Hello fellows. 93 4.3L CPI. I got this back on the road a couple months ago after sitting up for years. It has been running fine until recently it has lost power. And even more recently it has started back fireing when if I try to accelerate too fast or pull up hills.

I have found that as long as I do not give it too much throttle too fast it does fine. I can do 70-80mph as long as I take my time doing it. But if I give it too much throttle to fast it will not hardly go and will start to back fire. Let off the throttle somewhat and the RPM will creep up and the speed with it.

A friend suggested that it was the MAP sensor. Do you all have any ideas?

 

Does the engine feel RPM limited or is it more tied to throttle position?

If more tied to throttle position than RPM, have you tested the TPS sensor (~0.5V at closed throttle and ~4.5V at wide open throttle)?

I posted the MAP sensor values in another thread. I think it was for a '95 as well, but might have been a '94...

*EDIT* - It was a '95.

95 Blazer runs crappy

Found by searching for 'map+sensor+altitude'.

 

It isn't the position as much as it is the speed at which a press the pedal. For example, while in park it idles fine but to rev it up I must slowly press the pedal to get the RPM's up. If I press it quickly it acts as though I just run out of gas and it will backfire and sputter.

 

Test the TPS & MAP sensor.

 

I would replace the fuel filter . Or at least take it off and try blowing through it .

 

The fuel filter is only a couple of months old. Has new fuel pump and sending unit and new fuel injector.

It is worse now. If I'm running 60mph on level ground and come to a hill and try to maintain my speed it will cut out and backfire. I have to keep the pedal pressed the same as it was to maintain the 60mph on level ground. My speed will drop as I go up the hill but once I top it I can get back up to 60 or even 70+.

Also. my fuel economy has dropped significantly since this problem started if that helps in diagnosing the problem.

I have bee doing some research and the poor fuel economy does seem to be a symptom but I think I may have discovered another symptom that I would not have thought of. After reading what the MAP sensor does it seems I'm wondering if it being bad is also causing the engine to rev up when I first start it.

For a couple of weeks I have noticed that my engine will rev up as though I have pressed the gas while I'm cranking it. Am I right? would a bad MAP sensor cause that?

Well I put a new MAP sensor on and it did not help. So wonder if it is the TPS sensor? Not sure where that is?

 

The TPS sensor is on the throttle shaft at the front of the intake. TEST it before you just blindly replace it. Could have saved you the cost of the MAP sensor if you had of tested it too...

 

Thanks for the help Swartlkk. The guy at the parts store said I could bring the MAP sensor back. I will test the TPS sensor.

 

Let us know what you get for values from the TPS sensor and we'll go from there.

 

Sorry been busy and havent had time to work on it. Anyway I'm not sure how I'm supposed to check the voltage?