ComancheGurl Posted January 13, 2012 Share Posted January 13, 2012 The deal is I have a 88 mj 4.0 auto trans PO beat the piss out of it so far I've replaced one pushrod,timing chain&gears,vacuum lines,etc. Took apart head and replaced a bent pushrod,brand new gaskets on the thing,all vaccuum hoses have been replaced within the last 3 months,all injectors are firing,after installing new pushrod it still acts the same. Also replaced fuel filter&pump. Currently rebuilding another motor for it out of a 94. Any ideas?? thanks in advance Link to comment Share on other sites More sharing options...
HellCreek Posted January 13, 2012 Share Posted January 13, 2012 According to my limited mechanical knowledge, en engine backfires when an intake valve is open at the same time the spark plug is firing. I would look at either the valve timing or the ignition timing -- or both. Or, if you changed the plug wires, check the firing order. -Tom Link to comment Share on other sites More sharing options...
carnuck Posted January 13, 2012 Share Posted January 13, 2012 pump it for compression Link to comment Share on other sites More sharing options...
JeffN Posted January 13, 2012 Share Posted January 13, 2012 if you bent a pushrod you may have bent the valve, run a compression test on the cylinder to confirm Link to comment Share on other sites More sharing options...
ComancheGurl Posted January 13, 2012 Author Share Posted January 13, 2012 Timing is good. Different cylinder head so i'll check the valves and run a compression test. Firing order is correct. Link to comment Share on other sites More sharing options...
Eagle Posted January 14, 2012 Share Posted January 14, 2012 If it's backfiring, it is virtually 100 percent certain that the timing can't be good. Check it again. Be sure #1 is at top dead center ON THE COMPRESSION STROKE, then check the distributor to see if the rotor is pointing at the #1 terminal in the cap. Link to comment Share on other sites More sharing options...
ComancheGurl Posted January 14, 2012 Author Share Posted January 14, 2012 Already did that. It runs fine at idle but sputters when you step on it hard. Link to comment Share on other sites More sharing options...
raviolli Posted January 15, 2012 Share Posted January 15, 2012 clogged catalytic converter? :dunno: Link to comment Share on other sites More sharing options...
carnuck Posted January 15, 2012 Share Posted January 15, 2012 Rotor may need resetting in the dist. Link to comment Share on other sites More sharing options...
ComancheGurl Posted January 15, 2012 Author Share Posted January 15, 2012 The exhaust system seems to be in good shape but ill check it anyway. And ill check the setting of the rotor as well. Link to comment Share on other sites More sharing options...
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