Manager Forum

2001 lincoln ls 3.9 has an intermitant misfire; it happens under load more than any other time. we have replaced cops, plugs, boots, injector etc....you can be at idle have the a/c off turn the a/c on just to cycle the compessor and there is when it will miss also.

anyone have a clue?

Any misfire codes? have you done a compression test? How about a power balance test? Is it a single random miss or repeating single cylinder miss? First step is to identify the cylinder.

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We have seen a *LOT* of coil problems on these engines. And new don't mean good. There is a TSB on those, but like Ric says, the first step is to identify which cylinder, if possible. The easy way is if you can isolate one cylinder, swap coils with another hole. If the problem moves with the coil, that's usually the culprit.

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It's been my experience that if your scanner picks up the cylinder it's pure luck. I'm not saying it won't happen but at least in my shop i've only seen it about 10% of the time. An intermittent skip will cause a call to the customer with a quote including all the coils. It's not impossible to isolate and repair the bad coil, it's a bit time consuming and i can guarantee that within 6 months the customer will be back with the "same" skip. I explain to my customers it's better to take the hit and get it over with. The ones that question me move to my naughty list. I've had some i just knew i was going to regret doing and sent them on their way. I was accused of being a parts replacer. I only had one that didn't come back and tell me i was right and apologize. Trying to keep it short as possible for me i tell them that finding an intermittent skip will take at least two hours labor (as a rule) and if you calculate it out to 4 coils, only 1/2 of them, it exceeds the cost of replacing them all at once.

Well, with your scan tool, shouldn't you be able to identify which cylinder is the culprit by using mode 6? I use mode 6 in situations like this when there is no misfire code to identify which cylinder is the suspect.

You would think so but in these Fords i've found it almost impossible to isolate an intermittent skip. If your dealing with a skip that is so random it's only felt occasionally when driving mode 6 (in my experiences will not pick it up). If it's a constant hit it's there, if it is more than just once and a while it's there, if it's two or three times a trip it's not.

we have had a code in the past for cyl.#8 at this point we have replaced all coils twice,all spark plugs twice replaced the plug ins for the coils ran compression test,balnce test vacum test i have solus pro scanner wich does not have mode 6 but i have taken it to a freinds shop that has an ocilascope and still can not pin this problem down, at this point i am ready to call bill fulton in to see if he can figure it out. VERY FRUSTRATED!!!!!!!!!!!!!

If you can make it mis-fire while brake standing in shop, then isolating cylinder should be a lot easier. If this can be done then i would swap coil with another cylinder and see if skip moves. This can be done with plugs, boots, and injectors if their easy enough to swap. If none of that identifies the issue then its good old fashioned diag. Good luck and keep us posted

Is it a miss or a trans shutter? See it happen. The tell is if it happens within 5mph of a shift, especially into over drive.

no it will do it at idle if you cycle the a/c on and off as soon as the engine gets that little bit of a load it will miss a few times then stop but can not pin point the cyl. missing

The way it's being described with the a/c cycling on and off causing the skip i'm wondering if it's a stumble at that level being caused by a bad or filthy IAC. I see this often on Fords and Mercuries.