Hm...that's weird...maybe a stuck float??

[MDJEEPER]

First, Happy 4th everyone!!

So, I was driving back from the fireworks show tonight when the following happened...I had been driving several miles in 4th gear on one highway with no problems. I then took an interchange with a steep hill to merge onto another highway and downshifted to third gear. Started climbing the hill with no problems until I hit about 45 MPH...All of a sudden the engine started sputtering really badly like it was running out of gas. I quickly shifted it into 4th and the sputtering more or less went away and was able to finish climbing up the hill.

If that wasn't weird enough, for the next 5 minutes or so, anytime I tried to step on the gas at all...in 4th doing about 55 on flat ground...the sputtering started to return, but as long as I feathered the gas it was OK. Then after about 5 minutes, I could step on the gas again and everything was fine like it was before the interchange.

Thinking about it, I also think this may have happened to me a couple weeks ago, though the sputtering was not as severe then.

Anybody got any ideas? Could it be an intermittently stuck float, or maybe debris in the bowl??

 

[BusaDave9]

That will be easy and cheap to fix.
sounds like fuel filter

 

[MDJEEPER]

That will be easy and cheap to fix.
sounds like fuel filter

Thanks! My only concern is that I have already replaced the fuel filter about a month ago...could it be defective?

Also, the first similar incident I was thinking of actually happened about two months ago, before I replaced the filter.


How about switching to a "single barrel" fuel filter and dropping the free return line? Would that make any difference??

 

[mylittlecj5]

sounds like you have some gunk in the needle jets.

 

[BusaDave9]

Your jeep runs fine until you need a lot of gas - going uphill, higher RPMs, your float runs low on gas and the engine sputters. That's the classic symptoms of a clogged fuel filter. Now if you replaced the fuel filter it is unlikely that it is defective. You don't have the fuel lines reversed, do you? So that the fuel is going the wrong direction through the filter. That's unlikely in those filters with 3 lines.
Next I would think it's the fuel pump.
Have you made any changes to the carburetor or fuel system? This also sounds like the floats are set too low but that's something that shouldn't come out of adjustment on it's own.
Is there a kink in the fuel line to the carb?

 

[Old Dog]

Don't forget you have a sock type filter in the tank that can plugup also.
The fact that it comes and goes makes me think you might need a good carb clean. Or the fuel pump might be starting to go bad.

 

[BusaDave9]

sounds like you have some gunk in the needle jets.

You might be onto something although if that was it I would expect it to always run poorly.
Check the fuel delivery system first. If everything outside the carb is good then remove the carburetor, clean it and check the floats.

 

[MDJEEPER]

Your jeep runs fine until you need a lot of gas - going uphill, higher RPMs, your float runs low on gas and the engine sputters. That's the classic symptoms of a clogged fuel filter. Now if you replaced the fuel filter it is unlikely that it is defective. You don't have the fuel lines reversed, do you? So that the fuel is going the wrong direction through the filter. That's unlikely in those filters with 3 lines.
Next I would think it's the fuel pump.
Have you made any changes to the carburetor or fuel system? This also sounds like the floats are set too low but that's something that shouldn't come out of adjustment on it's own.
Is there a kink in the fuel line to the carb?

No, I don't think the fuel lines are reversed. The filter with the single end points toward the fuel pump and the dual outlet side is in the direction of the carb.

I only have a sketchy maintenance history for this Jeep, so it is hard to say what has happened to it. One PO supposedly had the fuel tank replaced, so I don't really know what may or may not have been done on the tank side, including the tank filter. Also, one of the POs probably ran some sort of different carb set-up since there is evidence of non-original pieces (i.e., manual choke, different manifold). However, a more recent PO put an original style "rebuilt" BBD carb on it...which is what it has right now. As far as the fuel pump goes, it looks to be pretty old (except for some teflon tape on the top threaded outlet)...and might even be original, but I'm not sure.

Basically, with the exception of the fuel filter and fuel lines that I replaced, I have no definite information about any part of the fuel delivery system!! That's why any ideas on the best place to start would be greatly appreciated!!

 

[dalefan88]

dump a can of seafoam in it and see if it helps.

 

[MDJEEPER]

Here are a couple pictures of the fuel filter and fuel pump...if they help any...

 

[BusaDave9]

Don't forget you have a sock type filter in the tank that can plugup also.
The fact that it comes and goes makes me think you might need a good carb clean. Or the fuel pump might be starting to go bad.

I like what Old Dog has to say. That in-tank filter could be the issue. Unfortunately it's a pain to drop your tank to check it out but you will want to keep it in mind after you check out the other options.
Rock Auto has a fuel pump for $20. I would do that before spending the time to remove your tank.

 

[MDJEEPER]

dump a can of seafoam in it and see if it helps.

Thanks! I haven't tried the seafoam product, but I did burn a few tanks with a Lucas Oil fuel cleaner additive awhile back, and really didn't notice any overall performance improvements. I've also been trying to burn premimum fuel.

 

[MDJEEPER]

I like what Old Dog has to say. That in-tank filter could be the issue. Unfortunately it's a pain to drop your tank to check it out but you will want to keep it in mind after you check out the other options.
Rock Auto has a fuel pump for $20. I would do that before spending the time to remove your tank.

Yeah, I think AZ, Advance Auto, and NAPA all have fuel pumps around $20. Probably not worth testing it first for that price? Just replace it??

 

[Old Dog]

I would hook up a fuel pres. gauge and see what it says before I replaced anything. Try to recreate the problem and see what kind of press. you have when it starts sputtering.

 

[MDJEEPER]

I would hook up a fuel pres. gauge and see what it says before I replaced anything. Try to recreate the problem and see what kind of press. you have when it starts sputtering.

Argh!! Why does a fuel pressure gauge kit cost more than a new fuel pump!!??

 

[ThisGuyUKnow]

Hey guys I dont mean to be a party pooper but If i am not mistaken that sounds like vapor lock to me not a clogged filter. I had the exact same problem with my waggy at speeds. when you down shift to go up hill or pick up speed you raise rpms, rpms heat engine, engine heats up the machanical pump, gas starts boiling off in the line. I eventually bypassed the mech pump with a electric inline from car quest. With the electric pump the only place the fuel gets heated is in the fuel bowl before entering the intake makes it less likely to boil off. I havent had the sputtering ever since

 

[BusaDave9]

Hey guys I dont mean to be a party pooper but If i am not mistaken that sounds like vapor lock to me not a clogged filter.

Hey you Party Pooper. We have our minds made up. Don't confuse us with facts.
Yes, you have excellent point. Vapor Lock - That makes sense.
That makes a lot of sense. The problem is now getting worse in the middle of the summer. The under-hood temps are higher.
So now we are back to the fuel pump. But now, with the lead from This Guy I Know, you need to replace your fuel pump with an electric.
Excellent idea!

.

 

[MDJEEPER]

Guys, I am not the sharpest tool...Why would there be a vapor lock if the original Jeep fuel system is more or less working...even with a mechanical fuel pump??

 

[ThisGuyUKnow]

because the sneaky little bastards at the petrol companies are putting more and more ethanol in our gas. Also gas these days is not as stable as it was when dinosaurs roamed the land and everyone had a carb. They dont have to worry about gas sitting around in fuel bowls or burning up in wet fuel intakes because now adays the majority of cars are injected so fuel goes straight from the tank to the intake port.

Thats my theory any way.

I purchased my wagoneer in 08 and drove it from Ft. Jackson, SC to Mobile, AL and then daily drove it. I also made a couple round trips to Monmouth,Il and back.Never had an issue. Then I deployed and came back this year and couldnt keep my vehicle running(same issue you are having except mine would actually completely boil off the bowl on the highway) I thought maybe it was from sitting but as far as I can tell all my systems were intact. Finally someone suggested vapor lock so like I said I went to carquest and gots me a electric pump and it has ran true ever since. As far as I can tell its the gas they are selling these days and not my rig but thats just my opinion.

 

[ThisGuyUKnow]

Guys, I am not the sharpest tool...Why would there be a vapor lock if the original Jeep fuel system is more or less working...even with a mechanical fuel pump??

Gas has a low vapor pressure(thats why it feels cold on your hand) and so does ethanol which is getting mixed into your gas in alot of places. Low vapor pressure means lower boiling point. One way to rais the boiling point is to put a substance under pressure. Your mechanical pump does at most 5 psi and modern cars run pumps that push 60-90+ PSI. So your jeep is passing fuel through your mesh screen in the tank, through your lines, through your fuel pump, through your fuel filter and into your carb. Now since fuel companies don't really have to tailor to carbed vehicles since they are going extinct little by little(Damn you cash for clunkers!) the fuel is designed to work in the higher PSI system which you do not have and is more likely to be susceptible to vapor lock.....

If your jeep is working at low rpms and when its really cool then I wouldn't suspect any clogs.

That mechanical pump is right on the block and therefore heats up with the block. The more load you put on your engine, i.e. gassing it up a steep hill or holding a high RPM the hotter your block gets. Your gas enters your fuel pump which is most likely getting hotter than the boiling point of your fuel and then begins to boil. Since your AMC 258 i6 / 4.2l doesn't get as hot as my 360 I would be willing to bet that some of your fuel is boiling off in the line and some of it is getting pushed through. So your carb isn't getting the enough fuel to the bowl to hold those high rpms. When you let your foot off the gas and let it coast you arent demanding as much fuel and your fuel bowl can fill back up until you gas it again and so on and what not.

Another solution is to install a carb spacer. But I don't think this will help you since you have an I6 and the 258s run coolant through the intake to help bring the temp down.

I hope that maybe helps you understand why a little better.....

All that is just my opinion so if some one wishes to correct me then feel free. That is just how I understand it.

Oh and if you do decide to install the fuel pump I would like to suggest that you put it across the front of the tank just above the diff instead of on the frame under the passenger seat. It looks real clean there and there are already bolts for holding the skid plate you could mount to. Also if you mount above the lip between the floor and the x-member you have some protection already for the pump, and you will be in line with the top of the tank as well as close as possible to the outlet and your pump will have less trouble priming itself and therefore have more life.

I can get you a pic of the one I installed in the CJ for the MPI kit if you want. It is a high pressure one but should be the same install procedure as any low pressure one.