I have a 93' S-10 Blazer with 4.3 CPI motor . Engine has 40,000 miles since rebuild. 138,000 miles on the rest of the vehicle.
Problem: Surging or misfire at part throttle, light load
Idles a little rough, does not rev cleanly while in park. Not noticeable at WOT. No codes
Have replaced plugs,cap,rotor, CPI unit and nut kit. Messed with timing, cleaned EGRwith no luck. Fuel pressure is 51psi KOEO, Drops to 50 withengine running. Leaks down to 40 psi after about 30 minutes of key off.
Are these numbers OK for fuel pump?
Any other thoughts?

 

I was at AutoZone last Saturday talking with them about a new fuel pump and sending unit. They gave me a printout that says the fuel pressure should be 58-62 psi If I remember correctly. If those are the numbers you are geting, then that might be your problem. This is just a guess though. I am sure someone else has more experience with this. I cant even figure out my own problems!!

 

Do you see your check engine light come on, at all. Like when your engine is not running, but the key in run position.
If not, I would replace the light behind it, and see if there is any codes. Your problem sounds like it would give codes.

 

The check engine light works when the ignition key is energized before starting the vehicle.
I'm going to replace the fuel pump and see what happens

 

Just a thought....before you replace the fuel pump, replace the fuel filter and re-check your pressure. If the pressure is still low, go ahead and replace the pump.

 

Replaced the fuel pump( what a bear to do by yourself). Now I have 60 psi key on and 54-51 psi running. At idle the fuel pressure bounces around and the idle speed "hunts". Don't really understand why the fuel pressure varys with engine rpm on an electric pump unless the regulator senses manifold pressure? Driveability a little better but still has a surge/misfire at light load.
Disconnected the MAF sensor and noticed no change in performance , also no codes were set even after shutting down the engine and restarting 4 times. Disconnected the MAP sensor and engine died instantly.
Still seaching- any thoughts?

 

Old Coach,

Let me know how it works out for you. I have a 92 doing the same exact thing.

 

Runs great now. Found a problem, Somewhere along the way I had the plug wires in the wrong order. So I don't know which thing I changed really fixed it. Hey call me dork, but its my birthday and the best gift is getting this sucker fixed.

 

Glad you found the problem!! It always pays to check over everything that you've done just to make sure. It happens to the best of us!

 

Sounds like one to many birthday drinks.

Happy b-day and glad oyu got her fixed.