So long story short i bought this 1990 yj that had the 4.2 but a previous owner put the top end of a post 95 4.0 on it. I don't know the exact year of the 4.0 but it has the returnless fuel rail. i've been fighting a misfire with it. it. it only does it when its hot outside or when you try to accelerate and it gets around 2k RPM. I've change the temp senor near the thermostat and checked the fuel pressure and it is in spec for the returnless system. i have replaced the injectors aswell. whoever did the swap put a inline fuel pump on it and recently the fuel gauge has stopped working so i was going to bypass the inline and just put a tj drop in pump in it but i'm unaware if that will for in the yj tank or if the tj pump will even work the yj gauge. As for the miss I'm down to maybe putting a new distributor in it but I don't know if that would cause the misfire because it only does it when its warm. If anyone has any ideas it would be really appriciated.
