Monsterbox

iTrader: (6)

I tuned my car on aem standalone and 67mm turbo all supporting mods and methanol inj to 518hp @ 24 psi a few months back in 40f weather at 11.2 afr.

Fast forward, pulled motor to paint engine bay and few other tricks but did not change performance mods. Reinstalled everything today, made a pull in 15f weather at 20psi (first time in these temps) pulled a 12 5-12.8 AFR...even my idle was sitting around 14.4 up from 13.4. Everything seems to work correclty all I can imagine is the ambient temp is so cold and ecu does not compensate for the extra density?

Does this sound sensible?

C. Ludwig

iTrader: (27)

The ECU will compensate for the change in air density as well as you tell it to. Since you're the tuner, you need to tune it.

eage8

iTrader: (9)

are you sure you hooked the fuel pressure regulator vacuum hose back up?

thewird

iTrader: (8)

There's a table called air temperature correction. Use it.

That wouldn't cause the described symptoms.

thewird

ryan1

iTrader: (5)

Since you had the motor out, first check your air temp sensor data and make sure it is reading correctly. Then thewird advice is right on.

Monsterbox

iTrader: (6)

Thanks!

Need to hook up tp ecu and datalog but looking over files at work pc, my air temp compensation adds 4.5 percent at 14f on the curve.

This seem within reason?

C. Ludwig

iTrader: (27)

That depends on the temp at which the base fuel map was done and where the zero point of the air temp compensation curve is. For example, if the original tune was done on an 80*F day and intake temp (the only number that matters) was 120*F and the air temp correction was 0% at that point, and now you have 14*F intake temps and you're adding 4.5% fuel, then no, it's not nearly enough.

The air density is easy enough to calculate based on air temp. It's part of the speed density calculation. So it's easy enough to back to the temps at which you originally calibrated the base fuel map and mathematically figure out what the correction factor should be under and over that temp. Like anything, the theoretical value may not be exactly correct, but it will get you very much in the ballpark.

Here is a chart I put together to compare relative values.

jacobcartmill

iTrader: (6)

OP, if you're tuning on planet earth, you need to use the air temp correction table.


i went through this recently with a strange/unknown air temp map.
i tuned my car on the dyno with 100-110*F as my "zero" point and had to offset my base map by the amount that was haltech's "zero," which is shown on the IAT/correction table ludwig posted above, in order to get real/correct/close air temp correction and not have to worry about it.

Monsterbox

iTrader: (6)

You guya are amazing. I found the primary source of my problem.

My exhaust gasket had blown out at my turbo to dp. Sensor was unable to read the correct amount of fuel.

Replaced gasket and now afr sits around 11.8-12.0 at WOT at 19psi.

Car pulls extremely hard and runs smoother then ever. Ambient temps are around 23 degrees F. My logs at 40-60f showed around 11.2-11.5. So, I'm contemplating increasing the compensation percentages, but do you guys think I'm safe running 11.8-12.0 in these super cold air temps and 660cc of water/meth?

jacobcartmill

iTrader: (6)

monsterbox, are you sure about that? the AFR of the exhaust coming out of the engine and going into the downpipe is still the same, exhaust leak or not, unless there's air leaking IN and affecting the AFR, but that's not happening.

jetlude

iTrader: (9)

The the oscillations from the exhaust pulses will draw in air from the hole created by the faulty gasket. The area of his leak (turbo to downpipe) will cause it a leaner condition to register on the wideband since the sensor would typically placed just after this joint.

Monsterbox

iTrader: (6)

I'm almost positive this was the problem. My afr was 14.7 at idle which is impossible. I can't get the car to even run at all past 13.3-13.5.

Car was tuned in 30-40f at 11.5-11.8 in the 19-21psi range.

Car pulled 12.0 today in 20's ambient temp. Whats amazing is that the car pulls way cleaner and harder then ever before. Not even a hint of breakup. 12.0 is leanest iv ever seen but zero backfires, zero hesitation and Just rips through 3rd so hard its breathtaking.

With nearly 700c of WM injection I feel like this could possibly be the sweet spot for this car. 12.0 winter time 11.0 summer. I wish I had egt sensors to determine if this is safe.

I guess I could go in and increase the compensation table. However I'm contemplating increasing the nozzle size of my ai to 800-900cc.

I had extreme breakup at anythint under 10.5-11 during tuning. But the closer to 12.0 the harder this thing pulls. I wonder if more AI and leaner AFR would be the key to opening up untapped power.

Vicoor

The exhaust leak will not change the AFR directly, but it will allow air into the exhaust stream on the negative pressure side of the pulse and cause the AFR sensor to incorrectly read lean. This will cause the ECM, if it is set for closed loop AFR, or the tuner to incorrectly add more fuel til a misfire happens. then the AFR sensor will "see" even more O2>>> add more fuel...

thewird

iTrader: (8)

An exhaust leak will make the wideband read lean. Mostly at idle and low rpm light cruise. It would have to be some serious exhaust leak to affect WOT readings. I used to use it as a way to know I had an exhaust leak when I had manifold cracking issues, AFR over 13.0 at idle and engine still smooth ment I had a leak LOL.

Just ignore Vicoor, he's a mechanic. You don't listen to mechanics for these cars LOL

thewird

Vicoor

HEY!
I'm not a mechanic,
I'm an automotive technician.