Supercharged backfire.

jhunt47

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Some info on the car. 2006 mustang gt 5 speed roush m90 kit with upgraded vmp 1.9l upgraded pulley and boost a pump running 9-9.5psi.
Last week was a bit cold in the morning on my way to work about 40 degrees. I was getting on it pretty hard and heard what I thought was a backfire. I got out of it and drove normal to work about 2 miles away. Nothing obvious no leaks of any kind no check engine lights nothing. I have drove the car 2 more times since then for about 100 miles total. Car runs and idles fine no codes. What I have is slightly less boost now around 7.5 psi max. Other than the lower boost I can't tell any difference in the car. I did a visual under the hood and nothing stands out. Any thoughts on what could have happened and still have the car run fine but loose some boost?
I'm ruling out the boost guage as it's been spot on since before this.
 

07 Boss

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Backfire... as an explosion in the intake? Or one in the exhaust?

If it was in the intake you may have blown off a vacuum line or something which would explain the low boost but I would also think you would be experiencing some other issues. maybe the rotors got damaged or you lost a seal on the SC. If it was an afterfire in the exhaust I don't know why you would lose boost.
 

jhunt47

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Seemed on intake side. I have no other running problems which would help car runs fine.
 

stkjock

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Was it on a shift by chance ??
 

slow06stang

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I agree with 07 Boss. I have had this issue with a centri and the turbo on my truck.
 

skwerl

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Maybe blew out a baffle in the muffler, reducing back pressure? By eliminating obstructions, pressure drops and flow increases.

I'd talk to my tuner about it.
 

jhunt47

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Maybe blew out a baffle in the muffler, reducing back pressure? By eliminating obstructions, pressure drops and flow increases.

I'd talk to my tuner about it.
I was thinking that as well may have to drop the exhaust and check. Have straight through mufflers maybe one of the disc in the factory piping.
 

skwerl

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Double check all the vacuum lines on the intake/ blower elbow as well as the line that runs down the back and underneath the intake manifold. If a vacuum line popped off you might not notice it running slightly lean. Then get hold of your tuner and they will probably want you to datalog for them. Then they can point you in the right direction.
 

jhunt47

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Double check all the vacuum lines on the intake/ blower elbow as well as the line that runs down the back and underneath the intake manifold. If a vacuum line popped off you might not notice it running slightly lean. Then get hold of your tuner and they will probably want you to datalog for them. Then they can point you in the right direction.
Thank you I will go over everything again may have over looked something.
 

06monera96

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Sounds like you blew out your cats (7)

You usually loose about 2psi when u go catless or LT

Wait VMP has a 1.9 Pulley for the M90??
 

jhunt47

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Well just got done going over all the vacuum lines. All is good the under the manifold, bubbler and all lines to the elbow. Guess I need to start looking else where.
 

jhunt47

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Well think I found the problem the noise I heard was a front inside wheel weight being slung off. The boost line had a hole in it that I guess decided to show around the same time guess I just wasn't paying attention.
 

jhunt47

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wow that crazy!

Yeah I know put my might vac in the boost guage it held. When I tested from the supply line it leaked. The wheels just got balanced a few days before this happened. Both front wheels had weight on the inside and outside lip of the inner wheel. Now 1 wheel is missing the outside inner wheel weight. I've had a weight come off on my truck before sounded like a gun shot. Me and the wife took the car today to see a movie and noticed the vibration. When we got back checked the wheels. The roads to work are pretty rough and I guess I wasn't paying much attention before. After the line fix getting the 9-9.5 psi reading now.

Thanks for all the help.
 

eighty6gt

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Hehe that's nuts. I had stick on wheel weights come off and destroy my front calipers. Dumb! Have to babysit the tire shops.
 

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