Too Rich And No Throttle After New Fuel Pump

[48MJ]

88 4.0 and auto, any way it was running great and very strong. The next morning it cranked great but would not start, diagnosed a bad fuel pump. Replaced fuel pump, now it starts but runs realy awful and rich and the throttle does nothing but make it richer. Pulled the plugs and they all looked the same, black and sooty. Put in new plugs and still have the same results, I'm at a loss as to what is going on because it ran so well before the fuel pump went out. Checed fuel pressure and it was 40 w/vacume unplugged and about 34 w/vacume plugged in? Thank you in advance for any input.

[HOrnbrod]

Did you drop the tank? Check the fuel return line for and blockages or crimps.

[48MJ]

Did not drop the tank just the driveline. Also the new pump wires were backwards. Didn't notice at first and tried to start w/ pump running backwards. Would this affect the pressure regulator?

[HOrnbrod]

It shouldn't have affected the regulator, but it's possible the suction applied by the pump running backwards may have broken the diaphragm. If all you have done is replace the fuel pump and disturbed nothing else (like the O2 sensor), I'd replace the regulator even though the pressure readings seem okay. Everything points to the regulator.

[48MJ]

Just thinking, you mentioned the O2 senser. What would starting fluid a few times down the intake affect the O2 senser?

[HOrnbrod]

It shouldn't, because most starting fluids are supposed to be sensor-safe. And the O2 sensor is on the exhaust header, so no problem. Just make sure the O2 sensor is plugged in, the connector contacts are clean, and the harness is not fried by the exhaust manifold.

[48MJ]

If the diaphram was bad in the fuel pressure regulator wouldn't gas be going into the vacume port? Put a vacume gauge in a intake port and vacume was right about 17 except when it would stutter. Giving it any kind of throttle just boggs it down and just cuts out, let off and it just goes back to it's weird idle. P.S it starts right up, just by turning the key just like it should. Just don't want to throw money and parts at it. Thank you, any input is appreciated.