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  #1  
Old 12-05-1999, 09:30 PM
Squad Squad is offline
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Problem: engine miss under a load. Idles good cruises good slightest load miss. Everything in the engine is new accept pistons rings, heads redone electronic ign,carb is new, just put in new plugs and wires cap rotor, a bad valve? what is it I'm going nuts. It didn't do it for 2 years. It got worse when I put on a single plane intake. It is one cylider can't figure out which one.
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  #2  
Old 12-06-1999, 01:02 AM
J.J.
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What Carb do you Have? if its a thermo quad you might have some Bent Metering Rods if its a AFB you might have to DO some jetting If its a HOLLEY get A ROPE!
Also the elect control box (the one on the Firewall) could be starting to go bad pull it off and look at the back of it and see if its real soft or melted if so get a new one, or the one that will make you pull your hair out is a Bad Plug Pull them all and look to see if they are burning correctly they should be a light grey color if not find a chiltons manual the ones they sell at autozone and look at the plug chart it will tell you if theres any internal problems ie:rings,too rich,lean ect
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  #3  
Old 12-06-1999, 06:07 PM
Squad Squad is offline
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I,ve switched the plugs a couple times, the carb is a new holley 3310, if it was the ign ecu wouldn't it miss on all the cylinders. Could it be a vacuum leak? And if it were the rings it should burn oil or something.
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  #4  
Old 12-06-1999, 09:30 PM
rat roaster rat roaster is offline
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Over the years I have found most under load misses to be caused by spark. Have the engine scoped this will tell you how each cylinder is working.I use Acell # 134 plugs and heli coil 8 mm wires , blaster coil ,Acell cap ,etc.Keep plug wires away from hot metal,and insure all your electrical connections are tight and clean.I have seen miss fires from dirty or damaged E C U plugs . If you have changed the intake and its worse ,check for leaks ,sray WD-40 around the gasket area to see if engine rpm changes ,also slowly cover the carb with your hand and see if the engine rpm speeds up both are signs of vacume leak.Check your plugs what colour are they ? Hows your fuel pump ? If the engine is pretty much stock use # 72 jets in the primarys and a 6.5 power valve . I myself like Hollies they are great carbs your 3310 should work great.Put a vacume gauge on a untimed intake vacume port,the vacume should stay steady at idle and if engine is stock well over 10 inches @ 900 rpm .If the vacume gauge bonces like crazy you may have a bad valve ,do a leak down or a compression test .What is your compression P S I .What happens when you hammer it to the floor ? Is the distributor new ,is it a MP distributor , I had one of these that was not phased properly inside and the engine ran good at light throttle untill you stepped on it,I recurved an old one ,12 degrees initial and 36 deg total all in @ 3000 rpm ,try a distributor from a wrecker.What is the shape of your distributor bushings,grab your rotor and see how much side play the shaft has ? Does it backfire through the carb or exhaust?Where is your timing at?How many miles are on the engine ? This is probably just a small problem you just have to step by step work through it .

[This message has been edited by rat roaster (edited December 06, 1999).]
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  #5  
Old 12-06-1999, 10:37 PM
PRO PRO is offline
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Hey Squad there could be a million different things,lets try to establish a logical line of thinking starting with is it an ign. or fuel related problem? Electrical failures outnumber mechanical ones,8 out of 10 are electrical,so take the odds and start there.The most common point of ign. miss I've seen in a mopar is the air gap(between the p/u coil and reluctor).To check it take a .010 and a .008 brass feeler gauge, the .oo8 should fit and the .010 shouldnt.if its off it adjust just like a set of points.Also make sure you dont have side play in the dist. shaft.If the reluctor(8 point metal ring attached to dist shaft right below your rotor) has scuff marks on the outer edges of the points it means its hitting the p/u coil because of too much side play.If this checks ok your next best thing might be to just exchange known good components(ECU,coil,ballast resistor,wires,cap,rotor).Ive also had a bad ballast resistor do the same thing also.One thing you say which could be a clue is that it got worse with the single plane, this could indicate your mixture is too lean as s/p intakes like a slighty richer mixture tjis would mean you were lean before the intake change.Hope this helps...PRO...
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  #6  
Old 12-07-1999, 01:26 AM
GILBO GILBO is offline
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i think pros on to something, when i first got my electronic ing. conversion, the air gap was set at .015 and i had some missing. reset air gap after much colorful language and stomping ran much better. p.s. i never even thought to check that! till all else failed. good luck!
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  #7  
Old 12-07-1999, 04:52 AM
Squad Squad is offline
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My ign. is MP 2 years old, already changed jets, adjusted the gap in the distributor, switched plugs wires more than once, tried a different coil, had 3 intakes on it. It is one cylinder, sometimes when I punch it the miss clears up it is not random in all 8 cyliders Here is what I did to the engine,new mp muscle car cam, 452's pocket ported by me, then I spun a bearing, put in new bearings (rods mains) one new rod, basically a rebuild without the pistons. Now that I think about it I don't remember it ever missing until the last time I had it apart(the new rod and bearings. At first it onlt did it when it was cold now all of the time. I guess I'll keep looking and taking sugestions.
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  #8  
Old 12-07-1999, 08:25 AM
rat roaster rat roaster is offline
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When you spun the bearing was it a result of over reving the engine . Did you float the valves ? The piston that you changed the rod on was there a mark on it where it hit a valve ? Was there a valve mark on any pistons? How much bearing junk was in the engine did you clean it out ? Did you ever take off the valve covers and measure or at least look at the valves to see if they are all moving up and down about the same amount. Do a compression test ! If you have one real low do a leak down on it and you will know if its a bent or burnt valve . If the leak down is good you may have a bad intake lobe or lifter or rocker or pushrod or spring. I had a 440 with a slightly burnt exhaust valve that would cruise ok but when you stepped on. it it would buck and pop . If an intake valve is hardly opening you could very well have one cylinder that is missing . Does the engine have any lifter noise ? (its not a solid is it I figure the muscle car cam is a magnum clone )Oil pressure is good and all the lifters are quiet and pumped . DO A COMPRESSION TEST .Warm the engine up and pull off the valve covers and watch the valves go up and down as you crank it.Take a good look at the valve train .It will eliminate alot of guessing . Sounds like you are tired of changing the electrical parts .

[This message has been edited by rat roaster (edited December 07, 1999).]
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  #9  
Old 12-07-1999, 06:18 PM
Squad Squad is offline
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The valve spings are MP 3690933 has a high volume oil pump, lifters never mad a sound. I didn't look at the piston but it never floated what happened was I was going faster than my speedo showed for about 3 miles(5800rpm) everything was fine. I started cruising home going about 55 and it started jerking I got out and heard a loud knock. I had to get home so I drove another 7 miles. I live in MN so I guess when sping comes back I'll pull it apart. I've heard of MP cams going flat (happened to a friend of mine) Wouldn't that be a constant miss?
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