I just got my car back from RMCR yesterday after they swapped my 42#'s for the stock 24#'s injectors and an FMU. I had to remove the 42's because i was getting a terrible bog in the midrange( due to the difficulty in tuning a 93"s computer), and was registering 10.5:1 af ratio and leaning out to 12:1 at 5k. With the fmu on and tuning changes, everything was running great (except for a random pop at redline in 2nd After a while of normal driving, I park the car for a couple hours, and when I come back, car would not start for about 20 minutes. I was getting enough juice, but wouldnt light for the longest time. After letting it sit for 20 more minutes, car started w/o a problem. Then on the highway at about 1/4 throttle in 5th gear at about 2k, i noticed that the car would hesitate (kind of like a bogging situation) for no reason, then go away. Pulled a couple plugs, and they are burning just fine. I also turned the engine over with a plug boot off and a screw driver and saw an arc. After that, car started right up and seems to be driving just fine. Any idea what could have kept the car from starting up right away then bogging (or missing) at low rpm for no reason? Also, could that small sputter at 5k in only 2nd gear be detonation even though it didnt sound like it?

 

So after a few minutes of checking, I found that one of the header bolts was loose enough to remove by hand, and the spark plug on the same cyl was exaclty the same. After start up, the car ran for a minute, then died when I tried to drive it...Does anyone have an idea wtf is going on with this

 

Since you already found some loose sh*t, double check everything. Look under the hood in the dark with the motor running and see if you have any arcing around the spark plugs. What fuel pump(s) are your running? The FMU is a high pressure system that requires a pump to keep up under pressure. I'd put a fuel pressure gauge on it and see what it does under load. Next time the car starts hard, try holding the pedal to the floor. This tells the computer to back off fuel when starting to solve a flooded condition.

 

Ive got a walbro 255 lph intank pump...ive also got an auto meter fuel pressure guage. At idle, it hold at about 45 psi, and increases with throttle of course. I put a screwdriver in one of the plug boots and turned it over and saw an arc (did this last night) and when I tried it again today...nothing. I checked the opti and everything is connected. Im thinking it may be the pcm, because the shop has been removing and replacing the chip due to tuning errors.