Open CAI and fan wash

[v8hgt]

I have spotted some strange behaviour in my logs and my tuner says it’s “fan wash”.
I’ve done some testing and this seems to pan out. I wasn’t aware of it before so thought I would post my findings and see if anyone else has experienced it.

So I put the gt350 IM and CAI on my car and had it tuned. When I log it doing a warm idle it run approx 745rpm with the short term fuel trims at 1.0 and long term trims at 1.0 which is perfect.
However as soon as the radiator fans come on, the short term trims ramp up to 1.1. So 10% lean compared to the fuel map. Not so good, not terrible as it’s closed loop so it compensates to hold the right AFR so doesn’t actually go lean by opening the throttle angle slightly and upping the fuel injector delivey amount.


If I turn the air con on to load up the engine they drop again. Which seems really odd.

I popped the hood and made a rudimentary cover for the gt350 air bucket and that seems to drop the trims to near normal levels.

I therefore suspect my gt350 cai is not sealing against my hood liner very well.

Has anyone else noticed anything like this in their open cai logging?

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[Ebm]

I have spotted some strange behaviour in my logs and my tuner says it’s “fan wash”.
I’ve done some testing and this seems to pan out. I wasn’t aware of it before so thought I would post my findings and see if anyone else has experienced it.

So I put the gt350 IM and CAI on my car and had it tuned. When I log it doing a warm idle it run approx 745rpm with the short term fuel trims at 1.0 and long term trims at 1.0 which is perfect.
However as soon as the radiator fans come on, the short term trims ramp up to 1.1. So 10% lean compared to the fuel map. Not so good, not terrible as it’s closed loop so it compensates to hold the right AFR so doesn’t actually go lean by opening the throttle angle slightly and upping the fuel injector delivey amount.


If I turn the air con on to load up the engine they drop again. Which seems really odd.

I popped the hood and made a rudimentary cover for the gt350 air bucket and that seems to drop the trims to near normal levels.

I therefore suspect my gt350 cai is not sealing against my hood liner very well.

Has anyone else noticed anything like this in their open cai logging?

Please don't think this is thread jacking, just an honest question for you.
Imagine this scenario: you're driving down the highway going 65 mph on a flat stretch of highway and you have the A/C on about halfway. You are applying constant throttle but sometimes it seems the throttle increases without you pushing it in more. It increases for around 5 seconds then goes back to normal. Would you say this is normal when the A/C is on? Would you say this is due to the compressor going on and off or the fan or what?

 

[V8EATR]

Most vehicles over about 40mph the fans won't come on at all because they can't match the airflow at that point.

 

[EFI]

the short term fuel trims at 1.0 and long term trims at 1.0 which is perfect.
However as soon as the radiator fans come on, the short term trims ramp up to 1.1. So 10% lean compared to the fuel map. Not so good

STFT of 1.1 is 1.1% lean, not 10%

And if 1.0 is perfect, than 1.1 is barely if at all different.

Or am I mis-understanding what you are saying? I can't imagine the fans being turned on is causing 10% more airflow to go into the intake.

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