Back fire at start - ZR-1 Net Registry Forums

efnfast · 04-25-2012

Just put headers and exhaust on the car. Now when I start the car in the morning, it backfires? kinda'. Injectors leaking fuel into cylinders? I've only had the car for a year and I don't know if they've ever been changed.
TIA Steve

VetteMed · 04-25-2012

I was experiencing backfires on a consistent basis when I had a vacuum leak.

efnfast · 04-25-2012

It only does it when I first turn the key, before it really fires up. Seems to be running fine. Altough the idel has been high, and fluctuating. Maybe a vacuum leak, or just 'cause it's breathing better.

-=Jeff=- · 04-25-2012

leak in the exhaust at one of the pipe joints will do it too

VetteMed · 04-25-2012

High fluctuating idle is another common sign of vacuum leak. How is your cruise control and HVAC working (do all the different vent positions function properly)?

efnfast · 04-25-2012

haven't used the cruise lately. HVAC seems to be ok, but I'll pay closer attention. It does this before the engine even fires up. Like one of the cylinders had some fuel sitting in it.

VetteMed · 04-25-2012

yes, mine was doing the same thing when I had a vacuum leak at the junction of the check valve and the line that supplies the HVAC and cruise systems with their vacuum.

efnfast · 04-25-2012

Sounds like I better start looking for a vacuum leak. I would have thought a vacuum leak would only be a problem after the car was running.
Key on, engine not running- vacuum pump cycled at 1 min, 45 sec's. It only ran for about 2 seconds.

scottfab · 04-25-2012

I get a backfire every time I release the key too early after a start.
Solution: I keep the key turned a little longer.

sammy · 04-25-2012

might ck and see if the hose connected to the sensor at the back of the plenum is tight , it gets oil and heat soaked and can leak .

04-25-2012	#1
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,241	Back fire at start Just put headers and exhaust on the car. Now when I start the car in the morning, it backfires? kinda'. Injectors leaking fuel into cylinders? I've only had the car for a year and I don't know if they've ever been changed. TIA Steve

04-25-2012	#2
VetteMed Join Date: Mar 2009 Location: Ocala, FL Posts: 1,827	Re: Back fire at start I was experiencing backfires on a consistent basis when I had a vacuum leak. __________________ No fun cars :( 1991 ZR-1 #302 White/Gray (sold) 1991 ZR-1 #1147 Red/Saddle (sold)

04-25-2012	#3
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,241	Re: Back fire at start It only does it when I first turn the key, before it really fires up. Seems to be running fine. Altough the idel has been high, and fluctuating. Maybe a vacuum leak, or just 'cause it's breathing better.

04-25-2012	#4
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,131	Re: Back fire at start leak in the exhaust at one of the pipe joints will do it too __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - 3" Magnaflow Bullet cats - LT4 Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

04-25-2012	#5
VetteMed Join Date: Mar 2009 Location: Ocala, FL Posts: 1,827	Re: Back fire at start High fluctuating idle is another common sign of vacuum leak. How is your cruise control and HVAC working (do all the different vent positions function properly)? __________________ No fun cars :( 1991 ZR-1 #302 White/Gray (sold) 1991 ZR-1 #1147 Red/Saddle (sold)

04-25-2012	#6
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,241	Re: Back fire at start haven't used the cruise lately. HVAC seems to be ok, but I'll pay closer attention. It does this before the engine even fires up. Like one of the cylinders had some fuel sitting in it.

04-25-2012	#7
VetteMed Join Date: Mar 2009 Location: Ocala, FL Posts: 1,827	Re: Back fire at start yes, mine was doing the same thing when I had a vacuum leak at the junction of the check valve and the line that supplies the HVAC and cruise systems with their vacuum. __________________ No fun cars :( 1991 ZR-1 #302 White/Gray (sold) 1991 ZR-1 #1147 Red/Saddle (sold)

04-25-2012	#8
efnfast Join Date: Nov 2011 Location: Dunbarton NH Posts: 7,241	Re: Back fire at start Sounds like I better start looking for a vacuum leak. I would have thought a vacuum leak would only be a problem after the car was running. Key on, engine not running- vacuum pump cycled at 1 min, 45 sec's. It only ran for about 2 seconds.

04-25-2012	#9
scottfab Join Date: Jan 2009 Location: Portland Oregon metro area (Washington side) Posts: 3,207	Re: Back fire at start I get a backfire every time I release the key too early after a start. Solution: I keep the key turned a little longer. __________________ Scott Vett owner since 1979._It's about the car and the people

04-25-2012	#10
sammy Join Date: Jun 2010 Location: back in lone pine Posts: 591	Re: Back fire at start might ck and see if the hose connected to the sensor at the back of the plenum is tight , it gets oil and heat soaked and can leak .