question about bad idle/misfiring on LS8

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gasisontheright

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Just picked up a 2001 LS8 and it doesn't run quite right. 107k miles. I've been driving it, and really only notice a rough idle, and sometimes when crusing in OD and I accelerate lightly i will get a bit of a miss. I've had it about 2 weeks and put around 650 miles on it. I have been carrying my code reader everywhere and checking the codes every time the light comes on and it kicks a p174 and p304 often. Randomly I will get a p172 and just got a p300 for the first time. I have replaced the plugs, and tested all the COPs to verify they are working right. I have cleaned the O2 sensors also. I'm pretty sure it has something to do with the fuel system, but wouldn't know where to start. Any help?
 
replace all plugs and cops. make sure the valve cover gaskets are not leaking.
 
You have marginal COPs. You did not test them unless you did a stress test using a scope as outlined here.

http://www.v8sho.com/SHO/TSB 04-16-1.pdf

Just testing the resistance of the coils is almost completely useless. It will not detect the most common failure mode of the LS coils. You are almost certainly not the exception here. Your symptoms classically point to coil failure. The same failure that almost everyone on this forum has experienced.

If the new plugs have been in there for more than a very few miles, you will also have to replace them too. The bad coils damage the plugs and the damaged plugs with kill the new coils.

After you have replaced all coils and plugs, you can see if you have any other issues to resolve. Don't be surprised if you find that your cats are going bad.
 
It seems silly to meaninglessly replace all coils. No reason to spend 200+ dollars to replace parts and hope it works. I have swapped the coils to all different cylinders and the misfire stays at the same cylinder. Its not the plugs or COPs. Does anybody have experience with any fuel system issues?
 
gasisontheright said:
It seems silly to meaninglessly replace all coils. No reason to spend 200+ dollars to replace parts and hope it works. I have swapped the coils to all different cylinders and the misfire stays at the same cylinder. Its not the plugs or COPs. Does anybody have experience with any fuel system issues?
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It's not silly. First off, how do you know the coils are "good"? Swapping them around won't find a failing/marginal coil, especially at idle. If they are original I can pretty much guarantee at least a few are in failure mode! If you don't replace the coils & plugs with quality units (NOT those el cheapo ebay units) you will be chasing this until the cows come home. Marginal coils (as well as a failing battery) exhibit many weird symptoms.

But hey, it's your car and none of us here know anything. I know I have dealt with this from the beginning with my 2000.
 
gasisontheright said:
It seems silly to meaninglessly replace all coils. No reason to spend 200+ dollars to replace parts and hope it works. I have swapped the coils to all different cylinders and the misfire stays at the same cylinder. Its not the plugs or COPs. Does anybody have experience with any fuel system issues?
Click to expand...

LMAO. It's silly to replace all the coils? All your posts before this one lead me to believe you were a smart guy. Everyone who owns/owned an LS knows that it eats coils. Also, everyone who owns/owned an LS knows when you replace one coil, you replace all coils and plugs. If you think $200 is a lot to replace parts to make your car run properly, you made a big mistake buying this car buddy.. The guys on here know what they're talking about, I'd suggest you listen. They're trying to help you.
 
185175133


Check this out.....
 
Im saying its meaningless because it seems like its just replacing parts and hoping it works. Alas, you are correct as I have zero experience in a Lincoln LS. I ordered all new COPs and spark plugs and will be replacing them all.
 
Trust me on this... Im not as well versed as these guys, I was just going through what you are going through and I did exactly what they said... now I get up in the RPM powerband with no stutter, I have clean take off and I'm saving gas again (well atleast I'm doing a damn shade better than I was before). Bottom Line, they know... have some faith in them. Oh and you really don't want to come into a forum discounting the guys who made it what it is... bad JuJu my friend.
 
gasisontheright said:
It seems silly to meaninglessly replace all coils.
Click to expand...
the reason that it is not silly is two fold. first, 95% of all Lincoln misfires are because of bad coils. and second, it will cost you the same price to have them properly tested as it would just to replace them, so you could pay the dealer a couple hundred bucks to have them tested, and then have to pay more to have the bad ones replaced, or you can just pay the couple hundred bucks and have all brand new coils and know that it s not going to be an issue.
 
Consider it a tune up .... like any car.
Then when you get rid of the misfire buy another new set of COPs and Plugs and keep them handy.
Keep on driving or messing with failing marginal coils and you'll be looking at a set of new expensive CATS to.

I've got one COP sitting here on my desk, that was "known" to throw codes on WOT,
7 good ones, that although didn't throw codes, are considered garbage as they would and will throw P03 codes soon enough.

Rule of thumb with the LS:
Misfire = replace ALL coils and ALL plugs (make sure they are gapped correctly)
Look for oil in the plug wells, if so, replace Valve Cover Gaskets before putting in new coils and plugs.
Coil covers could be "optional" depending on where you live and who you talk to.
 
Replaced all the plugs and COPs an still have the same problem. It does run a tad better, but still rough idle and missing and p300,172 and 174 codes.
 
gasisontheright said:
Replaced all the plugs and COPs an still have the same problem. It does run a tad better, but still rough idle and missing and p300,172 and 174 codes.
Click to expand...

Was there oil in the plug wells?

Something else to consider, and probably not the issue you're having, but couldn't hurt. Clean the MAF and IAC. Also check all vacuum lines and replace fuel filter. Cheap easy stuff to rule out.

Are you using premium gas?
 
gasisontheright said:
Replaced all the plugs and COPs an still have the same problem. It does run a tad better, but still rough idle and missing and p300,172 and 174 codes.
Click to expand...

Your cats may be clogged due to the previous misfires from the marginal COPs.

You should all look for vacuum leaks and check the MAF. The O2 sensors may have also had more gasoline on them than they could stand.
 
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