My Stype has began stuttering at idle and when accelerating normally between 50 and 55 mph w/o a code. I've narrowed it down to bad coils or a vacuum leak and plan on test driving it with an obd2 scanner. What other than the LTFT and STFT should I be looking at?

 

Mainly LTFT. Don't drive. Do it in Park, warmed up, at idle and at 2500rpm.

95% it'll be a hose elbow (use Search) under manifold. Read existing details if LTFTs show a leak (or anyway, as it'll happen sooner or later).

 

Mine was hesitating at light throttle settings and at idle. It didn't give any trouble codes but felt through the "backside code reader" like a misfire. I bought 4 coils online, changed a whole bank in one go and the problem is fixed.

I now need to work out which of the original coils is faulty......

 

Yes - but the 4.0 is not the engine in this thread and does not have the hoses concerned.

The OP could change a bunch of coils for $$$ and get nowhere...
Better to use OBD live data.

 

You can get a COP tester - you may have just pulled out 3 perfectly functioning coils for no reason. COP tester about $80 (3 new quality coils - not crappy aftermarket China knock offs - about $150 - $180)

 

So i did the test as suggested and got these readings
LTFTb1 idle .8 2500rpms -.8
LTFTb2 idle 3.1 2500rpms 2.3

Those are good as far as I can tell.

Thanks for the quick response.

 

Yep, they're good. Can't see any signs of an air leak. Probably coils or maybe wiring.

 

So after researching the scanner I bought I figured out how to pull info from the misfire monitor itself. It's showing misses on my #1 cylinder. That's the one on the passenger side of the car (in the US) closest to the grill correct?
And if so, is there a way to test the coil w/o removing the manifold?

 

It would be there, yes (pic in Vehicle Spec PDF in stickies).
Only half-way decent tests are COP tester or swap it (maybe with next one i.e. #2 on your era) - you'll need manifold off, sadly.

 

Thanks JagV8. Just means I'll have to wait for the weekend so I have time to test and replace.

 

Those are % Fuel Trim values, yes? If so, it might concern me to have consistent 3 - 4 % difference between the two banks. Doesn't this indicate consistent leak on one side(bank 2)?

 

The V-6 is known for several problems. Have you checked for oil in the plug wells? The PVC elbows go bad and one side of the engine you can't get to the coils without removing the intake.

It would be worth your while to read up on all this and do the maintenance all at once. I would change all coils and plugs if they have not been done. They are a wear item.
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yea I have:

coils
plugs
manifold gasket upper and lower
breather elbow
IMT O-ring
valve cover gasket set
spark plug boots

Hopefully I can get this misfire fixed over on friday, so I can play on saturday

 

Wouldn't be the first time a new coil was bad so maybe swap it with another and see if fault moves.

 

Just got the car back together today, Misfire's gone and she's running great. Thanks for all the help.