Missfire but no Codes?

BC 00GT · 05-30-2009, 11:02 AM

Ok so this week my car started to have what seems like a pretty serious missfire at low rpms and idle. when i start to drive it, it seems to miss really bad untill about 2000 Rpm so i automaticaly assumed COP. Took to the shop and Ran the comp and there were no codes for any missfires or any codes other the O2 codes that have been on for 3 years!

So we started pulling the wires off the coils at idle and the drivers side Bank makes a big diffrence every time you pull one but on the passenger side its not as obvious.

Didnt have time to do anything tell next week wich is ok as i have another car to drive but i am looking for ideas as what could be wrong! right now first plan is to pull the plugs and replace and see if we notice anything obvious well doing that!

Any help would be great!

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99BlackPonyGT · 05-30-2009, 11:17 AM

this happened to me twice

first time i had a crack in my intake manifold, in the area the thermostat sits...it wasnt bad enough to see it unless you had the t-stat out....it dripped coolant into the driveside spark plug wells and caused a nasty miss....it also fried 2 of my COPs, so i would look at fixing it asap...these are prone to cracking on gts before 02 (maybe 03...idr)....the coolant crossover is plastic and cracks easy...they sell a revised version with an aluminum crossover to fix it

the second time i had a valve cover gasket that was bad and it was dropping oil into the spark plug wells with the same effect

pull the COPs out and see if theres any liquid on the plugs, and go from there

900RR Puzzle · 05-30-2009, 12:02 PM

I had a similar problem 2-times last year. After pulling my hair out, I decided to bite the bullet and throw a set of coils at it. That took care of the problem. 6-months later, one of the new coils failed and I had to replace it. I put Accel coils on it, due to the fact that they were less expensive than the stock ones. They did nothing for the performance other than fix the intermittent missing (my car is all stock, with no power adders).

BC 00GT · 05-30-2009, 12:19 PM

Ok i pulled the coil off a couple of the plugs on the passenger side and there was no Oil or any Coolant or anything out of the ordinary. plugs look like they could be replaced and i will next friday with a new set of NGK!

Another question is What should the Coil pack BOOTS look like i pulled 3 off and there was no cracks along the side but the bottoms were they contact the plug were cracking looking like old rubber cracks? the car is 10 years old so that doesnt suprise me but could this have anything to do with it?

900RR Puzzle · 05-30-2009, 01:32 PM

Maybe...

I thought the same thing and put boot kits on my old coils. It worked great for about 3-4 days and was back to missing again.

New plugs couldn't hurt, especially if the ones you have have a lot of miles on them. Try that first. I did the boot kits with the plugs first. Did the coils after a few more things. If I would have know better, I would have done the coils and plugs together and saved some money on other stuff I replaced.

I had also heard before, and maybe some of the professional techs on here can tell you for sure, Ford has a revised ECU program for the earlier PI 4.6 Mustangs that has something to do with these coil failures. I have not looked into it for my 02 yet. I have only put about 800 miles on it, this past year.

BC 00GT · 05-31-2009, 10:18 AM

Ok it seems that the miss is the worst between 1000-1500 but at about 2000 and up and WOT you dont seem to notice it!

mustangman03 · 05-31-2009, 02:09 PM

the crack boots could also cause it but the boots are expensive also for what they are but they are cheaper than new coils what you could do is find somewhere that could do a power balence test and they can tell you which cylinders have the miss that will save you a little headache of trying to figure out which one it is as far as palces that can do im not sure but I know the dealership will do but it will cost you but that would still be cheaper than replaceing all of the plugs.

liljojo4711 · 05-31-2009, 02:57 PM

had the same problem. changed spark plugs and works like a charm now. mine is a 99 and the COP's have not been changed and the spark plugs hasnt been changed in like 60,000 miles lol.

99BlackPonyGT · 06-01-2009, 01:14 PM

if you change plugs, make sure to torque them properly, these cars will spit the plugs back out if not properly torqued, and then you have an even bigger problem

devongarver · 06-01-2009, 01:53 PM

hell you can replace all the COPS and plugs for under 100$, id just replace em all. I jsut did mine last month. I had the same issue as you, it fixed it right up.