pcmhacking.net

Maybe a simple question, I have a VX L67 running the modified RT DDJR (all be it heavily modified from the stock bin) and its with A5K V1.92 I have been able to get this far (side note who ever wrote that...your a legend...heaps of extra features now available)

Just before my engine gave up the ghost, it will still making great power up past 6300rpm and it was yet to taper out. The cam should be good up to 6800rpm but I cant raise the 'Fuel Cut RPM High' past 6375rpm. I did data log a run to 6500rpm but I beleive this may have just been an overshoot as i've got the 'soft cut' RPM Low set very close to the hard cut.

Any ideas how to achieve this?...ideally at the moment I would like at least 7000rpm available however the capacity to go out to 8400-8500rpm would be great.

The high & low fuel cut variables are to provide hysteresis - fuel is cut when engine rpm reaches the HIGH rpm and is resumed once the engine rpm drops below the LOW rpm. 6375 rpm is the limit of the internal variable in the PCM (255 * 25 = 6375).
internally the PCM uses tests whether the engine rpm is less than or equal to the fuel cut parameter, fuel cut is enabled once the set value is exceeded, so if you set it to 6375 it should not cut fuel.

personally I wouldnt be revving a v6 beyond 6k without bottom end work, they tend to fail quickly at sustained > 6000rpm

Thankyou for explaining the high/low fuel cuts better...a little different to what I am used to with other EMS systems.

My understanding is this function acts as the rev limiter, is this correct? I am a little confused by your comment of "so if you set it to 6375 it should not cut fuel" as my understanding is beyond the figure specified here, injection is cut?

Jayme; Agree entirely, theirs massive work been done to the engine as the cars now used almost exclusively for track work...makes a big difference having those extra revs and it seems to love winding out, comes alive past 5000rpm. Its in bits again but together with a engineering group over here who specialise in v6's for the VT Saloon car series and we are looking at making it reliable to 8000rpm, lots of custom work unfortunately but they have a great knowledge of these engines and what we will need to do...hence the need to get past this limiter.

Daniel.l87 wrote:My understanding is this function acts as the rev limiter, is this correct? I am a little confused by your comment of "so if you set it to 6375 it should not cut fuel" as my understanding is beyond the figure specified here, injection is cut?

You are correct, the engine RPM has to exceed the specified fuel cut RPM.
However, the PCM's internal engine RPM value (that it uses for the rev limiter function) maxes out at 6375.

run it on an 808 with $12P

Brilliant, that was going to be my next question if 12P can run it so that's excellent news.

Thanks for all your help guys, much appreciated

absolutely it can. knock detection wont be as good, thats the major catch.... you will have to put a buick coolant temp sensor, manifold tmep sensor and knock sensor on it. then buy a 2 bar map sensor, assuming you are running < 15 psi boost. everything else can just plug in / wire up in the 808 harness.

The other catch is that you also lose the ability to control a 4L60E.

and dash functions being a VX....