"Surging" or "Bucking" with T-56
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Member
Joined: May 2008
Posts: 286
Likes: 1
From: Cicero, IL.
Car: 1987 Pontiac Firebird Trans Am WS6
Engine: SBC 350
Transmission: T-56
Axle/Gears: 3.70:1 BW M78 9-Bolt Posi
"Surging" or "Bucking" with T-56
87 TA with T-56 from a 94 Z28. Clutch and pressure plate are new. The car surging or "bucking" under light throttle. It does not do so under heavy throttle. I'm wondering if this is a clutch issue? I'm in the process of tuning the car after an engine rebuild, which doesn't help one bit. The car did this even before the engine swap also. I'm not sure if it is the bad tune or the trans/clutch. Any ideas?
Joined: Jan 2008
Posts: 329
Likes: 14
From: Grand Rapids MI
Car: 88 IROC-Z
Engine: 6.9L TPI(FIRST) 421ci
Transmission: T56
Axle/Gears: Ford 9" Eaton truetrac 3.50
Re: "Surging" or "Bucking" with T-56
Stock engine? What tune are you using as a base line?
Joined: Jul 2000
Posts: 6,522
Likes: 92
From: Aridzona
Car: `86 SS / `87 SS
Engine: L69 w/ TPI on top / 305 4bbl
Transmission: `95 T56 \ `88 200-4R
Re: "Surging" or "Bucking" with T-56
I haven't done tuning in years, but timing tables are different for auto / manual. Baseline for an 89 L98 Vette 6 spd. might be your best starting point.
Thread Starter
Member
Joined: May 2008
Posts: 286
Likes: 1
From: Cicero, IL.
Car: 1987 Pontiac Firebird Trans Am WS6
Engine: SBC 350
Transmission: T-56
Axle/Gears: 3.70:1 BW M78 9-Bolt Posi
Re: "Surging" or "Bucking" with T-56
The engine is a 5.7 L with a Wieand stealth ram, Comp 306 cam, aftermarket aluminum heads, 1.6 roller rockers, and 27# injectors. I’m a newb at tuning so bear with me. I’m using a stock bin for the car that has been slightly modified. I cut down the bpw in the bpw vs rpm vs lv8 table bc it was running way rich. The thing wouldn’t idle. Cutting the bpw down has smoothed out the idle tremendously but now it makes no power under throttle, so I will have to play with it a little.
Joined: Sep 2005
Posts: 27,918
Likes: 2,448
Car: Yes
Engine: Usually
Transmission: Sometimes
Axle/Gears: Behind me somewhere
Re: "Surging" or "Bucking" with T-56
Not a clutch problem.
It's a combination of tuning and inadequate gears. The tuning issue is fuel; too lean under those particular conditions. An automatic transmission tune will do that with a manual.
It's a combination of tuning and inadequate gears. The tuning issue is fuel; too lean under those particular conditions. An automatic transmission tune will do that with a manual.
Last edited by sofakingdom; Jun 2, 2018 at 03:25 PM.
Supreme Member
Joined: Dec 2012
Posts: 1,356
Likes: 15
From: northern VA
Car: 88 Sport Coupe Camaro
Engine: V6 2.8
Transmission: Borg-Warner T-5
Axle/Gears: RPO/GU6: 3.42
Re: "Surging" or "Bucking" with T-56
If the throttle position sensor is feeding erratic voltage numbers to the ECU, the engine will starve and “buck” until the sensor is moved to a part of the sensor’s range of movement that does not have degraded electrical continuity.
The area of any TPS that is just a bit past the idle setting is the area that gets used most, and is therefore the area that is most prone to wearing thin, and giving poor continuity.
Running a voltage test on the TPS is always recommended, but beware that these continuity-failure issues in the TPS are notorious for being intermittent. It may test fine with a voltmeter, and then act the *** when you put it on the road with all the vibration and different stance-angles and inertia forces that come with bouncing, swerving,and jerking down the road.
The area of any TPS that is just a bit past the idle setting is the area that gets used most, and is therefore the area that is most prone to wearing thin, and giving poor continuity.
Running a voltage test on the TPS is always recommended, but beware that these continuity-failure issues in the TPS are notorious for being intermittent. It may test fine with a voltmeter, and then act the *** when you put it on the road with all the vibration and different stance-angles and inertia forces that come with bouncing, swerving,and jerking down the road.
Last edited by W.E.G.; Jun 3, 2018 at 02:53 PM.
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Joined: Oct 2006
Posts: 823
Likes: 1
From: erlangen, Germany
Car: 1991 Z28 1LE
Engine: LS1
Transmission: T56
Axle/Gears: 3.42
Re: "Surging" or "Bucking" with T-56
My old car had the same issue. Did it with both the 2.77s and the 4.10s. Mostly evident while cruising on the highway, I couldn't maintain speed I would either need to be accelerating or decelerating to avoid that bucking.
Tried different things throughout the years with no change, then the car started really running poorly, diagnosed it as an injector problem, replaced them and the running issue was fixed along with the bucking.
Since you've changed to a short runner intake, along with other things it's likely a tuning issue and would probably be there with or without the T56.
Tried different things throughout the years with no change, then the car started really running poorly, diagnosed it as an injector problem, replaced them and the running issue was fixed along with the bucking.
Since you've changed to a short runner intake, along with other things it's likely a tuning issue and would probably be there with or without the T56.
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