Flat spot when accellerating

:confused: Here is the deal. I rebuilt this engine for a friend. Halfway through the rebuild, I purchased it from him. It is a 1988 4x4 S-10 Blazer. 4.3L with TBI. All said and done, it idles great, seems to have plenty of power. However, upon accelleration, there is sort of a dead spot. Half throttle. If I punch it, it will sputter through the dead spot and then accellerate well. If I ease into the accelleration, it will go smooth as well. I have tried everything thay myself and all the people around me can figure out, but nothing seems to be making it any better. I am completely lost. No more Ideas. No codes either. No other running vehicles so I need to fix it ASAP!!!!!!! Anybody???????????? :confused:

whens the last time you changed your fuel filter?

today

If anybody knows the answer, please let me know. Or any Suggestions you may have that I have not thought of would be appreciated.

Holy crap , Finally someone has the same problem my 89 has. I have replaced every sensor on the throttle body and the ignition system with no luck . Does it run hotter now ? Does it do it mainly on hills from a dead stop? Can you get it up to highway speed and punch it and it go fine ? I am so fed up with it that I am about to pull the FI off and put an Edelbrock power package on it. I know my ignition system is good . Most of the time I am fighting it to keep it idling too . Do have these troubles too ?

I have not driven it farther than around the block a few times. Even at 40 when I punch it, it does it. My next step is to change the intake gasket(again).

I have the exact same problem on a '91 with a recently rebuilt 4.3. Engine runs well, idles well, no codes or anything abnormal, and gets good gas mileage. My next step is to clean up tbi and I have new fuel injectors to go in it. The reason I decided on new injectors is it looks to me that one has a non-uniform spray pattern. After all they do have about 250,000 miles on them. I am going to try to change them out this weekend.

I was researching on the net and came up with 2 possible solutions. The O2 sensor, or the fuel pump. The O2 sensor, being the cheaper and easier of the two, was the one I started with. And what do you know, that was the problem. Also, I called a shop and they said that you need to check your TPS in a situation like that. Check the voltage while the engine is off, and move the throttle manually(slowly), and make sure the voltage rises smooth. Mine was the cheap one thankfully. Thanks everyone!

by the way, I didn't have any codes come up either.

I've already tried the O2 sensor and the TPS. Glad you got yours fixed.

Not so fast. It still does it, but not as bad. Do you know which wires to test on the TPS? They didn't tell me that much

How about a tuneup.

I did the complete tune up. All sensors included . I have changed EVERYTHING but the computer and fuel pump still no luck .Mine did not start this until I started into the mountains and got into a higher altitude . A carb is my next step.