Missfiring
 

Hi Hope your all having a good Christmas :), I took the Silvia for a run on Christmas eve and it started missfiring badly at about 3000 rpm under heavy acceleration. It will run perfect all day until i press the accelerator and get the boost pressure up then i have to back off the throttle to stop the missfire.

Took a look at it today and the intercooler pipework looks ok and I swapped the AFM over too which made no difference. If I return boost pressure to standard 9 psi the missfire goes away... :confused: . If i increase the fuel rail pressure to 40 psi the missfire nearly goes away but still coughs a bit at 4000 rpm and doesn't have as much power as it did . Somethings gone wrong it was running perfectly and i'm out of ideas. Any help appreciated :)

Sounds like you need new spark plugs. Ive had the exact same problem. get some bcpr7es plugs and space them to 0.9mm. :)

pop off valve coming on boost leak ?

Thanks for replies :). My plugs are BCPR7E's gapped to 0.9mm...they have only done about 3k miles but I will change them anyway. The pop off valve is plugged and I can't see any other obvious boost leaks :confused:

All i can think off is the intercooler is leaking when it gets pressurised but it looks ok. Could the fuel pump be not supplying enough fuel ?

could be or fuel reg is stuck, to much pressure or not enough maybe

you can check for boost leaks with a gas blow lamp. have the car running turn on the gas (don't light it) blow the gas on to and around anything that may be a boost leak. the revs will pick up if the gas is sucked in through a leak

check inside the dizzy cap

Thats a good tip that is:)

Very good tip. i like that too:cool:


HT leads failing under load could be another possibility, Or your ignition timing could be out

sounds like a boost leak, really lean at idle and seriously rich on boost

Thanks for the replies :). I tryed checking for leaks with the gas lamp but that didnt show anything up. Engine runs fine on normal boost so I figure the fuel pump isn't supplying enough fuel...I did a check and it pumps about a litre pop bottle full in 30 seconds :confused: . ..I guess my next move is to fit the walbro 255 fuel pump in case mine is getting tired and starving the engine of fuel at high boost :confused:

still sounds like a boost leak to me:confused: