Ok, so i just did a zz4 cam swap into my 305 tbi and im having an issue with throttle response and hesitation. i did search for other threads and tried various remedies, to no avail. The problem is when i hit the throttle quickly from inside the car, the motor will hesitate and backfire through the throttle body, sometimes with flames, but if i open the throttle quickly at the throttle body itself, it doesnt hesitate or backfire and it sounds good with good fuel spray. Right now my fuel pressure is at 10 psi. my question is why would this happen and what do i do to resolve this problem. any suggestions would be great, thanx.

i have 113 heads with higher rated springs for the zz4 cam and just replaced the fuel pump with a tpi pump. i also have the 350 injectors.

 

Maybe the cable is out of adjustment?
I don't think its your tune because as you said, rev it with the peddle and it backfires but rev it at the TB, and it runs fine.

 

you will need to consider tuning. DIY-PROM. First you need to do some datalogging and see what the sensors are seeing.

 

I'd think it would be a non DIY tune issu considering he can get it to run right at the TBI but when the cable from the pedal is used it goes straight to hell. So in my opinion it has to do with the gas pedal physically.

 

Hey guys thanks for your input, i have yet to get out and play with it anymore and i know the car is going to need to be tuned which is something i am working on. i am going to datalog tomorrow and see if anything comes up, but out of curiousity how can you adjust the gas pedal/throttle cable. The cable is the stock cable and before I swapped the cam and heads, i did not have this issue. Its pretty much not driveable at the moment.

 

the throttle stop screw is typically capped and non adjustable. the idle "commanded" speed is adjusted by IAC counts(10-15?). For a stock application I would suggest the throttle lever is sitting on the stop screw with a tad bit of slack. I removed the cap on TSS and set the IAC counts in .bin to zero(idle rpms) and then adjusted the TSS to provide the idle speed I desired(manual trans/800 rpms). This provided the maximum amount of air coming thru the TB and improving atomization(thanks Grumpy).

 

Hmm, actually you bring up an interesting point about the throttle cable having a little slack at the throttle body, i do have an after market tbi from cfm technologies that has the adjuster screw accessible, but i did have to modify my cable bracket to get the tv cable adjusted properly but i did not think to really look at the throttle cable adjustment. I appreciate your input, i will check that out today and see what i come up with.

Well i went out and adjusted the cable as there was definately slack in the cable, so i tightened it up and the problem is gone, timing needs to be adjusted a little bit but i was hindered by another issue as i noticed it was giving off blue smoke, which is either valve seals or worse piston rings from what i understand. Oddly enough , prior to doing the cam swap this problem did not exist, so i wonder if when we changed the valve springs we messed up some of the valve seals.

 

I would think this has to do with load on the engine? While you twist the throttle at the TBI you car is in nuetral and there is no load on the engine, when you are in the car and hitting the gas, there is load on the engine. This can definitly effect things..(don't ask me how/why) but I've experienced it in boats and cars. Engine can idle fine...and rev-up fine while in nuetral, then put a load on and bang! or it will kill.