[davey gravey]

Anybody have an idea why my N54 suddenly developed a misfire on cylinder is 1, 2 and three. Car has been running great for years and all of a sudden this happened while I was driving. I changed the plugs and the coils but no difference. it had a high-pressure fuel pump replaced once, and a low pressure fuel pump replaced once. Car has 112 K & JB4. I put a stp fuel cleaner in tank 25 miles before this happened. Maybe Oxy sensors on that bank?

[sami1064]

Check for oil leaks that might’ve fell in spark plug wells

[frozenfire]

if there was oil in your spark plug well when you were doing the spark plug replacements then it is likely your valve cover gasket is shot and needs replacement. It's a cheap fix but a pain in the ass to do.

[lookalikehuuh]

It really quite difficult to diagnose without having some reading from a computer hooked up to the car.

The STP in the fuel tank might give us a clue though. It likely loosened up some trash in the tank and clogged 1 of your injectors. As a general rule of thumb I would say to never put any of those "treatment" in your gas tank. I would use only good quality fuels like shell or chevron and forget about those additives trash that just ruin pumps and everything else.

[BrutalN54]

Originally Posted by davey gravey

Anybody have an idea why my N54 suddenly developed a misfire on cylinder is 1, 2 and three. Car has been running great for years and all of a sudden this happened while I was driving. I changed the plugs and the coils but no difference. it had a high-pressure fuel pump replaced once, and a low pressure fuel pump replaced once. Car has 112 K & JB4. I put a stp fuel cleaner in tank 25 miles before this happened. Maybe Oxy sensors on that bank?

Ur bank 1 mosfets took a dump.. fairly common issue.. either buy new mosfets and solder them into DME or upgrade to MSD81

[hooppoor]

Originally Posted by BrutalN54

Ur bank 1 mosfets took a dump.. fairly common issue.. either buy new mosfets and solder them into DME or upgrade to MSD81

MSD8 works very stable.

[aphael]

upstream bank 1 o2 sensor. Same thing happened to my car and replacing it fixed my issues. Check your fuel trims to double check, if they are all over the place its definitely the o2