318 issue randomly..

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tjb1984

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Ok, Ive never owned a gasoline powered vehicle before, I work on em at my shop just never owned and operated one. Always diesel. So trouble shooting non OBD2 type vehicles isnt my strong point.

'71 dart, 3.91 rear gear 904 auto. 318 with std 360 heads (according to the casting numbers) Small to mild cam judging by the tone, Shorty headers with edelbrock intake manifold and 4bbl. Headed to a job this morning and it started missing bad, Felt like popped off acouple wires. Nothing under the hood is funky, All seemes fine by looking. Kept it running and pulled every plug wire one at a time to find that the only time idle changes (gets worse) is when i pull the #3 wire. When i pull the rest, even 2 of them at a time the idle seems the same and gets no worse.. Not that i can notice anyway. As i pulled each wire i plugged a new plug into the wire and i have spark at all of them just not very strong. Rotor and cap seem new within acouple hundred miles as there not wore at all.

If i use the old wooden stick trick i can hear ticking and some other noise in the passenger side valvetrain but smooth as new on drivers side. It does have a big ugly accell super coil and im sure its a pile but its worked thus far. Pulled the valve covers, nothing seems bent or outs place/loose.

Any pointers?
Thanks Tom
 
tjb1984 said:
Ok, Ive never owned a gasoline powered vehicle before, I work on em at my shop just never owned and operated one. Always diesel. So trouble shooting non OBD2 type vehicles isnt my strong point.

'71 dart, 3.91 rear gear 904 auto. 318 with std 360 heads (according to the casting numbers) Small to mild cam judging by the tone, Shorty headers with edelbrock intake manifold and 4bbl. Headed to a job this morning and it started missing bad, Felt like popped off acouple wires. Nothing under the hood is funky, All seemes fine by looking. Kept it running and pulled every plug wire one at a time to find that the only time idle changes (gets worse) is when i pull the #3 wire. When i pull the rest, even 2 of them at a time the idle seems the same and gets no worse.. Not that i can notice anyway. As i pulled each wire i plugged a new plug into the wire and i have spark at all of them just not very strong. Rotor and cap seem new within acouple hundred miles as there not wore at all.

If i use the old wooden stick trick i can hear ticking and some other noise in the passenger side valvetrain but smooth as new on drivers side. It does have a big ugly accell super coil and im sure its a pile but its worked thus far. Pulled the valve covers, nothing seems bent or outs place/loose.

Any pointers?
Thanks Tom
Click to expand...

Easy to try an different coil. A stock round black one would suffice. Check your timing also. If it's off much from the original setting, it could point to a weak timing chain. If that doesn't resolve the problem you might do a compression/leakdown test to determine if you are loosing a cylinder somewhere. Since there's some ticking in the valvetrain the worst case senario could be a cam lobe going away.
 
tjb1984 said:
Ok, Ive never owned a gasoline powered vehicle before, I work on em at my shop just never owned and operated one. Always diesel. So trouble shooting non OBD2 type vehicles isnt my strong point.

'71 dart, 3.91 rear gear 904 auto. 318 with std 360 heads (according to the casting numbers) Small to mild cam judging by the tone, Shorty headers with edelbrock intake manifold and 4bbl. Headed to a job this morning and it started missing bad, Felt like popped off acouple wires. Nothing under the hood is funky, All seemes fine by looking. Kept it running and pulled every plug wire one at a time to find that the only time idle changes (gets worse) is when i pull the #3 wire. When i pull the rest, even 2 of them at a time the idle seems the same and gets no worse.. Not that i can notice anyway. As i pulled each wire i plugged a new plug into the wire and i have spark at all of them just not very strong. Rotor and cap seem new within acouple hundred miles as there not wore at all.

If i use the old wooden stick trick i can hear ticking and some other noise in the passenger side valvetrain but smooth as new on drivers side. It does have a big ugly accell super coil and im sure its a pile but its worked thus far. Pulled the valve covers, nothing seems bent or outs place/loose.

Any pointers?
Thanks Tom
Click to expand...

does this have electronic ignition? the ticking could be low oil pressure or a lifter sticking/worn out. i recently just replaced all my lifters because one was going bad. you could try some sea foam in the crankcase to "unstick" the lifters. as for the missing, it could be your EI box if you have one or the points need attention. it could be the coil, its easy enough to put on another one to find out.
 
Sure sounds like a timing chain jump.
(Suddenly more than just one cyl not running)

You can pull the fuel pump and chk for how much slack in the timing chain.

"Check your timing also." Yep, that too.
 
i guess i should throw out the fact it could be a stuck float and dumping fuel, or , the fuel pump could be going south.
 
From your description it sounds like you pulled a wire and hooked it to a grounded plug? But you should not pull plug wires off a running engine. MUCH easier just to use a grounded probe at the dist. Pull the boots up, loosen the wires so you can get them out easily, and stuff the probe in as you remove the wire. If you have a thin enough probe, you can just insert it beside the wire. Alternatively, you can stick small nails/ brads down beside the wire, and ground them.

the advantage of that is that you don't get high voltage waltzing around which could damage components ---like the ignition box, AND if you are not sure that one cylinder is dropping, you can move to either side and quickly compare to adjacent cylinders.

I'd do some basic checks, the above balance test, then check plug wires with an ohmeter or test for spark quality, then pull and inspect plugs and compression and or leak down test.
 
Have you checked the carb to make sure the motor is getting gas? Remove the air cleaner and look down the carb with a flashlight. With motor running open the throttle and make sure it is spraying gas in a mist or spray from BOTH barrels of the primaries. Should be spraying from the boosters that stick out into the venturis. Could be some trash clogging the main circuit somewhere. If its not spraying fuel from both or if it's dripping or coming out in liquid form and not a mist or spray that is probably your issue. If there is not gas for the spark to burn its going I feel like a miss even though your ignition system seems ok. If you have access to a known good carb you could swap it on and see of that helps. At least it would help pinpoint your problem. Try systematically eliminating possible problem areas one at a time before just throwing parts at it or making wholesale changes. The fuel delivery an ignition systems must work in harmony, a problem with one area can often exhibit symptoms of a different unrelated issue do you need to be systematic about the diagnosis and testing. One thing at a time. Also check for good grounds with your ignition components. That is an easy fix that doesn't cost anything. You can find and fix this and we're here to help you through it.
 
another thing thats easy to miss is the tab on the ignition rotor. If the dizzy has excessive play up and down (approx 12 thousandths) ive had that tab kick off the button in the cap. It starts as a miss and gets progressively worse.
 
Thanks for all the replys, I was leaning in the direction of a chain jumping or being stretched out too much but im not sure. The carb sprays no fuel at idle but sprays as it should during driving. Once im driving everything smooths out around 1500rpm its up to 1500 that it feels like its falling apart. Buddys coming over with a timing gun to start off and see where were at. Now that this happens it starts easier than before, When warm it would have to be held open abit to start, Now it fires right up just sounds horrid. Lot of noise from the passengers side. Maybe more than one issue lol as always.
 
Looked into it more, Cracked #4 exhaust valve spring snapped in half and bent the rod.. Ill fill it with air, replace the rod and spring... See what happens this time
 
Took the spring off, the keeper has 4 ribs on it as opposed to 1 from the factory.. any idea of the brand of valves in this thing?
 
The valve springs could be from a lot of different manufacturers.

Best way is to pull another "good" valve spring, take it to a shop and measure the open and closed loads. In all likely hood if this is a street engine with a mild cam the stock 340 type spring should be a good bet. These are easily identified, they will have a single spring with a flat damping spring inside, most folks confuse these as being dual springs. Post a picture of them, that will help us ID them for you.
 
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