Truck 'Leans out'
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Fleet Mechanic
Joined: Jan 2007
Posts: 1,293
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Truck 'Leans out'
My truck has always done this so I'm pretty sure its how its programmed, but it will 'buck' in first or reverse if I give it too much throttle, mainly on cold engine but after warming up too sometimes. Otherwise, it runs like a scalded-*** rabbit, considering its a 4.2L. I just have to take it easy at first. Idle is fine, nothing has ever changed. Truck now has 25,000 miles. I wonder if cleaning the mass air flow sensor might help - I've never done it before. Hell, it might have a wasp's nest on it for all I know. I'm putting a new air filter in this fall so I'll get the spray and do it then.
ETA: I was wrong - its mainly when warmed up. Cold enrichment seems to be adequate, so I'm thinking its simply how its programmed.
ETA: I was wrong - its mainly when warmed up. Cold enrichment seems to be adequate, so I'm thinking its simply how its programmed.
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Joined: Oct 2017
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My 2008 4.2/manual has done the same since new. Has 29k on it now. SCT programmer did not change anything with regards to it. It only shows up every now and then. Oddly, my other car, a 2011 BMW also with a manual transmission, will do the same thing when cold under certain circumstances.
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Fleet Mechanic
Joined: Jan 2007
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Yeah, I have accepted it as just the way it is. It really only acts up like when leaving a parking space after a short hot soak where you have to go slow for a little while before getting out of the lot - it will buck unless I just let off and ease it up to speed - it doesn't like the throttle, which indicates inadequate enrichment for the air that I'm allowing with the throttle. I reckon this is all part of the ECU's programming. If it was a carburetor I'd know what to do. 
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