engine management & seasonal changes

[isnms]

this may be a stupid question, but then again, only stupid questions are the ones you don't ask

are you required to continually make adjustments through out the year, as the temperature changes, if you have, say an hks s-afr or the like?

 

[figgie]

short answer.. no

 

[isnms]

thank you figgie

 

[Blue87T(Dan)]

Wouldn't running your car in 40 degree temps VS 90 degree temps make a difference in your A/F ratio with nothing else changed.

I would think that you would remove more fuel with your piggyback tuning device when it is warmer and less when colder to achieve the same A/F ratio.

Please enlighten us Figgy, if I'm incorrect.

Dan

 

[drunk_medic]

I thought that most piggybacks just "see and modify" a signal coming to/from the ECU - in other words, the sensors in the engine bay see signals and send them to the ECU, which develops the fuel/ignition maps for that scenario and makes adjustments.
When you tune the piggyback, I thought that you are basically telling it to modify whatever signal it sees "this much". Therefore, the ECU is doing most of the work, and is already adjusting itself for ambient temperature, and the piggyback is just adjusting "this much" to supplement once again.

Then again, I could be wrong as well..

 

[turboa7mgte]

I agree with Drunk Medic

 

[Blue87T(Dan)]

I was thinking specificaly of tuning with a piggyback for open loop or WOT.

Our WOT fuel/timing maps are learned maps based on info from closed loop operation.

Timing is adjusted by the ECU based on the knock sensors.

Is the open loop learned fuel map constantly being adjusted each day as we drive?

In that case how could the Tech Tom upgrade work? Though this is assuming most of the benefits of that are in open loop.

 

[drunk_medic]

I was thinking specificaly of tuning with a piggyback for open loop or WOT.

Our WOT fuel/timing maps are learned maps based on info from closed loop operation.

Timing is adjusted by the ECU based on the knock sensors.

Is the open loop learned fuel map constantly being adjusted each day as we drive?

In that case how could the Tech Tom upgrade work? Though this is assuming most of the benefits of that are in open loop.

This is open to debate - many people get really pissed off that our ECUs learn the way they do. Some people have found their car running like crap a few weeks after a nice dyno tune session for their new piggyback because the ECU has re-learned and adjusted itself a little.

 

[figgie]

Wouldn't running your car in 40 degree temps VS 90 degree temps make a difference in your A/F ratio with nothing else changed.

I would think that you would remove more fuel with your piggyback tuning device when it is warmer and less when colder to achieve the same A/F ratio.

Please enlighten us Figgy, if I'm incorrect.

Dan

our ECU do. But once you tune a SAFR or any other piggy back. It stays that way... now this is talking about WOT as any other paramenters the ecu will adjust its own way and you are basically chasing tail.

So as i said above. Short answer.. NO.

 

[blake]

So long as you're using the stock (or lexus modded) AFM or a MAF you're measuring the actual MASS of the air entering the engine. So atmospheric pressure or temperature variations are automatically compensated for "at the sensor".

If you've gone "speed density", that is you're calculating fuel to inject based on a MAP sensor only, the temperature needs to be compensated for fairly significantly. The guys running AEM standalone always seem to be chasing their tales on this one (I don't really want to get into THAT discussion again, though).

My short answer is seasonal (or even daily) temperature changes are an issue only if you've changed your air flow sensing method, regardless of what piggybacks you're using.

Just for kicks here's a table from a spreadsheet of mine showing how much compensation needs to be made (all things being 'ideal', temps are in Deg Celsius, Google for "40 C in F" to convert):

Intake Temp	Trim
-40	0.34
-30	0.28
-20	0.23
-10	0.19
0	0.14
10	0.10
20	0.06
30	0.03
40	0
50	-0.03
60	-0.06
70	-0.08
80	-0.11
90	-0.13
100	-0.16
110	-0.18
120	-0.20

~Blake

 

[isnms]

Thanks all for the constructive information

This is the post that prompted me to ask the question. I printed it but now I can not find where I printed it from.

Here's some of my feedback after tuning a few MK3's with SAFC's.

Before you dyno, you will want to adjust your lexus screw so that the vf reference on the TCCS diagnostics block is putting out a 2.50v. If you want to read about it, you can visit this website:

http://suprasonic.org/lexusriemer/lexusnote.html (note, website is slow)

I usually tune the vf while cruising down the highway.

For throttle points, I set mine for 79%Lo and 80%Hi, also, don't adjust fuel below 3000rpm since the ECU is still trying to adjust below that rpm. On the dyno, just adjust the Hi Throttle settings.

I would shoot for 11.5:1 a/f since once you put the car back on the road and full load it will run even more lean. Depending on the dyno and how much load it applies, lowerer a/f for less inertia, higher a/f for high inertia. On a dynojet, another .5 a/f since on a colder day you will run leaner (colder intake temps and higher IC efficiency=more dense air), if it's over 75, shoot for 11:1, if it's under, shoot for 11.5:1. I've seen cars tuned in August in 90 degree weather hitting 11.5:1, then in November when it's in the 40-50's high 12.5:1 with the same settings.

Hope that helps.

--
Joseph Schesso
Extreme Turbo Systems
PacNW Supras Portland/Metro Event Coordinator

 

[Blue87T(Dan)]

I stand corrected. The Karman Vortex AFM on our cars has an integrated temp sensor so the ECU should be receiving a signal based on on air temp and flow.

Just like Blake said.

Edit- It appears that the temp sensor in the AFM sends a separate signal to the ECU.

The Karman signal should then be based just on flow.

 

[blake]

It's funny. All this time I've been under the impression that a KV meter gave a signal based on mass flow, not volume flow. Two minutes with Google and now it's pretty clear it's flow velocity and since the flow area remains constant, volume over time (see these links: http://www.galleryoffluidmechanics.com/vortex/karman.htm http://www.kofloc.co.jp/kofloc_e/fm31.html ).

You'll still get far more consistent results with a KV sensor mounted pre-turbo than speed-density systems for a couple of reasons. For one thing you don't need to empirically determine the volumetric efficiency of your engine at every possible load point. Additionally the temperature of air you're measuring doesn't fluctuate so wildly when you're measuring pre-turbo as it does in your intake manifold. Air temperature sensors, while they start responding immediately, won't give you accurate results quickly enough (see this page which shows a common air temp and its response rate http://www.race-technology.com/WebPage2/Products/Sensors/AirTemperature.html ).

As you can probably guess I've done a fair amount of digging on this topic and am not really enthused about speed-density for a turbo application. On an NA application intake air temps aren't fluctuating nearly so much, however. The Intercooler on a turbo car does a significant job of keeping the temps more sane, but the air coming out of your turbo is commonly above boiling. I saw a post recently where someone reported measuring temps above 300degF, though this was pretty high boost on a CT-26 so it was quite outside its efficient range.

Ok, I'm done rambling =)

~Blake