Car jolts violently on boost?

[Jon R33]

Originally posted by Gradenko

Before anyone tries this and gets into trouble, WD40 and AFMs do not mix well! Use electronic contact cleaner (1st choice) or carby cleaner (2nd choice).

I remember a previous thread on this and carby cleaner was said to be a no no as it leaves a residue. Brake cleaner was recommended and I have used this on my AFM with no issues and a noticeable improvement. Always have to be gently with the AFM though, and take it off the car before cleaning, don't go spraying this stuff up your intake.

[rev210]

Any old CO or isopropyl alcohol spray will do fine.

The brake cleaner is ok as long as its non-residue.

[Blitz]

Strich9: I had the same problem and was told by several workshops its very common with these cars, the ECU retards the timing when higher boost is applied which leaves a big flat spot as was evident on my dyno sheet.

Solution: run lower boost or add an Apexi Power FC

[whatsisname]

Trust me here people! The RB25DET boost cut is a voltage commanded signal that occurs independant of a FIXED boost limit! I.E - it may be 12psi,14psi or even as low as 10psi if the ambient air temp is low enough (& therefore air density is high enough). IT IS NOT A FIXED BOOST LIMIT SET INTO THE ECU!

Both the ECU commanded timing retard & boost cut limit are based on the voltage signal from the AFM (I imagine this would be close to 5.0V) These two voltage based limits don't appear to occur @ the same time from my experiences.

As I explained in my post above the sudden rush of intake air when you go to WOT will very easily cause the voltage from the AFM to exceed these voltage limits. The more air into your engine via improved breathing (i.e intake, FMIC, more boost etc etc..) the more these cuts will occur.

As Gradenko mentioned a quick fix for this is an FCD, not a great device but it works. Personally I'd steer well clear of this method.

The only 100% fool proof way around it is to bite the bullet & get some form of aftermarket ECU. Or run less boost

Having mentioned all this I have seen some GTS25t's (ALL 95 models too!) that seem to be uneffected but either of the stock ECU's boost or timing AFM voltage limits.

I was using a Unichip (that performed the task perfectly - up to a point) & this gave me a 13-14psi boost cut free power curve that was spot on till redline. It wasn't until I fitted & set-up an adjustable exhaust cam gear that the dreaded timing retard started to rear its ugly head again, I say 'again' because my car displayed these cuts as soon as I began to mod. With the cam gear I picked up 10rwkw & 3 HUGE (one almost 30rwkw) power drops (flatspots when on the road) This could literally be seen as the ECU pulled huge amounts of timing out each time this happened, & the dyno curve was like a mountain range! I didn't however have any boost cut issues occuring? Maybe because I'd removed the factory boost solenoid long ago?

Fast foward to today & I now get around this issue by having removed my AFM completely I run via MAP vs throttle position - & I love it! Hard to go past the well proven PFC, but if you like to do things a bit different & get the right people to assist in the process PFC alternatives can be very good.