Slight bucking - where to start?

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Slight bucking - where to start?

Unread postby studleyjay126 » Mon Jul 24, 2017 10:08 am

Truck in my profile -So I have a slight bucking under load (TC locked, RPM over ~1800) and also at higher RPM's (200+). It is enough that I feel it, but not enough to actually buck the truck physically. I just feel the lack of power like it is trying but can't do it. I have checked fuel pressure (measured 35psi). Timing is set perfectly, all new plugs, wires, accel coil, etc. The only thing I haven't changed is the TFI module, but I don't think it is it. Im thinking it is programming based problem. It feels like a timing issue, but Im not sure.

Where should I start? I'm all about trial and error, but I would at least like to know my trials are not just changing random things. I haven't logged yet, which I know I should do. Im I wasting my time without data logs, or is there something I can be looking at first?
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Re: Slight bucking - where to start?

Unread postby SlowBox » Mon Jul 24, 2017 10:58 am

Does it do it all the time or just when the motor is cold?
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Re: Slight bucking - where to start?

Unread postby studleyjay126 » Mon Jul 24, 2017 12:27 pm

All the time
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Re: Slight bucking - where to start?

Unread postby SlowBox » Mon Jul 24, 2017 3:20 pm

Log it and see what it's doing and post up. Surging is almost always fuel related.
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GT-40 upper and lower
65mm TB
70mm Tbird MAF
Decapped injectors
E85
Motorsport shorties
A9L/A9L2/GUFB
TunerPro v5
Moates QH v1.6

Re: Slight bucking - where to start?

Unread postby decipha » Mon Jul 24, 2017 5:29 pm

bucking is usually caused by a bad iac valve

if that checks out dump some timing in it
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Re: Slight bucking - where to start?

Unread postby studleyjay126 » Mon Jul 24, 2017 10:06 pm

So, unfortunately I just found out my Tweecer doesn't do datalogging because I didn't buy the upgraded one. TunerPro doesn't have the strategy for my truck (VEX1) that I know of. So it is trial and error until I figure out what to do.

Mike - What function / table is the one I should be looking at?
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Joined: Mon Jun 12, 2017 8:58 pm
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Vehicle Information: 1994 Bronco 5.8L, MAF from 95 Bronco 5.0L (WAY1), E40D, Tweecer tuner w/ Caledit,
Vehicle 2 Information: 70 VW EMPI Imp Dune Buggy 1600CC

Re: Slight bucking - where to start?

Unread postby decipha » Tue Jul 25, 2017 9:10 am

without being able to see what the ecu is doing you have to narrow it down the hard way

see 2 posts up ^^

if the iac valve is functioning correctly then dump some timing in it
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91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
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