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its in my wifes mustang, 4.6 coil on plug SOHC. i was driving it yesterday, and it has what at best i can describe as a skip. i scanned it with the snapon scanner, even though the CEL never illuminated, and as expected came up with nothing.
it will chug as if its being lugged too hard anything under 2500 rpms, at idle it will randomly "cough". when its really bad, it sounds like a subaru boxer motor (like a wrx/sti).
i think its still fueling when its happening, because i can sometimes hear what sounds like fuel ignitinig in the exhaust, but im not 100% sure. (silly factory ehxaust muffles it too much)
it has 69000 on it, and i think its on the factory plugs. i was going to change the fuel filter, and plugs, but i was wondering if those dont fix it, if there is a way to test the COP's or if i should be looking somewhere else. im not very familiar with these modular engines as i havent had any trouble other than the shooting plug fun.
PS - i was driving it because the transmission is SCREAMING (project number one on the car). i bring this up because i had a thought about knock sensors picking up tranny noise.....does this engine even have them, and could it be?
Checking the COPS using an ohm meter according to my Haynes manual does not accurately show a bad COP. I replaced one a month ago that both the secondary and primary ohms were comparable to a good COP but it was definitely bad.
Plugs should be good to 100k but you might want to look at them. Others have said to replace the COP boots when doing the plugs. Possible the boot is the problem.
It's really strange though because I don't believe this is just one cylinder as you should still have quite a bit of power on a 4.6 mustang, yet it doesn't seem to be fuel problem if it coughs at idle.
My test would be to stress the engine with some hard driving and hope for a CEL and Code. I had to do this with my 5.4 to get it to throw the code when I had a bad COP.
If it is lugging below 2500 and you hit it hard, does it straighten up? If so, it does sound electrical, like a COP or boot. I'd pull the plugs if it's feasible. With my van, pulling plugs and COPS are ridiculous.
its very noticable 2000rpm and under, but at about 2500 and up it sounds good, however is definatly lacking in power. i think it sounds good because it is buried in rpms (my friends powerstroke is running on 7 cylinders, but you cant tell once you hit 1500rpms, i think this is the same thing.) it stumbles the same be it full throttle under load or just mantaining speed barely on the pedal.
as for beating a fault code into it.......i did my best for the half tank i drove it, and i know the wife drives the car pretty hard to begin with. i actually gave up with the heavy foot method and went to granny mode to see if that would do it...no codes, just my luck.
the COP boots: if they were the culprit, would there be any visible defects such as melted rubber or carbon tracking? or is it pretty much a crap shoot?
I just saw suggestions about changing the boots. Visually seeing a problem would be difficult. They are so deep down there I don't think it will do any good, but watch over the top of the engine with it running, while dark. I've found some goofy stuff observing engines dark like that. I remember my Mom's Citation. I was like 16 and trying to figure out why it was missing. When I pulled into the driveway one night I just happen to pop the hood before I got a flashlight. There was sparking and arcing going all up and down the plug wires. Being 16 I thought, COOL! One hot car though for a stock 4 door V6. It was an automatic and would burn 'em off all the way through 1st gear even with the bad plug wires.
I'm trying to think if something that could happen this bad, and not cause a code. I can't think of anything at the moment.
I guess if you can get to the plugs fairly easy, you should pull them. When I replace them on my 2000 the other day, they were worn enough to throw a misfire code on one cylinder but I have a few more miles on them than you. Actually, just replace the the plugs anyway. I probably would do the boots too. At least you can drop those from the diagnosis for fairly cheap.
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