I went through a vapor lock type issue when I got my Jeep back on the road a few years ago. Would work fine until it got heat soaked. Never had a problem when I had it running before.
In searching for a solution this is what I found.
-First thing I though was the fuel pump. Changed fuel pump and filter at this point. Helped but still had issues.
-Second thing I found was the short rubber hoses going from the tank to the steel lines were weathered and cracked. Figured this out by trying to track down a raw fuel smell when parked. Fuel was actually leaking out through the rubber and onto the top of the tank. It would not leak when running due to the pump suction, but once shut off would slowly leak out onto the top of the tank. Just enough that it was hard to see when I looked for where the smell was coming from. Took a bit to figure this out. I figured that was also the issue to the fuel starvation since the pump was probably sucking air through the cracks. Although it made a big difference, especially at start up since it did not have to reprime the lines, I still had a vapor lock issue.
At this point I was getting pretty frustrated with this issue.
-Third thing I thought was the issue, since I did not have the issue before it was parked, was the fuel pick up sock in the tank. Took the tank out and found no major issue. Tank looked fine, sock looked fine, but I removed it completely just to make sure. Went ahead and flushed tank. No change at all
Removing the tank was a big pain and it wound up being a big zero on performance. Not happy!
-Fourth thing I though, by reading forum posts is that the fuel pumps are made in China now and everyone says they are junk. Hit and miss if you get a good one. Now I really don't believe that myself, But...……….. at this point I am grabbing at straws. I replaced the pump again with a different pump brand. Well no change in performance.
-Just a note for reference. After I removed the sock in the tank I installed a clear fuel filter before the pump to compensate for no tank sock. On my way home from a off road trip the Jeep began to fuel starve bad. Maintained road speed slowly decreased to where I could barely maintain 10 mph when I got home. I thought the pump was going out. It turned out the clear filter, which looked fine, had clogged up. I had tapped it on the driveway just to see if anything would drop out of the element and found what looked to be clear sand fall out of it. Not sure where it would come from. Though maybe from the pump, but who knows. I carried spare filters with me and changed them out about 3 times before this condition went away. Usually the issue happened just after a off road trip. I figured the rough roads sloshed the fuel enough to suspend this contaminate in the fuel and then through the lines. Just so you know the filters looked fine when inspecting them, but once tapped to knock out the particles from the element you can clearly see clear sandy deposits.
-Fifth thing I tried was putting 3/4" heater hose around the fuel lines to try and keep them cool. At this point it was vapor locking on 90+ hot days and only once it was driven on the freeway for over 10 miles (heat soaking, I thought).
-Sixth thing I tried was installing a Holley Red electric fuel pump from online recommendations to cure vapor lock (I don't recommend Holley Red), but
fuel starvation problem fixed!
-Reading a lot of post online I finally found some great information on vapor lock. Turns out there is a lot of misconceptions cure.
1. Vapor lock occurs in the lines before the pump, not behind the pump. Metal lines get hot and turns liquid fuel to vapor. Mechanical and electric pumps mounted towards the front of the vehicle can both have vapor lock issues. Electric pumps mounted towards the back of the vehicle are not as prone to vapor lock since they pressurize the fuel in the line where heat occurs. Higher line pressure cures lower boiling point issues.
2. This is the one that made sense to me. Fuel formulas today have a lower boiling point since modern cars are fuel injected. This is why even if everything is working fine in a older vehicle you may still have issues with vapor lock. Of course this does depend on how the original fuel system was set up. With the Jeep the fuel lines do run close to the exhaust manifold.
Conclusion-Yes it was a frustrating task to find out the issue. In actuality all these things or just one of these things could be the problem. The fuel formula information I read really made a lot of sense to me. I was chasing my tail, in a way, because I had no issues at all when the Jeep was on the road before. Thinking that I could achieve that reliability again with the stock type pump was what I was after. Once I realized the fuel formula difference it made sense that I had to look at this entirely in a different matter. The electric pump was the last thing I did to the fuel system outside of replacing the steel lines. It solved the problem.
Things to note If I was to do this again knowing what I know now.
-First thing I would do is check the rubber fuel lines going from the tank to the steel fuel lines.
-Second install a electric fuel pump. I found these pumps to work great
https://www.oreillyauto.com/detail/b/pr ... pump&pos=2 . I chose these pumps since they are available at O'reilly's auto parts and carry a lifetime warranty. They are sold under different brand names as well such as Carter, which I believe is the original manufacture for this style of pump. They run fuel through the motor to keep it cool and they are pretty quiet. I run two, one for each tank, and have been running one over 2 years and the other a little over a year with no issues at all. My experience with the Holley Red, which was recommended, is dismal. Started to leak out the motor in under a year and was very noisy. Not to mention expensive.
-Since these repairs and installation of electric fuel pumps I have had absolutely no fuel starvation issues at all. I used this Jeep as a daily driver to work and back 50 miles round trip as well as off road adventures. Many trips requiring high speed, long distance freeway travel. Often pulling my tear drop trailer on these trips. You can check them out here
https://www.youtube.com/channel/UCYuRx2 ... wVwZJ5oztg? . Yes it is good to have dependability back. See you on the trails, George.