hi , ived recently rebuild a 350 tbi ived put some vortec head with vortec cam in it, i have a carb intake with tbi plate adaptor. So my problem is and i cant find it , when i slam the gaz pedal it hesatate and back fire through the intake . ived check every thing timming 0 tdc , gaz pressure 12 psi cylinder pressure all good, distributor is new , spark plug new, wire new, ived try 2 coil nothing change also try two tbi unit right now is a 454 tbi on it but didnt change anything also change the ecm but still backfirering . got no code all sensor in specs , so maybe someone can help me with that thanks

 

Intake backfiring is usually caused by a lean mixture, retarded timing, or wrong firing order (possibly due to damaged plug wires allowing firing to the wrong cylinder).

Assuming that the ECM and PROM are correct for your application and it otherwise runs fine:

- Check for vacuum leaks.

- As a troubleshooting step you might try advancing the timing just a little to see if the condition changes. This probably is not a solution but if it makes a positive change then it could help isolate the issue.

- Check fuel flow. Maybe one of the hard lines got pinched or something.

Does it run fine at idle and through the RPM range under load if you are easy on the gas? What injectors and ECM/PROM are you running?

 

Only suggestion I have is to set the base distributor timing to 6* - 8* BTDC. That will help make up for the difference in chamber shape/burn rate.

A full tune would be better, but just bumping the timing for now will help.

RBob.

 

Hi, thanks for reply. The engine run fine if im gentle with the pedal. FIrering order is good Ived Check 3 Time fuel pressure dont move at all with load or not

 

its a tbi 95 of a tahoe with stock ecm and tbi, engine run fine at idle and run fine if im easy on the gas yes if i slam the gas it backfire or when im in OD it stumble to accelerate under load thanks

 

That is the issue, GM never put TBI on top of a Vortec V8. There isn't a proper PROM unless it is custom.

RBob.

 

hi, maybe there a way to make it work i can make some custom chip but i dont realy know where to start.. thanks

 

Did you try changing timing to 6-8° yet?

 

oh the truck was to one of my friends and it was a vortec tbi but with the gm tbi-vortec inatake and it was running good with the same ecm and tbi that i have ... ived buy the tahoe without the motor but its the same spec as mine beside the intake , its strange.

 

yes i have try to advance more and retard also same thing

 

hi, i have try several thing ived try to add AE like 30% in the chip i think its helping but still got backfire i also notice that when im in open loop i cant get it to backfirering im little confuse now. Someone got an idea?

 

one more thing if the est wire is disconnected the timing should be at 0 deg at any rpm right ? its shouldnt move at all?

 

yes run fine at idle and trough the rpm if im easy on the gaz its exacly what happend here do you an idea what should be its a 95 tbi 95 tbi ecm thanks

 

are you sure an exhaust lobe on the camshaft hasn't failed ?