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Username Post: TBI Backfire/Hesitation at WOT        (Topic#356846)
Posts: 33

Loc: Southwest Washington
Reg: 05-12-12
06-16-19 02:32 PM - Post#2768589    

Fresh TBI swap onto a internally stock, Vortec-headed 350.

Truck runs great, pulls great, sounds great, except for a hesitation/TB back fire when going from idle to WOT. Also, sometimes from part throttle to WOT (like from turning a corner, then flooring it). Sometimes it's a single "pop", then it takes off. Other times, its a series of "pops" and I have to get off the pedal before it will recover. I've been playing with the base timing (yes...bypass was unplugged each time). Started at 0° and up to about 6°. As you might expect, it gets worse with more advance. It gets better at 0°, but still does it. No stored trouble codes, other than code 42 that I never cleared after unplugging the bypass.

I've got it locked down at 0° for now. Haven't spent much time troubleshooting it. Just got the truck running Friday, trans dialed in Saturday, and started playing with this issue today. I'm out of town all week for work. Just looking for ideas and things to check when I get home next weekend.


Valued Contributor
Posts: 4290
Age: 37
Loc: wv
Reg: 08-29-12
06-17-19 06:55 PM - Post#2768722    
    In response to JCampbell

It could be lean from low fuel pressure so check that. My guess is a flat cam lobe. A lot of people think they don't have to use a zinc additive since it's a stock cam,but it's a flat tappet which has to have the zinc. They started phasing it out of oil in the mid 90s. The cam still needs it so you have to add it now days.


'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap

Posts: 127
Age: 37
Loc: Millersburg,Ohio
Reg: 01-02-12
06-17-19 09:19 PM - Post#2768727    
    In response to JCampbell

Was the ecm re-tuned for the vortec head swap? If not that's what it be looking into..

1950 Styleline Deluxe 2-door sedan..
348 tripower/NP833 4-Speed/3.73
1950 Styleline Deluxe 4-door..
Vortec 4200 I-6/4l60e/3.42/current project car
1956 Cadillac Coupe de Ville 500 efi/4l80e
1987 GMC R1500 Sierra Classic
454 tbi/700r4/3.42

Posts: 33

Loc: Southwest Washington
Reg: 05-12-12
06-18-19 03:44 PM - Post#2768774    
    In response to kzhurley

That looks like the likely culprit. I've gotten some good feedback over at Gearhead EFI. Getting a starter chip burned with updated ignition and fuel maps. We'll see where it goes from there. r...


Edited by JCampbell on 06-18-19 03:46 PM. Reason for edit: No reason given.

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