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Vortec Fuel Problem Please Help!

cjauto

By cjauto
in Ask A GM Technician

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cjauto Enthusiast

cjauto

Posted
Posted

Have had this truck for about 8 months now and has had the problem intermittantly for a little while. 99 K1500 w/ 5.7L has had good service w/ many common parts already replaced, all o2 sensors, pump and filter, recent tune-up, etc. The problem started occuring more often recently. Chugging then stalls. Acts like it is out of fuel. No rhyme or reason to when it happens. Park it and it may or may not have the problem. Awhile back i noticed fuel running out of the evap can, so i replaced it figuring the valve was bad. Didn't fix the problem. I found when the fuel pump was replaced they crimped the vent line. That was fixed. The problem didn't occur much after that. Recently it started acting up again w/ the same symptons. Thought the fuel pump was bad, so i replaced it w/ new Delphi pump. Found some debris in the tank and flushed and new filter. Within a couple hundred yards the problem happened again and is much worse now. I limped it home from my buddy's shop, barely. It was chugging and go about 10 feet and stall. Hard to restart. Give a little gas to start and it would stumble around till the rpm came up and cleaned out. Did not blow any smoke. Go another 10 feet and it starts again. Once i got it in the driveway i noticed fuel running out of the evap can again, alot. Loosened the tank cap which was pressurized and the fuel stopped leaking from the evap can, but the problem was still there. It seems as though no fuel is getting to the motor, its trying to return it all to the tank. It has never tripped a service light and no codes. Pressure is good. There must be a vlave in the system that determines how much fuel gets to the motor and what gets returned. I have a good knowledge of older motors and electronics, but am at a loss w/ the newer vortec electronics. I am more than capable of fixing the problem if i knew what it was. I just don't want to start changing parts. I would greatly appreciated any help and advise. This is a daily driver for work and I really need to rely on it.

C6Racer Enthusiast

C6Racer

Posted
Posted

The only explanation I can come up with is that a fuel line or something is plugged up. Other than that, I'm stumped. Try testing the MAF sensor(keyword: testing, those things are expensive as hell). Even though this car is completely different, my brother's '94 BMW had a similar problem where it seemed it wasn't getting fuel. It was stumbling onto its face. We replaced the pump and the fuel filter but, that did nothing. We finally gave up and took it to a shop where the MAF sensor was replaced and it runs good as new. Who woulda thunk it!

waltv Enthusiast

waltv

Posted
Posted

To answer your question about the valve, yes there is a pressure regulator assembly. It is part of the fuel metering assembly, which is mounted to the lower portion of the intake manifold. It is a vacuum controlled diaphragm type valve. It gets its vacuum supply from the intake manifold.

I'm curious about your tank being 'pressurized' and liquid fuel coming from you EVAP canister though. How much fuel was is the tank? When you say 'pressurized', do you mean the cap tried to blow off when you loosened it, or vacuum was applied to the cap? It sounds to me like you have an EVAP system problem. For instance, if your EVAP vent valve was stuck closed/clogged, your tank was full, and the EVAP system started applying vacuum pressure then, I could see liquid fuel being sucked into your EVAP canister. Anyway, I'd take a look at your EVAP vent valve and purge solenoid. You're going to need to replace that canister again if the charcoal got all contaminated with liquid fuel. Hope this helps.

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

the tank only had less than 1/2, but has happened near full and empty. as far as the tank pressure, when the cap was loosened i could clearly hear air blowing out. evap vent valve was already replaced. purge valve is on order.

thanks, any info helps.

waltv Enthusiast

waltv

Posted
Posted

Did you hook a vacuum gauge up to the purge solenoid to see if it was stuck open? Curious if its a control problem or if the valve is just stuck open. That is if it's the purge solenoid. If you can easily duplicate the problem, you should just be able to plug off the vacuum line from the purge solenoid and notice a difference. It sucks that no codes are being set.

C6Racer Enthusiast

C6Racer

Posted
Posted

Well, I wasn't saying to just go ahead and buy the MAF sensor. I just meant that it might be a good idea to test it and make sure it's working properly.

papastoy Enthusiast

papastoy

Posted
Posted

I'll second the purge soleinoid idea. I had similar problem with a carbed early 80's car and the canister purge soleinoid was full of gas from a broken diaphram in it.

silveradobobby Enthusiast

silveradobobby

Posted
Posted

Sound like maybe a purge valve stuck the chuging coming from the vacuum line sucking excess fuel from the evap system into the motor and bogging it down and flooding it. If the valve is sticking the gas vapors could be pressurizing the tank and not venting and forcing gas to the evap system and causing your flooding problems, its hard trying to find this problem without being there and seeing everything for myself.

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

thanks for the info guys. i'm trying a purge valve in the morn. had to wait for the dealer order. holiday weekend. no camping. :rolleyes: hope fully its just the purge. is that a common prob?

cjauto Enthusiast

cjauto

Posted
  • Author
Posted

well $45 purge valve and 30 miles later..... same prob. the only thing i noticed different is that it did not fill the evap can w/ fuel or pressurize the tank. prob occurred for about 1.5 mile then kind of cleared. felt low on power after. still no ses or codes. this is one of those really agrgravting probs. electrical? damaged harness somewhere? i have access to a snap-on diagnostic. what should i look for at this point?

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