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Hi Moses, So I have the 4.0L head on the 258 block, with the Mopar/Hesco MPI kit installed. I love it, except for the vapor lock problem, and that the gas mileage still seems poor (14.5mpg) MILEAGE AND HEAT I experience vapor lock after long drives on hot days and/or going up mountains. There is a pressure and return line running up the driver side, where the exhaust is also located. External fuel pump mount near the exhaust pipe on drivers side of the rear cross member, filter also on cross member in center of vehicle. I tried wrapping the exhaust from manifold, over cat conv and muffler (and put a heat shield fabric tube over the fuel lines from firewall to injector rail). This did not fix the problem at all. However, the gas mileage jumped up to 16-17mpg! Why do you think this happened? I am guessing that since the air intake sits right about the exhaust, cooler air into the engine is more efficient since it can expand more in combustion than hot air? I also heard something about "Scavenging" with hotter (insulated) exhaust, but I don't understand that.. Why do you think the mileage got better? Any tradeoffs to keeping it this way (exhaust wrapped)? VAPOR LOCK Then with the vapor lock, there are a few ways to go, and I'm not sure which to try: (1) Move fuel lines to passenger side, route under radiator and back up to injector rail. However, I've read some people have this set-up and still experience vapor lock. Some speculate because of the radiator, but I'm guessing it's the low pressure line before the pump. (2) Switch to using a regulator near tank, instead of in the fuel rail. Hesco sells parts for this. The advantage is there will be no return line. I heard that gas vaporizes much easier at low pressures, but I'm really not sure if vaporized / aerated fuel returning to the tank is the problem? This could be combined with (1) above to make things easier and cleaner. http://www.hesco.us/products/7902/40l-conversion-parts/313496/hes409606-1-regulator-kit#.WbbvWmeWzIV (3a) Novak sells an in-tank pump. I like this idea because currently fuel travels across the rear xmember from passenger to driver side at low pressure (the external pump is on the drivers side). I am suspicious that this low pressure run before the pump is where the vapor lock might be happening. The in-tank pump would eliminate this. (3b) I believe I'd also still have the option of locating the regulator in the rear and running a single line up to the engine (and could also be on the passenger side?) https://www.novak-adapt.com/catalog/fuel-system/cj-fuel-module The drawback I'm concerned about is that I do a lot of outdoor adventure road trips and remote backcountry travel. I carry a spare external fuel pump. If the in-tank pump fails, wouldn't this be much harder to replace on the trial? Do you think a spare external pump could still be installed inline if the in-tank pump failed to get me home? Or would the failed in-tnnk pump prevent fuel from flowing? So, which option do you think makes the most sense? (1), (1) & (2) Combined? or (3a) or (3b) Thanks!