I recently started to have an issue cold starting my truck on warm days. On colder days, it doesn't seem to be too big of an issue - my guess is that it takes longer to hit closed loop. It's a 2001 F-350 5.4L 5 speed. Engine has north of 120K miles on it. New intake manifold and gaskets. New left side exhaust manifold, double gasketed.
Problem: When I cold start my truck on warm days, it has a very bad multiple cylinder misfire after about 15 seconds. To the point that there's gas dripping out the muffler. It will run extremely poorly and smell like raw gas for a minute or two, then clear up and idle/run smoothly. Any restarts after that run just like a new truck. I recently took it on a trip, empty, and it got 14 MPG. That's as good as it's ever got
The passenger side exhaust manifold is very rotted out. I'm replacing that next month as time allows.
I have had people tell me it has bad valve seals causing it to foul the plugs with oil (which could be a thing, but I have no visible smoke on startup), or that it has a leaky head gasket --- I haven't had any change in coolant level. I marked it on the pressure bottle when I started having this problem and it hasn't gone down.
I plugged in the scanner and this is what I'm seeing:
Long Term fuel trim is at 3.91% for bank 1. Bank 2 long term fuel trim is at .05%.
When I start the truck and let it idle, bank 1 fuel trim will go up to 28% or so, sometimes more or slightly less. Obviously the higher it goes, the worse the truck runs. If I rev up the engine to 2500 or 3000 RPM, it will go down. to 11%-15% and it will run better and stop misfiring as horrible.
Then after 2 minutes or so of idling, the fuel trim for bank 1 will drop down to 4 or 5% and the truck will run perfect again.
From what I understand - this points to a bad vacuum leak? A bad exhaust manifold would be okay at idle and then cause positive high fuel trims when revved up , right? I've sprayed starting fluid and carb cleaner at different gaskets and vacuum junctions around the engine and I can't find any leaks. Intake gasket(s) seem to be fine as far as I can tell. As is PCV system and the lines to the evap canister. Truck doesn't have EGR, even if it did, that would be on the driver's side (bank 2)
When slowing down in gear, both banks have close to the same fuel trim. If there was some sort of severe vacuum leak on bank 1, seems like a high vacuum situation like decelerating in gear would affect it.
Help?
Problem: When I cold start my truck on warm days, it has a very bad multiple cylinder misfire after about 15 seconds. To the point that there's gas dripping out the muffler. It will run extremely poorly and smell like raw gas for a minute or two, then clear up and idle/run smoothly. Any restarts after that run just like a new truck. I recently took it on a trip, empty, and it got 14 MPG. That's as good as it's ever got
The passenger side exhaust manifold is very rotted out. I'm replacing that next month as time allows.
I have had people tell me it has bad valve seals causing it to foul the plugs with oil (which could be a thing, but I have no visible smoke on startup), or that it has a leaky head gasket --- I haven't had any change in coolant level. I marked it on the pressure bottle when I started having this problem and it hasn't gone down.
I plugged in the scanner and this is what I'm seeing:
Long Term fuel trim is at 3.91% for bank 1. Bank 2 long term fuel trim is at .05%.
When I start the truck and let it idle, bank 1 fuel trim will go up to 28% or so, sometimes more or slightly less. Obviously the higher it goes, the worse the truck runs. If I rev up the engine to 2500 or 3000 RPM, it will go down. to 11%-15% and it will run better and stop misfiring as horrible.
Then after 2 minutes or so of idling, the fuel trim for bank 1 will drop down to 4 or 5% and the truck will run perfect again.
From what I understand - this points to a bad vacuum leak? A bad exhaust manifold would be okay at idle and then cause positive high fuel trims when revved up , right? I've sprayed starting fluid and carb cleaner at different gaskets and vacuum junctions around the engine and I can't find any leaks. Intake gasket(s) seem to be fine as far as I can tell. As is PCV system and the lines to the evap canister. Truck doesn't have EGR, even if it did, that would be on the driver's side (bank 2)
When slowing down in gear, both banks have close to the same fuel trim. If there was some sort of severe vacuum leak on bank 1, seems like a high vacuum situation like decelerating in gear would affect it.
Help?