Couldn't have said it better myself.. Aftermarket filters are REALLY prone to this, stock airbox with snorkle doesn't experience this because it doesnt source its air from anywhere but the snorkle.. When you slam the hood its a different disruption, its sudden positive pressure through the sensor throwing off the metering, combination of disrupting the airflow sensor and Map sensor in the unit.

Want to watch an EVO stall? Set off a blockbuster somewhere close to the car.. the concussion will completely confuse the sensor.. If you can feel the "Bass" of that escalade in front of you, your Evo can too..

Plus the 1bar map sensor built into the MAF is likely what causes it, since a concussion pressure wave can change the air pressure the MAF thinks its seeing and thinks you've dropped from whatever altitude you live at to the depths of hell and then suddenly back to where you were..

 

Oh and someone asked why a hard gust of wind doesnt cause this also? Its a SUDDEN change in air pressure where the sensor reacts faster than the ECU can compensate for..

Its not the knock sensor, you would literally have to tap the engine with a hammer to get the knock sensor to pick up anything let alone loud noises outside the engine bay..

 

Hey guys,

I thought there was a post that mentioned that the CAS is very sensitive and may cause the stumble as well? I think it was my thread where I asked how to fix the CAS that I broke when installing my Forge BPV.

FB

 

Nah, the CAS uses a hall effect sensor, it wouldn't be sensitive to loud noises or concussion.. It is very sensitive, but not to slamming your hood since it would require enough vibration to affect the engine block, slamming the hood wont transfer anywhere near enough vibration to the engine.

 

ecu knock sensor...no biggy

 

Yup...me too...it drove me nuts at Bradenton...

 

If there was a little monkey under your hood tapping on the engine block while you dropped the hood shut, then it could be the knock sensor. Otherwise it's the MAF. I never had an issue until I "upgraded" to a cone filter intake.

Think about it, if the knock sensor was sensitive to that sort of "sound", expansion joints in the pavement would screw with it too. It doesn't though, does it? The knock sensor is tuned to listen for very specific frequencies. I seriously doubt the knock sensor even "bats an eyelash" when the hood is closed.

If you'd like, I'll log the voltage output of the knock sensor AND the MAF output frequency while I close the hood, slam the door or fart in close proximity.

 

Dude I'd check your diet if your farts can alter the MAF.. ROFL!!!

The long and short of it, is its nothing really wrong, just try not to slam the hood shut..

 

Mine is full-on stock and it does it when I drop the hood from 10" up. I would never press on an aluminum hood to close it.

 

I don't recall it happening to me when the car had the stock airbox.. I do recall it happening a few times after I put on the cone filter. But I don't recall it happening more than a handful of times, again, I don't think I've opened and closed the hood with the engine running more than a few times though.

What I do remember is a harley motorcycle with really loud exhaust drive by and my car would stumble, and one or two other occasions on the road while I was idling and some sudden loud sound would cause the car to stumble.

 

Mine does it with the stock airbox. No biggie.

 

This happened to our shop EVO. We are still running the stock air box. We closed the hood and the idle stummbled. So we pulled out the laptop and logged the UTEC(I will look around for the log but it was awhile ago and has probably been deleted by now).

Answer: MJ's is right you can see it in the frequency of the MAF. We figured it could be the positive air flow or the MAF actually picking up the vibration from the hood slamming down.

Each EVO seams to be very different. some evos stumble some don't. It will not affect you much. Unless you decide to slam your hood as your going down the track.

Ben

 

Last time I was at the track, when I was in the staging lanes with open-exhaust V-8's my idle was very unstable. If I was next in line after one of those cars, I would have to hold the gas to keep my car from stalling. Holding it to around 1500 RPM kept the car running fine. It is very frustrating to have to do that to keep the car running, but luckily the lines in the staging lanes weren't too long.

Paul

 

I have had an ultra loud Harley completely stall my car when at a red light

I also can barely keep the car idling when in the staging lanes at the track.

What about people with 12 or 15" subs in their car....any problems when the bass is bumpin?

 

I pulled up to a signal where a road crew was working and when a guy started using a jack hammer my car almost died.