93' Explorer runs poorly

[Bulldawg8971]

First of all I'd like to say hello...my name is Danny. Secondly, I just got my truck back from a mechanic yesterday. He was supposed to fix a problem of very poor running condition, black smoke and black liquid specs coming from tailpipe not to mention getting very poor gas mileage.
He stated that the code reader showed multiple errors, most regarding MAFS (mass airflow sensor) which he replaced with a new one. He also changed the spark plugs as they were bad. But my idle continues to be very rough, almost like it has a hot cam in it lol, and gas mileage is still very poor (6-8 mpg). Additionally it is still smoking from tailpipe.
Thanks in advance for any suggestions I might receive!!!

 

[natenkiki2004]

Still smoking from the tailpipe; black or blue?
If it's black then it's dumping way too much fuel in. Probably more than any intake sensor could account for. I've read things about a leak in the exhaust system before the O2 sensor would mean that the O2 sensor sees more oxygen and dumps more fuel in to burn that oxygen, eventually maxing out the fuel trim as it compensates.

If your plugs were fouled, the O2 sensor could also be fouled (even if it's not the cause of the problem) and should be replaced. The battery should also be disconnected if sensors are replaced to reset the computer and force it to re-learn everything.

 

[Bulldawg8971]

Ok thanks Nate (hope that's right) for your suggestions. I will bring it up when I speak to my mechanic again!

 

[Sonofbumperbolt]

Check the fuel pressure. I had a 4.0 Ranger behave exactly as you describe. A new Fuel pressure regulator fixed it.

 

[Bulldawg8971]

Thanks sonofbumperbolt! Will check that also

 

[natenkiki2004]

Yea, could be fuel pressure regulator isn't doing it's job and the injectors are over-pressurized and shooting too much fuel into the engine. Again, the PCM could compensate but only to a point.

It's getting too much fuel from somewhere and the options are kinda limited.

 

[Bulldawg8971]

Cool Nate that's my concerns as well. I spoke to my mechanic yesterday and expressed my disappointment with how it's behaving and he is gonna give it another look for no charge. Hopefully some of these leads will get to the root of the problem. Thanks for all the help guys!!

 

[natenkiki2004]

Let us know how it goes

 

[Bulldawg8971]

It may be a few days but will update when fixed. Thanks!

 

[Bulldawg8971]

Ok I have spoken with my mechanic. The O2 sensor is ok and the fuel pressure regulator is holding good pressure after shutting the engine off. He is gonna check the code reader once more. He believes the problem is the catalytic converter, if it is he's gonna cut it out and replace with straight pipe being it's a 93' year model. Will update again and post results!