suicidejockey

My DD is a 99 K1500Suburban LS 350 auto 4wd. The problem I'm having is if the truck idles for more than a few minutes, the check engine light comes on,it idles terribly and there's a strong smell of gasoline under the hood. The code it sets (I forgot the number) comes back as small leak detected in evap system. The parts stores say it's usually the gas cap. I've changed it twice along with cap,rotor,wires, plugs and air filter. If the truck is full, I can usually shut it off and retighten the cap and let it sit for a few hours and when I restart it,the light is off. Still has a bit of a rough idle but no gas smell. However if it has less than a half tank of gas, nothing helps until I fill it up. Any ideas or help would be greatly appreciated.
Bob

94z07fx3

Take the lines off of the canister and see if they are full of charcoal.

If your canister is one of the type that can be opened check it for wet gas.

If you run the lines and don't find a hole and if the canister checks out take it to a shop that has a smoke machine and they can find the hole in short order.

suicidejockey

Thanks for the help. I hope you don't mind a couple of questions. So if there's charcoal in the lines or wet gas in the canister, that means the canister is bad? Not finding either of those conditions, then I have a hole in the lines somewhere? Just want to make sure I understand what you're saying. I've never messed with an evap system.
Thanks again,
Bob

centuryoldracer

A leak in the evap system would not affect drivability. There is a fuel filter in the frame rail even with the driver door on the inside of the frame, so you have to get under there to see it. I would try changing it. You will need a 13/16, and a 5/8 open end wrench. Does it run good when you are driving it? Or does it run bad all the time. If the evap canister is full of liquid (gasoline) then it may be ingesting some of it causing a rich condition at idle. The fords do this also. You should be able to remove it (the canister) and see if anything dumps out of it.

suicidejockey

You know, with all the other crap I changed, I did forget the fuel filter. I'll change that tomorrow. But I don't see how the fuel filter could give an intermittent problem. Maybe I'm missing something. When the SES light is out, it actually runs pretty good except for a slight miss at idle. But when the light is on, it runs like crap and fuel econ goes into the toilet. So I'm going to check the canister and the lines tomorrow when I do the filter. Also forgot to mention I repaired a bad ground strap between the pass cyl head and the firewall. Doesn't seem to have helped. Thanks for the reply and the reminder about the filter. I'll update tomorrow.
Bob

centuryoldracer

Do you have a way to check fuel pressure? The fuel lines run next to the distributor on the driver side of it, and the port to hook your pressure guage up is right there. Could be the regulator is bad giving it full pressure at idle. The pressure should be lowest at idle (full vacuum throttle closed)and increase as the throttle opens and the vacuum decreases.

Closer_2001

Those trucks are notorious for a worn out distributor which can cause random check engine lights. It's a reach, but you may be smelling unburned fuel if you are getting lots of misfires...

centuryoldracer

Not a reach at all. The distributor is a very common problem on 95-99 4.3, and 5.7 engines. Plastic housing, and steel shaft. They wear out and the cam sensor (in the distributor) starts losing the signal.

suicidejockey

Thanks for the help guys. If it's the distributor that's worn, should I be looking for movement in the shaft the rotor sits on, or the whole thing? I'm going to borrow a pressure gauge this weekend because I've also read where the"spider" is bad for leaking. As far as the evap system, if I find charcoal in the lines or its full of gasoline, that means the canister went bad? Otherwise I need to look for a hole or a broken line? I did change the fuel filter. Didn't help. At least now I have some more things to check.
Thanks again.
Bob