is my 400 shot?
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Senior User
Joined: Aug 2003
Posts: 137
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is my 400 shot?
hey guys i need your advise asap, my truck has been frequently backfiring and cutting out when in drive, it's only a sometimes thing, i took it to my mechanic and he told me that my number 3 cyclinder has no compression, he suggested that i buy a rebuilt engine to replace mine, is he full of it or do i need to do this. i know he knows more than me but his explination doesn't make sense to me, my truck did this some during the summer too and i replaced a few things, like a distributor, and it stopped that's been several months ago and it's just now starting to do it again, how could my engine run for that long on just 7 cyclinders, it runs rough at idle but i have never been able to tell a power loss, please give me whatever advise you can and how much would i have to spend to get a professionaly rebuilt motor. also what kinds of things could cause a problem like this?
thanks
thanks
Elder User
Joined: Sep 2003
Posts: 908
Likes: 4
Burned valve; head gasket blown to the outside; stuck valve.
A burned or stuck intake valve can cause backfiring. This opens up the intake manifold and contents (vaporized gas) to a spark when that cylinder fires. If you have backfiring through the carb, that's the likely suspect. The engine then cuts out momentarily, because all the gas mixture that was in the manifold has been burnt.
An engine can run a LONG time on just 7 cylinders. With a burned valve, that cylinder is basically just an air pump. That backfiring is no good for your carb, though.
Sounds like your mechanic just wants to sell you an engine. Whether it needs rebuilding or not depends on the general condition of the block. Does it smoke, burn oil? If not, pull that head off and see what the problem is.
A burned or stuck intake valve can cause backfiring. This opens up the intake manifold and contents (vaporized gas) to a spark when that cylinder fires. If you have backfiring through the carb, that's the likely suspect. The engine then cuts out momentarily, because all the gas mixture that was in the manifold has been burnt.
An engine can run a LONG time on just 7 cylinders. With a burned valve, that cylinder is basically just an air pump. That backfiring is no good for your carb, though.
Sounds like your mechanic just wants to sell you an engine. Whether it needs rebuilding or not depends on the general condition of the block. Does it smoke, burn oil? If not, pull that head off and see what the problem is.
Postmaster
Joined: Jul 2003
Posts: 3,934
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From: iowa
superman, do the compression test and if you have 0 psi you have a hole in the piston or the valve is burnt up if there is compression but low it could be excessive carbon or some crap. I bet you burnt your valve cause i did the same thing this last summer. THe carb backfired and such and the biggest problem was that i have way to much timing. I had like 55+ degrees of total timing. I would tear the carb, intake, and heads off and get it replaced (the valve).
