Problems with the rear lambda probe and a little less engine power below ~ 3000rpm (rear = cylinder 2-4-6).

3000GT twin Turbo, MK1 EU-spec

Below the ~ 3000rpm the rear lambda probe reads all the time 0 V. Assumption: the rear fuel trim does not fit (but HHH cannot read the rear fuel trim).

If you accelerate very slowly, you will notice very clearly when you get over the ~ 3000rpm.
The engine has more power, the lambda probe measures the same values ​​as the other (and with the same speed).

Normal function of the lambda probes: Below this speed, the fuel trim is adjusted, i.e. it is operated with lambda control (FBO2). Above this, the engine runs with fixed injection quantities.

The motor runs like clockwork above ~ 3000rpm and has full power. Everything is as it should be!
When idling you can hear that the control unit is trying to find a "correct" value.

  • Engine is new, forged engine.
  • Compression is OK.
  • No leakage in the suction / intake.
  • No noticeable leaks on the exhaust.
  • Engine ground (for electrics) is complete and OK.
  • Lambda probes both already exchanged twice (Denso).
  • Cables between ECU and Lambda are correct (correct positions / pins) and have continuity.
  • Injectors are OK. Cables between ECU and nozzles are correct (correct positions / pins) and have continuity.
  • ECU checked and overhauled. Installed in another 3000GT, everything is OK.
  • Tried 2 other working ECUs (3000GT and GTO).



With my other 3000GT (twin turbo, MK1 EU-spec) and cold start, the rear lambda also measures later than the front, but only within the first minute.
I don't find any difference, they are all almost identical. I've been working on these cars since 2010, also for friends.
The only difference. The car burned briefly on the engine. I had to renew some cables. But all cables have been checked several times for function and position.
I just don't find it!

HHH log on sendspace, file name is: 2020-10-11_00_18_11 xls original Steuergerät.xlsx

Greetings from Germany,
GTblue