1998 Classic XJ with 4.0 - Back story - Installed a new pump in late 2019. Everything was fine until the Fall of last year when it would not start on the first crank. It actually required a long cranking cycle to start. I ended up cycling the key On/Off several times to prime the line before cranking and that worked better than just letting it crank until it caught. This problem was due to either a failed pump check valve or a faulty injector. I suppose I could have attached an air source to the rail and listened for gurgling in the tank goose neck, or pulled the rail up and checked each of the installed injectors for blow-by. Instead, and just for grins I decided to retrofit the fuel line with a check valve. I was pretty sure it was a failed pump check valve because the engine ran smoothly without any tell-tale shuddering (hesitation).

The Fix - I bought a brass check valve and compression fittings needed to adapt it to my fuel line. I bought them from McMaster-Carr. The check valve is Item #7768K53 and the compression fittings are Item #5220K69 (2-each). I assembled the compression fittings to the valve, measured the distance between where the fuel line raw ends seat in them and cut that length out of the fuel line. I chose to install the valve under the left rocker about 6 inches aft of where the hard line meets the flex line that follows the contour of the wheel house up to the rail. I used a small tubing cutter. The fuel line can be pulled away enough at that location to easily rotate the cutter around the line (5/16" line). After removing the section of line I slid the fitting compression nuts onto the raw ends, seated the tube ends into the fittings and tightened everything up. Due to zero fuel in the line I cycled the key On/Off about 5 times to prime the line and started the engine. I checked for leaks where I installed the check valve with the engine running. None noted, I shut the engine off and returned 1/2 hour later. It fired up first crank telling me it was indeed the check valve and not a faulty injector. I repeated the start-up check several times over the balance of the day and it started each time on the first crank.

The brass check valve was chosen because the internal piston is brass and seats onto gasoline compatible material. The cheapo check valves I researched from the auto stores all have sad stories from customers claiming that they did not last long due to internal material deterioration.

https://www.mcmaster.com/7768K53/