LS1 Backfire (VIDEO) what do you think?
03-22-2008, 03:16 PM
#21
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
Well guys i traded the xpipe for a off road y pipe (hooker that goes with the headers) and I installed it and fired it up, still runs the same, still throws fire out the back and pops etc. Well ive basically taken the o2 situation out of it. Im thinking either bad coil or timing chain. I can also get it flashed back to stock and see how that goes. I dont know the tune history on the engine but the guy did work for a performance shop and im sure it had a tune atleast once. How can I test the coils on the car? or where should I take them? I have a volt/ohm meter. Thanks for any input or ideas. New video coming soon.
03-23-2008, 11:09 AM
#24
Are you getting a MIL or any trouble codes? Does it only pop on initial startup and is fine after it's running? The video isn't long enough for me to tell, but it seems to rev fine after it fires up(maybe a little lazy/poor throttle response). What year engine and PCM are you running?
03-23-2008, 01:58 PM
#25
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
all 98 SS stuff, it pops on start up, sounds alright on idle but you can hear it missing a little i believe and once you put in gear and drive it, it pops more. MIL is not lit, still need to scan for codes.
03-23-2008, 03:07 PM
#26
Open headers will do that, especially since the O2 sensors are right there in the open air, they will send a false lean signal to the PCM which will dump more fuel in trying to compensate for a false lean which will in turn make it really rich. A very rich mix will not fully burn in the chamber and instead will dump into the header and ignite there. Get some pipes on it and you should be fine, you should not need a tune, the PCM can compensate.
Dead on Brad. 
03-24-2008, 06:36 PM
#32
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
Just tested the wires, from what I found, resistance should be around 351 ohms (6in ls1 wire). Here's what I found:
Cylinder
#1 - 392 Ohms
#3 - 398 Ohms
#5 - 394 Ohms
#7 - 400 Ohms
#2 - 393 Ohms
#4 - 390 Ohms
#6 - O.L. (Out of Limit most of the time) Initial reading was around 3,000 and I only got it to read this wire about 3 times in total out of the 30 times of trying. When it did test the other 2 times, it was 386 and 393.
#8 - 380-1700 Ohms was the range for this one, it was in range a couple times but most of the time it was way out of range, initial reading was 980 Ohms.
So what I concluded was that wires 6 and 8 are bad and probably firing only a couple times and causing it to back fire, ill replace those first to see what it helps. I will check plugs next, when they were new though the car acted the same.
I also tested one coil, it had no resistance, which is what I was told it should be.
Cylinder
#1 - 392 Ohms
#3 - 398 Ohms
#5 - 394 Ohms
#7 - 400 Ohms
#2 - 393 Ohms
#4 - 390 Ohms
#6 - O.L. (Out of Limit most of the time) Initial reading was around 3,000 and I only got it to read this wire about 3 times in total out of the 30 times of trying. When it did test the other 2 times, it was 386 and 393.
#8 - 380-1700 Ohms was the range for this one, it was in range a couple times but most of the time it was way out of range, initial reading was 980 Ohms.
So what I concluded was that wires 6 and 8 are bad and probably firing only a couple times and causing it to back fire, ill replace those first to see what it helps. I will check plugs next, when they were new though the car acted the same.
I also tested one coil, it had no resistance, which is what I was told it should be.
03-25-2008, 04:48 AM
#33
TECH Addict
iTrader: (1)
Join Date: May 2007
Location: NY
Posts: 2,516
Likes: 0
Received 0 Likes
on
0 Posts
Open headers will do that, especially since the O2 sensors are right there in the open air, they will send a false lean signal to the PCM which will dump more fuel in trying to compensate for a false lean which will in turn make it really rich. A very rich mix will not fully burn in the chamber and instead will dump into the header and ignite there. Get some pipes on it and you should be fine, you should not need a tune, the PCM can compensate.
I can practically smell the rich-ness through the computer!
03-25-2008, 08:07 AM
#34
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
once again, not running open headers anymore, the o2's arent close to open air, still doing it, thats not the problem. but it is probably running rich.
04-04-2008, 08:57 PM
#35
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
replaced the faulty stock wires with MSD 8.5mm wires and i fired it up, didnt pop, could still hear it hesitate a little but I will test it for real tommorow, try to drive it and see what it does under load. I did get some smoke from the cylinder that had the bad wire and that says to me it wasnt even firing because i coated the headers and when you start a car for the first time after coating them they smoke a little. Well it was smoking from that cylinder. I still have a little work to do and well see how everything goes.
04-10-2008, 01:31 PM
#36
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
im going to check the timing chain. but i put MSd wires and after watching my vid again i just noticed only the passenger side is throwing flames........... and 6 & 8 had bad plug wires but it is still popping. What could I check for ...... may just be that side only.
04-10-2008, 02:16 PM
#38
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
they have new plugs, ima check them out today, i ordered a double roller cc kit just in case. im leaning towards maybe a bad coil on 6 & 8. Cant believe i just noticed the fire only on one side. Thanks
04-10-2008, 03:53 PM
#40
TECH Fanatic
Thread Starter
iTrader: (78)
Join Date: Feb 2007
Location: Dallas, TX
Posts: 1,075
Likes: 0
Received 0 Likes
on
0 Posts
good thinking. i will check the pushrod fist, take my y pipe off, see if it only shoots fire out the passenger side. If it is then ill move the pass coils to driverside and driverside coils to pass side. if it shoots flames out the drivers side then it was the coils. if it doesnt i can check the pushrod and possibly pull the passenger head.