Background. Engine replaced and has about 15k miles on it. Ran awesome for a few years and then I started noticing some lower power at load and high throttle. Missing and sounds like misfires in engine. It got worse and worse to the point of not being able to go up a simple hill.

No vacuum leaks. Even the elbow behind engine. Fuel pressure checks out. Changed all injectors. COPs are fairly new. Replaced fuel filter AND fuel sender module in tank. Air filter replaced. MAF unplugged results in same issue.

Removed entire exhaust system to eliminate

clogged cat and o2 sensors as the DTCs did note o2 sensor issues but I have read many things can cause this.

After all this with exhaust removed it idles fine but SAME issue with revving it up. Once past half throttle and smashing peddle in park it sputters and just misses like it has a plug issue or fuel issue.

No misfire in codes. I am stumped. Any ideas?

 

Did you check your spark plugs and wires -- fuel filter ?

 

When was the last time you changed plugs, coils, and all that?
Are any of your fuel nozzles leaking and how old are they? (Nozzles need to be changed out if they are the ones that came in that old of a truck)

Check your intake tube after the air temp sensor to the intake for leaks. I am finding more and more air tubes leaking at the rubber parts which makes a lope of the engine and throws some fun codes if any codes. The butterfly valve in the throttle can leak at the spring housing shaft and not let the valve close correctly and bring outside air into the engine. Oil tube o-ring where the tube goes into the engine can suck air also. (The tube where you check oil)

You can check the o2's to see if they are getting power and doing their job. (Look on youtube for checking Ford o2's)

Check your fuel pressure regulator switch (driver's side of the truck on the rear part of the fuel rail) by pulling the vacuum line off and seeing if gas comes out of it. Then do a fuel pressure check on the engine to see if it is correct and run the engine up to see if the fuel pressure drops.

On checking CAT on 1998-2003 go and get a laser temp reader and point the beam at the front of the Cat, read that, and at the back of the CAT on each Cat after the truck is at operating temp. If they are within 100 degrees of from front to back of a Cat change Cat that reads that. (This will not work on newer stile Cats in newer trucks)

 

Yes all plugs and cops replaced. Fuel injectors were in the engine I purchased and swapped in about 15k miles ago so can’t be those.

I’ll check the other stuff and report back. Thanks

 

Ok have made some progress. Grabbed a fuel pressure tester and hooked to schrader valve. No pressure. Maybe a pound. I looked underneath and remember when I last changed the fuel filter I broke a quick connect tab to the filter. I chopped the lines and used barb fittings. Well one of the patch jobs I did was kinked. Fixed the kink with new fitting and pressure was now 30 while running. Revved slowly up to 5k and pressure never dropped. Pulled off regulator vacuum hose and it jumped to 40psi.

I am closer but still noticing something strange. The entire exhaust is off the vehicle except the manifolds. I do have a small leak in passengers side manifold but when I SMASH the pedal the pressure actually increases a bit but the engine stumbles pretty bad.

if you slowly increase throttle up to high rpms very smooth engine. But smash it and very bad stumbling. Any ideas on this one? Would the exhaust being removed with no O2 sensors cause this behavior ?

thanks for the help.

 

In your original post you said the fuel pressure checked out ok..... But glad you found the problem.

As far as the engine stumbling when you smash the gas pedal, I don't see how the exhaust has anything to do with it. With the O2 sensors gone I believe the computer defaults to preset air/fuel ratio to keep the engine running. When this has happened to me I saw no difference in engine performance. It will affect fuel efficiency.

Your problem is possibly related to the engine not getting enough fuel to accelerate...or not enough air.

 

<I do have a small leak in the passenger's side manifold >

Well, that small leak will cause a false reading of the o2's on that side (Number one bank) and make the PCM think you are running lean.
That is why you have a lean on bank one and rich on bank two. (Look at the scanner codes you posted)
The o2's will not switch correctly as they are doing what they think is right and the PCM has gone to a set fuel table from FORD. I would just about bet, you have a Closed-loop fault or an Open-loop fault on the scanner.

 

Quick update. I got a nicer obd2 scan tool which showed a bad cop on cylinder 1. Put a new one on and the engine runs much smoother. Still noticing a few odd things. After sitting overnight the fuel pressure slowly rises to 30 after cranking and running. Like a minute. When I smash throttle it stays and doesn’t drop. Any reason for slow build up of pressure?

I installed a brands new fuel pump and also fuel filter. I also had a rubber boot leak at throttle body so replaced that too.

I also recorded some data when I was revving and idling. Short term fuel trim bank 1 0. Stft bank 2 0. Stft b1s1 0. Stft b1s2 99.22%. Stft b2s1 0. Stft b2s2 99.22%.

also an open loop fault with fuel system

Would I need exhaust system hooked up with i2 sensors to get the engine to rev correctly? Could I just put the o2 sensors in their connectors and run it like that to rule out any remaining fuel/air issues?

 

You need to fix your postings. They appear in some form of html showing up in a light gray font - basically unreadable.

 

The slow build up of fuel pressure could be caused by a number of things. What is voltage measured at the fuel pump connector when the engine is idling?

I’m not sure what the downstream sensors have to do with short term fuel trims. They are not used for fuel control.

Your STFTs are at zero because the fuel system is in open loop.

When you “smash” the throttle, the fuel pressure shouldn’t “stay”. It should rise!

The reason your fuel system is “open loop” is because the conditions haven’t been met for the PCM to take over fuel control. When in open loop the PCM is just using engine temp/engine load/engine rpm tables and suppling the injector duty cycle from the appropriate fuel table cell.

The O2 sensors are oxygen sensors and need to be in the exhaust stream to sense the amount of oxygen in the exhaust. The PCM will use that data to fine tune the fuel mixture once the fuel system goes Closed Loop.

 

As you can see, it has been corrected.

 

Sorry but yes when I smash the pedal fuel pressure rises from 30 to 35. At the point I will just replace the exhaust manifolds and put the new exhaust and o2 sensors in and hope this was all a fuel hose kink issue and a bad COP. Keep you posted.