What is going on?

[OXX1973]

I have a 1998 Ford Expedition XLT 4x4 with the 5.4. My CEL came on and when I checked it with my scanner it threw the Cylinder 4 misfire code. I replaced it this weekend and I am no longer getting a CEL nor is there a pending code showing. When the engine is cold and running, it drives smooth but after about 10 minutes of driving I start getting vibrations and what can only be described as misfires. I checked all my COPs by pulling the fuel injector harness to see if it would throw a CEL or if it would drop the rpms but no such luck. I am officially stuck and need help.

Thank you

 

[CaperCanadian]

I had the same thing on mine, I had a bad plug, would work fine cold, and start bucking when it warmed up. Pull the plugs and give them a check.

 

[docraymund]

Check the coolant temperature sensor. It is the primary sensor used during open loop conditions.

 

[OXX1973]

Check the coolant temperature sensor. It is the primary sensor used during open loop conditions.

Would this cause my expedition to act like it is misfiring?

 

[1955moose]

In your post you didn't say what you replaced? Was it the coil, wire, what? You stated the code went away, if you have a miss, the order of things, usually is to run diagnostic codes, which you did, run a fuel pressure test, to eliminate a weak fuel pump, clogged filter, or fuel pump wiring. I would change all 8 spark plugs with motor craft plugs, along with spark plug wires. Do you have the coil on plugs, or the early style coil/ wires? For what it's worth that's where I'd start. Working out of your home a full tune-up is where your probably heading. As tempting as it is, don't change coils, with the cheaper Asian ones available online. You can cause more problems. These vehicles tend to like oem Ford parts, keep us posted what fixes your hiccups.


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[OXX1973]

In your post you didn't say what you replaced? Was it the coil, wire, what? You stated the code went away, if you have a miss, the order of things, usually is to run diagnostic codes, which you did, run a fuel pressure test, to eliminate a weak fuel pump, clogged filter, or fuel pump wiring. I would change all 8 spark plugs with motor craft plugs, along with spark plug wires. Do you have the coil on plugs, or the early style coil/ wires? For what it's worth that's where I'd start. Working out of your home a full tune-up is where your probably heading. As tempting as it is, don't change coils, with the cheaper Asian ones available online. You can cause more problems. These vehicles tend to like oem Ford parts, keep us posted what fixes your hiccups.


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Sorry for not giving all the information. Yes I changed the Coil on Plug (COP) for the #4 cylinder. I had a tune up a couple of years ago that involved replacing all of my plugs with motorcraft plugs and the fuel filter. I thought they would change all of the COPs but they did not and the itemized receipt shows they did not charge for them so at least I did not get swindled. I have already replaced 3 COPs with motercraft COPs. I do not the ability to run a fuel pressure test but when I pulled the wire harness of the fuel injectors one by one, there was a noticeable drop in RPMs

 

[1955moose]

You can usually borrow a fuel pressure tester from the name brand auto parts stores, like auto zone and Oreillys. It's not a bad idea to purchase a mid priced one, under $100.00 just to have. Missing under load can be fuel or electrical related, is why you do diagnostic, so you don't look like curly from the three stooges, doing his spinning in a circle routine. Easiest way to tell electrical misfires vs fuel, is electrical makes a strong off/ on bucking, fuel make a softer sputtering, and bad coils/ boots act up real bad at highway speeds under constant throttle. If you have no particular cylinder codes, could be insufficient fuel. You might also want to use a noid light set on your injector harness,to be sure all 8 are getting power and ground. If everything electrical, fuel, compression checks out, you might consider injection clean out. Keep us posted on yours/ mechanics diagnosis.


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[OXX1973]

So my expedition finally through a pending code. P0303 (misfire in cylinder 3). I took off the COP and exchanged it for cylinder 2 and it still through p0303. I pulled the plug and it was pretty nasty like someone left paper on the spark plug well. I cleaned it and installed the plug and it is still bucking so I will replace the spark plug tomorrow. Since I will be at Orielly's, I will see if they have a fuel pressure tester to check my injectors. Hopefully this will get resolved.

 

[docraymund]

Also buy a spark tester to actually verify the firing of that cylinder. And ask if you could rent a compression tester to verify if it's a dead cylinder.

 

[1955moose]

I agree with doc, on both items. Be sure you don't have a leaky valve, or non functioning injector. If power to the injector and coil check out as well as sufficient compression, pull that injector, to be sure it's spraying proper fuel. Injectors clog up easy.


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