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4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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Old 11-04-2011
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Misfire under load

If this has already been asked and answered, my apologies, please just point me to the thread.

I modified my 2011 V6/Automatic with:

K&N 63-1108 cold air intake
Magnaflow 17114 off road pro series exhaust

Sounds and feels strong, but noticed while highway towing a ~ 1,200 lb. trailer uphill I could hear it misfiring. Not badly enough to feel, but I could hear it. Mileage was around 15 MPG over the 2,000 mile trip, dunno if that's good or bad. But the misfiring can't be a good thing. Any ideas on how to cure, or if I should even try?


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Tom
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Old 11-08-2011
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Verify that no vacuum lines are loose...including the one that goes into the air intake just after the MAF.
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Old 11-23-2011
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2 types of fuel delivery systems out there
- MAF (Ranger's style) calculates the mass of the air coming across the sensor
- speed density, uses many sensors to calculate the proper parameters including its main sensor - the MAP - which is used to calculate LOAD

you say it's missing under load, so let's look there. the PCM is determining load based on the MAF readings (seeing as you dont' have a MAP). it will draw more air under load, and adds fuel accordingly.

MAF sensors tend to hate K&N stuff. the oil required on most K&Ns has a nasty habit of being drawn past the filter by manifold vacuum, and of course the first thing past the filter is the MAF sensor.

Ford's MAF sensor uses a hot wire to determine air density. the wire is heated to a specific temp and that temp is maintained by flowing more current through it as needed. air passing over the wire cools it, so the sensor draws more current to keep it hot. the current required to keep temperature consistent correlates to a mass of air entering the engine.

what happens with the oil from the K&N is that it often coats the very fine current carrying wire. this insulates the wire and throws everything off.

if i were you i would try to clean the MAF with sensor cleaner and run a paper filter. if you have no more miss under load promptly throw your K&N in the garbage and run the factory setup : )

happy hunting. (not saying this is 100% your issue, but 100% it is where i would start troubleshooting. i have replaced many a customer's MAF due to oily air filters)


edit: and yes, try to fix it. a miss of any kind (rich mix, lean mix, no spark or no compression) dumps fuel into the exhaust. great way to plug and blow up cats, creating a much more expensive repair than originally necessary.
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