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Nurzh_rt

AFR problem at idle

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Hello

we have some problem with AFR at idle, above 1-2 hour lambda reads AFR 10-11 at idle and its really rich (tested with external wideband)

But if we turn off engine for 30min, than AFR is ok, but only for 1 hour

ECT, IAT, charge temp, ecu temp, Bat volt, Inj PW actual and effective all same

may be its fuel temp but usually must be lean

idle lean after 30 min Log 2018-07-10 8;34;51 pm.llg

Idle rich AFR Log 2018-07-10 7;00;47 pm.llg

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Pretty odd problem for sure.  You have a mixture difference of 25% so that is a significant change in fuel or air mass. I dont see anything in the log that could cause that.  Does it actually run completely different or does it still run ok when rich Vs normal?  What injectors are they?  If they are the Bosch CNG injectors then I would be suspicious of those.  Have you checked fuel pressure?  What about a tight valve clearance or vacuum leak or similar that causes 1 cylinder to misfire?

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4 hours ago, Adamw said:

Pretty odd problem for sure.  You have a mixture difference of 25% so that is a significant change in fuel or air mass. I dont see anything in the log that could cause that.  Does it actually run completely different or does it still run ok when rich Vs normal?  What injectors are they?  If they are the Bosch CNG injectors then I would be suspicious of those.  Have you checked fuel pressure?  What about a tight valve clearance or vacuum leak or similar that causes 1 cylinder to misfire?

When its rich its really rich, with black smoke from exhaust

Injectors is Delphi 42lb 01d030b high impedance

still not checked FP

i will check leak test later

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Following - I have similar but less dramatic symptoms myself and have the same setup (onboard LSU 4.9 digital wideband). Mine has swings from around 0.97 down to sometimes ~0.91 after running for a while. I have pressure and temp data from fuel and oil so I have a little more to work with. Ultimately, I am chalking it down to not having proper data for my injectors. They are running at 1.4% DC (similar to what your log is showing) at idle and I dont think its possible for the pull enough fuel out when responding to fuel temp/intake charge temp. Due to it still being quite within reason and not generating any negative effects (poor idle/smoke/etc), I can ignore it in my case, but what you are facing sounds more significant. Just giving you an idea of what I logged and observed when trying to resolve the issue myself.

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