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Alberto_YJ

Jeep YJ Wrangler 4.2L Fuel Supply Issue or Vapor Lock

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Hello people, I've had a hard time traveling in my YJ. Everything was ok until I stoped by a grocery store.

The engine have been having some abnormal behavior, I've been smelling fuel when I shut off the engine and step out of the jeep, when the tank is not full (say 1/4 of the tank) and I open the gas tank cap it releives a lot of pressure.

If I let the jeep sitting overnight, next day will give a hard starting and I have noticed that the carb bowl seems to be empty, as I can see there are no squirts when the pedal is pumping.

Now, regarding the day it completely failed, it was starting and then stallin unless I give it a hard acceleration, then start moving and it would keep the engine running for a while then dies.

Started troubleshooting by checking the squirts in the carb. No squirt.

Disconnected fuel hose at fuel pump inlet. Completely dry.

Attached an electrical reciprocating fuel pump. Same behavior after a while.

Fuel filter replaced with a single outlet one to eliminate return line. Could get the engine running longer but sometimes carb was flooded and sometimes I heared the electrical pump noise which means it is empty.

I've decided to get back home with the single oulet filter setup and both fuel pumps connected in line. The engine runs great even in hard acceleration when overtaking other vehicles. But if I slow down in traffic I will hear the electrical pump is getting dry again.

Now at home, tryed a new fuel hose from an external gas tank to the electrical pump. Same thing.

Routed a new fuel hose to bypass mechanical pump and steel line over the engine. Same behavior.

I've tried removing gas cap with no difference.

I've rebuilt the carburator and noted the base gasket was just with two barrel holes and no grove on the sides to let vac flow from the port that goes to canister (I think). Replaced that with the oval hole and side groves. But I'm still getting the pump dry.

As this is my DD vehicle I'm in a rush to fix this problem asap. Any help will be highly appreciated.

Going to drop the gas tank right now to discard pickup tube clogging.

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UPDATE:

After dropping the tank found that it is kind of collapsed from the bottom, put some heat with a heat gun and it straighten itself, but when it coola down it will go back to the same shape.

No clogging in the pickup tube.

Today I was thinking about the pressure when open the gas cap and thought that maybe the tank is not venting, I was right. The steel line to the canister is completely blocked. I've disconected the hose coming from the tee at top of the tank but now it seems like the fuel filter is restricted. I can't blow by when I plug the return outlet.

Is there any way to replace that filter with a Tee and a clear filter? This is because it is hard to get here in town.

 

Regards. 

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Alberto, you did a very thorough troubleshooting job on this problem.  Sounds like you're near a cure.  The factory three pipe fuel filter is actually an asset.  When the fuel volume exceeds the amount that needs to flow into the carburetor bowl, the third pipe on the filter directs fuel back to the fuel tank (if the line is not restricted).  This continual, excess return fuel flow is a good thing, as it prevents the fuel from "pooling" in the line or filter and getting hot from engine heat.  When fuel between the pump and carburetor gets hot, it can cause a classic case of fuel vapor lock.  Fuel stops flowing...

So, be sure that the return line to the tank is not restricted.  The mechanical fuel pump should produce enough fuel volume and pressure to create the excess that flows back to the tank from the third pipe on the fuel filter.

I would not eliminate the 3-pipe filter.  If you can only find a 2-pipe (inlet and outlet) fuel filter, make a "T" at the line near the carburetor/fuel filter location to simulate the 3-pipe fuel system.  That way, you can maintain the fuel flow back to the fuel tank, which will keep fuel cooler at the carburetor.

Make sure the float level is correct in the BBD carburetor and that the needle is not sticking in its seat...

Moses

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Hi Moses, Ironically the first thing I did was to replace the fuel filter, assuming that it was restricted to the carburetor. After finding the gas tank vent line clogged I deducted that all the extra pressure from gasoline vapors was traveling backwards to the filter throught the return line, then the vapor lock occurred.

After disconecting the vent hose from the steel line that goes to the canister I've noted that the pump is not getting dry anymore and next issue was the New fuel filter, it seems to be defective, fortunatelly I was keeping the old one and after putting it back the problem is temporarily cured.

I will have either to replace or unclog the  vent steel line.

Is there any reason to avoid replacing it with rubber hose from the tank tee?

another question, I noted that the whool on bottom of the cainster is not there, is there any problem running the engine like that?

 

Thanks for your comments. Regards. 

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9 hours ago, Alberto_YJ said:

Hi Moses, Ironically the first thing I did was to replace the fuel filter, assuming that it was restricted to the carburetor. After finding the gas tank vent line clogged I deducted that all the extra pressure from gasoline vapors was traveling backwards to the filter throught the return line, then the vapor lock occurred.

Good call here, Alberto...

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After disconecting the vent hose from the steel line that goes to the canister I've noted that the pump is not getting dry anymore and next issue was the New fuel filter, it seems to be defective, fortunatelly I was keeping the old one and after putting it back the problem is temporarily cured.

Good...These filters should be available, the 4.2L BBD carbureted engine was popular, and the filter fits nearly a decade of AMC and Jeep models.  Do you have the NAPA part number for the filter?  Is there a NAPA distributor in your area of Colombia?  That would be the easiest parts source in the U.S.

Quote

I will have either to replace or unclog the  vent steel line.

Is there any reason to avoid replacing it with rubber hose from the tank tee?

The issue with fuel hose is safety.  There is heat and the risk of chafing/damage on the underside of the vehicle.  By choice and safety requirements, the vehicle manufacturers use steel pipe to prevent risk of fire around gasoline or gas fumes.  I prefer steel pipe.

Here is an article I did on EFI and carburetor fuel pressure requirements for Jeep inline sixes.  In the article, you will find details on how I form steel fuel/brake grade pipe ends to accept a hose.  I also talk about proper hose types and EFI grade hose clamp needs.  You can use standard fuel/brake tubing with double flared ends and flare nuts to piece together (if not long enough) a replacement steel line to match the original.  Sections of pipes can be joined together with flare seat couplers to match the tubing ends.  If you need to tie into hose at each end of the long pipe, see my method for cutting off the flare ends from the tubing and re-forming it as "bubble flares" to prevent the hose from coming loose or possibly getting nicked by a sharp tubing end.

Note:  You can buy 25' rolls of fuel tubing without flared ends.  Summit Racing has examples of steel tubing in bulk:  https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=fuel tubing.  Note the tubing sizes available, match your tubing diameter.  You need a tubing cutter and flaring tool to complete the tasks shown in the article.

Look down through the article linked below.  If you cannot unclog the factory steel line, you will get insights into how to fabricate safe steel fuel line with safer hose ends:

http://www.4wdmechanix.com/Jeep-Fuel-Pressure-Requirements?r=1

 

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another question, I noted that the whool on bottom of the cainster is not there, is there any problem running the engine like that?

Do you mean the foam mesh that the canister contains?  Take one of your quality photos and attach it.  I'll comment back...

Quote

 

Thanks for your comments. Regards. 

You're welcome, Alberto!

Moses

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Fortunately the issue has been cured, had to replace the vent line, didn't find a steel one, so I had to put copper tubing instead of steel.

 

Regarding the canister please see attached picture taken from under the vehicle.

I still have an issue with the carb bowl getting empty after I let it sit over night. Any suggestion to fix this? (Return line from the filter is already on top, carb has been rebuilt - al gaskets replaced)

thanks.

IMG_4381.JPG

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Hi, Alberto...The canister looks typical with its waffled bottom grille; the foam looks in place, that's normal...

When the carburetor bowl bleeds down after setting, look for an internal leak within the carburetor.  This is usually 1) a check ball either not seating properly (possibly the wrong size ball) or  2) a check ball not in place at a level either below the float bowl or low in the carburetor.  Evaporation of all the fuel in the bowl, as you know, would not occur overnight.

I would check for a fuel bleed-off low in the bowl, like the accelerator pump's check ball, the check ball's weight or poorly adjusted accelerator pump linkage.  Refer to your carburetor rebuilding kit's parts diagram/schematic.  The bleed is from a passageway or a circuit that is lower than the fuel bowl...A leaking float needle would not drain the fuel bowl.

Moses 

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