Anyone experienced this? Combo is a 370 w/a s475. I bumped my boost from ~16psi to ~20psi last night at the track and my data log shows huge swings from super lean back to normal, to super lean back to normal when I was making full boost. Didn't do this on the passes before turning up the boost and didn't notice anything weird on the drive home from the wideband. This is typically an indication of a miss-fire but I cannot figure out why it is misfiring.

Car should have picked up MPH, but did not, it did go faster but it was in the 60', the MPH was right around where it is 16psi. I didn't pick up any knock so I do not believe it was actually lean.

I am running BR7EF's gapped at .028". Stock coils and wires.

One oddity, not sure it is of any consequence, my MSD 2 step was set at 5500rpm but I was only able to get up to ~4600 on the trans brake, so we moved it down to 4300 thinking I was hitting the converter before the 2 step. Next time out the motor was far more responsive on the tbrake but flew right past 4300 up to past 5k and made boost like crazy. It didn't experience the spark blow out on this pass (was only at 16psi) but the next pass I rechecked the 2 step (thinking it might have been stuck between settings on the potientiometer) but it did the same thing when I got on the tbrake, rev'd much more freely straight up to over 5k rpm (and made lots of boost).


Any ideas on where to start with this thing? I guess I should make sure the 2 step is getting a proper activation from the tbrake still (not sure why it would have a problem out of nowhere, but I'll check), throw some new plugs in it gapped a little tighter, check the resistance on the plug wires, remove the 2 step from the mix, etc. Any way to check the coils? Anything I am missing here?

 

Kinda sounds like blow out. I tuned a car that any time the boost was turned up it ran like crap. It was noticable miss though. There was no question. Changed the coil packs and it went away. Turned out thoe 2 coils were only getting a half charge so under light driving or light boost it was fine. Heavy load and it missed bad. Only way I know of to really check coils is to scope them. Before you go to all that though I would gap the plugs down (using a good quality ffeeler guage) to around 24-26.

 

Ever seen an MSD 2 step crap out like this? Unit is less then 6 months old.

 

I have not personally....but hoping their products have not gone to crap, about to put one on. My car, lol.

 

here is the reading i got, the bottom green line is the wideband, bottom red is the commanded afr, top red is rpm. this is shot basically shows me on the tbrake, launch, then shift into high gear and through the traps. if you notice, the afr starts swinging widly after i click into second.

 

try another set of wiers

 

my buddy thinks it is a failing bosch sensor.

 

Can you feel it when it happens? From the looks of it, that would be pretty noticable.

 

nope, didn't feel anything different, car should have been a little quicker (at least mph wise), but went 5.92 on that pass.

 

guessing if it was missing hard you would feel it.

 

I had to drop plug gap from .026 at 16psi to .018 at 23psi to correct issues with my car shutting down.

 

The cars I have experienced this with though it was very noticeable feeling. You could feel the car bucking and surging not just losing a mph or two. Maybe it was due to those cars having coil issues and not just plug gap issues.

 

Just try tightening the gap, it wont hurt anything.

BTW Dville this is Fbodyjunkie how is the car coming along?

 

new plugs and tighten them up, seen it before

 

Spark blow out it is. You have the wrong plug and gap for your power level.

 

thought you had forgot about me. if you have some time i'd love to shoot you a call and bounce some ideas/issues off you. car went 5.92 on sunday, should have gone faster though.

 

What was the 60 ft on the 5.92 pass.

 

1.37 with a little wheelie

 

not bad. congrats on getting the 60ft under control. any vids?

 

nope, my buddy who was out there is pretty low tech! i really want to make this 275 race at nsd on sat but don't want to drive all the way out there. the dfwmustangs cruise is the following saturday at kdale and i'll def. be there.