My 2006 Expedition has a skip that comes and goes. About once every couple of days it will skip very badly for 10 to 15 minutes. It skips so badly it will hardly run. The check engine light flashes while this is happening. The skipping stops, the light goes out, and the vehicle runs perfectly until it happens again. No codes are being left in the computer.
Any ideas?

 

What do you mean by skipping? Misfiring?

 

By skipping I'm assuming you mean misfiring? Even if the light goes out there will still be codes stored in the computer as memory codes. Take it and get it scanned, report back with the codes.

 

Actually, there are no stored memory codes. That is why I am having problems diagnosing it. I do mean misfiring when I say skipping.
The first time, I checked it with a Snap On computer, no codes. I drove it until it misfired again and the light flashed. Then took it to my friend at the Dealership, read it with dealers computer, no codes. He is a Ford tech that has been to pretty much every school Ford has and he is baffled by it. According to the computer, nothing is wrong with the vehicle.

 

When you brought it to be scanned, did you leave it running or did you turn it off?

 

Turned it off. I called before I brought it and asked if I needed to keep it running and he said no, the codes are not volatile, they can be recovered until the computer is cleared.

 

That's somewhat but not entirely accurate. With an intermittent code like you're getting, turning the key off resets the ECM and clears the memory buffers. If the CEL comes on and you scan it without turning the key off, 9 out of 10 times that intermittent code will show up in the scan.

If that still doesn't do it for you, then beg borrow, or buy a scan tool and keep it plugged whenever you're driving. Then the moment the CEL comes on initiate a scan. This might give you enough time to catch the code before it clears itself.

If you have to buy one, remember that the cost of the scanner can be less than the cost of replacing good working parts. Plus you'll already own one for next time.

 

Thanks, I finally got a code on the snap on machine. "Random misfire."
That was not really a big help.

 

I know, I hate that code because all it means is you have a misfire that comes and goes. Just driving the truck tells you that much. You're looking to get a code in the P0301-P0308 range. The last digit 1-8 represent the cylinder number that's misfiring.

 

Well, it might be a help. If they are all having trouble firing, I look to the fuel supply, as it would effect all cylinders equally.

Have your Ford Tech look at the freeze frame data to see if this happens under load (when extra fuel is required).

What kind of shape is your fuel filter?

Does this usually happen when the tank is below 1/4 tank?

Have you put a fuel pressure gauge on it to see if the pump os putting out good pressure?

A persnikity fuel pump relay could reduce the amperage to the pump.

Have your Ford Tech friend put an amp clamp and a DSO (Digital Storage Oscilloscope) on the fuel pump circuit and monitor the fuel pump draw and/or look for fuel pump brushes/commutators irregularities.

 

This particular computer interprets the codes into plain English. Several months ago I had a bad coil pack on 6 and it read "misfire 6." The random misfire code is or no help to me. The only suggestion I have gotten so far is to take it to a different Ford dealership that has the equipment to load test the coil packs. My first thought on this is that the engine has 93,000 miles on it and I can probably change all the coil packs for what it will cost to have them tested.
About 15,000 miles ago I replaced the crank trigger. It was also causing a "random misfire." I am kind of running out of things to go bad on this engine. The plugs are OEM and less than 5000 miles old. I am sure Ford has a more proper name for "crank trigger", but being from a race engine building background, they are crank triggers to me.
I love Fords, but if I got many Fords like this one, I would probably have to swap my brand loyalty.

 

Thanks, we will look at it again. Fuel pump is an OEM pump with less than 10k miles on it. We did not check the amperage, but we did check fuel pressure under load and it was within specs. Fuel filter was changed when pump was. It misfires no matter how much fuel is in the tank.
The condition happens the most frequently when just cruising down the road between 50 and 65. You can actually floor the engine and cause it to eventually recover from the condition.

 

You can change all 8 of the COPs yourself for under $100. For another $20 or so, you can change the plugs while you're in there since they're due in 7,000 miles anyway. For that matter, I suppose it could be one of those 93,000 miles plugs that is causing your misfire. So you're really going to want to change them along with any of the COPs you change.

 

Are they Motorcraft plugs?

 

Yep. From the dealership. I learned a long time ago Fords do not like aftermarket plugs too well.