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  #1  
Old 12-30-2006, 03:07 PM
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Exclamation New Motor backfiring

Hey all,
I just bought this car.http://www.turbobuicks.com/forums/sh...ad.php?t=56233
Its in the shop right now, and they've installed the CAM sensor correctly, and fixeda fuel problem we've been having for a few weeks.(a smashed wire near the ECM) So, we have spark and gas, but the car won't turn over. It just pops and pops and then backfires after a few seconds. We did not build this motor, it was in the car when I bought it. We think that the valves clearances are set too tight. Maybe its not getting enough air into the cylinders?
Does this sound like a good place to start troubleshooting? All input is appresciated!!!
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Old 12-30-2006, 07:15 PM
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Default Re: New Motor backfiring

check the timing marks on the cam and crank
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Old 12-30-2006, 09:16 PM
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Default Re: New Motor backfiring

first.. to make sure your are working with an engine that is in good conditon..
Id do a compression test .. its free and can give some good info.
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Old 12-30-2006, 11:44 PM
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Default Re: New Motor backfiring

All good advice. And doulbe check that sparkplug wires are correct.
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Old 12-31-2006, 05:28 PM
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Default Re: New Motor backfiring

Thanks,
Next Week we're gonna pull the valves covers and rotate the motor by hand and check the clearances. If the timing marks are right the #1 cylinder valves will open at TDC? Please correct me if i'm wrong. I don't want to pull the timing cover if I don't have to. We will check compression and wires(again) before we pull the covers.
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Old 12-31-2006, 05:46 PM
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Default Re: New Motor backfiring

Well, at TDC on the power stroke, the valves will be closed....
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Old 01-02-2007, 09:23 AM
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Default Re: New Motor backfiring

thanks,
is rotating the crank by hand and watching the valves an effective way to see if the timing is set? Or am i better off breaking the motor down? Can I take the timing cover off without taking off the water pump?

Last edited by BoostedEvIL; 01-02-2007 at 09:25 AM. Reason: typos
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Old 01-02-2007, 10:03 AM
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Exclamation Re: New Motor backfiring

You can leave the pump on.

I really wonder if you're going at this too hard. If its turning over OK, things can't be that far off. Might want to give the crank and cam sensors a hard look before you get your hands too dirty. Hate for you to tear a motor down that just has those items set a little off.
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Old 01-02-2007, 10:38 AM
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Default Re: New Motor backfiring

I agree with Scott! Most likely it's something simple like the crank sensor/cam sensor.

Does this car have roller rockers? If so, check the lash .. if they are too tight, it can hold open the valves and cause all sorts of chaos.

If it comes to taking the front cover off, check to see that you aren't a tooth off on the timing chain.
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Old 01-02-2007, 09:21 PM
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Default Re: New Motor backfiring

thanks again guys.
yes, it does have roller rockers.
I finally got in touch with the guy that build the motor. He said that he adjusted the lifter preload before he primed the oil pump. (The car has The comp cam 206/206 matched kit with hydo lifters.) Is this a big deal? Could the lifters have collapsed?

Last edited by BoostedEvIL; 01-03-2007 at 07:41 AM.
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