Stock 1 UZFE Rev Limiter

[SC400TT]

Gang, I have been pondering this just for the last day now, and have not found anyone that is sure of the answer, so I want to post up here to see if anyone can provide the correct information.

I will be keeping the stock ECU on my SC400 Project Car even after I install the built engine which I am just now picking up from the machine shop. I will be adding a piggy back with an external Delco MAP to the system. So, I will have 2 Walbro 255 pumps, and 2 separate fuel systems in the car. The stock one stays in place, and the secondary includes 8 440 cc injectors run by the piggy nack that will connect to the stock ECU, and will adjust fuel on the secondary fuel system, and will change timing as necessary.

MY question is does anybody know what the Stock ECU is doing when we hit the Rev limiter past 6500 rpm? Is it an ignition cut, a fuel cut, a timing change, or a combination of the above? My reason for asking is this:

I am adding the BoostLogic built A340 4 speed trans and Precision trany to the equation, and I have no experience on how the car will shift until I get it on the road. They did adjust line pressures and make several modifications to the stock valve body so that the tranny will shift much quicker, but it will still be civil during normal driving. I am sure there will still be a delay between gears, although shorter. If I shift the gears manually, and miss the sift point and cause the rpm to hit the rev limiter, if this is a fuel cut, will this not caus ea temporary lean condition? If I am in high boost when this occurs, I am concerned about the danger to my engine...

I can adjust the piggy back to change the pulse cycle of the secondary injectors in the map and adjust the timing when past 6500 rpm as a safety factor, if needed, or I can tune in a fuel cut as well. But, I will need to know what the stock ECU is doing...

Thanks,

Ryan

 

[rivmasta]

My understanding is that generally a softcut is a fuel cut to certain cylinders, hard cut is a ignition cut.

IE, with the EMS we use, the soft cut cut cuts fuel every alternate cycle to 1&4 (batched) injectors and every other to 2&3. We had that kicking in (on a 4age) at 7500, hard cut (ignition) at 8k.

That engine spent a looooong time crackling and popping, but never leaned out far enough to melt a piston or damage the motor.

Not sure if stock ECU is the same, but would guess it would be similar, though the redline is lower.

 

[KDog]

Leaving the stock system controlling fuel is asking for big trouble. Not to mention a nightmare to tune for. The stock system stays in closed loop for most of its operation, you will not be able to tune the piggy back sufficiently to take all condition into account.