Any Ford techs on here I've got a question about a 2010 5.4l triton f150?

[V45 sabre]

So I had my drivers side manifold replaced. After thar point once the truck sits more than a day it becomes hard to start. It will start and the fuel usage will spike then if you put it in gear it will stall. Letting it run for awhile it will stay running. The fuel mileage will stay high for a couple minutes when it will go back to normal. I have replaced the drivers fuel pump drive module that helped a but. Then I replaced the mass air flow sensor that has helped with the starting issue. No codes since exhaust manifold repair except a p0420 which it hasn't done since. Wondering about a blocked catalytic converter. Thanks for reading.

[Dean2]

Originally Posted by V45 sabre

So I had my drivers side manifold replaced. After thar point once the truck sits more than a day it becomes hard to start. It will start and the fuel usage will spike then if you put it in gear it will stall. Letting it run for awhile it will stay running. The fuel mileage will stay high for a couple minutes when it will go back to normal. I have replaced the drivers fuel pump drive module that helped a but. Then I replaced the mass air flow sensor that has helped with the starting issue. No codes since exhaust manifold repair except a p0420 which it hasn't done since. Wondering about a blocked catalytic converter. Thanks for reading.

Going to be pretty hard for anyone to help without a better description of what is happening. When you say fuel usage will spike, how are you measuring the fuel usage and what is the usage rate when it spikes and the usage rate at normal consumption? Next you say fuel mileage will stay high for a couple of minutes then go back to normal. Are you by any chance meaning RPM rather than fuel usage or fuel mileage?

[V45 sabre]

Sorry more info. When it starts the truck normally goes up to just over 20l per 100 on the computer. Then once driving goes down to around 11 or 12 per 100. Right now when the truck starts its spikes to over 40 to 50 per 100 computer read. The exhaust coming out smells incredibly rich. But once it's driven a bit will drop down to 12 per 100 as normal. The truck has 250 000km and was running perfectly before the manifold was replaced except for the slight exhaust smell until it was warm.

[V45 sabre]

And by fuel usage I'm just reading the computer read readout on the dash.

[V45 sabre]

Thanks for the help and sorry for being vague in the first post.

[elkhunter11]

It sounds like a sensor is causing the computer to overfuel the engine at startup. Were any sensors removed or disconnected to change the manifold?

[Tungsten,]

One or maybe both oxygen sensors are not reading properly?

[V45 sabre]

Only sensor unplugged was an o2 sensor to remove the catalytic converter assembly.

[JBE]

Originally Posted by V45 sabre

Only sensor unplugged was an o2 sensor to remove the catalytic converter assembly.

Did the sensor get reinstalled into the exhaust pipe?

[Dean2]

Okay, fuel usage I now understand. What is happening with the RPM. Are they normal for cold start, as in about 1400 then drop to around 800 when warm, but just sucking a bunch more fuel. If that is what is happening, I agree with the O2 sensor likely being the issue. Test the one they disconnected first, then the other one.

The error code it threw is suggesting the O2 sensor issue. The error code says Bank 1 Catalytic converter operating below efficiency on Bank 1.
Unlikely the catalytic converter just happened to plug up at the same time the manifold was changed.

https://mechanicbase.com/trouble-code/p0420/

[V45 sabre]

Yes rpm at those normal levels. But if I don't let it run for awhile before shifting it into drive it will stall.

[Dean2]

Originally Posted by V45 sabre

Yes rpm at those normal levels. But if I don't let it run for awhile before shifting it into drive it will stall.

It will run even richer cold, it should normally to account for the cold start and the ECU adds extra fuel normally until the engine warms a bit, but an O2 sensor out will make it run even richer yet. That extra over fueling on cold start means when you put it in gear, and the RPM drops, it basically floods itself out, stumbles and dies.
It is probably tough to restart when that happens.

[elkhunter11]

Originally Posted by Dean2

It will run even richer cold, it should normally to account for the cold start and the ECU adds extra fuel normally until the engine warms a bit, but an O2 sensor out will make it run even richer yet. That extra over fueling on cold start means when you put it in gear, and the RPM drops, it basically floods itself out, stumbles and dies.
It is probably tough to restart when that happens.

That is pretty much my thought as well, a sensor was
damaged or was not hooked up properly, and is causing
the computer to add too much fuel. A plugged catalytic converter would make the engine run poorly , especially under load and higher rpm.

[Dean2]

Did the new sensors fix your issues?