88 Jimmy Fuel Vapor Canister Problems

[donnyb88]

Hey everyone, long time reader and now finally a member. Ive always wanted to get a K5 since I was a kid and made it a reality last May. It also happens to be the first truck/4x4 Ive owned.

Its a 1988 GMC Jimmy 4x4, 5.7L fully loaded. I love the truck but it has been giving me problems for the last few months. So far Ive replaced the:

fuel pump, fuel filter, fuel injectors, tbi gasket, gas cap, plugs/wires, coolant temp sensor, oxygen sensor, knock sensor, alternator, belts, pcv, brakes and the fuel vapor canister.

Currently my problem is that it will start and idle fine, but the second I put my foot on the gas pedal it wants to die. When I popped the hood I noticed that the new canister was soaked in gas and it appeared to be leaking from the bottom, so I opened the gas cap to relieve the pressure to stop it for now. The same thing happened with the old one thats why I replaced it, its less then a month old. It has been pretty steadily cold here (about -20C average) and it has been running fine. Overnight the temp went up to about -5C which Im guessing warmed up the tank expanding the vapor?

The same problem has happened to me multiple times now, and it seemed to go away after a few days except it was so bad once I brought it to my mechanic and he said it was leaky injectors so I had them replaced.

I was just wondering if anyone had any ideas or suggestions about whats going on or what I could do to fix this problem for good.

Thanks in advance for taking the time to read this and for any replies!

Cheers!

 

[496truck]

Liquid fuel should not be getting to the canister. It is there to capture and hold vapor till it can be purged/burned in the engine.

Leaky injectors? I highly doubt it. For one, if the injectors are leaking it's a fairly obvious problem, easy to find. Plus, when they leak down (on a TBI unit) the fuel will leak down past the throttle blades and end up in the intake manifold or into the combustion chambers.

Follow the vapor line back to the tank. I want to say there is a check valve back there to keep liquid from entering the system.

Or the return line is hooked up to the vapor line and vice/versa. Has anyone done a fuel pump or sending unit work on this truck? For liquid to enter the vapor line, the vapor inlet tube would have to be submerged below the fuel level. The return line is deposited down low in the tank while the vapor line ends at the top. So, if someone hooked up lines wrong....

 

[donnyb88]

Thanks for the reply!

The guy who sold it to me said he changed the tank and fuel pump before I bought it. Which outlet on the sending unit is for the return line and which one is for the vapor line? I Followed the line back from the canister to the tank and its going to the second outlet of the sending unit (3 outlet) not sure which line is which?

 

[British Slave]

I could be wrong, but the fuel pump discharge and the return line have fittings and the vapor line has a rubber hose and clamps at the tank.

 

[donnyb88]

I thought they should have had fittings on them too, but I guess maybe he cut them or something because they are all rubber lines with clamps.

 

[British Slave]

In that case, go to a parts house and ask them to show you a pump, and go fom there.

 

[496truck]

In that case, go to a parts house and ask them to show you a pump, and go fom there.

Not so much a pump, you want to see a sending unit.

 

[donnyb88]

Thanks for all the help! When I got a chance to check out a sending unit and crawl under there it turns out the lines were mixed up. I hooked up everything properly and its running good again.

Thanks again

 

[85k5dsl]

The return line has no fitting just like the picture. I high jacked the pic from the TBI trail fix thread.

 

[496truck]

Thanks for all the help! When I got a chance to check out a sending unit and crawl under there it turns out the lines were mixed up. I hooked up everything properly and its running good again.

Thanks again

Sweet!