lt1 backfire through the intake when warmed up
Thread Starter
Heel & Toe
Joined: Apr 2004
Posts: 19
Likes: 0
From: fort wayne in
lt1 backfire through the intake when warmed up
tested all injectors resistance hot and cold 11.9-12.8 ohms, checked for intake leaks. installed vaccuum guage 21 inches at idle. install fuel pressure guage 40 lbs. replaced plugs,wires . replaced waterpump and optispark per forum members still doing the same thing :beatdeadhorse: any help would be appreciated
Le Mans Master
Joined: Feb 2000
Posts: 9,715
Likes: 27
From: Kempner Texas
Re: lt1 backfire through the intake when warmed up (jpslt1)
Have you made any adjustment to the lifter preload? Are you absolutely sure you don't have a crossed plug wire? 5 and 7 are easy to cross.
Jake
Jake
Thread Starter
Heel & Toe
Joined: Apr 2004
Posts: 19
Likes: 0
From: fort wayne in
Re: lt1 backfire through the intake when warmed up (JAKE)
no adjustments to the preload , only backfires warm vaccuum guage is steady at 21 inches , before vehicle goes into closed loop it runs great no backfire
Thread Starter
Heel & Toe
Joined: Apr 2004
Posts: 19
Likes: 0
From: fort wayne in
Re: lt1 backfire through the intake when warmed up (JAKE)
no adjustments to the preload , only backfires warm vaccuum guage is steady at 21 inches , before vehicle goes into closed loop it runs great no backfire checked the wires 3 times all are in the right places
Drifting
Joined: May 2002
Posts: 1,581
Likes: 2
From: The Motor City
Re: lt1 backfire through the intake when warmed up (tlc85)
May sound dumb, but check the 4 bolts holding the throttle body to the plenum.
I had a backfire problem a few years ago that was coming through the intake. Sure enough (and don't ask how I figured this one out), the shop that had done work to the car only days ealier didn't tighten the throttle body bolds down properly. Under acceleration or cruising everything was fine, but on deceleration the throttle body would shift forward slightly creating a gap between the throttle body and the plenum. This gap allowed unmetered air (bypassing the MAF) to enter the plenum and cause the computer to do weird things and causing the backfire.
Hope that helps. :cheers:
I had a backfire problem a few years ago that was coming through the intake. Sure enough (and don't ask how I figured this one out), the shop that had done work to the car only days ealier didn't tighten the throttle body bolds down properly. Under acceleration or cruising everything was fine, but on deceleration the throttle body would shift forward slightly creating a gap between the throttle body and the plenum. This gap allowed unmetered air (bypassing the MAF) to enter the plenum and cause the computer to do weird things and causing the backfire.
Hope that helps. :cheers:
5th Gear
Joined: Sep 2012
Posts: 5
Likes: 0
I'm having the same problem with my 96 LT1 it backfires thru the intake also. I have changed the fuel filter, sparkplugs and even the PCV valve. I have good ohm reading on all of the injectors as well as good. Fuel pressure with the key on around 15psi and at idle 2psi and 30 psi while driving. I'm not sure where to look next. The car idles and starts right up. But I can drive it a mile or two and then know power. Help please!
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Race Director
Joined: Apr 2000
Posts: 15,344
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From: Texas
I'm having the same problem with my 96 LT1 it backfires thru the intake also. I have changed the fuel filter, sparkplugs and even the PCV valve. I have good ohm reading on all of the injectors as well as good. Fuel pressure with the key on around 15psi and at idle 2psi and 30 psi while driving. I'm not sure where to look next. The car idles and starts right up. But I can drive it a mile or two and then know power. Help please!
If you fuel pressure is that low, then either your fuel pump is shot or the fuel pressure regulator is bad. Plenty of threads on both of these items regarding how to check and replace them as needed.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
I'm having the same problem with my 96 LT1 it backfires thru the intake also. I have changed the fuel filter, sparkplugs and even the PCV valve. I have good ohm reading on all of the injectors as well as good. Fuel pressure with the key on around 15psi and at idle 2psi and 30 psi while driving. I'm not sure where to look next. The car idles and starts right up. But I can drive it a mile or two and then know power. Help please!
it takes 40 psi to run...right.
15 psi won;t get anything but a backfire...
Get yourself a FSM so you know what these numbers are and what they mean to your car.
Racer
Joined: Jun 2006
Posts: 361
Likes: 6
Backfiring through the intake is a good indication that you are running lean.
Race Director
Joined: Apr 2000
Posts: 15,344
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From: Texas
...rather than check the fuel pressure regulator and perhaps only have to spend $50 rather than $200 
