0.18 hertz lambda oscillations

[flipski]

I am trying to stabilize my fuel in some cells and cannot figure out some oscillations in AFR values that happens at a very specific frequency. Every 5.5s , it looks like my AFR gets rich and drop by 1point. The only input that fluctuate is the MAP , going from 4.2 to 4.4 for a very short instant and thus changing the Inj PW actual time by a few microseconds but I doubt this would create such dip in the AFR readings.

 

Nobody has any idea where that could come from ? I don't have a fuel pressure gauge and didn't want to invest in 1 , just yet ! all fuel corrections are turned off.

I've attached my logs and tune file.

Thank you.

1500rpm.llg

350z.pclr

[Adamw]

I agree, PW doesnt change so it is unlikely ecu related.  Could be fuel pressure or the lambda measurement.  I see your lambda device is an innovate, is it one with a gauge/display or is it a LC1/2 with no display?  My suspicion is due to innovate not having an analog ground it is quite possibly something else in the car turning on/off that varies the ground offset hence measured lambda.  If it has a gauge and the gauge shows the same swing then you could rule that out.

[flipski]

7 minutes ago, Adamw said:

I agree, PW doesnt change so it is unlikely ecu related.  Could be fuel pressure or the lambda measurement.  I see your lambda device is an innovate, is it one with a gauge/display or is it a LC1/2 with no display?  My suspicion is due to innovate not having an analog ground it is quite possibly something else in the car turning on/off that varies the ground offset hence measured lambda.  If it has a gauge and the gauge shows the same swing then you could rule that out. 

yep, it is a lc2. I grounded the lc2 to the battery directly and joined the ground to the ecu sensor ground. will try a digital readout from the LC2 and see if it fluctuates. I am puzzled because it only happens in a few cells below 2krpm , I am showing a "steady" afr after that.

Thank you.

[cj]

That grounding isnt good, you've effectively joined the sensor ground to the battery negative, which will make ground offset problems like you quite possibly have worse. Try grounding it directly to the engine block at the same point as your main ECU grounds, and disconnect it from the sensor ground. The LC2 manual says it can draw up to 3A, which I'm sure is more than you can safely put through the sensor ground wiring so dont even try (cant remember the actual safe number right now).

if you want to try something much easier but less likely to actually fix the problem, some engines create an EGR effect using VVT advance at cruise-ish MAP values. any EGR effect will cause lambda changes even with constant air+fuel input. You are seeing 2-3 degrees of VVT advance that has a very loose correlation with the LH VVT solenoid position Try setting this to 0 in the 10% TPS row at 1000-2000rpm just to rule it out as its much easier to test that re-wiring your lambda sensor, but you'll probably have to do that anyway.

[flipski]

42 minutes ago, cj said:

That grounding isnt good, you've effectively joined the sensor ground to the battery negative, which will make ground offset problems like you quite possibly have worse. Try grounding it directly to the engine block at the same point as your main ECU grounds, and disconnect it from the sensor ground. 



 The ECU is grounded at the IPDM box ( basically a ignition relay box), this common ground is directly connected to the battery , engine block is grounded at the battery terminal directly.

The LC2 states to ground the controller to the battery. which I did. I guess I should not connect that ground to the sensor ground on the internal aux port, is this correct ?

 

AS far as sensor reading, I forgot that my original downstream o2 were still connected to AN 10 and 11. I am getting the same pulse on the left bank which makes me think this is mechanical. I'll investigate the vvt and see if that changes.  Thank you for the lead. it looks like they have about the same pulse frequency.