ECU air temperature compensation values

[YLD-16L]

Just a query some people may have an answer to or would like to discuss......

Most/all aftermarket ECUs have the ability to trim fuel as a result of air intake temperature sensor input. Some ECUs come with a pre configured temp compensation table, some don't.

Mine doesn't, so the options are:

1. Make adjustments to the compensation table as and when inlet air temperatures change to maintain the target air : fuel ratios across varying inlet air temps. Problem is you won't experience much variation within one tuning session and you don't want to be tuning the car every time the temps change to a range you haven't adjusted yet.

2. Use the ideal gas law to calculate trim % values. This method seems quite good but in reality I have found the values to be a little over estimated, by being a little bit more conservative on the calculated values it appears to work quite well and has the added bonus of setting trim values in temp sites not easily visited in a tuning session.

3. Just leave the values at zero. Not a good option at all, but quite common.

Any other methods people care to share or values they could share from their ECU's that came pre-installed for comparison??

I can post my current values if anyone is interested from -17 through to about 115 deg C.

Cheers.

[CrUZida]

I have basically left mine at all zero from memory, except below 20deg I've added some timing, and above 60degC I've taken some timing and added some fuel.

[YLD-16L]

I have basically left mine at all zero from memory, except below 20deg I've added some timing, and above 60degC I've taken some timing and added some fuel.

Interesting, I've not added any timing below 20 deg C but have, as you've done pulled 1 - 2 deg above 60 deg C.

This raises the other thought I had, where using the ideal gas law trim values you are bascially aiming to maintain the air:fuel values that are achieved at 20 deg C (zero compensation temp) right through to temp range either side of 20 deg C which means it pulls fuel out above that value and add fuel in below that temp value.

In terms of thermal management though I have been erring on the side of caution and thinking above around 60 deg C or thereabouts I'll not pull out as much or any (or even add fuel) to richen the mixture and achieve a cooler burn.

Thoughts on this theory?? What are other people doing?

[CrUZida]

I've basically used it for a safety net (hence the extra fuel/reducing timing at high temps) to try and prevent a bit of detonation.

[YLD-16L]

I've basically used it for a safety net (hence the extra fuel/reducing timing at high temps) to try and prevent a bit of detonation.

It does seem like a good idea.

I'd love to see some factory values on a highly strung engine to see how they manage this side of things.

[thechuckster]

if the fuel calculation is based on a 'Speed Density' algorithm, air temp is part of the fueling equation rather than a separate trim table. (edit 2: i guess you guys already know that)

Temperature is critical in determining air density and the MSEFI setup is more concerned with using the right temp sensor or (if used) an accurate temp to resistance table for your particular sensor.

but...

the current versions of the MSEFI and MSextra code have IAT (Intake Air Temp) compensation tables for spark (6x6 temp versus retard table) and fuel (6x6 temp versus % correction table) as well as using AIT for enabling/disabling other features (O2, boost or AFR control, knock, etc.).

fwiw: reference website used by MSEFI manual for air density and altitude calculations: http://wahiduddin.net/calc/density_altitude.htm


edit: the MSExtra manuals mention to AIT correction in relation to dealing with intake manifold heat-soak and detonation control.

edit 3: the MSextra manuals have some screenshots of the tables - from memory, the data you see is based on real-world use by the manual authors ... usually a chev v8 with port injection but one never knows... note MAT = IAT

MAT Correction

The MS2-Extra code also allows the user to fine tune the amount of correction given for the Air Density calculations that is worked out using the air temperature sensor. This compensates for some heat saturation from the plenum, or intake if the air sensor is in a particularly prone position to heat up due to heat saturation from the engine. This should be set to Zero for starters so the standard Air Density correction factor is used.

Fuel:

MAT Based Timing Retard

The inlet air temperature has a massive effect on how much advance you can safely run (especially on a boosted engine), if the temperature increases too much, due to sitting in traffic, long/hard runs in boost, etc, the amount of ignition advance can be retarded proportionately with the temp increase to help prevent detonation. The MS2-Extra code has a MAT Based Timing Retard table. This works in much the same way as the Cold Ignition Advance but it RETARDS the ignition from the base map to keep away from detonation. So in the example below, if the engine is running at 20deg on the base map, then at 93C the engine would be retarded to 18deg BTDC

Timing:

[YLD-16L]

Great post Chuck, interestingly I always search MS sites for this sort of info as a lot of cluey people seem to play with them and share info.

[OnAll-FOUR]

I was asking some similar questions of the guys on www.hybridz.org about the wolfv500 and this was his response.

I liked the methodical approach, looking at the particular cars operating range.

Each car is different. I am using the intake air temperature modifiers for fuel and timing. I drop timing when IAT's hit 48 *C up to a maximum of -4 degrees at 60 *C. My fuel is modified using a linear relationship; +5% at -64 *C to -10% at 190 *C.

It would be difficult to dyno tune IAT compensation since it is typically only experienced at the "extremes".

I picked temperatures that were just on the hot side of normal operating temperatures. IAT's have less of an impact than engine temperature on detonation. I am also modifying fuel and timing based on engine temperature.

For instance, I've logged my IAT (before methanol injection) and recorded a faily consistent 40/42 *C during pulls. I start to pull timing at 48 *C. This was with engine temps at the time around 80 *C (normal operating temps). Now, I could have high IATs and high engine temps, and would be modifying my fuel and timing with both. Some supercharged applications run from 65 *C up to 87 *C when heat soaked. I selected a value that was conservatively low, but outside of the normal operating temperature.

Once my engine temps get over 90 *C, I start to pull timing. This is because the entire engine is now "hot". The cylinder head is quite hot and the cooling system is working overtime.

[YLD-16L]

Thanks Ben, his post just confirms what most of us already do, in that we aim to compensate outside the normal operating temps for fuel and ignition. It does highlight a good point though that each type of engine is different and the normal operating parameters should be established.

I'd be interested to see how he worked out that IAT fuel correction linear relationship. His temp range for the compensations is huge too, it's defnitely degree Celcius he's working with isn't it?

[YLD-16L]

Apparently Haltechs come preconfigured with temp compensation values for fuel (not sure about timing). Perhaps if someone on here owns a Haltech they could note the figures and post them up?