ok i just went to an inspection, and they said it failed for having no back pressure, could this knock and no lt4 km do this? i just ordered a km today online, and hope that fixes the knock and the backpressure problem. does anyone know what can cause the backpressure problem, or is this the problem?

 

Backpressure is exhaust based... basically they told you you're failing because your exhaust flows to easially...

sounds like BS to me... where is this inspection and what kind of inspection???

 

its in MA, and i didnt get my car inspected for 2 years cause it was in the backyard cause my uncles were savin it for me so now it has 58k miles, and i just turned 16 so they gave it to me cuz they want a vette or viper... so its like some ghetto little inspection place, and idk maybe the flase knock/retard timing will solve it? like the lt4 km?

 

Knock retard and the LT4 module have nothing at all to do with back pressure. They were telling you your exhaust flows too well, which AFAIK has never been a cause for failure on its own. Try a different shop, or call that same shop and ask them to elaborate on the problem.

 

oh and they said you cant pass wihtout backpressure because you cannot reach a certain rpm...

 

Thats BS. Maybe this is their way of saying they aren't gonna pass you with LT's

 

they dont know the diff between stock, they didnt even do a visual...

 

Are you sure you understood what they were talking about? Back pressure is not tested for. In order to do that, they would have to put the car on a rack and pull a sensor and screw in a meter to test it and then run the car. Go to a different inspection station.

What makes you think the KM has anything to do with what they said?

 

cause it lost a whole lot of power at one point after driving for a while after headers, and it gets flase knock so i need to get an lt4 km, thats why, and ya i need to go back to them the 2nd time though, then i can go to somewhere else...

 

How do you know it's getting false knock?

 

with the exhaust set you have in your sig, you would have very little back pressure. In which case, you egr valve will not open correctly. The back pressure is used to help open the vavle. It they are testing for NOx, then you will fail this test.

I was running the open plate on my borla and I failed. Put in the closed plate and it passed.

 

Sounds like this guy hit on the head, nice job. So I guess try hollowed out potato in your tailpipe and go back and test it.

 

Sorry, back pressure is used to close the EGR not open it. That is why some people who modify the exhaust with little back pressure run poorly even at idle since the EGR is not closing properly. On top of that, it doesn't open at idle anyway. Since he didn't say he was running on a dyno for exhaust gas evaluation, we have to assume it was at idle when the EGR is closed normally.

 

That comment alone should give you reason enough to never go to that place again.

 

SO, I guess the service manual is incorrect, as well? The statement in Manual must be a typo, too?

The amount of exhaust gas admitted is regulated by a vacuum or backpressurecontrolled (EGR) valve in response to engine operating conditions.

If vacuum was the only way the valve to open the egr valve. My guess would be that it would never open. Due to the fact that, backpressure and spring pressure would keep it closed.

If you read further on in the SERVICE manual, you will read the side note which states.......Some models use a backpressure-type EGR valve. On models so equipped, backpressure must be created in the exhaust system before the vacuum will actuate the valve.

I guess this is all wrong, right? Ever though it came straight out of the service manual?