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Discussion Starter #1
My engine is dieseling when I turn it off. It happens more when I use the leadfoot, which is more often than not. I noticed this problem about the same time our premium fuel was changed from 92 to 91 octane. Could this weak fuel be the problem. My 351C is running like a champ other than the dieseling when I turn it off. What gives?
 

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My boat was doing the same thing, so I added some NOS octane boost, and it was still doing it, so then I changed the spark plugs and it stopped. If I run it on cheap gas [87 or 89 even] with no octane boost it will do it, so I guess the plugs made the extra difference. - Chad
 

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Do I read right? You guys drive your cats with 91 or 92 octan? I did`nt know if this is possible. I drive a 1969 std. convertible (since 1994) and a 1969 XR7. Here in my country we have three kind of gasoline: 91 octan, 95 octan and 98 octan. Since 1994 I use only 98 octan for this cars (both have a 351W) . Not very cheap here in good old Europe. Do you realy think I can try the cheaper 95 octan or even 91 octan?
Sorry for my bad english.
 

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haha you're very lucky. You should be able to yes - unless your compression is really high. Here in California - the cheap stuff is 87 octane then 89 and then the good stuff is 91. In other states it's higher then 91oct. but California sucks :( - I ran my 351-w on 89, and never had any problems. - Chad
 

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Irun the 91 also but I do add an octane booster and have naverhad any problems.

don:cool:
 

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Discussion Starter #7
octane booster helps, but I can't afford to use it everytime I fill my tank. This is my daily driver. I drive only about 5 miles to work, but then about 8 miles to school. I could have the mechanic at work adjust my timing. How do you suggest setting it Logan?
 

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If you don't have a timing light, you can back it off by guesstimating... (Heck, my car is tuned by complete guesstimation)...

Anyway, Just loosen the distributor hold down clamp and rotate the distributor counter-clockwise to retard timing, clockwise to advance it. The important thing here is to make VERY small adjustments and then test. I never move my distributor more than 1/16"-1/8" before clamping it back down and test driving it.

Chances are it's only a little bitty bit outta whack.
 

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Discussion Starter #9
Thanks Logan. Funny thing is, today the cougar didn't diesel at all, and I haven't done anything to it. It must be just a little out of whack. I'll play with it when I get some time.
 

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Run On

Catz octane boost is not the answer for run on. What you want to do is either retard your timing a few degrees or back off on the idle a bit to 650 rpm in neutral.Octane boost is good for acceleration purposes. I use 87 octane in all my catz with no problems at all once the engine timing etc is set for the fuel being used Catz yaz Ray
 

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runon

I'm supprised the real answer for this problem hasent been offered yet. And that supprises me with all the smart owners found here. I most cases. (most not all) the main reason for runon is carbon build-up on the pistons. The carbon starts to get really hot and almost glow. When you shut off your engine, the spark is disabled, but the hot glowing carbon keeps igniting the incoming fuel at a very inificient rate thus the hoppy idle. Run a can of 44k through it and condider it done. Putting a higher octane fuel in raises the flash point of the fuel making it harder for the carbon to ignite the fuel and sometimes giving the impression low octane was the problem.
 

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Yes while its true that carbon will set off fuel so will any sharp edges on pistons from valve reliefs etc.Do not dismiss the timing and idle though.Those both will cause run on also, Catz yaz :)
 

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Vfret's answer reminded me of a trick we used 20 odd years ago when I was wrenchin' for a livin'.
We used to dribble a cup or two of water (yes, H2-O) down the carb throat to get rid of carbon knock on Mopar products. This tip came from the Mopar boys themselves. The theory being that the water will turn to steam and knock off the offending particles. Of course you have to be careful not to stall the engine - it has to be dribbled in slowly - but it does work! Or at least it used to.
Don't let this secret out or I'm sure the EPA or a tree hugger will take away our water or find us a cleaner, more environmentally safe chemical to use. :D
By the way, we used to use this trick to pass the early emissions tests, too. ;)
 

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You also can use trans fluid same way dribble in rev high.Another is to use oxygen thru carb at idle removes carbon instantly and another way is to hook up water injection system that will remove and reduce carbon deposits on a regular basis,Catz yaz:)
 

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Discussion Starter #16
That's It!!

My mechanic buddy just told me the same thing a couple days ago! It makes so much sense, yet I never thought of it.
This buddy of mine that I've known for five years is a mechanic who specializes in classic mustangs, and I just found out. He's just an old buddy from the bar scene that I never knew very much about. We got to talking about cars and turns out he manages a major auto shop and rebuilds cars on the side in his garage. He used to work at a classic mustang and cougar shop, and really knows his way aroun a Ford. And he charges by the twelve pack. And he can get the parts Wholesale through his work. I am soooooo lucky! I'll have the baddest cougar in town pretty soon!
 
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