Consistent backfire out exhaust?
Thread Starter
On The Tree
Joined: Jul 2006
Posts: 133
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Consistent backfire out exhaust? Alright guys, got a fresh short block in the car with my old heads and cam. Old motor threw a rod, heads seemed okay, I replaced an intake valve because it was bent. Now, motor starts great but it backfires every 10-15 seconds or so. It is a loud sharp crack, deff. out the exhaust, kinda like the fuel is loading up in the exhaust and then lighting off. When I check the primaries when first starting the car 7 of them will be at say 200* and then the number 8 primary will be at 150*, so quite a bit cooler. When I pulled the plugs, most were black, but the number 8 cylinder was white... Now I haven't run the car for more than 5minutes because I don't know what is causing this. Valve lash is good, oil pressure good, coolant good, no fluids seem to be mixing... Now, when I crank the motor over by hand, I can hear air "hissing" through the motor, but it is much more noticeable on the passengers side. I have no clue what to do next, I think I am going to pull the injector on the #8 cylinder and see what happens, pretty sure the popping will go away. Next, I am thinking do a leak down test...? Any other ideas, could the opti cause this? If there was a small crack in it would it cause this?
Thanks, throw all the ideas at me :-)
Bill
Thanks, throw all the ideas at me :-)
Bill
Teching In
Joined: Feb 2010
Posts: 23
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From: Grand Rapids, MI
Was the intake valve you replaced on the #8 cylinder? if so sounds like you bent the exhaust valve as well which is why it is popping out the exhaust. If all other cylinders are firing good then its not spark plug wires but i would check those also to make sure the firing order isn't messed up. Good luck let me know if you figure it out.
Thread Starter
On The Tree
Joined: Jul 2006
Posts: 133
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Yeah, that's what I was thinking too and why I am going to get a leakdown tester to check that cylinder and the others as well... Only weird thing is I hear air entering ear cylinder loudly on the passenger side, but not the drivers side. Probably just me, I dunno lol... Anyone have a good source for a leak down tester? Harbor Freight has this one pretty cheap http://www.harborfreight.com/cpi/cta...emnumber=94190 I just want to know if the hose is flexible enough to bend to the #8 cylinder or if they make like a 90* extension.
Thanks,
Bill
Thanks,
Bill
Thread Starter
On The Tree
Joined: Jul 2006
Posts: 133
Likes: 0
So does anyone know of a better place to get a leak down tester from? Autozone, Advance nor NAPA sell them, as far as I can tell... The one from HF seems to have a short hose, is there a 90* adapter I can buy or an extension that anyone knows of? Or can I just use a regular quick fitting and my own air line..?
Thanks,
Bill
Thanks,
Bill
it sounds like you injector is leaking and too much gas is getting into the combustion chamber before the plug fires
