backfire after injector R&R - ZR-1 Net Registry Forums

dallas · 09-24-2010

My son and I just changed out the injectors, cleaned out a little gunk, and checked all the hoses and wires under the plenum. I started and ran the car for about 20 minutes. It started right up, but did seem to have a slight miss at idle. You know...the little "pup-pup-pup" that comes out of the exhaust even though the engine sounds smooth up front. We figured it might need a little "relearning" from the computers since it was down and disconnected for several months.

I started it again today after a week of sitting. It started right up, but still has the "pup-pup" at the exhaust. This time, however, when I made some quick stabs on the throttle from idle speed I got a very sharp backfire Not a low "pop", but more of a higher pitched "crack" or "snap" sound. When punched from approx. 2000 rpms it responded very well and was smooth till I let off around 5K.

I checked all the hoses that would normally blow off or have a problem and they all seem to be attached and ok.

SOoooooo...what would be causing this backfire?

OH...the TB is open in front and I have not put the air filter tube back on yet.

John Boothby · 09-24-2010

I wouldn't run the engine w/o the intake duct and air cleaner attached. The LT5 will suck in a lot of air and if any debris is in the area it will get sucked in. NOT GOOD!

tccrab · 09-24-2010

Have you driven it at all?
Your post makes it sound like you've only started it but not driven it.
Maybe you have a little carbon build up in the cylinders and in the exhaust.

Take it out and flog it good.
Bounce it off of the revv limiter in first and second a couple of times.
Get the old girl nice and hot.
If it's something major it'll throw a code and you'll have something better to work with.

TomC
'Crabs

rhipsher · 09-24-2010

Once you had the injectors installed on the fuel rails did you use any kinda lube on the orings to help press them in to the I/H. Cause if they don't seat right that might cause this. I used some all lube when I've installed injectors in the past and not only does it make them go in easy but you can feel when they seat right. Just my .02.

dallas · 09-25-2010

1- we did lube the o-rings as we installed the injectors. We also tested the whole rail and injectors for leaks before reinstalling. None.

2- no, I haven't taken it out of the garage yet. Maybe tomorrow.

3- Yes, I need to put the air filter and tube back in the mix. Maybe there's too much air sucking right into the TB. I'll do that tomorrow for sure.

Thanks.

09-24-2010	#1
dallas Join Date: Feb 2004 Location: Las Vegas Posts: 17	backfire after injector R&R My son and I just changed out the injectors, cleaned out a little gunk, and checked all the hoses and wires under the plenum. I started and ran the car for about 20 minutes. It started right up, but did seem to have a slight miss at idle. You know...the little "pup-pup-pup" that comes out of the exhaust even though the engine sounds smooth up front. We figured it might need a little "relearning" from the computers since it was down and disconnected for several months. I started it again today after a week of sitting. It started right up, but still has the "pup-pup" at the exhaust. This time, however, when I made some quick stabs on the throttle from idle speed I got a very sharp backfire Not a low "pop", but more of a higher pitched "crack" or "snap" sound. When punched from approx. 2000 rpms it responded very well and was smooth till I let off around 5K. I checked all the hoses that would normally blow off or have a problem and they all seem to be attached and ok. SOoooooo...what would be causing this backfire? OH...the TB is open in front and I have not put the air filter tube back on yet. Last edited by dallas; 09-24-2010 at 04:36 PM.

09-24-2010	#2
John Boothby Join Date: Jul 2005 Location: Las Vegas, Nevada Posts: 777	Re: backfire after injector R&R I wouldn't run the engine w/o the intake duct and air cleaner attached. The LT5 will suck in a lot of air and if any debris is in the area it will get sucked in. NOT GOOD! __________________ JB 1990 #148 Red/Saddle Haibeck AYBKG5 Chip/RC Engineering/Flowmasters/K&N/Samco/Fuzzy Dice :cheers:

09-24-2010	#3
tccrab Join Date: Oct 2004 Location: Folsom CA Posts: 1,655	Re: backfire after injector R&R Have you driven it at all? Your post makes it sound like you've only started it but not driven it. Maybe you have a little carbon build up in the cylinders and in the exhaust. Take it out and flog it good. Bounce it off of the revv limiter in first and second a couple of times. Get the old girl nice and hot. If it's something major it'll throw a code and you'll have something better to work with. TomC 'Crabs __________________ TomC '90ZR1 #792 Honorary Pirate [B]If it ain't FUN, you're doing something terribly WRONG. [/B]

09-24-2010	#4
rhipsher Join Date: Aug 2008 Location: Houston 90 Red ZR-1 Posts: 2,320	Re: backfire after injector R&R Once you had the injectors installed on the fuel rails did you use any kinda lube on the orings to help press them in to the I/H. Cause if they don't seat right that might cause this. I used some all lube when I've installed injectors in the past and not only does it make them go in easy but you can feel when they seat right. Just my .02.

09-25-2010	#5
dallas Join Date: Feb 2004 Location: Las Vegas Posts: 17	Re: backfire after injector R&R 1- we did lube the o-rings as we installed the injectors. We also tested the whole rail and injectors for leaks before reinstalling. None. 2- no, I haven't taken it out of the garage yet. Maybe tomorrow. 3- Yes, I need to put the air filter and tube back in the mix. Maybe there's too much air sucking right into the TB. I'll do that tomorrow for sure. Thanks.