Engine Management - Afr Variances In Other Gears

[paulr33]

Hi All,

Am posting this based on something cubes has discovered whilst reading some tuning material.

He found that some ecu's tend to have the AFRS (tuned in) vary based on what gear is used.

Ie: have a range of cells set to say 12.1 AFR and then when done and tuned in 4th its fine.

When a subsequent run is done in 3rd or 2nd the AFRS vary slightly and could be leaner, say 11.8

It is envisaged that the ecu is looking at the previous snapshot of sensors and deciding injection amounts but when this is happening in real time in low gears it happens a lot quicker and thus, the ECU typically lags. The outcome is that the AFRS to lend to sway a little as its always looking at the previous set of numbers instead of predictive load checking, ie: check thats its on WOT and predict the load and precalculate the injection coming up.

Ive had some thoughts regarding this and the only way I would agree with it would be to see a dyno plot of AFRS side by side with both gears and a show of the map tracer plots showing the same block of cells were hit. it sounds like to me its simply a case of some alternate cells are being hit in the lower gears, as load varies compared to 4th. The main source of comments was found on another forum here -> http://www.innovatemotorsports.com/forums/...read.php?t=4109

Has anyone else heard similar comments or seen similar results? I've never checked my AFRS in other gears.

Cubes deserves all the credit, im just posting it up for discussion

[The Dan]

Isn't 11.8 richer than 12.1? Off topic I know but thought I would mention it.

[Adriano]

what management?

[mad082]

i'd take a guess and say that it is un an ecu that runs a map sensor not a afm, and they have tuned it off the TPS. and at the lower gears it hasn't spooled up quite as much.

[Sydneykid]

I have logs of a couple of runs from the R33GTST down the ¼ mile at WSID, they are posted up in the Teach Edge thread. I can’t see any real differences in A/F ratios between 2nd , 3rd or 4th gears. Keeping in mind that I do most of the high load/rpm tuning in 3rd gear on the road, 4th gear is simply too many kph.

cheers

[paulr33]

yeah sorry i worded it wrong. meant to say richer. im not sure what ecu it was, but we were thinking the powerfc had the same problem and was possibly lagged in the lower gears. i havent seen any evidence, more just a thought

[StockyMcStock]

theoretically if the ECU was a bit on the slow side, in the first couple of gears where the rate of change of RPM is higher it could be slow in calculating what injector pulse to run at the next predicted RPM/load point.

i would have expected this to have been predicted by the ECU manufacturer though, and the processor speed upped enough to discount it. maybe i'm wrong?

[Cubes]

I'd think the pfc is more than capable.. They really are an awesome no frills ecu powerful ecu.

Mad082, check out the link posted, more likely with maf, apparently.

Leaner conditions in 1st and 2nd are very common with many ECUs. I've seen it more pronounced on MAF based systems. an ECU calculates the next injector duty cycle on the previous engine cycle(s). When RPM is fast rising, it is behind. Some higher end aftermarked ECUs and some OEM ECUs try to compensate either by looking at the current gear or trying to predict from RPM rise rate. That's why tuning should be done in higher gears.

[T04GTR]

its only input (if factory or powerfc) is the neutral switch. so any varieation is a coincedence. ie.. diferant load on the rollers etc etc.

so if the revs rise up faster the afr meter will lag abit

[MR331307]

Yeah i think it is a MAP sensor ECU.

I think the ECU he is talking about is a Microtech.They need to be tuned in MATRIX mode to be most Effective on street cars.They USUALLY run off a LOAD MAP which is tuned in vacumm and PSI.They dont tune in Different RPMS unless in matrix mode.So i think that might be a problem.If you tune in matrix mode you will get rid of the problem.But the ecu only has a 16 x16 graph from what i remember.

Another Problem you might have is if you tune a car with a map sensor that has Multiple throttle bodys or BIG cams with low vacuum you will find it will change AFRS in different gears as well. To fix this problem you need to tune in a TPS x MAP screen which is usually found in the Settings page.

this isnt a problem with the ECUS its a problem with Who set it up and tuned it.

If you have a AIR FLOW METER ECU it wont have this problem to what i remember,Only map Sensor cars but they need to be tuned and setup correct to fix it.

[Thunderbolt]

Interesting topic. On a related note, it can also vary when in the same gear:

For example, when I first had my tune, it was showing a rich mixture as it comes onto boost (about 11.3) before settling to almost bang on 12. Took it elsewhere with the same tune, and this one showed the rich patch going to 11 before settling on about 11.7. Air intake temps were showing the same, the runs were both done in third, so the consistancy was there, just showing different results.

Edited August 2, 2006 by Thunderbolt

[Cubes]

Difference in the wideband calibration..