Well maintained 01 S40 with just intake and MBC @12PSI in otherwise good health.

Recent fuel filter

My car will hesitate and misfire on different cylinders at hardish and full throttle with the dreaded flashing CEL. Sometimes it just flashes and has a pending code, then if not cleared after a few WOTs it will go steady and have a real code. I have tried swapping coils and wires, even using a brand new coil. I have replaced all the plugs too. Then I thought it was following the injector when I swapped those around, so I got another complete injector/rail/FPR setup from another boneyard. It seemed to help a little but its still there. Could it be the fuel pressure regulator? I don't have a gas odor or hard starts like I did when the FPR was bad when I first got the car. It would explain starving injectors right? Or could my pump be bad? So frustrating!

I'm aware of the damage misfires can cause, so I really hate having to force them to test possible solutions.

Otherwise the car runs great and at most throttle positions theres no issue. I don't get it! Any help would be greatly appreciated!

 

I take it the addition of a MBC and the misfire did not occur at the same time? Do you know the duty cycle of the injectors at 12psi? Going lean at this boost level could be very bad. Do you have a wide band O2?

Normally a misfire means you need at least two new coils. On my 2001 only two brand new coils solved my misfire. The old coils ohmmed fine which threw me off for a week until I read where the misfire comes from the coil (or spark plug wire) arcing to the head INSIDE the spark plug tube. You cannot see it with the coil and spark plug wire in place. Assuming you have gapped the plugs correctly I'd bet coils and wires are needed. I'd also bet running 12psi puts tremendous strain on the stock ignition system (bet it's fun though).

 

Actually I've had the slight hesitation for some time before the mbc. It did however exacerbate the problem lol due in part, I'm sure, to the fact that I probably accelerate a bit harder sometimes now. Someone on another forum said to not trust the pre-gap on the plugs and to pull and re-gap them. If that doesn't help I guess I'm going back to coils and wires. Although they look so good! I just don't understand how it could be them... Will report back tomorrow.

 

I once helped a girl with a poor running 740 engine where everything looked good. We replaced everything but the wires because they were the most expensive item and the resistance was fine. While still checking out the engine I pulled a plug wire off the suspect cylinder and I could see the blue spark jump from the hard plastic to the head. It did not even try to jump to the plug, it went directly to the head. Must of been a hairline crack in the plastic. You could not see it with the dust boot in place. New wires fixed it right up. Can you see any burn marks in the spark plug tubes?

 

Check the connectors going into the coils.Upon a coil replacement I did notice that the connectors are actually lose.I had to remove the plastic parts from the actual copper slip-on ends to gain a proper connection to feed the power to the coils.