car stopped pulling in 4th

[wolfie1]

my 94 fd is pretty much standard apart from a back box and an apexi filter kit, i was pulling hard through 1st, 2nd and 3rd changed into 4th pulled a bit then it deceided it didnt like that and it felt like somebody had just pushed the brakes on, i did just change the plugs recently and all 4 were 9s and i noticed the workshop manual is 2 9s and 2 7s. is this most likely an overboost problem over the filters or could it be something else, would i be best off taking them off the car until i get it remaped? thanks

[wolfie1]

ok update on this after looking over the car i have found a little pipe off leading from the vaccum tank and now put the right plugs in and i reckons thats it good to go