Boost/fuel Cut @ 6000rpm - Rb20det

[rx-line]

Hey folks,

got the rb20 back in my rx-7 and sourced a stock ecu to replace my mines tuned ecu. Seems to pull as hard, runs about 15-16 afr's running down the road and quickly changes to 10-11 when throttle is opened. If you back off it richens down to 8's and goes to the 14.5-16 again.

Which I can live with, car pulls very hard. and creeps around 14 psi high in the rev range. However the car feels like it is completely shutting off at about 6000RPM in 3rd gear and has done this consistently since i have swaped the ecu.

I do not have the transmission wiring wired as I never got the lower harness. As well my rx7 dash is run by the speedo drive and does output a signal to the ecu.

I am thinking it is one of three things.

AFM air flow cut

knock sensor

speed sensor.

Anyone know of a bypass or way to check these? if not I will have to put the mines ecu back in for drag weekend.

Rx,

[Hadouken]

stock ecu

/thread

[GTSBoy]

The most likely suspect is TP cut, which is what you are calling AFM air flow cut. There is no way to bypass this without Nistuning the ECU, so you can raise the setting for it in there.

Knock sensor will not do a "cut". It will switch you first to the knock maps then it will go even further and cut ignition timing right back, but it will not actually "cut" the engine.

Speed sensor will do it at 180 km/h on a stock ECU. Assuming that you have the RB20 gearbox sender and drive cable and RB20 compatible speedo head from a Nissan installed, and that the wiring from that speedo head is connected to the ECU, then you could be having this cause a cut. But it won't do it at 6000rpm....it will do it at ~180km/h (depending on diff gearing). And I don't think it likely that you have every link in the chain I described above in a transplant to an RX7.

[rx-line]

TP cut as in Throttle position???

Will the speed sensor not wired have the ecu reading different signals? or just one?

As I stated the mines ecu had never gave me this problem. And as far as I know they heighten the rev limit and delete speed cut, anything else? That's why I think it is speedo related.

I have no power steering, no clutch fan, no ac, rb25 turbo, fmic, ffp. fuel pump, 3" exhaust, etc. Pulls hard and was beating an overboosted tuned mr2 last night until boost cut at around 14psi.

[GTSBoy]

TP means Theoretical Pulse. It is the fundamental load index for all maps in a Nissan ECU. It is driven by AFM signal, but it is not just the AFM signal.

The Mines ECU will have had the TP load limit increased along with those other changes.

It will be the TP limit, no alternative.

[rx-line]

Okay, Thanks man. Explains a lot!

I've ran that mines ecu for a while and seems to work fairly good, I like the stock with the lower rev limit but I may switch back. Are they as bad as everyone says they are?

I have three ecu's; a mines tuned, stock and a chipped one for 555cc injectors and z32 maf which i do not have.

Thinking of nistune but cant shell the cash now.

Can you tell me anything from my Afr's above? Seems they should not be that lean cruising or rich as i back off the throttle.

Rx,

[KiwiRS4T]

Mines ECUs are not inherently "bad". The problem is that they have been chipped to suit a particular set-up and cannot be tuned to suit your set-up. Some people say "my car runs great on my Mines ECU" when really all they know is that it starts and runs. If by some chance it does suit your car (and you can only really be sure of that by sticking it on a dyno to make sure AFRs and timing are correct) then you can run it.

[iruvyouskyrine]

Selling the stock ecu and the chipped ecu will almost get you enough money for a nistune. Which will be 100x better than either of those are.

[rx-line]

Those are my thoughts skyrine, Thinking I'll post them up on ebay unless a member wants one

Timing is the unknown for me, my wideband shows it running rich in boost around 10's with 30psi fuel pressure. keeping the throttle in spot reads 16's with it though.

RX

[STATUS]

needs speed input, its hitting tp cut, speed input 0.

[rx-line]

How would I wire the speed input? Get a wheel sensor and resistors or try a retro fit to the skyline dash.

[GTSBoy]

What STATUS has said is true. There is a lower TP cut point for zero speed conditions, which is why the old Skyline trick of cutting the speed signal wire to beat the 180km/h speed cut problem was not a good solution. You might still hit a normal TP cut even after restoring a speed signal to the ECU anyway. This is because running even the stock turbo at 14 psi with enough other mods (exhaust, cooler, etc) can get you to that point.

Search for posts by me on the topic of the voltages and signal types involved in the speed signal. The speed signal sent from the Skyline dash to the ECU is a square wave 0-5v signal. If you can fake that then you can keep the ECU happy. But I still reckon that Nistune is required.