Long-term fuel trim remains nailed to 0 on PRA ECU?

K-Series Programmable ECU installation questions / support issues
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Arno
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Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Arno » Tue Jun 10, 2014 12:01 am

Hi,

Just curious if this is something that's simply part of how the PRA ECU works with a Kpro, a display issue or some (minor) bug.

Over time I noticed that the short term fuel trim will vary with the lambda sensor feedback (of course the narrowband on the PRA) cycle, but the long-term remains fixed/nailed at 0 all the time no matter what you do.

Both the Kmanager readout as well as the OBD2 readout show the exact same behaviour. This seems to have been the default behaviour since the very early K100/Kpro days (2005) as I have used the car with a K100 and a simple OBD reader for several years and it always showed this effect. So it seems to be a very old 'feature'.

I use an EUDM K20A2 in a Lotus Elise (mildly modified with PRC pistons and PRC intake manifold, TODA A3 cams+springs, custom 4-2-1 exhaust manifold) and have not used/diagnosed an un-modified/stock ECU in a Civic TypeR.

So I don't know if the PRA ECU in stock form doesn't apply any long term trims either (would be curious, but could be..) or if this feature is 'lost' when the PRA ECU is upgraded with a K100/Kpro due to memory or CPU cycle constraints with the Hondata firmware.

Having said that, I did once try a PRB kal on the Kpro in my ECU and even though this gave some 'interesting' errors (as was to be expected with a PRB kal on a PRA), I did see that the long term trim values did move in this case.

Again, nothing serious but just something I noticed and was curious about.

Bye, Arno.

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Hondata
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Re: Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Hondata » Tue Jun 10, 2014 6:41 am

Does the ECU correctly received back up power via E7?
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Arno
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Re: Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Arno » Tue Jun 10, 2014 11:57 pm

Yup.. Constant/battery 12V (via main EFI relay coil) applied to E7. The main relay is actuated when the ECU pulls E7 to ground on detecting (ignition) power on A2/A3. DTC's are also retained across ignition on-off-on cycles. It also retains, for instance, idle valve learned positions as long as you do not disconnect the battery itself (obviously.. ;) )

Having said that..

Even if it were to lose any learned settings like long term trims on each ignition-off-on cycle I'd still expect this value to deviate slowly from 0 when driving for an hour or so. But it's just happily sitting there nailed at 0 and not moving one little bit in either positive or negative direction.

It may well be (internally) actually doing/applying long term trims but the Hondata firmware in the ECU is perhaps looking in the wrong location on a PRA ECU and returning a zero value via both KManager and OBD2 reader (at least they are consistent). But that's something you guys can determine :)

Bye, Arno.

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Re: Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Hondata » Wed Jun 11, 2014 8:54 am

We don't change the stock ECU closed loop behavior. From what I've seen it only alters long term trim under certain conditions, and it is possible to create a calibration which does not meet any of those conditions ever.
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Arno
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Re: Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Arno » Fri Jun 13, 2014 3:22 am

OK, so the values in the maps of the calibration itself may stop it from updating the long-term fuel trim. Interesting..

At the moment my calibration is pretty spot on as far as fuel on the closed-loop areas goes (withing +/- 2%), so it won't need to trim much anyway.

Will play around with this a bit more when I have my new exhaust system done (more quiet system and probably will make the second O2 sensor functional again as well so I can re-enable most of the OBD checks) and will re-tune it for 95RON octane running as 98RON is getting harder and harder to come by these days.

Just need to figure out why I seem to have some knocks logged at load cells that I would not expect like column 3/4 around 2000-2500rpm. (light load cruise in closed-loop)

Suspecting it's not really knock, but some resonance/noise from the rather rigid engine mounts and the 4-2-1 that's making it 'see' knock because of the much lower knock threshold values in these areas.

Thanks for the info!

Bye, Arno.

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Re: Long-term fuel trim remains nailed to 0 on PRA ECU?

Post by Hondata » Fri Jun 13, 2014 7:27 am

Given the choice (eg 2006 Civic) I disable long term trim anyhow.
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