91 k15oo rus good at times

Discussion in 'Chevy C/K Truck Forum' started by brtresto, Feb 23, 2014.

  1. brtresto

    brtresto New Member

    I have a 91 k1500 with the 4.3 about 6 months ago it sat for a month and a half while I located and installed a used 5 speed. Before it was parked it ran fine every since I replaced the tranny it has lacked in power off and on.At times it runs like it use to but most of the time it is low on power and sucks gas down like there is no tomorrow.It started shooting oil out the dipstick tube so I replaced the pvc valve that didnt help so I replaced the left valve cover (it was stopped up so bad carb cleaner wouldnt run thru it that cured that problem it has dtcs #12 and 44 in it so I replaced the O2 sensor it still has code 44 and 12.It doesnt smoke and like I said it runs normal sometimes mostly the colder outside the better it runs I have drove this truck to work for years and it has always taken 11.5 gallons of gas a week to get there and back it now takes 17 to 18 gallons a week for the same drive.I have replaced the plugs plug wires cap rotor fuelpump and filter along with air filter pvc valve and O2 sensor I have also ran seafoam thru it and checked the engine wiring along with the O2 sensor wire.If any one has any ideas I would realy thank you.
  2. Scott_Anderson

    Scott_Anderson Rockstar 100 Posts

    I could think of a couple of things to look for.
    While it sat for that 6 weeks or so, by chance did any critters visit for a snack on the wiring under the hood.
    Or did any make a nest in the exhaust? BTDT.......
    By chance have you run any seafoam in the oil? sticking rings?
  3. brtresto

    brtresto New Member

    No I didnt run seafoam in the oil just the fuel and the truck was in a garage while setting so not likely any critters are the problem but I will check for that .There couldnt be much in the exhaust since I have driven it daily for a couple of months,I guess the cat could be stopped up but why would it run fine in the morning and bad later in the day when it warms up? Thank you for your reply Im still open for any suggestions.
  4. edsmagichands

    edsmagichands Member 2 Years 100 Posts

    Code 12 should always be there KOEO (key on engine off), it's for no crank reference. code 44 is 02 lean condition. since you did the tranny, i'd start by checking for exhaust leak. if outside air is drawn in across 02 it will go lean even though the engine is not. at this point pcm will start adding fuel to compensate for the false lean code, since it's not really lean it will now be running extremely rich.when its cold it needs more fuel so it would run better, but when warm it doesn't need as much. hence sluggish & poor fuel mileage. also check that you didn't pinch or damage 02 wiring harness . also check for vacuum leaks. lack of fuel will cause lean code but wouldn't running better when cold. not a bad idea to check for pinched fuel line around tranny an do a fuel pressure test to rule that out.

    Good luck, and let us know!
  5. brtresto

    brtresto New Member

    Thank you for your suggestions I could have an intake leak the engine has 27100 miles on it an a little coolant leak here and there. I have checked for pinched wires and kinked fuel lines but havent done a pressure check because of new fuel pump.but as we all know these days just because a part is new doesnt mean its good.Yhanks again for your input Ill post my findings when I get a chance to work on it again.I work dusk till dawn and drive it daily so not much time to check it out.

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