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P0171 with 3.5" SRI

Posted: Sat Apr 06, 2019 7:11 pm
by Qyota
Hello - first time poster.

I have a 2006 Civic Si with a 3.5" K-tuned SRI, and cat-back exhaust. Otherwise stock. I have uploaded the AFM-based map for the AEM SRI, figuring it would be "close enough". I've taken a few drives and datalogged, and the short and long fuel trims are off the charts. Short term was 25% or more, and long term pegged at 25%. So the ECU thinks there is much more air than there is, and is loading fuel to compensate. Instant-MPG reads high, when actual MPG is low.

Got code P0171 today - system too lean.

This car has a new MAF (stock DENSO), new A/F meter (DENSO), and downstream O2 sensor (DENSO). Is it better to alter the AFM calibration table, or switch to a MAP calibration for this intake in particular?

Also, knock count on cylinder #2 seems high...30 knocks in a 15 minute easy trip home (no VTEC, short-shifting, etc). No other cylinders are showing any knock counts.

I have attached a datalog for that 15 minute ride home if anyone wants to see it.

Thanks for your help!

Re: P0171 with 3.5" SRI

Posted: Mon Apr 08, 2019 9:21 am
by Spunkster
It really depends on the person tuning. You can try tuning via MAP and see if that works better for you.

Re: P0171 with 3.5" SRI

Posted: Mon Apr 08, 2019 1:00 pm
by Qyota
I think I'll try a MAP calibration, thanks.

I'm also trying to find a used stock/OEM air intake for this car. It's been harder than I figured it would be.

Re: P0171 with 3.5" SRI

Posted: Mon Apr 08, 2019 8:00 pm
by Qyota
Uploaded the MAP-based calibration for an Injen SRI, and noticed immediate improvement in A/F and fuel trims. Car runs and drives MUCH better with this change. I'll drive it a few more days watching and datalogging, and then get to the tuning.

Re: P0171 with 3.5" SRI

Posted: Tue Apr 09, 2019 5:40 pm
by Qyota
Day 2, so far so good. Fuel trims are normal, A/F is good, if not a tad rich especially during 1/2 - WOT. Start-up fueling seems a bit "off", especially when cold. Car takes at least one more crank cycle to start, and then sort of stumbles to life. Warm starts are good.

Re: P0171 with 3.5" SRI

Posted: Sun May 10, 2020 3:18 pm
by jcauto
When intake shopping, I found a lot of companies specifying that any of their intakes over 3" in diameter need to be speed density tuned. Remember that the MAF is only reading a sample of airflow and the ecu is calibrated to determine how much air is actually entering the engine based on intake design. If there isn't a pre-made tune for your exact intake, these are the troubles you'll encounter. I disagree with using an AFM tune on any car, the best all around results I've had in both WOT and part throttle driving has been with a MAP tune.