87 TBI Vapor Canister Filling with gas

[hundvonkrieg]

Which is then being sucked into the engine causing it to sputter on the interstate/ die at slow speeds/ shoot gasoline out of the canister into the engine bay. I've replaced the charcoal canister twice. The "Purge" line is going into the correct port on the TBI from the canister. The "Tank Vent" line from the tank is hooked up to the correct spot on the canister. This had some mechanics around here scratching their heads. No one's been able to offer much past replacing the charcoal canister or just pulling the vacuum line. I want to keep everything hooked up.

Do ya'll have any ideas? I've had this truck for 8 years, and it's been in my family since new with ALL maintenance records kept. This hasnt happened before. It just cropped up after I had the transmission rebuilt. The only thing I could think of would be if the shop that rebuilt the transmission somehow crossed up the fuel lines, but I can't imagine why they'd need to touch those to pull the tranny.

I did a search and found a few posts on this, but it never was resolved that I could tell. Long post, sorry! and hi guys!

[VileZambonie]

See Attached pic and make sure everything is hooked up correctly.

Some engines equipped with Computer Command Control (C-3) and V6 engines with Throttle Body Injection (TBI) use an ECM operated solenoid to control canister purge vacuum, Fig. 72 . The ECM completes the solenoid ground path, energizing the solenoid to block purge vacuum and de-energizing the solenoid to allow the canister to be purged. The ECM energizes the solenoid during cold engine operation, at idle and when the vehicle is stopped with the engine running. The ECM de-energizes the solenoid and allows canister purge during normal engine operation, with the throttle open and road speed above approximately 5 m.p.h..

[454Man]

See Attached pic and make sure everything is hooked up correctly.

Some engines equipped with Computer Command Control (C-3) and V6 engines with Throttle Body Injection (TBI) use an ECM operated solenoid to control canister purge vacuum, Fig. 72 . The ECM completes the solenoid ground path, energizing the solenoid to block purge vacuum and de-energizing the solenoid to allow the canister to be purged. The ECM energizes the solenoid during cold engine operation, at idle and when the vehicle is stopped with the engine running. The ECM de-energizes the solenoid and allows canister purge during normal engine operation, with the throttle open and road speed above approximately 5 m.p.h..

Thank you for explaining this I never knew the sequence of operation. Again thanks. Now I know why you can't just hook up the line from the tank vapor straight to the carb

[hundvonkrieg]

Hey great info! Yeah I used that exact diagram. There never was a solenoid that you could see between the canister and the TBI. Is there a switch IN the throttle body that could get clogged? Would the EGR control solenoid have anything to do with it?

[bd]

Hello from California!
EGR would not cause flooding of the vapor canister.
The TBI base has a simple ported vacuum port without any internal valves or controls.  There should be no vacuum on the purge line until you open the throttle.

Do you have the 350?
Is the "Vent" nipple at the canister open to atmosphere?
Do you have dual fuel tanks? 
Have you done any work to your fuel supply system?

[hundvonkrieg]

Hey good questions. It was originally a 305, but a 350 was swapped in 5 years ago. The vent nipple? The only two that are connected to hoses are the fuel tank vent nipple and the "Purge" that goes to the TBI. The center, taller nipple is open to the atmosphere. One of the local shop's solutions was to connect that to the throttle body and leave the purge line uncovered.

It has dual tanks

I've not done any work to the fuel system since HS about 6 years ago.  and I've had no problems with it either

[bd]

...One of the local shop's solutions was to connect that to the throttle body and leave the purge line uncovered.

What was the outcome of switching the lines?

Here are some ideas for the weekend:

Make sure when you perform the following that you are completely away from any source of ignition, and that you have a fire extinguisher handy!

* What's the part number of the canister?  (Should be 17087115).
* Does fuel siphon out of the "Tank" hose when you pull it loose from the canister?
* With the "Tank" hose unplugged from the canister, connect a vacuum gauge directly to the canister's "Tank" nipple.  Drive the vehicle around the block.  Do you measure any vacuum?  (Answer should be "No").
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* Is it possible that the fuel return hoses running between the 6-port fuel selector valve and the two fuel tanks got accidently "switched" at the selector valve?
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* Remove both fuel tank gas caps.  Do the symptoms go away?
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* Have you recently started "overfilling" your fuel tanks?
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* Is there a "low spot" in the tank vent line(s) that could collect condensed fuel vapor that might later be forced into the canister as liquid?  To purge the vent lines, remove both fuel tank caps and apply about 5 PSI of regulated air pressure back through the tank vent line.  (There are fuel vapor restrictors incorporated into the fuel sending units, so you won't have a completely free flow of air, but you should hear some air escaping into both tanks).  DO NOT PLACE YOUR EAR OR FACE DIRECTLY UP TO EITHER FUEL TANK FILLER PIPE IN CASE FUEL BLOWS OUT OF THE PIPE!!!!

Let us know what you find.

[hundvonkrieg]

Heya,

I found a few forum postings on the net that I missed before. Number one on my list of things to do is to replace the Tank Selector Valve. Seems that sometimes the fuel return can get routed wrongly if the valve begins to fail (i.e. selecting the RH tank will sometime send return fuel to the LH). This is supported by some weird fuel level readings I've been getting and the fact that it only seems to happen when one or both tanks are above 3/4 full. I'll keep ya'll posted. If this doesn't fix the issue I'll dive into your suggestions.

To answer some of your questions: *The gas caps being removed doesn't fix the issue, though when I unscrew them while the fuel is leaking out the canister it lets some pressure out of the tank, but now I'm thinking that pressure is just build up from the fuel level rising past the vent line.
*Have not been over filling the tanks
*Lines are hooked up correctly at the selector and haven't been touched in years.
*The tank is the correct part number

[VileZambonie]

This didn't start happening until you had service work performed? I wouldn't assume everything is hooked up correctly or is untouched. Trace it out. Take some pix as well. Usually when the vent and return get crossed is when you see this happen.

[hundvonkrieg]

That's good advice. I rechecked short of dropping the tanks to check the sending units. The lines to the Tank Selector Valve are set up right. The vent lines look fine too.

 The only service I authorized was for them to rebuild the transmission. I can't imagine them even needing to look at the fuel lines to do that. Ill post up again next week when I can take it in to get them to change out the selector. Cheers.