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Old 06-17-2019, 11:18 AM   #1
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Misfire #6

2012 Ram 1500 5.7 . Cylinder 6 missfire only after a long drive . Runs amazing for 50 or 60 miles then cylinder 6 randomly misfires. Replaced coil pack last night rechecked plug gap . Tried again took the wife out after about 50 miles it starts misfiring. Shut the truck down and restart and it's fine for another 50 or 60 miles. I'm scratching my head on this one. Compression is 165 psi so valves are holding . I dont see a broken valve spring. And if it was any of that it would be constant . Its almost like it reaches operating temp and cylinder 6 drops out . I'm leaning towards ecm or injector on this one. Any ideas or tips would be appreciated.

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Old 06-17-2019, 01:35 PM   #2
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Standard troubleshooting is to swap the coil with another cylinder. If miss doesn't follow the coil then swap spark plugs. If miss remains swap the injector with another cylinder. Monitor the fuel rail pressure. Inspect the wiring harness for breaks and scraps. Let us know what you find.
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Old 06-17-2019, 01:50 PM   #3
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Did all of that with the exception of the injector. It's just weird that it isnt all the time. Just once you drive 50 or 60 miles .
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Old 06-17-2019, 07:04 PM   #4
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UPDATE. Fuel pump losing pressure once it has run for a bit. Causing a lean mixture and detonation. It just happens to flag cylinder 6 first
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Old 06-17-2019, 07:57 PM   #5
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Well done..
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2003 RCSB, 2wd, "Pro-Street"
6.4L/cog driven V7-Ysi/46rh trans/HTH Truckarm coilover suspension. HP Tuning...

1# 2017 HTC FASTEST HEMI List....
Current 1/4 mile [email protected] (2018)
Current 60' PB 1.351 (2019) mechanical issue for 1/4m

HTC 2018 TOTY

Support vehicle- 2007 QC G56 4x4 diesel
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Old 06-17-2019, 09:25 PM   #6
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Well that’s a good find. Change it out and take it for another drive make sure it’s all good if not we will go deaper
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Old 06-18-2019, 08:43 AM   #7
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Truck lit right off. Power level is much higher than when I bought it. I cant blame the dealer you never know with a used vehicle. Mainly because a fuel pump wont throw a code. It causes secondary symptoms. Fuel pressure is holding steady under hard acceleration with no power lag . All the secondary symptoms cleared and check engine light shut off by itself. Now I went and cleared the hard codes drove 120 miles with no pending codes .
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Old 06-18-2019, 10:18 AM   #8
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Glad to see you got the problem sorted. How many miles on your truck, just wondering when I can expect to replace my fuel pump.
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Old 06-18-2019, 01:37 PM   #9
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It has 110k on it. Since I've owned it I use nothing but full royal purple synthetic with a wix filter changed every 8k . NGK iridium plugs , K&N airfilter , true dual exhaust and a mild tune . Have it set to run on 91 octane and no governor. 6 inch lift with 35/12.50/20
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Old 06-19-2019, 01:15 PM   #10
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Just fyi in my case it was much easier to unbolt the bed to access the pump assembly . Instead of trying to fight and get the wiring and lines off the tank where you cant see. I unbolted the bed lifted it with 3 of us set it to the side and had full access to the tank and pump assembly . The shortbed isnt heavy just awkward. So grab a buddy and make it easier
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