rough idle and hesitation?

[Mr.Duff99V8SHO]

hello fellow gen 3 SHO owners. Im having a problem with the SHO and was wondering if you guys have any ideas. When it gets warmed up it has a rough idle alomost like it wants to stall but it hasnt. When im cruising between 1500 and 2000 rpms sometimes it acts up. I want to say its hesitating but i dont know if thats describing it right. And when i have it floored it feels alomost like the normal SHO power comes and goes as it feels. Ive had a couple of people tell me that it might be "bad" gas, but ive added dry gas and ive gone through a couple tanks since this started. It hasnt got any worse or better. I took it to FoRd and they said it wasnt throwing any codes and that it wasnt acting up for them. I dont think they let it warm up all the way though, cause it doesnt do anything abnormal when cold. Any Ideas?? Thanks.

 

[Ian Macoomb]

Does the car feel like it hiccups at idle? Like the rpms drop a bit and you can feel it in the car. Happens every few seconds? And is intermittent?

If that's the case then it's a coil.

You can wait for it to throw a code or you can get a load balance test done to find out which is misfiring.

Another thing I've found is that I can get it to throw a pending code if you put the car in second gear and floor it from a stop. It seems that putting a good load on it like that will sometimes get a code. Do that when it's acting up and you'll need to have a code reader handy because it doesn't take long for the pending code to disappear.

 

[Mr.Duff99V8SHO]

Yep thats it. Would a bad coil cause the other problems im experiencing at speeds? If i wait for it to throw a code will i cause any damage? And is this an expensive fix? Thanks

 

[Mr. SHO]

I concur that it's most likely a coil. I had similar problems... when I went WOT, about 1 out of 10-20 times, the car would act like it was losing a bit of acceleration power, like you are describing. If I kept racing light-to-light, it would do this a few times, and then eventually it would stall out and refuse to restart. I had to put it in N or P, turn the key to OFF and then restart. It would be fine for a while then.

Check out the various articles on V8SHO.com relating to coils. The loss of power is apparently b/c of a misfiring (or non-firing) coil. The bad coil will create a lot of electrical noise and this will eventually cause the PCM to malfunction, shutting the ignition circuit down. (This is all theoretical info, I think.)

The rears are substantially more likely to fail, b/c of heat buildup in that area. I had the whole rear row of coils replaced when I got the cams welded, and the problem hasn't been back. I got lucky I replaced the right one(s). I would highly recommend that if you need to replace one back row coil, you replace them all, as it involves a lot of labor to get back there.

*EDIT* Forgot to answer the other 2 questions. I don't think a bad coil has every caused any damage to an engine, esp. in the early stages of coil failure. The coils run between $55 and $75, depending on your location. Most of the aftermarket branded coils are actually the same coils that Ford sells for upwards of $100. Labor for the rear coils can be 4 hours or more, even for a good mechanic. They front coils can be replaced easily in half an hour. I wouldn't hesitate to do the front coils myself.

<small>[ February 06, 2004, 02:14 PM: Message edited by: Mr. SHO ]</small>

 

[Ian Macoomb]

Some say that the misfiring can cause the cats to go bad but I doubt that. If it's a miss every couple of seconds at idle it's probably only missfiring once every 40 rotations and it's usually only in one cylinder. When the car is cold and it's running rich it's probably dumping about the same amount of fuel.

I've had a bunch of bad coils and my cats are still fine.

 

[Mr.Duff99V8SHO]

Thank you for the info guys.

 

[MarkieSHO]

Speaking of coils, i have one that is pretty much done, where would be the best place (cheapest)to get a new one, I live in NH, and the cheapest ive seen so far is 90 bucks at Autozone..

 

[SHOZ123]

Murray's auto parts if you have one around. Otherwise Rock Auto will ship them and have three different ones ranging from $79 to $94 plus there is always a coupon floating around.

 

[MarkieSHO]

Never heard of eitehr hehe

 

[Ian Macoomb]

MarkieSHO:
Never heard of eitehr hehe

Try Napa. Ask for the trade price. It's something like $75. If they don't give you that price don't buy it.

 

[MarkieSHO]

Allrighty then, theres one like 5 min away form me thumb