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Stumped! p0301 p0306 p0171 p0174

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Old 01-13-2018, 06:03 PM
bren_tx bren_tx is offline
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Stumped! p0301 p0306 p0171 p0174

I was pulling a trailer the other day and noticed the truck began running rough and now is hardly driveable. Engine has a hard miss both cold and hot. If I reset the codes, the p0301 comes back very quick and the other codes will eventually come back after driving. I have dual exhaust and I can hear the bank 1 is much more rough than 2.
So, I've changed all of the plugs, except for #4, may do that one today. I've changed 3 coils on 1, 5, 6. I've taken most of the fuel injectors off and cleaned them using carb cleaner and a 9v battery, so I know they're all working. Tested fuel pressure...its low but within spec at 31psi. New fuel filter.
I'm going to changed the #4 plug and coil today, but I have a feeling that it won't solve my problem. I'm totally stumped. I didn't have any lean codes until this happened. Could it be the maf?
99 f250 5.4
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Old 01-14-2018, 07:51 AM
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enriched&beyound enriched&beyound is offline
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Did you check the PCV elbow on the passenger side way back on the firewall. This goes to the rear of the intake manifold. Best to check all the vacuum lines. The p0171 and p0174 indicate a vacuum leak, which can create misfire condition. OR....you may have a intake leak, depending on how yours is equipt, either crack in a plastic intake manifold or gasket failure with either the plastic or alum intakes.

What you have done so far is good, but probably would good to change all the spark plugs and reseal the boots with dielectric grease
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Old 01-14-2018, 03:28 PM
bren_tx bren_tx is offline
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I will check for leaks in the intake. Its just crazy to me that the engine went immediately from great to poor, instead of a gradual decline. Its obvious that something mechanically failed.
Ive been thinking about how #6 fires opposite of #1 (so when #1 is TDC on the exhaust stroke) and what this could mean.
I havent noticed any coolant leaking but have come across many articles about intake leaks when I googled the codes.
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