Loss of power

[BigSexy250]

Hello there. I am new to this forum. I am new to ford as I now own a 99 Ranger 2.5 5 speed. For the most part I have been really pleased with her. The problem I have been having in I get a misfire code when I run her full throttle up incline. I have recently replaced coils, fuel injectors, plugs and wires. Funny thing is it just passes smog with no problems. I have tested the fuel pressure and it holds steady at 65psi. I tested this while driving. I am out of ideas as the previous owner had updated records of maintenance. Cat is fairly new but I noticed it has another cat before that. Any input would be appreciated. Thanks

 

[RonD]

I would do a couple of tests.

Have someone rev the engine while you have your hand over the tail pipe to feel if it is passing pressure, a Vacuum Gauge test would be better for this.
You can also remove the O2 sensor, upstream, and go for a drive, if engine has more power then Cat has collapsed and is blocking flow, yes it will be loud, lol

Unhook EGR Valve vacuum line and plug it, the line.
Drive it up a hill again and see what happens, you should get pinging, and don't let it ping too long, but you should also get power back if EGR is the issue.
Computer uses the DPFE sensor to tell how much exhaust gas is being mixed with air/fuel via the EGR Valve, but this is a pressure sensor not a "gas" sensor, so if one or both of the DPFE sensor's hoses get partially blocked then the pressure difference(what it measures) will not be accurate, so computer may be dumping too much exhaust gas into intake, this will cause missing and lack of power.
Exhaust gas is only added when engine is under load, this reduces NOx emissions by cooling the cylinders, yes hot exhaust gas cools cylinders, lol.
Cooling the cylinders also reduces pinging.

 

[work2do]

Report back if you figure things out...sounds like you are off to a good start with good advice for diagnosis. Putting in a fuel pump on the 99 2.5 5spd this weekend. Has a similar intermittent problem. At 265k, I won't feel bad about replacing the pump if it doesn't fix it....

 

[black_demon69]

Report back if you figure things out...sounds like you are off to a good start with good advice for diagnosis. Putting in a fuel pump on the 99 2.5 5spd this weekend. Has a similar intermittent problem. At 265k, I won't feel bad about replacing the pump if it doesn't fix it....

when you replace fuel pump pull bed off truck its much easier then dropping the tank...

 

[work2do]

Yepper demon...one look under this rusty thing and the prospect of laying under it didn't look pleasant...knowing how easy it is, it will be coming off again soon when the boy gets the $$$ for spring shackles, E brake cables and tank straps...The be off exposes a lot of work to be done and how easy it is to get at things...

To keep this post relevant, I will say we did a fuel pressure test and found it to be intermittent. Sounds like the OP has done it while his condition is happening (while driving). Hope to hear back on that too

 

[BigSexy250]

Ok. Fellas....after determining that the Cat was welded on backwards and upside down....I replaced plugs again cause they were fowled...hollowed the cats out. Welded up the leaks. Now I get a code of 122 and 303...I drive it and it hesitates and feels like loss of power. The EGR valve is good and working. Also the DPFE sensor is good. Any suggestions....

 

[RonD]

p0122 is TPS(throttle position sensor) voltage issue, make sure it is plugged in.
Computer sends TPS 5 volts, this voltage is passed thru TPS's variable resistor(like a volume control or light dimmer) and returned to the computer.
Closed throttle will return .6-.9volts
Wide open throttle will return 4.5-5.0volts

If voltage is below .2volts computer will set code p0122
So either 5volts from computer is low or missing, or connector is bad or TPS is bad.
Or Computer itself could be bad.

p0303 is a specific "cylinder #3 is mis-firing", make sure spark plug wires are in correct firing order.
Could be fuel injector, coil.

What did the "fouled" spark plugs look like?
Why were they fouled?
oil, fuel fouled?

 

[BigSexy250]

Plugs were fouled from a bad cat.