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Anthony, Ford Technician
Category: Ford
Satisfied Customers: 11808
Experience:  ASE Master Automobile Technician with over 20 years exp.
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2003 E350: intermittent misfire problem..coils and injectors

Customer Question

2003 E350 5.4L Code P0174B. This van has had an intermittent misfire problem for about two months. Changed all the plugs and boots, moved coils and injectors, Mode 6 showed #5 and #6 every single time. Performed compression test and everything looks good. Finally, swapped engine computer with a known good one. Now, misfire seems to be gone as it no longer shows up on my scanner but their is still a hesitation and rough idle problem. Also, I get P0174B consistently, no other codes. Only bank 2 shows lean. All fuel trims, and O2's look good at idle after warm up. This new problem is intermittent. Do I have a leaky intake manifold? Intermittent? Oh! I checked the PCV hose and it is OK. Ideas?
Submitted: 8 years ago.
Category: Ford
Expert:  Anthony replied 8 years ago.

Hello! Welcome to justanswer!


Believe it or not the Airflow sensor can cause one bank along with misfires go lean. I would replace it if it has more than 60K on it.

Anthony and 4 other Ford Specialists are ready to help you
Customer: replied 8 years ago.
Just to be clear. You have experienced intermittent misfires on a particular cylinder because of a bad MAF? After posting this question I went ahead and changed the upstream O2 sensor for bank 2 figuring that it might have gotten damaged after two months of misfiring on cylinders 5 and 6. After an unpleasant test drive, I found no code P0174 pending or current but instead got a P0306! Checked Mode 6 and found cylinders 5 and 6 are misfiring again. It's always been those two cylinders and a bad MAF can cause that? I would image a bad MAF would throw codes all over the cylinders. I forgot to mention I have pulled P0316 a number of times too.
Expert:  Anthony replied 8 years ago.
Yes, Ive seen the MAF cause what you describe. You need to reset everthing though and run it with the new MAF.
Customer: replied 8 years ago.
I will have to give the MAF a try. If this works, I will probably owe you my sanity. Thanks.
Expert:  Anthony replied 8 years ago.
Ok, good luck with it. If for some reason it dosent work, ill be here.
Customer: replied 8 years ago.
Installed new MAF. Sorry didn't work. Still having misfires on 5 and 6. P0174B seems to have gone away with the installation of O2 sensor. Any ideas?
Expert:  Anthony replied 8 years ago.
Ok, are you receiving any new codes?
Customer: replied 8 years ago.
No codes. Mode 6 shows a low percentage of misfires on cylinders 5 and 6 only. Cylinder 6 showing the highest percentage. The misfires are not appearent at idle much of the time. The misfire is most notable under load, after warm up, such as, pulling away from a traffic light. The misfire does not always occurs in these situations. Sometimes the van pulls away smooth. I have changed, MAF, plugs, boots, coils, injectors, O2 sensor. Performed a compression test of all cylinders on that bank. Tested OK.
Expert:  Anthony replied 8 years ago.
Is the PCV system's hoses in good shape?
Customer: replied 8 years ago.
Yes PCV hose, PCV, and grommet in valve cover are all free of defects.
Expert:  Anthony replied 8 years ago.
Id suspect a leak in the head gasket between the two cylinders, maybe. When the engine is hot, are 5 & 6 lower compression than the rest?
Customer: replied 8 years ago.
No, compression was nomal. #5 was 160 and #6 was 165 after 5 revolutions. The 2nd attempt was almost identicle. I performed a test of ten revolutions and the compression was 195 for #5 and 185 for #6. The second attempt was similar. Nothing surprising. The van has 73k on it. I was hoping they would be exactly the same indicating a leak between the two cylinders.
Expert:  Anthony replied 8 years ago.
You are at a leaking intake or bad wiring going to #5 and 6's components.