Backfires
Thread Starter
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Joined: Oct 2003
Posts: 91
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From: Central OH
Backfires
I have been able to take my Z out a couple of times this week thanks to Mother Nature and I noticed that when I am slowing down and I engage the clutch to downshift, the car backfires sometimes. 
Any suggestions?? I have read that having a vacuum leak can cause this, but being new to Z's, I thought I would ask some of the experts here.
Thanks for your help in advance.
Jim
Any suggestions?? I have read that having a vacuum leak can cause this, but being new to Z's, I thought I would ask some of the experts here.
Thanks for your help in advance.
Jim
Drifting
Joined: Sep 2003
Posts: 1,948
Likes: 2
From: Southern England
Vacum leak, from memory ,when you turn the key you should here a derrrrring noise from the passenger side Headlight area (vacum pump)for around 8 secs,then the noise will stop,this is normal,but if the noise carries on intermitently or continuous then you have a leak.
Vacum parts you can see,a vacum pipe comes out around the oil filter/alternator side goes out to wheel well under water overflow and to pump just ahead of overflow,be careful with the vacum pipes they can get very brittle.
Vacum parts you can see,a vacum pipe comes out around the oil filter/alternator side goes out to wheel well under water overflow and to pump just ahead of overflow,be careful with the vacum pipes they can get very brittle.
Melting Slicks
Joined: Dec 2004
Posts: 3,285
Likes: 52
From: Jacksonville, FL
St. Jude Donor '08 thru '26
Service Manual?
Hi, Look I'm a rookie Z owner so I'm not LT5 literate yet. I looked up Backfire in the ser. manual I got from Helm in the "Driveability and Emissions" section. Under "Full engine power" it says the fault could be in the secondary port throttle valve operation. It says ubder "normal power" to check:
Compression - look for sticking or leaking valves.
Valve Timming, see section 6, mechanical diagnosis
Do fuel sys. diagnostic test. See Chart A-7
Check plug wires for crossfiring & routing
Ignition sys for intermittant condition, see section C4
Injector balance test, Chart C-2A
Output voltage of coils, spark tester
Intake & exh. manifold casting flash.
sorry I'm not a mechanic, but I've heard that the vacume leaks will play havoc on a LT5. That might be a place to start. I type too slow. Disregard my reply cause the other guy is telling you straight! Tom
Compression - look for sticking or leaking valves.
Valve Timming, see section 6, mechanical diagnosis
Do fuel sys. diagnostic test. See Chart A-7
Check plug wires for crossfiring & routing
Ignition sys for intermittant condition, see section C4
Injector balance test, Chart C-2A
Output voltage of coils, spark tester
Intake & exh. manifold casting flash.
sorry I'm not a mechanic, but I've heard that the vacume leaks will play havoc on a LT5. That might be a place to start. I type too slow. Disregard my reply cause the other guy is telling you straight! Tom
Last edited by tomtom72; Apr 9, 2005 at 09:01 AM. Reason: I type to slow!
Melting Slicks
Joined: Feb 2001
Posts: 2,512
Likes: 5
From: ZR1 Gathering '04, '05 Northlake Texas
The LT5 runs a little rich, I know mine does and it backfires every once in awhile when you let off the gas at high speeds, like at the drag strip when I let off at the end of the run. I don't think it is anything to worry about at least that is what I have been told. I just always check my MAP connection after a back fire to make sure the hose wasn't blown off.
Thread Starter
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Joined: Oct 2003
Posts: 91
Likes: 0
From: Central OH
Thanks for the suggestions. No mods to the vette other than the Corsa exhaust. I called a local vette mechanic who actually know the car. He asked me who the original owner was and I told him and he knows the car!! I was pretty happy to hear that. He said the computer in the car may not be able to adjust fast enough with the Corsas. He said he would hook it up to the computer at no charge.
So, I'm taking it to him tomorrow and I'll know more after that.
So, I'm taking it to him tomorrow and I'll know more after that.
Team Owner
Joined: Jul 2002
Posts: 37,049
Likes: 69
From: This city NEVER sleeps! Frank's back yard!
Originally Posted by koolaid117
Thanks for the suggestions. No mods to the vette other than the Corsa exhaust. I called a local vette mechanic who actually know the car. He asked me who the original owner was and I told him and he knows the car!! I was pretty happy to hear that. He said the computer in the car may not be able to adjust fast enough with the Corsas. He said he would hook it up to the computer at no charge.
So, I'm taking it to him tomorrow and I'll know more after that.
So, I'm taking it to him tomorrow and I'll know more after that.
There is absolutely nothing wrong with your car. You're not hearing backfires, just extra fuel being burnt - it is just louder with the corsa.
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Drifting
Joined: May 2000
Posts: 1,651
Likes: 0
From: Missoula Montana
Hi Jim-
Whether you have a vacume leak or not you should become familiar with how to check if you do have one. Not to get exicited if you do, it would have to be very bad to have a noticable effect in typical street use. Check this link out it is an excellent intro to the world of the LT5 vacume system: http://corvetteactioncenter.com/foru...ad.php?t=14272
Also, you should join the ZR1Net registry, you can get allot of help from people there also, as most of us here are.
Whether you have a vacume leak or not you should become familiar with how to check if you do have one. Not to get exicited if you do, it would have to be very bad to have a noticable effect in typical street use. Check this link out it is an excellent intro to the world of the LT5 vacume system: http://corvetteactioncenter.com/foru...ad.php?t=14272
Also, you should join the ZR1Net registry, you can get allot of help from people there also, as most of us here are.
Thread Starter
Advanced
Joined: Oct 2003
Posts: 91
Likes: 0
From: Central OH
I took the car to a local vette mechanic who put the car on the computer and said that it was running fine and that he believes that the computer in the 1990 just can't make adjustments fast enough.
