60%, 80%, and 90% blindly in my opinion.
The ve table is a large part of the airflow calculation at low rpm, low load because the MAF isn't very accurate down there. If you look at your ve table chances are it's not accurate with your cam, and it's also pretty rough, which in turn makes your fueling transition pretty sharply with rpm. By smoothing out the ve table your engine won't be as touchy for lack of a better word.
As for still being in closed loop even though you're in boost, PE is based on throttle position, not manifold pressure. At low rpms you don't go into PE (open loop) until around 60% throttle. You can change that in the PE threshold tables.
The ve table is a large part of the airflow calculation at low rpm, low load because the MAF isn't very accurate down there. If you look at your ve table chances are it's not accurate with your cam, and it's also pretty rough, which in turn makes your fueling transition pretty sharply with rpm. By smoothing out the ve table your engine won't be as touchy for lack of a better word.
As for still being in closed loop even though you're in boost, PE is based on throttle position, not manifold pressure. At low rpms you don't go into PE (open loop) until around 60% throttle. You can change that in the PE threshold tables.
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From: Germantown, MD
If I were to try and adjust the VE table using the mafless technique... Would it be better to fab a new intake tube that doesn't include the MAF or just pull the MAF and let it run open atmosphere?
Mike
Mike
Since you won't be getting rid of your maf permanently, leave the maf in place and just unplug the connector and tuck it away from the belts. Just a heads up, when I unplugged my maf the car started idling at like 300 rpm, then jumped up to almost 2000, then once it figured out what the hell was going on it went back to 800, then i started tuning. After 10 minutes or so it will set the check engine light, but it doesn't hurt anything.
