Ok, so I have 2000 4.0L v6 supercab with a 2006 4.0L engine in it (installed in 2008).... in short, a big pain in the butt!!

Been having a real issue with it not wanting to start right away, idling rough to begin with before warming up, and kicking real hard over 65mph (though, now it's gotten worse, anything over 50 it'll kick it seems, and just gets worse the faster you try and go). Accelerate is bogged down, overall low on power. Rattles when you accelerate. Previously disscussed in thread https://www.ford-trucks.com/forums/1...ytic+converter

Right now the check engine light is on and it's throwing the codes P0171 and P0174, fuel lean bank 1 and 2. We've replaced the MAF, the fuel pump assembly, fuel filter, spark plugs/wires.... no luck. It used to be throwing the P0154 but replaced all O2 sensors along the MAF and that solved that code. But these other two won't go away!!!

So, we've gotten two people tell us now to check the Catalytic converters. I called a repair shop to see if they could do a test to see if one of them is going bad (as I had talked to someone there previously who said they would just do a simple test to see if one was clogged up or not) well the gal I spoke with said "oh no, your cat won't be bad... only if you have a catalytic converter CEL code would it be bad. it's something in the engine" whaaatt?? then why would two other mechanics recommend I replace it? She wanted to do a diagnostic, I said no thanks as we've already had one done by another shop and we were told "replace the fuel pump, if that's not it, check the cats"

We're also considering replacing the fuel injectors. We did do the whole fuel pump assembly just recently with 2000 parts, and it ran better for a little bit before going south again... still need to test fuel pressure, maybe this weekend we can do it. But there has been literally 0 change, and we've had three different fuel pumps in it. So we think it's something else. But we could be wrong of course.....

Which would you replace first: Cat or injectors? Or say screw it and do both! Or... any other ideas? Husband was talking about replacing the entire intake, but that seems like a lot of unnecessary work and expense (to me anyway--he could know something I don't!)

If I left off any needed info, let me know. Also... please try and answer in plain english, I'm a horse gal, not a truck man, this is not my forte

 

huh, well if money is a concern then try going a cheaper route by cleaning the fuel injectors. There are tons of different brands out there that are just additives to your fuel, our you could drive it to a local walmart and have them clean it for about 30$ or so. Worth a shot before you buy the whole shibang

 

I am an expert on exhaust, catalytic converters in particular. Those two codes are an indication of one of the following.
Vacuum leak
low fuel pressure
faulty or dirty MAF
faulty O2 sensors (unlikely that both would fail simultaneously)

The rattle you hear when you accelerate is calling pinging or knocking, it happens because a lean burn is much hotter than a regular burn. As you accelerate, the engine is supposed to enrich the mixture for maximum power. If there is inadequate fuel or there is too much air, then the mixture burns hot.

A basic description of what is happening is that the spark is igniting the mixture. This creates an expanding flame front that is supposed to move smoothly and consistently. This causes a rise in the pressure, which drives the piston down and produces power. What is actually happening is that because the mixture is lean, it ignites too easily, and the rising pressure causes the mixture to ignite from a second point sometime after the primary spark has occurred. This second ignition is basically an explosion rather than a burn, and it creates a powerful shockwave that resonated through the entire engine. If ignored, it can cause serious damage. The sound will be like marbles of a loose piece of something rattling inside the engine.

I know you just stated that you had your fuel pump replaced. Was the inline fuel filter replaced (I think a 2000 should still have one, but I could be wrong). Was the fuel pump an OEM pump. I have personally had issues with aftermarket pumps not delivering the required flow or decreasing in flow after they warm up.

I would continue to look for a major vacuum leak, you may need to have someone with a smoke machine find it. I would also suspect that you may have the wrong motor. Yes, it may be the same type of motor, I suspect that both are the SOHC 4.0L, but sometimes there are changes in the design of engines that can seriously affect they way they perform.

I will give an example. I have a 1997 Ford Aerostar 4.0L OHV engine. I can use the heads from another '97 Aerostar, a '95-'98 Ranger or Explorer. If I use the head from and older model, the performance and gas mileage will suffer. If I use my heads on the older engine, it will melt the pistons down and cause serious damage to the engine. Why? Because the size and shape of the combustion chamber has changed, which in turn requires adjustments to the fuel and ignition tables. The newer head burns faster, which requires less spark advance. This lowers emissions and reduces the tendency or opportunity for the engine to knock or ping. If I use the older head, the mixture will burn too slowly, causing lost power because the timing would be too late. If the fast burn head is used on the older engine, of the fast burn engine is swapped in place of the older engine, the stock timing is used, which is way to early, too far advanced. This causes the pressure to build too rapidly, causing the mixture to ignite from a second source, causing the knocking and ping. The advance in this case is far enough that the pinging would quickly cause the pistons to heat up, softening the metal until it deforms and fails.

You might be experiencing in part, and similar situation. You are using a newer engine, and your stock computer does not understand how to use it. Its fuel and timing maps are wrong. Because the maps are wrong, it can also set the lean codes. If this is the cause, then you would have a few choices. Either reprogram your computer to accept the new engine (this will require a professionaly made tune that overrides the stock one) or swap a 2006 computer and any required wiring, or swap to the correct engine.

I think some troubleshooting may still be required to figure out for sure what is going on. But hopefully this information is helpful and not detrimental.

A clogged cat will cause low power, and would probably be accompanied with a CEL with either a P0420 or P0430 code. However, the problems you are experiencing can clog a cat if not resolved. Its a cause and effect thing, cats don't cause lean codes, or misfires, etc. But they can be clogged by other running and drivability issues.

If you are still concerned about it, have a muffler shop do the diagnostic. They can do the diagnostics much better than a regular repair shop. A lot of regular repair shops and DIY mechanics are really quick to blame power loss on clogged cats. Much of the time when a car comes in because of clogged cats, it ends up being a fuel delivery problem, low fuel pressure or some other issue. If you really want, a muffler shop can hook up a gauge and measure the actual backpressure, which will quickly confirm whether or not they are clogged. If they are clogged, then you can pursue replacing them, but be advised, they will not cause your lean codes, and unless that issue gets resolved, it can damage the new cats.