Engine stalls, cause unknown

[b3uhbp]

Hey guys, I've got one of those issues that's very hard to diagnose. My jeep recently stalled but started back up and allowed me to get home but with a lot of hesitation. I began by replacing the ignition module and the rotor inside the HEI distributor and I tested the pick up coil and it seemed okay. Stalled again. This time, after restarting the engine I noticed that the fuel pressure had fallen to zero but the engine was still running. After the engine cooled off I restarted the engine and the pressure returned to around 4psi so I replaced the fuel filter. Stalled again so I replaced the fuel pump. I tore open the old pump but couldn't see anything wrong with it so it will probably stall again. Since I've replaced lots of parts there aren't many things left that it can be. I'm getting good fuel flow through the line, no obstructions etc. I'm wondering if it could be a problem with the fuel pressure gauge. It's a gauge that allows the pressure to be adjusted and I noticed some clear oil coming from it. Any suggestions would be appreciated. Sorry for the long message.

 

[Saddle Tramp]

Could also be a vacuum leak, check your hoses or an electrical/ground issue, check the connections.

 

[hole]

Vapor lock? It's been in the low 90's here in SoCal, so I thought I'd throw it out

 

[Torxhead]

Yeah, I think you should consider the vapor lock. The later CJs were set up for it with the fuel return line, fuel tank venting system and the 3 hole fuel filter. If any of these have been removed they can easily be replaced and set up to work properly. The next time it stalls check for pressure in the fuel tank by removing the fuel cap and listening for air rushing in indicating vacumn in the fuel tank.

 

[Lumpy Grits]

Make sure you fuel tank is full.
Ck the base of your carb for vacuum leaks(use VERY soapy water in a spray bottle for this). Make sure ALL manifold bolts are tight. Ck ALL of your vacuum hoses.
Are you using the OEM style fuel filter(1 inlet/2 outlets)? Make sure the smaller outlet to the return line is at 12 o'clock position.
Are you using the OEM mechanical pump or ele?? 4psi is very low.
Need more info from you on your mods to chase this down--
LG

 

[Torxhead]

Lumpy, I have done just fine w/4 psi, btw. Back when I had a mechanical pump. There could also be a clog at the fuel tank pickup sock.

 

[Lumpy Grits]

Lumpy, I have done just fine w/4 psi, btw. Back when I had a mechanical pump. There could also be a clog at the fuel tank pickup sock.

If your mechanical pump is only put'n out 4psi at idle, that's OK-But not drive'n down the road.
BTW: My mechanical FP shows 6psi at idle.
Need to know how the OP measured his FP psi.
Also need to know if the OP's die'n deal is either and overchoke/flood or fuel starvation
LG

 

[b3uhbp]

Could also be a vacuum leak, check your hoses or an electrical/ground issue, check the connections.

I thought of that but most all of the vacuum hoses have been removed and other than when it stalls it runs very smooth. I will check the grounding connections but they appear clean and tight and that doesn't explain the fall in fuel pressure. Thanks

 

[b3uhbp]

Vapor lock? It's been in the low 90's here in SoCal, so I thought I'd throw it out

You may have something there but what causes it and how can I fix it? Also, would that cause the drop in fuel pressure.

 

[hdgapeach]

You may have something there but what causes it and how can I fix it? Also, would that cause the drop in fuel pressure.

Heat is the cause and a return fuel line can fix it. A fiber or synthetic spacer between the carb and manifold helps isolate the heat from the carb, also. The return line for the fuel will help keep fuel circulating, thus keeping the heat down.

 

[b3uhbp]

Yeah, I think you should consider the vapor lock. The later CJs were set up for it with the fuel return line, fuel tank venting system and the 3 hole fuel filter. If any of these have been removed they can easily be replaced and set up to work properly. The next time it stalls check for pressure in the fuel tank by removing the fuel cap and listening for air rushing in indicating vacumn in the fuel tank.

It does have the fuel return line and a three hole fuel filter. I went out and checked the filter position and the return line was in the 6 o'clock position so I moved it to 12 o'clock. It did stall again today and when I removed the gas cap I did hear air but couldn't tell if it was vacuum or pressure. It seems that vapor lock is the likely cause but how do I make sure and how do I correct it? Thanks

 

[hdgapeach]

If you have a manual fuel pump, that could be the source of the bad fuel pressure. Since you've replaced that, you're gonna have to run it some to see if that solved your problem. If it actually was a bad mechanical pump, pull your oil dip stick and smell to see if gas got in the crankcase. You'll need to change the oil if gas seeped in there.

As far as your gauge, all I have is questions; where and how do you have it mounted? Is it an oil filled gauge?

 

[b3uhbp]

Make sure you fuel tank is full.
Ck the base of your carb for vacuum leaks(use VERY soapy water in a spray bottle for this). Make sure ALL manifold bolts are tight. Ck ALL of your vacuum hoses.
Are you using the OEM style fuel filter(1 inlet/2 outlets)? Make sure the smaller outlet to the return line is at 12 o'clock position.
Are you using the OEM mechanical pump or ele?? 4psi is very low.
Need more info from you on your mods to chase this down--
LG

I will check the components you suggested to eliminate vacuum leaks. I do have the OEM style filter and I corrected the position so the return is in the 12 o'clock position. The fuel pump is mechanical and I have had no issues with 4-5 psi. When is stalls and then restarts the pressure is zero. As far as mods go, it has a weber 32/36 carb, HEI distributor and nutter bypass. I think that's it. Thanks

 

[b3uhbp]

If your mechanical pump is only put'n out 4psi at idle, that's OK-But not drive'n down the road.
BTW: My mechanical FP shows 6psi at idle.
Need to know how the OP measured his FP psi.
Also need to know if the OP's die'n deal is either and overchoke/flood or fuel starvation
LG

Confused, what is "OP"? I'm pretty sure the issue is fuel starvation.

 

[Lumpy Grits]

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

 

[b3uhbp]

If you have a manual fuel pump, that could be the source of the bad fuel pressure. Since you've replaced that, you're gonna have to run it some to see if that solved your problem. If it actually was a bad mechanical pump, pull your oil dip stick and smell to see if gas got in the crankcase. You'll need to change the oil if gas seeped in there.

As far as your gauge, all I have is questions; where and how do you have it mounted? Is it an oil filled gauge?

It is a mechanical FP. I ran it today and it stalled so the pump was not the issue. The guage is mounted to the driver side wheel well. Since it is leaking oil I assume it's oil filled. I'm not familiar with these gauges.

 

[hdgapeach]

"OP" would be "original poster" and that'd be you. The stuff Lumpy Grits suggested to check is worth looking into.

If all your rubber lines are in good shape and your steel lines are good to go, you may have an issue inside the fuel tank; crud in the tank, sock filter, etc.

Not trying to jump ahead of Lumpy, but that seems like the direction he's headed.

 

[Lumpy Grits]

"OP" would be "original poster" and that'd be you. The stuff Lumpy Grits suggested to check is worth looking into.

If all your rubber lines are in good shape and your steel lines are good to go, you may have an issue inside the fuel tank; crud in the tank, sock filter, etc.

Not trying to jump ahead of Lumpy, but that seems like the direction he's headed.

Yup-Head'd down that bumpy road-
One other thing I will add, is to check the carb's float level.
Do this AFTER you ck'd for vacuum leaks.
LG

 

[b3uhbp]

"OP" would be "original poster" and that'd be you. The stuff Lumpy Grits suggested to check is worth looking into.

If all your rubber lines are in good shape and your steel lines are good to go, you may have an issue inside the fuel tank; crud in the tank, sock filter, etc.

Not trying to jump ahead of Lumpy, but that seems like the direction he's headed.

OP=original poster, got it.

 

[Torxhead]

It does have the fuel return line and a three hole fuel filter. I went out and checked the filter position and the return line was in the 6 o'clock position so I moved it to 12 o'clock. It did stall again today and when I removed the gas cap I did hear air but couldn't tell if it was vacuum or pressure. It seems that vapor lock is the likely cause but how do I make sure and how do I correct it? Thanks

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.