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Dandd

Pacifica, CA

Lead Diagnostic Technician for a California Gold Shield Emissions Inspection and Repair Station. Over 25 years of Automotive Technician Experience in Dealerships and Independent Shops. Worked as a Technical Trainer for Snap On Tools and helped write the Exam questions for the California Smog Technician License Exam. RepairPal Staff member since October 2007.


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Question Answered: 

Hi, my name is Dan. It would be nice to know what engine you have. It would be great to know what the fuel trim is, just so you know whether the engine is running lean. I mention this because you say that the misfire gets worse as the engine warms up. As the engine warms up, the fuel mixture goes leaner, because a cold engine needs a richer air/fuel mixture. If the long term fuel trim is say 11-14%, that can cause a rough idle and may not set a lean code. You say the rough idle never sets any misfire codes, have you sprayed carb cleaner or used propane to see if you have any vacuum leaks i.e intake manifold/plenum gasket etc ? Does the EGR valve stay fully seated? I test for this by raising the valve and then SLOWLY closing it to see if there is any leakage. Then I raise it and snap it closed by suddenly pulling the vacuum line off. If the idle is different when snapped shut, you have discovered something real. Also, check for any oil on the ends of the spark plug boots, as I have repaired many misfires due to the spark plug wells leaking oil on the spark plug boots. The oil acts as a conductor and the spark voltage bypasses going to the plug and goes directly to the head. I assume you are using OEM plugs and wires i.e genuine Ford/Motorcraft. This really helps as I have chased so many issues with aftermarket parts, so keep this in mind. Also, a fuel system cleaning can really help, I always do this whenever I repair a misfire in the shop where I work. I have a machine to do this. You can use Chevron Textron, just put a bottle ( as per the instructions )in your tank. I would use it for at lest 2 full tanks, Mercedes uses it on all of their vehicles when they come in for a service, that speaks volumes. To check long term fuel trim ( lean or rich compensation. a high positive number i.e. 15% means the power train computer is adding 15% more fuel than normal etc ) you can get an Autel CAN/OBD II code reader at AutoZone. ($50 ? or so) It has a data stream feature that shows long term fuel trim, I use one on test drives to set the OBD-II monitors, because I don't want to lug around the Modis or another heavy, full featured scan tool. Let me know if any of these suggestions shed some light, I will help you any way I can. Sincerely, Dan


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Question Answered: 

Or, it could be a defective transmission cooler , if you have an automatic OR, it could be a defective oil cooler. Best to have a Pro look at this, so you get it correct.


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Question Answered: 

This is a cam sensor code, so about $100 for the sensor and about 1/2 hour of labor, so figure 150.


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Question Answered: 

Remove the upper intake manifold, pretty common on newer V6 engines.


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Question Answered: 

You may have a leaking air shock, that sags over night. Every time you start the engine the air suspension does a self-test and the suspension pump runs to level out any of the shocks. If a shock sags too much because it is leaking air, then this will set a code and turn the air suspension light on for awhile.


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Question Answered: 

This sounds like a weakened ground problem in your dash. When you operate different devices, they can not utilize their normal ground, so they cannibalize the ground from another device, which makes that device go 'wacky'.


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Question Answered: 

There are about 2000 codes for this engine, so the best thing to do is to have a Pro level tech diagnose this problem, by scanning the engine/transmission computer while performing a test drive and duplicating the problem.


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Question Answered: 

Checking all the fuses is an excellent place to begin your inspection of this problem.


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Question Answered: 

There are about 4000 codes for this engine, so the best thing to do is to have a Pro level tech diagnose this hesitation problem, by scanning the engine/transmission computers while performing a test drive and duplicating the hesitation.


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Question Answered: 

This could be so many things. How are your mode 6 readings? This is the scientific data for the OBD-II system, not just scan data. See if something is borderline, like fuel trim, misfire counts, EGR ( if equipped ) and yes air/vacuum leaks. How are your coils? And how old is the mass air flow sensor? Again, check your fuel long term fuel trim, It needed to be no more than 4-5% on either bank.


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