Backfire Question

[4DSZR1]

Well, it finally happened to me this morning. Crank and pow, backfire and rough running and smokey. Shut it off looked at the area behind the plenun and didn't see anything readily apparent so left it and came to work. My question, if the probplem is is the map sensor hose, could it come loose under the plenum or can it only come loose at the back of the plenum and at the sensor itself? The reason I ask is after I shut it off for about 6 or 7 seconds there is a slight hissing, like a air leak, coming from under the plenum.

Thanks

Rick

[GOLDCYLON]

In short No Rick. I had a back fire event and blew the hose fitting that runs on the hose on the Driverside that runs to under the air horn and plenum. Hissing, high idle and a plenum pull was required. Normally during a back fire event only the MAP sensor hose blows but so can the PCV valves hose. Check On the back side of the plenuim and look around with a flash light. But with hissing after shut down I am not sure, but it sure sounds like a plenum pull is in the future.

[4DSZR1]

Good advice.... thanks

I tend to agree with what's in my future ;-)

[Aurora40]

My two cents, if it's hissing after shutdown, I'd think it would have to be something on the vacuum side of the 2ndary system. It holds a vacuum and could be it leaks. Maybe a check valve didn't take the backfire too well?

For what it's worth, I've had my car backfire several (lots of) times. I've never had anything blow off of anywhere. I don't know why that is, maybe the K&N filters offer little resistance and the pressure is relieved through there? I dunno.

[4DSZR1]

That's a good two cents, I'll check'em also

Thanks for all the input

Originally Posted by Aurora40

My two cents, if it's hissing after shutdown, I'd think it would have to be something on the vacuum side of the 2ndary system. It holds a vacuum and could be it leaks. Maybe a check valve didn't take the backfire too well?

Except a blown of secondary vacuum hose will not cause smoke. The smoke is from the MAP sensor not getting the vacuum and sending a incorrect voltage reading.

[Aurora40]

Originally Posted by Jeffvette

Except a blown of secondary vacuum hose will not cause smoke. The smoke is from the MAP sensor not getting the vacuum and sending a incorrect voltage reading.

I guess I misread. I thought he meant it was rough and smokey after the backfire. Not after the backfire and subsequent restarting. There's always some smoke in my engine bay after a backfire too.

If it runs rough, to answer the first question, yes the MAP line could come off the plenum vs the sensor. But it's not "under" the plenum, it's right there on the back, you can get to it without removing anything.

I guess I don't quite follow exactly what happened?

[4DSZR1]

Heres how it went down

Backfire....smoke in garage form exhaust
Went in and got truck keys
Came back and open the Corvette hood...smoke was present (never before)
Started up, ran rough and smoke from both the exhaust and engine area
Shut off could hear a hissing sound from what I thought was under the plenum

Post on ZR1netregistry
Call Jeff


:-)

Thanks everyone for the input

[Nick]

Rick, I gave all of my plenum pull tools away, but not my knowledge. I'm always willing to help!

I'll bet if you look hard enough with a flashlight, you'll see the MAP sensor hose is off. Good luck!

[4DSZR1]

The experts/experienced were right again... What the hell would we (ME) do without this place.

The elbow and plastic piece had blown off the maf and the plenum and were on the floor in my garage cleaned them up reinstalled and giddeeup she was running again.

Thanks again you guys!

Rick