Expy Problem

[digitalH2O]

Not sure where to post this because I don't know if it's electrical, drivetrain, or what. So, I'll post it here and hopefully it'll be moved to the appropriate forum. I assume it's a fuel system or drivetrain issue, but who knows. I'm certainly no expert.

The vehicle: completely stock 2005 Expedition XLT, 5.4 V8 w/83000 miles.

The problem: If I sit at about 1500 RMP, usually while doing between 50 and 55 MPH, the truck starts to buck very gently as if it's not getting enough fuel or something. The "Check Engine" light comes on when this happens.

If I'm heading uphill when this happens, the "Check Engine" light comes on and starts to blink.

I can usually fix this problem short-term using cruise control. However, it doesn't last long, only until the next time.

I can usually avoid this problem by powering through 55 MPH or cruising slower than that. The bucking can sometimes be felt briefly, but the light only comes on if I stay at that speed/rmp.

Any ideas what may be causing this? Any suggestions? Thanks!

 

[chadly]

Get the codes read since you have a check engine light. That will give us a better idea of what it might be.

 

[davesexplorer]

When the work truck had some missing that sounded like that it turned out to be a bad COP. That was on a 2V engine, I would assume that your 3V could have the same issue but the sure thing to do is get the code(s) read as chadly said.

 

[digitalH2O]

So there's no "good COP," only a "bad COP" in this situation? Okay, horrible pun. That is one sweet-looking truck in your signature, man!

So how do I get the codes read without needing to take out a second mortguage? Can I do it myself? Are there affordable tools that you folks trust to handle a job like this?

Thanks!

 

[98EXPY 5-0]

Places like Advance Auto, AutoZone, Trak Auto, PepBoys offer free code reading in the parking lot.

I'd say hit one or more of those.

 

[digitalH2O]

Went to Kragan and Autozone, the two big places in town. Both declined to read it (free or otherwise), so then I found this little hole in the wall shop. Guy did it for free, but there were no error codes found. He said I needed a tune up, and that the likely cause was a miss in one of the cylinders. Fuel didn't ignite like it was supposed to, it gets sucked out the exhaust valves and then jacks up the catylitic (sp) converter, which is what makes the check engine light flash sometimes.

He also mentioned he'd seen many Expys come in with a "7 plug" tune-up, due to the last one being hard to get to, so he's aware that's a common problem, as I've read here on the forum. So the question is, if I want to make damned sure I get all 8 changed, how do I ask him about that without offending him? He seems like a really nice guy, but I don't want to be one of the guys he mentioned who get the 7 plug tune. How do I handle this delicately? Do I just take his word for it? Or am I being naive?

 

[98EXPY 5-0]

My guess is if he told you about it, he was saying what OTHER shops do. Not his shop.

 

[digitalH2O]

Yeah, that's a good point. Thanks man.

 

[JUST4FUN]

Do not try to change the plugs in the 3V 5.4 my work truck is sitting in the shop now with broken plugs in it ford says to break the plugs loose and fill the the plug hole with carb cleaner. let it sit,so we are letting it sit overnight in the morning they are giong to spray PB BLASTER IN IT THEN TRY TO GER THE PLUGS OUT

 

[ELVATO]

For a 3v 5.4, I'd go to a dealership, and only to one where they will cover if they break any plugs. Things can get real expensive real quick once plugs start break, especially for a truck of your milage.

 

[gto78]

I've seen almost the same exact problem quite a few times before, and it's always been a faulty spark plug wire. The wire gets worn out/old/dry rotted/or actually pinched against something. Then there's always one particular RPM under light load that just sets it off, makes it spark against the engine block and cause that cylinder to misfire.

During a misfire the check engine light will flash. It won't save a code unless it does it longer than a certain length of time continously. Even then I believe the misfire code will erase after you shut down. Best bet is to drive with the scanner connected and try to get a reading while the check engine light is flashing, at least you'll know which cylinder to look at.

The last time it happened to me, I had recently installed new wires so I didn't even attempt to look at them. Instead I changed all kinds of crap, spent wads of $$, and still same problem. Finally found a spark plug wire rubbing between the valve cover and firewall (known issue with SOHC 4.0 Explorers). You can find it by looking at it in the dark while having someone powerbrake it in gear.... just be safe lol. In the dark you'll see the sparking wire IF it is at the right load conditions.