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Old 01-03-2004, 02:27 AM
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305 Misfiring

Ok heres the deal.. My car has been sittin for about a month with the front of the motor stripped off.. Well anyways I get it all put back together and it seems to have a miss in it under a load. I took all the spark plugs out and cleaned them up nicely and made sure that each one was gettin a spark to it. This has left me stumped.. I think this was the exact problem we took the front of the motor off for.. To check and see if the timing chain was jumping teeth. It wasn't so instead we put it back together and replaced the distributor with still no avail... Anyone else got any more ideas?

They are AC Delco spark plugs.. Could it be that the insulator in one may have gotten damaged and cause it not to spark at above idle?

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Old 01-03-2004, 08:08 AM
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Since you didn't list it, I'm guessing that this is a HEI distributor on your 305. First off, if the timing chain was loose enough to provide the possibility to jump teeth, I would have replaced it while you had it apart. You say you replaced the distributor, but did you replace the cap, the rotor, or the module (providing it is an HEI)? Sometimes, with large plug wires on the HEI, if you do a lot of cranking without disconnecting your coil, you can burn up your module (I've done it!), and it still may work partially, but not provide accurate enough timing under load, sometimes causing a miss. I doubt that it's the insulator, because engine speed would not affect if it sparks or not; if it is the insulator it shouldn't spark to begin with. If it's none of these, and you're only noticing the miss under load for the most part, you could have wiped a cam lobe. I did this same things and diagnosed it as a timing problem, but after exhausting that avenue, I found it to be an exhaust lobe worn off. Maybe I'm way off, but for the information that you provided, this is what popped into my mind.
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Old 01-03-2004, 12:18 PM
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Thanks adryan... Yes its an HEI. The timing chain ended up being a double roller that was nice and snug. I replaced the distributor only keeping the same cap and the center plastic rotor piece. The HEI and everything else is new. Could it possibly be the coil goin bad and not providing enough spark at higher rpms? I don't think it would be my cam because I'd hear a rocker clapping wouldn't I? I'm thinking about replacing the cap, coil, and rotor today. Let me know if u think this may by some chance help.
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Old 01-03-2004, 01:43 PM
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ok just got through replacing the cap, coil, and rotor... Still no luck. Could it be the distributor gear on the cam maybe got chipped or sumthing causing this? I'm bout to just give up on this motor... Was plannin on replacing it with a stock 400 but didn't have enough money to buy a radiator yet so figured we would try to get this 305 running again.
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Old 01-03-2004, 02:04 PM
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Silver, the stock radiator that came with your Camaro should cool a 400 small block just fine. as long as the cooling mods have been done such as a few small holes drilled in the thermostat, a good water pump, and a good system flush has been done.
which HEI are you using? a computer controlled HEI or a mechanical advance type? even so you`ve checked all your wires, one still could be arcing off idle, since off idle the alternator is putting out full voltage and the HEI reciveves it so it too moves up in sparking power. It`s not very likely the distributor gear is chipped causing the problem. I would start the car, move the idle to a high idle at the carb, and pull off 1 plug wire at a time until I found the offending cylinder, however be careful since you could get shocked rather hard. if a cam lobe was bad you wouldn`t hear a rocker clacking, i`ve seen them be completely shot and never hear a clacking at all. pull the valve covers if the ignition checks out okay and give a look at the valve train, make sure all the rockers are in adjustment, and fire the car up at lowest idle possible and check the motion of each rocker arm, check for broken valve springs also. also check all vacuum connections and make sure there are none. if all these things check out, the next thing I would do would be a compression check, if you find the offending cylinder with the 1 plug wire removal system at a time, then you`ll know the first cylinder to check, if compression on that cylinder shows very low PSI, then you found the problem.
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Old 01-03-2004, 05:37 PM
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i would do the spark plug idea like double vision said.

also are the motor mounts shot. ive seen a problem like this before. only under load the engine would mis cause the engine would torque and pull on a plug wire or something and cause a mis. also when the guy turned on his wipers one of the wiper arms inside the cowl was hitting the dist. cap. when the engine was under load.

those are crazy but theyre true.

hope i can help.

oh and that car was a camaro also. i dont remember the year though.

bond
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Old 01-03-2004, 06:14 PM
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You say you have a miss under load. You haven't said what kind of load, if it does it while in gear and stopped. If it will do it when put in gear, foot on the brake, slight pressure on gas, do the plug wire test that way with someone helping. That should help isolate which cyl is causing the problem. An easy tens then is to switch plug wires or plugs with an adjacent cyl and see if the problem moves. If the problem stays at the same cyl., check to see if you have a rocker loose or a bad cam lobe. Hydraulic lifters will take up quite a bit of slack from a worn cam before making noise.

HTH
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Old 01-03-2004, 07:35 PM
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If the timing chain skipped your engine would be running a lot worse than just a miss under load. I would check your carb tuning.
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Old 01-03-2004, 07:39 PM
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Alright.. Thanks everyone for the reply's. I will try idiling the engine up tomarrow and pull the plug wires (weather permitting). If no luck there then I guess i'll have to pull the valve covers... (such a pain in the butt... Fuel and cooling lines running over the passenger side. ) Hopefully the shop gloves will help a little from getting shocked or anything... Usually I can take a good cap shock... But not really in the mood for one any time soon.. Anyways thanks a lot and I'll keep ya all posted on what happens.
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Old 01-03-2004, 08:20 PM
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Come on...I'm an electrician. I get shocked all the time. There is nn...nnnn..nnn..nnn.nnnnn.nn.nn.nothing...ww..w..w w..ww
wrong with me.
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Old 01-04-2004, 02:45 AM
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Yeah.. I play with electricity all the time... but when i'm under the hood of a running car I tend to be a little edgy about bein shocked or startled. I've been grabbed by househole electrical outlets numerous times... Even have had a couple computer power supplys fry and zap me while sitting in my lap (don't ask.. long story). Just under the hood there's too many things to accidently hit that could burn, cut, or mutilate your hands or other body parts while pulling away from the shock.
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Old 01-11-2004, 12:05 AM
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Ok here's an update on the 305 situation... I took the valve covers off today. There does not seem to be any worn lobes on the cam or broken valve springs. Sooooo. I put it back together.. Fed up with it. Then later tonight a friend gave me the idea of maybe runnin some stuff through the gas tank to clean out the carb and stuff. So went and bought a cheap bottle and it seems to be acting a little better... Hopefully with a little bit more time it will clear up and it was just junk in the carb causin me all the problems.
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Old 01-11-2004, 03:50 PM
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check for vacuum leaks and replace all of the ignition components, one of your spark plugs could be cracked on the inside or getting poor spark from a crappy wire. If that doesn't help, its probably the cam.

K
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Old 01-11-2004, 09:31 PM
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killerformula.. Thanks for the reply.. Already checked for vacuum leaks. Replaced the ENTIRE distributor and checked and cleaned every spark plug. And has brand new plug wires as well. Dad is supposed to pick me up some carb cleaner, power steering fluid, and tranny fluid tomarrow. After I ran the cleaner through my gas it started acting MUCH better. I'm really starting to think that it was just a clogged jet on the carb. Will know more tomarrow after I clean it out thuroughly.

Thanks
-Silver-
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Old 01-14-2004, 09:17 PM
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It is finally running again!.. Wasn't the carb.. Was a bad spark plug or two.. They would all fire when I checked them but I guess one or a few would not fire quickly enough (bad insulators maybe?). Anyways never expected it to be the plugs cuz they were only a month old... But problem solved now... So glad to have my baby back..
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