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V6 one back erratic lean other steady

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Hi there!

I have this new project im working on which has me stumbled. Im running the car on the dyno and on random spots the left bank suddenly reads lean. quite erratic. I will attach a picture of the logs. This happens in the low load area's(-60 kpa,-40 kpa). When running this on the dyno i also notice that the engine does not like the lean spot. it bogs a little bit just like what you expect from a real lean spot. with this i have the idea that the reading from the wideband is not wrong and that bank suddenly actually is lean. My thoughts are on the injectors. What is your take on this? Love to hear insights.

Thanks so far!

Kind regards,


Attached Files


i would be checking a few other things also is it vvti ? what are the cams doing at that point

if you can test injectors do it and see what the results show a miss fire will also give a lean spot but most often a rapid spike not a slow to show lean area

if bothe the cams and injectors are not the issue then i would be scoping the injectors for a inj driver type issue

Regards Ross

Hi Ross,

Thanks for you reply. The spikes are really rapid. I would call them all over the board. It is an engine with vvt's, yes. I dont see anything weird there. both banks follow the demands with no weird behavior. I was planning on swapping the injectors over van left to right to see if the problem moves to the other sensor. If so i will replace the injectors. If the problem then still exist i indeed need to look into the driver. Really happy with your feedback!

Kind regards,


Hi there!

So this turned out to be a grounding problem. The friend forgot to mention that he removed al the ground wires to "clean up the engine bay". After adding the engine grounding wires back the problem was resolved.

Kind regards,


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