Breaking Down, Dropping Cylinder

[Headsex]

Grr where's me dramatic hamster link.....

When boost is tuned in open loop, a cold night WILL make boost higher.

More dense air = more power = more exhaust gas = more boost

The pcm does not auto adjust boost in open loop, it only feeds acertain duty cycle per rpm, With no feedback to adjust dutycycle

Closed loop boost will adjust, but will still vary if things aint right.. Ie using my car as a example, during the day, my car makes approx 17.5psi using 100% duty cycle, and during the night when its colder, it makes 18.5psi with 85% duty.

Pcm has desired boost of 18.5psi, but runs out of duty trying to get it during the day, but it gets there at night.

Having the wastegate port done, generally makes a actuator "psi rating" smaller because there is more presure on a larger port pushing against the actuator spring (same presure, just more wastegate flap area with presure applied to it).

Ie, a 12psi actuator and 0.1 duty, I've seen as low as 9psi boost.

Ideally in my case a stronger actuator will help.... or I could punch my cat, which I'm not a fan of.

It could be quite possible that your car is overboosting. Get a boost guage onto it and see the boost difference at night compared to day.

Danny.

[wal89]

Yes, very frustrating. I did some more testing tonight. Throttle about 50%, entering highway so could hear the zorst off the armco. Got to about 4500 in 2nd and a slight pop then it was breaking down but didnt loose a cylinder. Again, not as bad as before when the coils where stuffed. About an hour ago I took a mate who owns an SS for a drive. Not gving it much more than about 60% throttle and pop, pop, breakdown lossed a cylinder again. As before, a few seconds later it came back and all is good.

I've tried both V-groove copper and irridiums pre-gapped to .8.

I'm not running that much boost. It made the power at 16.88 psi but that's as much boost as it would make. I haven't got a boost gauge so I'm not sure how much extra boost it is making on a cold night. It is definitely making more boost at night so I don't know if that may be another factor.

My car was breaking spark running 15psi and a lot less power with .8 plugs regapped them too .70-.65 and all is good. Not saying this is your problem but its quick and easy thing to try.