2nd Generation Specific 1986-1992 Discussion

Severe Bucking After Emissions Removal

Old 02-05-2004, 11:25 AM
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I have a 88 tII and removed my emissions, did the TB mod, and now whenever I drive under about 4k rpm I get severe bucking which is even worse during deceleration. Seems to be worse the lower the RPM is. It runs smooth after the secondaries come on, which leads me to believe its a problem with the primary injectors. I have changed the fuel filter, and installed a walbro 255lph high pressure fuel pump hoping that it would cure this problem. I have checked for vac leaks, but found none. The car idles fine. The cats are still on the car, because I don't want to put a DP on until I remedy this problem or fear of blowing my motor due to running too lean. It also misfires pretty often under deceleration (pop pop pop). Could the cats be causing this since there is no airpump/emissions anymore? Does the TPS usually require adjustment after emissions removal? Would it be wise to try swapping my primary and secondary injectors? All these problems arose as soon as I removed emissions. I removed the entire hard line vac spider too, which includes the twin scroll solenoid, could that be the culprit?



Any suggestions would be greatly appreciated!
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Old 02-05-2004, 11:28 AM
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try the tps first
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Old 02-05-2004, 03:22 PM
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If your deceleration involves just lifting your foot and slowing down, this is to be expected. The TB mod removes the things that are there to allow people to drive the car with no attachment to the throttle plates. After the mod, YOU regulate the position completely. This means that on acceleration, you cannot just slam the pedal to the floor, you have to ease into it, matching the air amount to the fuel amount (in order to maximize acceleration/efficiency). Exactly the same on decel. It is required that you don't do on/off transitions quickly, you need to smoothly let the pedal return (remember smooth, not necessarily slow).



Also, tps should be adjusted to be safe and ensure there is no vacuum nipples still exposed on the throttle body.



Good luck.



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Old 02-05-2004, 03:35 PM
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the above is only true when you have the stock afm setup, theres too much latency between the throttle and afm for the ecu to respond to the quick transients.



go to a haltech and tune the throttle pumps properly and you can mash all you want, the crap on the throttle is a kludge for the crappy stock engine management.
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Old 02-05-2004, 04:55 PM
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Originally Posted by pengaru' date='Feb 5 2004, 01:35 PM
the above is only true when you have the stock afm setup, theres too much latency between the throttle and afm for the ecu to respond to the quick transients.



go to a haltech and tune the throttle pumps properly and you can mash all you want, the crap on the throttle is a kludge for the crappy stock engine management.
True, but it seems that going to a stand-alone to remedy this may be a bit extreme. I do agree though, that crap on the linkage is just that, crap.



Redwood
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Old 02-05-2004, 05:06 PM
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it might be possible to improve the response by moving the afm closer to the throttle body.



and I wouldnt try to sway someone to going standalone based on this factor alone, but it is another factor worth considering, among many.
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Old 02-05-2004, 05:40 PM
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I have a few friends who have done the throttle body mod and removed emissions, and they don't have these problems. I do not have the bucking problem during acceleration. As soon as my car drops to 2k rpm the bucking becomes much more violent. I tried smoothly easing off/on the pedal as Redwood suggested but this doesn't help, it is still just as bad as before. Would an exhaust leak cause problems like this? I suppose I will eventually try swapping the TB with a stock one, to see if that fixes the problem but I'm skeptical that it would help. Thanks for all your input.
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Old 02-05-2004, 05:43 PM
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Originally Posted by TexanSeven' date='Feb 5 2004, 11:40 PM
I have a few friends who have done the throttle body mod and removed emissions, and they don't have these problems. I do not have the bucking problem during acceleration. As soon as my car drops to 2k rpm the bucking becomes much more violent. I tried smoothly easing off/on the pedal as Redwood suggested but this doesn't help, it is still just as bad as before. Would an exhaust leak cause problems like this? I suppose I will eventually try swapping the TB with a stock one, to see if that fixes the problem but I'm skeptical that it would help. Thanks for all your input.
well make sure the TPS is calibrated properly and all.



But on the t2's the double throttle acts as a damper for throttle movements, it doesnt just open when the car is warmed up and stay open like the NA does. It's suspected this is due to the t2 having an intercooler and turbo between the AFM and the throttle.



It's pretty common for T2's to hesitate/buck with the double throttle removed on stock ECU/AFM layout when you slam the gas pedal... this is the condition the double throttle would normally smooth out with it's sprung linkage.
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Old 02-05-2004, 11:00 PM
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on my old n/a i had this problem pretty bad and after i calibrated tps and closed up vaccum leaks it stopped, would the leaks contribute to this too or is it just tps?



tps reset https://www.nopistons.com/forums/ind...howtopic=17710
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Old 02-06-2004, 03:25 PM
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Thanks to everyone who helped. Checked my TPS this afternoon, and sure enough it was out of alignment. Reset it and now the problem is still present, nowhere near as bad. I will play with the TPS some more tonight, but I'm certain this was my problem.
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