85 302EFI backfire
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From: North Carolina
85 302EFI backfire
Bought a 1985 4x4. Man told me he had the motor rebuilt bored 60 over. Trouble is it backfire through the air intake during hard acceleration. It will start and idle fine. Have replaced plugs, wires, rotor and cap. Poured in two cans of gumout and it still does it. Sounds like popcorn popping , if you let off it quits. The smog air pump is gone. Can I do away with the EGR valve? I get a 44, 34, and 13(i think)codes. One says thermactor system trouble, one say EGR soemthing or other and the last one is idle speed. Hey, this is an old farm truck, I dont want to sink a lot of cash in it. What do I need to try next?
Gary
Gary
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Joined: Jul 1999
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85 302EFI backfire
Usually what you describe indicates burned intake valves , They dont seal so you get part of the combustion process making its way back up thru the intake . If the air pump isnt there that would account for one code (44) The egr related code is likely the egr valve is stuck closed & the Idle air valve likely needs cleaning , Code 13 would indicate its not closing fully .
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Joined: Jul 1999
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85 302EFI backfire
Well , Removing the valve covers & running the engine will turn into a mess in a hurry . The backfiring problem you described sounds like burned valves . You may want to have your local mechanic drive the truck & give you his opinion .
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From: Virginia
85 302EFI backfire
Doing a compression check on the engine should uncover any problem with the valves.
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Moderator
Joined: Jan 2001
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From: Virginia
85 302EFI backfire
Doing a compression check on the engine should uncover any valve problems. A burnt valve would also cause a dead miss which you can hear and test for by pulling the sparkplug wires off one at a time and see if the engine slows. If it does slow and run rough with the wire off=good cylinder. If it doesn't slow=bad cylinder.
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Joined: Jan 2001
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From: Virginia
85 302EFI backfire
Doing a compression check on the engine should uncover any valve problems. A burnt valve would also cause a dead miss which you can hear and test for by pulling the sparkplug wires off one at a time and see if the engine slows. If it does slow and run rough with the wire off=good cylinder. If it doesn't slow=bad cylinder.
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Freshman User
Joined: Oct 2000
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From: North Carolina
85 302EFI backfire
Here's an update. I went today to start it up and it wouldn't start! I looked for a Schrader fitting to check fuel pressure but can't find it. It's not on the fuel rail unless it's stuck under the upper intake manifold. Checked for spark and it was good so I figured it was fuel related. I checked the frame mounted fuel filter and couldn't believe it!! There was dirt/crud caked all in the thing, there was no room for fuel!. Decided to pull the tank and man was it bad, rust everywhere. Took it to the radiator shop to flush and he said it would run me 50-75 bucks and could show up a lot of leaks or I could get a new tank for 125. I was a sucker and ordered a new tank. Since my fuel sending unit was bad I also ordered a new low pressure pump/sending unit assembly. I 'll post later if that cures my backfire/ cutting out problem. By the way I busted my accelerator cable white plastic thing near where it connects to the throttle body. Can I get just that piece or a whole new cable assembly? Forgot to ask the parts man and I'm working until Monday.
Gary
Gary
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Freshman User
Joined: Oct 2000
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From: North Carolina
85 302EFI backfire
Well, I put everything back and it runs like a champ. Like I read in an earlier article, check the simple stuff first. My trouble was a gummed up fuel system. Thanks for the help everybody.
