Engine stalls, cause unknown

[Lumpy Grits]

Our fuel system was made to hold about 3-4 positive psi within the fuel system.
Ck'n for this is part of our dang SMOG testing.
I want the OP to run his Jeep with OUT the gas cap on. To see if he's pull'n a vacuum on the tank because his cap isn't venting correctly.
LG

 

[hagar]

He could tee in a vacuum gauge on the inlet side of the fuel pump.
That would show right away with a very high vacuum reading.
ie, pump working too hard to draw fuel.

 

[b3uhbp]

Take the gas cap off the tank and see IF that does anydangthing when you start up.
Take the line off that feeds the FP from the tank and blow it out(tank cap off)with compressed air.
Check the metal line from the tank to the FP to be sure it is not pinched some place.
When it dies-Where is the choke baffle sitting?
Have you look'd for vacuum leaks yet at the carb's base plate using soapy water.
Does this stall only happen with a hot engine after it's sat for a few minutes or is this a cold start issue?
Can you post pictures of your engine bay lay-out?
LG

Well I drove it again, it didn't stall but when I got home I checked the Pressureand it was near zero. Removed the gas cap and it returned to normal. When I put the cap back on the pressure started falling, I removed the gas cap and the FP returned to normal again. I did blow air through fuel line from the fuel pump and could hear bubbles in the tank. Checked the lines and hoses, all okay. Don't yet know where the baffle is when it stalls but will check. Have not done all the vacuum checks but based on what I'm seeing I doubt that is the problem. The problem only happens when the engine is hot and it's warm out. This stalling/hesitation happens while driving not just at idle. I will attach some pics of layout. I feel like we're getting closer. Thanks for your help.

 

[Lumpy Grits]

Buy another gas cap. A vented gas cap--
Your pull'n a vacuum in the tank, the cap ain't allow'n the tank to equalize to the atmosphere.

LG

 

[b3uhbp]

Here are the pics I promised.

 

[b3uhbp]

Maybe we are getting somewhere. When you remove the gas cap there should be no air going in or out. This indicates a problem with the fuel tank vent system, or in other words, do you have the charcoal cannister hooked up? As fuel is used up in the tank a vacuum is left in its place and can create problems pumping fuel out. There are a number of componets that go with a charcoal cannister and can be pictured in a Jeep CJ repair manual. There is also a filter in the bottom of it and if clogged can cause problems.

Never thought of that. I knew of the canister but I'm not sure it is hooked up. It probably is. Where is it and how do I service it? See pic.

 

[b3uhbp]

Buy another gas cap. A vented gas cap--
Your pull'n a vacuum in the tank, the cap ain't allow'n the tank to equalize to the atmosphere.

LG

I will. Hopefully it's that simple. I'll let you know how it goes. Thanks

 

[Torxhead]

Yeah, get a new gas cap as they are vented, or yours should be and maybe it is not working. Watch for vacuum developing in the gas tank. That charcoal cannister is not hooked up correctly, a Jeep manual or searching the internet should provide more light on that. If you look closer at that cannister, at each hose port there is lettering indicating where each hose goes. There is one of those hoses that goes to the tank along with some check valves so gas does not run into that cannister. Look for a funny looking filter at the bottom of it. Thanks for sending in the pics.

 

[Lumpy Grits]

Get rid of that view-all filter next to the carb. Serves no use!
You don't need any of that pluming on the fender. Get rid of it also.
Move the metal OEM filter away from the exhaust manifold. That filter gets very hot there, and that's also a well known source for engine fires.
Follow up on the evap canister pluming/function.
LG

 

[Lumpy Grits]

Never thought of that. I knew of the canister but I'm not sure it is hooked up. It probably is. Where is it and how do I service it? See pic.

That canister is your problem-Read the link below
Evaporation Canister

No-it's not 'hooked up' at all.

LG

 

[Torxhead]

After the cannister is a check valve then a rollover valve in that system to the gas tank. For proper operation their location is critical and a pain to get at, it is possible that they still are correctly located and properly plumbed. These are too prevent fuel from going all the way to the cannister and running out. Its purpose is to vent the gas tank and prevent the fuel from running out when you roll the Jeep over on its lid or side. If it happens you will be glad it was installed and working correctly. So, a little research could help here.

Lumpy, those see thru filters will show like water in the fuel system, but can leak quite easily.

 

[b3uhbp]

That canister is your problem-Read the link below
Evaporation Canister

No-it's not 'hooked up' at all.

LG

Correct. That is the way it was when I purchased the jeep two years ago. The only part still hooked is the hose from the carb bowl. Always ran great until recently so I doubt that's the culprit. I bought a new cap, looks like the original, I assume it's vented but not sure. Symptom persists, everything works fine until I twist on the gas cap. I pushed a little compressed air through the fuel return line just to ensure it was clear (hope that was not a mistake). Anyway, it seems that if I can get a gas cap that allows pressure equalization it will fix the problem but I'm concerned that is not the genesis of the problem. Seems there aren't a lot of options left. Trying to avoid taking her in to the local jeep shop. Thanks much.

 

[Lumpy Grits]

Did you ask for a vented cap?
Please post pictures of the underside of both caps.
LG

 

[b3uhbp]

Yeah, get a new gas cap as they are vented, or yours should be and maybe it is not working. Watch for vacuum developing in the gas tank. That charcoal cannister is not hooked up correctly, a Jeep manual or searching the internet should provide more light on that. If you look closer at that cannister, at each hose port there is lettering indicating where each hose goes. There is one of those hoses that goes to the tank along with some check valves so gas does not run into that cannister. Look for a funny looking filter at the bottom of it. Thanks for sending in the pics.

The new cap I bought looks identical to the original. I get positive pressure build up, not vacuum, pretty quickly after I twist on the cap which immediately triggers the fall in fuel pressure. Take off the cap and pressure returns to normal. What am I missing? I really appreciate everyone's assistance. I have been working on restoring this jeep almost constantly for two years and everything is working perfectly except this. Frustrating but I will find it.

 

[Lumpy Grits]

After the cannister is a check valve then a rollover valve in that system to the gas tank. For proper operation their location is critical and a pain to get at, it is possible that they still are correctly located and properly plumbed. These are too prevent fuel from going all the way to the cannister and running out. Its purpose is to vent the gas tank and prevent the fuel from running out when you roll the Jeep over on its lid or side. If it happens you will be glad it was installed and working correctly. So, a little research could help here.

Lumpy, those see thru filters will show like water in the fuel system, but can leak quite easily.

The OP has the OEM filter(MUCH better at filtering).
There is no need for that see-thru one.
All those 'filters' do cause restriction and allow for leaks.
LG

 

[b3uhbp]

Did you ask for a vented cap?
Please post pictures of the underside of both caps.
LG

I assumed the original was vented so I just asked for a replacement. Here is a pic. The one on the left is the new one.

 

[b3uhbp]

I took my old cap apart and it is vented but only to allow vacuum release, not positive pressure. I may just disable the mechanism to allow it to breath in both directions. Should fix/band-aid the problem. Still pretty sure there is another underlying problem with the venting of the tank.

 

[Lumpy Grits]

Both of those are 'vented'.
The relief valve works both ways for vacuum and positive pressure, to a point.
I believe you are now see'n this issue because of the warmer weather.
Look for a cap'd vent line back at the gas tank or up in the rear driver side fender well(roll-over ck valve).
IF, I were you-I would ditch the fuel pressure regulator on the fender for now. It's just not needed. The 2 out going fuel lines on the OEM fuel filter is a 'por-mans' fuel pressure regulator.
Where does the fuel return line go??
The previous owner did you NO favors, with this set-up.
LG

 

[b3uhbp]

Both of those are 'vented'.
The relief valve works both ways for vacuum and positive pressure, to a point.
I believe you are now see'n this issue because of the warmer weather.
Look for a cap'd vent line back at the gas tank or up in the rear driver side fender well(roll-over ck valve).
IF, I were you-I would ditch the fuel pressure regulator on the fender for now. It's just not needed. The 2 out going fuel lines on the OEM fuel filter is a 'por-mans' fuel pressure regulator.
Where does the fuel return line go??
The previous owner did you NO favors, with this set-up.
LG

I examined the return line and seems to end at the tank. I don't know what the roll over check valve looks like so I don't know what to look for. I push some air through the return line and seems like it is going into the tank. I agree that the warm weather is part of the problem but I drove it all last summer with no problem, but I know things change and wear out. It has also undergone an extensive refurb as well but didn't really mess with the fuel system. I certainly have no issue with getting rid of the gauge and see through filter. Getting a little desperate. May have to break down and take it to the local jeep shop and have them try and run it down but I hate to do it. Like to do as much as I can myself.

 

[Lumpy Grits]

You so NEED a real factory shop manual(MR-252).
Hanes & Chilton are very much lacking with many errors.
Jeep Service Manuals
Money well spent!
Have you ck'd for the vacuum leaks yet???
LG