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| Rough idle - can't figure out https://slantsix.org/forum/viewtopic.php?t=52109 |
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| Author: | ESP47 [ Sat May 18, 2013 1:56 pm ] |
| Post subject: | Rough idle - can't figure out |
For the last year or so my car's idle has been getting progressively rougher. This is only when I'm in gear and the car isn't moving. As soon as I put it in park or get on the gas, the car runs perfect. It ran nearly perfect for years before starting to roughen up. This is a 71 Duster with a Super Six. I'm idling 750 in park and 600 in drive. Timing is at 8* BTDC. I've adjusted the valves twice in the last year with zero change to the rough idle after the adjustment. Vacuum is at 20hg. I've done a tune up with ZFR5N plugs, blue cap and MO-3000 long tip rotor. It has an HEI ignition and I've replaced the HEI module due to failure as well as checked the reluctor gap in the dist. I rebuilt the Carter BBD as well. While the car has a little more "kick" to it after the tune up and rebuild, the idle in gear is still rough. Do you guys have any other ideas? |
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| Author: | ILMopars [ Sat May 18, 2013 3:23 pm ] |
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Retard the timing a little. My idle in gear has improved closer to TDC. |
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| Author: | Aggressive Ted [ Sat May 18, 2013 5:35 pm ] |
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A thought........ How much blow by does the engine have when you pull the PCV out? When you have lots of oil collecting in the intake and the valves from the PCV, it will cause the engine to run a little rough. I noticed that after installing an air/oil separator on my shot engine, after about a month of running, it idles so smooth it is scary.... Give one a try, the Jeg's unit is cheap! Click on the red link to view pictures of the install. |
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| Author: | ILMopars [ Sat May 18, 2013 7:44 pm ] |
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Would it be because it is too rich or is it just getting gunked up Ted? |
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| Author: | slantsik [ Sun May 19, 2013 1:40 am ] |
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Spark plug Leads? Clean and tighten all grounds on ignition system. Brendan. |
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| Author: | olafla [ Sun May 19, 2013 7:48 am ] |
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Hi ESP47. I can add to the guesswork list, and suggest 1) That you have a manifold vacuum leak. Why? Because it only manifest itself when the manifold vacuum is at max when idling. 2) A leaky valve. Carbon buildup? You should attach a vacuum gauge anyway, and check out this link to an animated version on how to interpret different vacuum gauge readings: (some of the clickable green buttons have a two-stage response). How to Use and Interpret a Vacuum Gauge Olaf |
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| Author: | Aggressive Ted [ Sun May 19, 2013 11:02 am ] |
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Quote: Would it be because it is too rich or is it just getting gunked up Ted?
After you have done all the basics and ruled them out like extra lash to be sure the valves are seating fully, and after you have a good clean running engine, good spark, good air mixture, good choke that doesn't stay on too long like a lot of SL6's (most folks are not aware of how to adjust the spring tension on one)......there are some subtle things to check for....... The example I was making was in terms of the "gunk" from excess blow-by entering the intake thru the PCV system and coating the valves. When the oil randomly fires it will throw off the idle to where it is not crisp and tight. On my race engine it is very crisp, on this old trashed stock motor the excessive blow-by makes a huge difference in idle quality and responsiveness when I step on it. With the Jeg's air/oil separator it has really cleaned up the idle and over all engine response. Example: decelerating hard into a corner and then getting back on the throttle is much smoother. I do this around 15 corners every morning and night. Not bad for an old $100 rusty barn find motor with over 260,000 miles. |
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