how can you tell the difference between the 2 assemblies? i have a 305, but i dont know what a 350 looks like. how can i tell which is which?

 

On a 88 and up with the TBI setup, the 305 an 350 throttle bodies are the same.

 

Ithought the injectors were bigger on a 350 though. The throttle bodies themselves are the same cast.

 

I don't think they are, matter of fact I am 99% sure they are the same flow-rate and all. Check into it to be sure, but I am almost positive that they are the exact same. Only difference between the throttle bodies is a 4.3 (smaller) and 454 (bigger).

 

Yeah you're right. The ECM controls the account of spray, but the injectors are the same. So that leads me to a question I haven't figured out yet. When I drive my truck, it runs fine for about five minutes. After five minutes, when I begin to accelerate, the engine begins to misfire. While it misfires, if I get on it more, the misfiring goes away. I checked the timing, checked all the wires. No trouble codes, at ALL. Vaccum lines are good, plugs are good, O2 sensor works. I'm baffled.

 

Check the distributor, cap and rotor. The coil might be bad too. When the truck is first started and the engine is cold, do you see the injectors spraying evenly? Does it look like there might be a clog in the screen or something? Mine used to drip as much as it sprayed so I got a couple cans of SeaFoam through it (one per tank) and it seemed to get better every time.

When is the last time you replaced the fuel filter. This could be your problem too.

 

Basically everything in the truck has been replaced within the past 2 years. The distributor is a month old, cap and rotor are good (although about a year old), the fuel filter is a little over a year as well. Injectors spray fine. We even hooked up a video camera to see if it would change while i drove no problems there. I put in a new TPS but I'm not convinced that is the problem either. Plus and wires are about 5 months old. The coil could be going bad, although it too is only a year old. I have gone through 3 or 4 in 2 years.... My MSD box is working with no problems.

 

check to make sure the coil is grounded well...and buy a rebuild kit for the tb and do it...there are tiny little filters that go in the injectors themselves and its real easy to do...the kit sells for like 50 bucks at autozone...and try setting the initial timing advanced like 2-4 degrees makes the truck run a lil better any way..if u have headers and exhaust upgrade to a 3 wire o2 sensor, for more info on that go to cfm-tech.com

 

Rebuilt the TB a year ago, timing is set at 4 degrees advanced, already have a 3-wire O2 sensor, and i've bought alot of stuff from cfm-tech already lol. Fuel pressure regulator, hypertech power charger, 1" tb spacer, and injector spacer. I've got it all. MSD coil andignition box, cap/rotor. Accel shorty plugs. 160 degree thermostat.

 

The throttle body on the 305 and th3 350 are the same. INfact in 1998 the throttle body that was on the 88's were determined to be too small. So GM used the throttle body off the 454 on both the 305 and the 350. That is why they are the same.