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Old 09-01-2014, 02:33 PM   #1
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Another Engine Misfire Question

2003 E350 SMB RB50 5.4 engine that misfires at low RPMs. The check engine is not on. We have been staying in Wyoming for the past two months. The elevation here is between 5000' and 8000'. This problem started 5 days ago. I do not have a tach and am 2 hours from any auto service.

Engine will idle smoothly when started even on a cool morning (elevation here is over 7600 feet).

Shift into D or L and the engine will start missing (1 maybe 2 cylinders) without stepping on the gas.

Shift back into P and it will idle smoothly.

Shift into D and start driving. Engine will misfire while running at slow RPMs.

Stomp on the gas - miss seems to fade away.

Accelerate in low gear and the miss seems to go away until it shifts into 2nd.

Drive over 40 in second and the miss seems to go away or is less evident.

Bottom line is that the engine runs rough at low RPMs.

I am guessing that if the check engine is not lit up that a code scan will not show anything (Y/N?). All of the coils have >70,000 miles on them. Might be bad gas so I will take it for a drive tomorrow. Everything else seems to be working OK. Before I get stranded out here I would like to get a few opinions as to what might be happening.

Thanks
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Old 09-02-2014, 12:47 AM   #2
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Re: Another Engine Misfire Question

I should still show a "pending code" which will be a P030x code, with "x" being the misfiring cylinder.

Another way (but tedious) way to diagnose is to individually unplug coils until you find the one that doesn't make it worse.

Bad coil is likely. Seems like once 10 yrs rolls around, they become much more failure prone, and milage doesn't seem to matter.

I would not expect bad gas to have such a distinct misfire patter. Bad age tends to cause stalling or hesitation, but not what you are describing. But that does fit the symptoms exactly of a weak coil.
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Old 09-02-2014, 07:42 PM   #3
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Re: Another Engine Misfire Question

I just went through this last weekend in the middle of Nv. In my case it was a miss fire at 50 to 60 mph. At first it was intermittent but took probable 80 miles of desert driving before the coil finally
failed completely, I was lucky to make it back to base camp. I always carry a code reader and sure enough it was miss fire on no. 6 cylinder and miss fire on start up. Well after a drive into Fallon and 30 min. to replace back on the road. I did get an extra coil for next time. I have about 130k on my engine, I think I will replace them all. Im also considering getting spares for the following parts.

Throttle position sensor
crank shaft position sensor
air intake sensor
mass flow sensor???
4r100 solenoid???
fuel pump

any other spares I'm missing(a trip to Pick and Pull will keep the cost down)
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Old 09-02-2014, 09:54 PM   #4
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Re: Another Engine Misfire Question

I carry a spare coil, a spare starter relay (the fender one) and a can of MAF-sensor cleaner, since I have an oiled air filter (AFE). Really the starter relay has been the only thing to sideline me, and only for a minute while I dug out the Leatherman to jumper the relay terminals. Of course, its always managed to happen at awkward moments...

A failed coil certainly makes the drive less pleasant, but once the misfire gets bad enough the PCM just shuts fuel off to that cylinder (and turns on the SES light), and at that point no further damage will occur.

Fuel pump generally gives some early warning symptoms, but even if it doesn't, a good solid thump to the tank while cranking will usually get you going at least a few more times.e
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Old 09-02-2014, 10:33 PM   #5
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Re: Another Engine Misfire Question

I didnt realize the fuel was shut off, I was rather worried about trashing a catalitic converter or washing the oil off the cylinder wall or oil delusion. Rather smart of Ford.

Dave
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Old 09-03-2014, 03:41 PM   #6
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Re: Another Engine Misfire Question

Thanks for the responses. I drove for about 4 hours yesterday - needed to pick up groceries. Started the engine....no miss. Put it in D....no miss. Drove out to the street, down the street, onto the main road...no miss. Actually no miss all day. I am happy for now. We will be leaving for Bend, OR on the 21st. I do think that I will need a new set of coils and hope we can get to Bend before there is a failure.
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Old 09-04-2014, 03:19 AM   #7
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Re: Another Engine Misfire Question

Why the hesitation to re-fit new coils, boots and plugs now instead of hoping there's no failure?
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Old 09-04-2014, 05:43 PM   #8
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Re: Another Engine Misfire Question

We are in Yellowstone but leaving in 12 days. The closest parts store is 2 hours away (one way) and too late to order parts on line. If it starts to miss I will stop in Bozeman and find out which coil(s) is/are weak.
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Old 09-04-2014, 09:38 PM   #9
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Re: Another Engine Misfire Question

Their are several youtube videos that show how to replace the coils,Its a little tight in the vans but if your patient and careful its a simple job. It touck me 20 min to replace no 6 in the middle of Dixie Valley. Some say you need to remove the fuel rail but i found you dont need to. Good luck in your travels.... Dave
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Old 09-05-2014, 05:55 AM   #10
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Re: Another Engine Misfire Question

Quote:
Originally Posted by unimogdave
Their are several youtube videos that show how to replace the coils,Its a little tight in the vans but if your patient and careful its a simple job. It touck me 20 min to replace no 6 in the middle of Dixie Valley. Some say you need to remove the fuel rail but i found you dont need to. Good luck in your travels.... Dave
If you have a tablet or at least a large phone, you could download the video ahead of time so you have it handy for reference.


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