Lambda difference front and rear cyinders twin turbo rb26

Hello,

I am in the process of slightly enhance the tune of my M84 Motec which is managing an RB26 in speed density with a secondary load table in tps percentage trimming off the fuel not needed from the part throttle areas (with my ecu I can’t do it in the correct way so I had to reverse it).

my problem:

La1 is a 4.9 taking care of the first three cylinders

La2 is another 4.9 Bosch taking care of 4-5-6 cyl but this one is controlled by AEM AFR meter and then the signal is sent to the ECU. There’s a very little latency in this.

now that I’ve explained setup I’ll tell you my recent issues.

car was tuned with lambda trim in each lambda taking care of its cylinders short trimwise.

Problem is that the two lambda have a big delta (0,06 lambda) with the la1 reading richer. Also sometimes I got la1 error, so I’ve plugged an innovate in the exhaust and it was reading the same of the La2 (the AEM afr one).

well, decided to buy a new lambda sensor (Bosch 0 258 017 025) and air calibrate it before fitting it.

same readings.

Well, I thought it might be the gauge or wiring maybe different grounds (I did the wiring myself but always doubt everything, so swapped connectors, and the reading switched: la1 was reading leaner and la2 richer.

Damn, it’s not electrical then, it’s engine related. But looking at old tuning videos there’s always been this difference.

what do you guys would advice, also as a quick fix strategy as I have a time attack event this Sunday?

Video of reading after swapping connectors, but you can appreciate the delta

grazie

Luca

Just swapping connectors may not actually be accurate given you've done zero calibration, be it 'free air' or by Motec's inscribed calibration (if you bought the sensor from motec). That said the REAL way to address this is to add 6 EGTs and calibrate the AFRs with an individual sensor. Other than that, a gross trim on the rear 3 cylinders is at least a CYA.

I'd also double check that using the bank trim function is working as intended - pretty easy to fat finger what lambda sensor contains cyl 1 vs one that doesnt.