Jeep starts and idles for a minute, then sputters out

[Jackson LeBlanc]

I start my jeep, it turns over no problem, its a 6 cylinder 4.2 L from 87. once it starts, it runs fine for about a minute, then slowly sputters out, and when i press on the gas to keep it alive, it spits blackish grey smoke, and then i let it die. my dad and i think it is a vacuum leak, which is preventing air from getting into the engine block, and making the air fuel mixture too rich on fuel. I tried looking into the carburetor to see how the screws were adjusted, and they were adjusted just fine. I will note my dad when rebuilding the engine took out the idler air control valve, which may be causing this problem, but it ran fine without one for 2 years. I will also note that a tube connecting the air filter to the valve cover is loose, and there is a valve that is missing a cover, and has depressurized. there are 5 other of these little valves that all have covers on them and the one that is missing hasnt had one on there for a while.

 

[Snugsblue]

I'm interested in answers on this one.

 

[Sorin CNC]

I am not sure if this is what your issue might be but I had something similar happen to my 2.5 liter 4 banger. Come to find out that it was the fuel pump getting hot and providing only interrupting fuel.. it was a pain to replace it because I had to drop the fuel thank to have access to it. When I had it out, I cut an access hole and made a cover so I can replace it next time without dropping the thank.

 

[Jackson LeBlanc]

I am not sure if this is what your issue might be but I had something similar happen to my 2.5 liter 4 banger. Come to find out that it was the fuel pump getting hot and providing only interrupting fuel.. it was a pain to replace it because I had to drop the fuel thank to have access to it. When I had it out, I cut an access hole and made a cover so I can replace it next time without dropping the thank.

I popped the air filter off the carb (stock Carter BBD), and held the throttle open, and fuel squirted into the carb like normal, and mixed with air, but instead of being sucked into the vacuum lines, the mist came up. So it basically confirmed my suspicion of a vacuum leak which will be a pain to find. will keep y'all updated on it. I don't think its the fuel pumps because the jeep is running too rich rather than lean, and i just had freezeplugs and coolant lines changed.

 

[Sorin CNC]

I popped the air filter off the carb (stock Carter BBD), and held the throttle open, and fuel squirted into the carb like normal, and mixed with air, but instead of being sucked into the vacuum lines, the mist came up. So it basically confirmed my suspicion of a vacuum leak which will be a pain to find. will keep y'all updated on it. I don't think its the fuel pumps because the jeep is running too rich rather than lean, and i just had freezeplugs and coolant lines changed.

Many years ago we used to spray starting fluid or carburetor spray over the suspected hoses or the intake manifold and you could notice a change on how the engine ran. That was the culprit.. Good luck to you and please let us know what you find out. It might help someone else.. Have a great day!

 

[TimberTim]

Harbor Freight sells a $16.00 Vacuum/Fuel pump Tester. It's well worth the price considering it will take the guess work out of the question for the rest of your life! Check your exhaust system for proper torq/cracks/leaks or warps up stream of the Oxygen Sensor. If air is entering the system between the combustion chamber and O2 Sensor the computer will see it as a Lean condition and increase the fuel demand ( creating a Rich condition).

 

[Jackson LeBlanc]

Harbor Freight sells a $16.00 Vacuum/Fuel pump Tester. It's well worth the price considering it will take the guess work out of the question for the rest of your life! Check your exhaust system for proper torq/cracks/leaks or warps up stream of the Oxygen Sensor. If air is entering the system between the combustion chamber and O2 Sensor the computer will see it as a Lean condition and increase the fuel demand ( creating a Rich condition).

This is an interesting thought, I will definitely look into this, and I have a vacuum gauge I'm going to use as well as a smoker to see where the smoke comes out of a vacuum line.

 

[TimberTim]

does your fuel gauge on your dash work ? Your Fuel Gauge is a good indicator of the condition of your In-Tank Submersible Electric Fuel Pump Ground ! Turn your Ignition key to the On position with out starting the Engine. If the Fuel Gauge moves to the full position and stays there and reads Full all the time (even with an Empty tank) it indicates your Fuel pump Ground needs some attention, I'm not experienced enough to tell you how to correctly make this repair nor was I ambitious enough to tear the whole jeep apart looking for the problem so I simply ran a jumper wire from the ground wire by the fuel tank and grounded it to the body. I used the Black w/ Yellow stripe wire . it is located in and above the 3 wire connector (towards the engine) that plugs the fuel tank to the wire loom. The positive wire to the pump doesn't energize until you turn the key to start. Hope this helps you or someone else.

 

[Jackson LeBlanc]

does your fuel gauge on your dash work ? Your Fuel Gauge is a good indicator of the condition of your In-Tank Submersible Electric Fuel Pump Ground ! Turn your Ignition key to the On position with out starting the Engine. If the Fuel Gauge moves to the full position and stays there and reads Full all the time (even with an Empty tank) it indicates your Fuel pump Ground needs some attention, I'm not experienced enough to tell you how to correctly make this repair nor was I ambitious enough to tear the whole jeep apart looking for the problem so I simply ran a jumper wire from the ground wire by the fuel tank and grounded it to the body. I used the Black w/ Yellow stripe wire . it is located in and above the 3 wire connector (towards the engine) that plugs the fuel tank to the wire loom. The positive wire to the pump doesn't energize until you turn the key to start. Hope this helps you or someone else.

this is one of the things on the dashboard my dad has replaced. so it functions properly. the last two things on our bucket list for that is the oil pressure gauge (just previously changed oil so thats not the problem), and the clock, of course.

 

[Jackson LeBlanc]

Many years ago we used to spray starting fluid or carburetor spray over the suspected hoses or the intake manifold and you could notice a change on how the engine ran. That was the culprit.. Good luck to you and please let us know what you find out. It might help someone else.. Have a great day!

tried this today, completely solved the probem. Cleaned the venturi, fired it up with no air filter to try and blow stuff out the floats, and it started running like a charm. looked like it ran rich at first but it was blowing gunk out of the exhaust after sitting for a few weeks. Works perfect now.

 

[TimberTim]

good job ! thanks for following thru to the end and posting the final remedy

 

[Jackson LeBlanc]

I’d like to reopen this thread. Jeep ran fine for about 5 days and this morning I cranked it and the issue arose again except this time I started noticing the carburetor flooded when I tried to keep it alive. Very frustrated because I thought I fixed the problem and it seems like it’s time to invest in a rebuild kit.

 

[Sorin CNC]

Oh no!!! Sorry to hear that. Perhaos not a bad idea to find a shop that does carburetor rebuilding. It will be like new when you get it back and hopefully it will fix your problem. Pkease jeep us posted.

 

[Jackson LeBlanc]

Oh no!!! Sorry to hear that. Perhaos not a bad idea to find a shop that does carburetor rebuilding. It will be like new when you get it back and hopefully it will fix your problem. Pkease jeep us posted.

Doing everything in my power to try and avoid having to rebuild carburetor. Me and my dad are using a vacuum gauge tomorrow to determine if there may be a vacuum leak like we have suspected and it would be nice if there is because it’s easy and cheap to fix just hard to find. If there isn’t a vacuum leak we’ll just buy a carb kit online and rebuild it. Will keep y’all posted! This has been a frustrating but fun journey

 

[Flyer58]

I don't know anything about this carb. Does it have an automatic choke and it it fully opening as the engine warms up?

 

[Jackson LeBlanc]

I don't know anything about this carb. Does it have an automatic choke and it it fully opening as the engine warms up?

Yes. From what I’ve been told it’s similar to the stock Carter carb except it doesn’t have a servomotor on it like the cj7 carbs (I previously thought it was stock until I realized the servomotor wasn’t there so I questioned my dad.)

 

[Jackson LeBlanc]

I need someone to confirm my suspicion. I think I have a bad PCV valve, which is causing my air/fuel mixture to get thrown off. I think it’s also causing my vacuum leak because the O-ring that holds the PCV valve in isnt holding it tight enough and I can pull the valve off with little to no difficulty. And when I ran the jeep with no PCV valve it has no interest in starting which just further confirmed what I was thinking

 

[TimberTim]

shake the pvc valve , if it rattles it's good. if not soak it cleaner

 

[Jackson LeBlanc]

Final update- sorry I haven’t been very vocal on here, I’ve been doing a lot of research and after a lot of frustration I’ve found the issue and fixed it. Part of the reason it wasn’t pulling vacuum was because the idle mixture screws were adjusted all wonky and that’s why the engine ran super rich. The other reason it wasn’t pulling vacuum was because the EGR valve was stuck open which created a huge vacuum leak. There was also an exhaust manifold leak. Once I adjusted the carb and addressed all the other problems, it worked again. Only God knows how it managed to work the first time before going bad again.

 

[TimberTim]

Harbor Freight sells a $16.00 Vacuum/Fuel pump Tester. It's well worth the price considering it will take the guess work out of the question for the rest of your life! Check your exhaust system for proper torq/cracks/leaks or warps up stream of the Oxygen Sensor. If air is entering the system between the combustion chamber and O2 Sensor the computer will see it as a Lean condition and increase the fuel demand ( creating a Rich condition).

Taa- Daa !!!!!