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| Engine Miss/Rough Idle - At Witt's End https://slantsix.org/forum/viewtopic.php?t=56952 |
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| Author: | bossanova5 [ Mon Jan 19, 2015 5:15 pm ] |
| Post subject: | Engine Miss/Rough Idle - At Witt's End |
Hello All, I have a 65 convertible Valiant that I restored and modded about ten years ago. Here's what's been done: Super six two barrel set up with a carter two barrel carb Electronic ignition from a 75-76 dart (Distributor and Ignition module, new module installed 3-4 years ago) Electronic Voltage regulator It was running great up until last drive (I only drive it 3-4 times a year) The engine has a bad miss at idle and clears up above 2000 RPM Compression at each cylinder is: 1) 145 psi 2) 147 psi 3) 145 psi 4) 150 psi 5) 145 psi 6) 145 psi Vacuum at idle is 15 with very little needle movement. Idle is 700-725 rpm in park I pull the number six plug wire and no change while idling, I pull the other wires on the other cylinders and there is a noticeable change in RPM. I pulled the valve cover and all valves are moving on all cylinders with no excessive valve train clatter from any cylinder All plug wires have spark at the spark plug cap (Boot that connects at the plug) I swap plugs and plug wires from other cylinders and put them on #6 no change I thought it might be the distributor cap as the contact looks worn, but the new one from autozone looks identical where the rotor makes contact Sprayed starter fluid around the manifolds, and the bottom of the carb no noticeable increase in idle I've tried to include as much details as possible Thanks in advance for everyone's help |
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| Author: | Pierre [ Mon Jan 19, 2015 5:26 pm ] |
| Post subject: | |
Check the cap itself? |
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| Author: | Serj22 [ Mon Jan 19, 2015 5:41 pm ] |
| Post subject: | |
Maybe the exhaust valve on #6 is not fully seating? If you take the valve cover off, and put a feeler between it and the arm while it's running it should miss kind of. |
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| Author: | imanexcellentdriver [ Mon Jan 19, 2015 5:49 pm ] |
| Post subject: | |
Hey, I had a similar problem...try this...since the vacuum ports are on the #6 runner, a minor vacuum leak there will cause your miss on the #6. Try capping off the vacuum ports and seeing if you still have the same problem. After ruling out everything else, I figured out that I had a tiny leak in the brake booster...drove w/o power brakes until I could locate a replacement (I do NOT recommend this  I replaced the booster and she's happy again... Hope this helps. |
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| Author: | nm9stheham [ Tue Jan 20, 2015 6:18 am ] |
| Post subject: | |
I have had a slightly gummed valve in a cylinder act similarly. It slowed the closing of the valve enough to effect idle but would close well in slow cranking to give good compression readings. The booster leak is good idea too; the vacuum reading is a bit on the low side for a stock cam. Try a plug swap and plug wire swap with another cylinder just to eliminate that. |
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| Author: | bcschief [ Tue Jan 20, 2015 6:22 am ] |
| Post subject: | |
Also take a close look at the valve springs on #6 maybe you have a broken valve spring. Brian |
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| Author: | Doctor Dodge [ Thu Jan 22, 2015 9:49 am ] |
| Post subject: | |
FYI... I always check / adjust the valve lash any time the valve cover(s) comes-off a solid lifter (mechanical cam) engine. DD |
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