Fuel vap canister overflowing?

[Pearlmoto]

Hello everyone.  Have a curious problem and was wondering if anyone has any insight.

Truck is an 86 K30 4spd, all original and bone stock w 22K miles, LT9 350.  Since this truck is my daily driver, I have replaced the following items with all AC delco parts:

fuel pump
water pump
all belts
fan clutch
TVS switches
Intake manifold gaskets
Cap/rotor/plug wires/plugs
hydroboost pressure lines
both oil pressure switches
temp switch
tstat and water neck
upper/lower radiator hoses
clutch slave cylinder

When I bought the truck my fuel pump went out and I replaced it and all was well.  Today, after a long cruise on the highway, I park the truck and return to it noticing an odor akin to locktite, and the truck was hard to start.  In traffic a mile later it dies.  I manage to restart to a huge cloud of white smoke, park and pop the hood, and notice the fuel evap canister is overflowing with gas (hence the odor I was noticing).  I remove the air cleaner assembly and manage to limp the truck home, but it will only limp in first gear, any additional load and the motor will quit.  The oil pressure is good and the temp is good.  It revs fine out of gear if not a little weak.

These are the same symptoms I experienced when my fuel pump initially went out, but seeing as the replacement only has about 500 miles, and given the evap canister was overflowing, I'm concerned it may be something else. 

I have the factory service manual and will test the fuel pump per chevy instructions.  But the overflowing evap canister is obviously dangerous and I'd like to figure out why that is happening too.

Does anyone have any experience or suggestions?

[Pearlmoto]

Update:

I pulled the vapor canister and it was indeed filled to the brim with fuel.  Obviously, this probably will have an impact on driveability....

I did fill up yesterday.  I have read that overfilling can cause this problem.  Any merit to that with our year trucks?

Why would the canister just fill up like that?

I did find this.  Looks like I may have figured out my problem:

"Should it become saturated, the tank will be unable to breath in, the pump will struggle, the car may stall, and you might experience premature pump failure."

[bd]

How full did you fill the tank?  With the engine idling, does fuel visibly drip from the carburetor main nozzles?  With the engine idling, is there strong continuous vacuum reaching the vapor canister through the 1/4" hose from the engine?  If you draw a vacuum on the 3/32" vacuum hose ports on the vapor canister, will they maintain vacuum or do they bleed off?  Be careful that you don't get a mouthful of fuel....  Is the canister "vent port" obstructed?

[blazer74]

Possible fuel tank pressurized and forcing fuel in to can.
Fuel has to go uphill to get in the can.
The gas cap should vent into the tank.

[Pearlmoto]

It's unusual bc I did nothing different than I normally do when filling up.  I didn't spend any extra time trying to squeeze in every drop.

The vapor canister was filled to the brim.  When I removed it I managed to pour out a full quart or so.  There is strong continuous vacuum going to the canister w the engine idling.  Fuel is not visibly dripping from the carb main nozzles.

I have ordered both new canisters for my truck, the main vapor canister and the smaller secondary canister that is connected to the port labeled "air cleaner" off the main canister.

When I was broken down and pulled the gas cap it did hiss as pressure was relieved.

[bd]

Fuel tank(s) plumbed to a vapor canister employ sealed fuel fill caps, forcing the tanks to "vent" through the canister.  Did you check whether the small ports on the purge and bowl vent valves will maintain vacuum that is applied to them?  Does the truck have single or dual fuel tanks?

[Pearlmoto]

I have not tested the vent valves on the canister as I have purchased new ones.  However, I can go and hook up the mightyvac to the old canister and check to see if theyll hold vacuum.  My understanding is that once saturated with gas, the charcoal is ruined and the canisters must be replaced, so I didn't do any testing on the old unit.

The truck has dual tanks.  I only use the driver side bc I am unsure of the condition of the passenger and do not want to risk sucking gunk into the fuel system until I drop that tank to clean it.  I have never attempted to swap over to the passenger tank.

I wonder if the accumulation has been happening over time - yesterday I did notice evidence of gas leaking out the canister before I saw it actually happening as I limped home.  The raw fuel leaking out the canister did not smell fresh, as I mentioned before, but more similarly to locktite?  Perhaps simply running through the charcoal made it smell that way.

[Rapid Roy]

You stated...There is strong continuous vacuum going to the canister w the engine idling. IIRC should only have higher vacuum with higher RPM's. At least that is how my 74 is working. Don't think high vacuum at idle is normal. I could be wrong.

[bd]

You stated...There is strong continuous vacuum going to the canister w the engine idling. IIRC should only have higher vacuum with higher RPM's. At least that is how my 74 is working. Don't think high vacuum at idle is normal. I could be wrong.

The canister receives both manifold and ported vacuum.

I have not tested the vent valves on the canister as I have purchased new ones.  However, I can go and hook up the mightyvac to the old canister and check to see if theyll hold vacuum.  My understanding is that once saturated with gas, the charcoal is ruined and the canisters must be replaced, so I didn't do any testing on the old unit.

The truck has dual tanks.  I only use the driver side bc I am unsure of the condition of the passenger and do not want to risk sucking gunk into the fuel system until I drop that tank to clean it.  I have never attempted to swap over to the passenger tank.

I wonder if the accumulation has been happening over time - yesterday I did notice evidence of gas leaking out the canister before I saw it actually happening as I limped home.  The raw fuel leaking out the canister did not smell fresh, as I mentioned before, but more similarly to locktite?  Perhaps simply running through the charcoal made it smell that way.

My thought is to discover the cause to avoid a recurrence of symptoms with the new canisters.  The reason for testing the purge and bowl vent valves on the old canister is to determine whether the valve diaphragms are perforated.  And, again, make sure the canister vent ports are not obstructed.  In addition, without running the engine, switch tanks and check the fuel level in the tank you do not use.  Is it FULL?  How many lines connect to the fuel pump?

[Pearlmoto]

Thank you everyone for your feedback, BD thank you for your suggestions.

I checked the canister, and both purge and bowl vent valves hold vacuum.

The fuel pump has three lines - the threaded hardline to the carb, and large and small 90* nipples for inlet and vent.  It's the delco 41378.

The passenger tank fuel sender is grounding out when I hit the fuel selector button and pegging to past full, but the tank selector is humming when I hit the button.  But I don't believe there's any fuel in that tank given it makes no sloshing noises at all when I rock the truck back and forth. 

Something I just discovered....I removed the passenger filler cap and there is gas sitting right inside the neck!  I rocked the truck a bit and it drained back....

Perhaps I need to drop the gas tank sooner than later?

[bd]

The third (1/4" ID) line connecting to the fuel pump is a fuel return line to the fuel tank.  The return line's purpose is to help cool the fuel pump and prevent vapor lock.  It is not a vent line. 

Although, both fuel tanks are plumbed directly to the vapor canisters for tank venting and evaporative emissions control, the fuel return line is supposed to be plumbed through the tank selector valve so that fuel returns to the same tank from which it is drawn.  The tank selector valve on your truck is a motorized valve (hence the "humming" sound) as opposed to the older solenoid type valves that "click" when energized.  Motorized valves sometimes bind mid-travel and/or leak internally, resulting in various symptoms, which can include drawing and/or returning fuel to both tanks simultaneously, or returning fuel to the opposite tank from which fuel is drawn.  The fact that the fuel gauge pins past full when selecting the passenger tank (an indication of an "open" fuel sender electrical circuit) suggests the selector valve is binding mid-travel.  Consequently, I suspect that fuel has gradually transferred into the passenger tank through the malfunctioning selector valve, causing the tank to overfill, flooding the vapor canisters. 

Assuming this scenario is correct, you will need to restore proper operation of the tank selector valve or suffer a recurrence of symptoms with the new canisters.  Likely, you will need to replace the motorized selector valve and verify proper operation of the dash mounted selector switch.  Keep us apprised.

[Pearlmoto]

I replaced the fuel selector valve yesterday upon receiving my parts - I used ac delco U7000.  I also ordered a new switch, ac delco d7003, but I have yet to install it.  I will get to that this evening. 

The fuel reading on the passenger tank is still way past full.  I did start the truck and run it for a few minutes on each tank, so perhaps the passenger tank is simply brimming with fuel?  Before I changed the valve the needle would peg out to nearly 6 oclock:



This selector also doesn't hum like the last one, it just kinda clicks.

I have also replaced the vapor canisters with new delco units.  I have not connected the fuel tank vent and would like to drive the truck a few miles to ensure it won't overflow and foul another canister - aside from the obvious, would it be otherwise inadvisable to vent to tank to atmosphere and cap the fitting at the canister while I test drive?

My plan is to run the passenger tank until it's empty and see if the needle does anything.  I purchased a spare fuel filter to replace after I've run it through just in case that gasoline is old.

[Pearlmoto]

Wanted to update this thread.  I'm still having a bit of a headache!

The selector repair worked, and both tanks and gauges are functional.  Yesterday I drove 60 miles to pick up some motorcycles and the truck did great.

This morning I filled the opposite tank w gas, switched over, and drove off.  About a quarter mile down the road the truck sputters and dies. If I try to restart it'll run if I hold the gas and immediately die. I figure it's the new valve malfunctioning, so I attempt to switch back to the other tank, but the truck operated the same and left me stranded.  Remember, the selector valve, switch, and fuel pump are new.  The valve was still reading the fuel levels accurately when I'd switch the tanks after the truck stalled.

So far I have:

checked fuel flow - it filled a 16oz bottle overflowing after 20 seconds of cranking
replaced fuel filter - it looked ok
loosened gas caps to check for any pressure but tanks are vented to atmosphere right now anyway
checked all fuses - OK

I haven't done pressure or vacuum checks on the fuel pump as the truck is sitting in a parking lot a ways from my house.  Since flow was adequate and it's new, I'm trusting it's ok.

I was convinced I had a fuel issue, but pump flow is there and that has me wondering if this new problem and the tank switching are unrelated.

I'm headed back over there now to try a good coil and ignition control module next to round out those items.  Any ideas would be helpful.

[bd]

Does the engine start and run once it cools down? 

Try to determine whether the problem is fuel delivery or ignition related.  When the engine stalls, remove the air cleaner and look down the carburetor throat while opening the throttle a couple of times; is there a strong flow of fuel from both accelerator pump nozzles?  Remove the wire from the most accessible spark plug and hold it near a bare ground while an assistant cranks the engine; is there a spark?  What color is it?

FYI - The fuel pump should deliver about one quart (32 fl oz) of fuel in 30 seconds of cranking using a fully charged battery (1 qt in 20 sec is common).  So, 16 fl oz in 20 sec is slightly low, although still workable if draw and pressure are suitable.

[Pearlmoto]

Thank you for your reply BD.

The motor will not run on its own at all.  It will fire up and struggle if I pump the pedal but it will not idle - it immediately dies if I don't nurse the pedal.  If I hold the pedal down to achieve any kind of RPMs, it will surge and fall to near stall, then surge again.

I am seeing the accelerator pump function, and fuel is draining the bowl whenever I disconnected the line to check on the new filter.

My distributor has a new coil, cap, rotor, and ignition control module, and plug wires are new.  That just leaves the pickup coil as suspect.  However, I will do a spark test this evening to verify.

After I verify 12v at the coil and proper spark, I will test the fuel pump using a gas can for feed and see if the engine fires from there.  If it does, I can assume I have a fuel line or selector valve failure.  If it doesn't start, I will pull the carb and see if there's junk in the needle and seat.

I have been using the right side tank since I repaired the valve and have filled up about 3 times.  Perhaps there's some gunk in the carb, but the old filter did not have a bunch of crap in it.  Perhaps the new fuel pump ate it all up...

I'll report back after my tests.  It really does feel like a fuel delivery issue in my experience and not an ignition issue.

Frustrating issue considering I spent the dime on all new AC Delco parts!