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'99 K1500 5.7 Vortec Fuel Starvation during damp weather

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My '99 Chevy K1500 5.7 L Vortec has problem starting when it sits overnight in very damp, foggy type weather. It tries to start after cranking for longer than usual but will only partially turn over & mostly just sputter & chug a little. I suspected ignition problem like moisture under distributor cap Or coil but found that if I spray starting fluid or dump gas in throttle body it starts but dies as soon as it burns what was added. As long as I keep slowly pouring fuel in the TB it will keep running. The moisture is a definite factor because the only way I can get it to stay running is to dry it out with a small electric heater or heat gun. It only does this when the weather is just the right sort of condition, damp & foggy where when you lift the hood everything on the motor is damp with condensation. Once it is dried out it runs perfectly smooth with no missing. I can drive 100 miles down the interstate in the pouring rain & it will perform perfect with great acceleration/ throttle response Etc. Once I get it dried out & it starts on its' own, I can turn it off & on & it starts right up just like normal, no problem.

Is there some electrical component on the fuel system that could be shorting out when damp weather conditions are present? It seems like it has to be something electrical in the fuel system that would be affected by moisture. I would appreciate anyones help with this.

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This has me interested seeing I have never heard nor seen anything like this similar situation but involving ignition like you mentioned please with what ever you find please post the solution


Sent from my Z981 using Tapatalk

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I have had this condition twice in the past couple of years. Both times the problem started after the truck sat in the driveway overnight in heavy rain. In both cases, changing the fuel filter solved the problem. Coincidentally, I bought gas from questionable sources (i.e. Bob's Stop & Save instead of Chevron) both times right before the problem started, so that may have had something to do with it. The problem never set a code, which is what I typically see with electrical issues, so this is what lead me to start with the fuel filter.

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things to check.

top of the tank, and a ground nearby.


my weirdest problem was the tail lamp circuit boards,


interior lights was even a cuplrit.


tying that into the fuel system was a ground in the same rail as the fuel pump...and electic trailer brake. absolute monster. it over ruled other stuff.


behind driver side wheel well underhood..where stuff gathers, check all those plugins...and for wet organic stuff.


headlamps and parking, another big monster.

full LED swap, fuse sizes smaller, changed my truck entirely.

knocked off a 60 amp potential.


there is also a strange flow that goes to the alternator, heavy rain. I made a stainless cover for a brand new swap.


the biggest ciurcuit is ABS, the ecm and all its fingers is a close second needing super smooth power.

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Thanks for the input Bronyaur I will try changing the fuel filter which can't hurt, it probably hasn't been changed in a while anyway. Mine has not set any codes either. It haven't had any trouble since I first posted because the weather has been for the most part pretty dry.

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