Hello, a few weeks back, I completed the engine rebuild on my truck (2006 Expedition, 5.4l 3V), and it's now clocked around 700 miles. Overall, things seem great, but there's this one annoying issue I can't quite pinpoint. When the engine is idling at operating temperature, specifically in D or R gear, I feel these light vibrations or shaking. It's most noticeable when the truck is parked, and it disappears when it's in motion. The vibrations are irregular, similar to a random misfire, though not as pronounced. It's like the feeling of sitting in a car with a small diesel engine idling. Interestingly, when the engine is cold or in parking/neutral gear, everything is smooth with no shaking.

Here's what I've checked and done so far:

• No MIL light, and no DTC codes.
• RPMs are stable, not fluctuating.
• No misfiring detected.
• The engine underwent a complete rebuild. Most of the parts are new (Motorcraft and Melling), all reused parts were machined by reputable machine shop. Everything was measured with precise tools + plastiguage. Everything torqued precisely within the specs.
• New spark plugs and ignition coils.
• Replaced transmission mount.
• Engine mounts were inspected and are in good condition.
• Fresh transmission fluid.
• Thorough inspection of the engine harness and electrical connectors, with replacements where needed.
• No vacuum leaks found.
• Cleaning of all intake components, throttle body, PCV valve, and associated plumbing.
• Brand new engine gaskets, o-rings, and sealants (mostly Fel-Pro).

Despite all these efforts, I'm still grappling with this issue. I know diagnosing this remotely is challenging, but perhaps someone out there has some ideas on what else I can check or consider. Any thoughts or suggestions would be greatly appreciated!

Thank you,

MC

 

So just to be clear you have monitored the misfire counters and they all stay at zero?

 

Yes.

 

could it be torque converter or pressure plate related ?

 

Question: Do passengers comment on the slight vibration? I also think mine has one but when I say something to a passenger about it, they comment that they can't feel anything. I also "noticed it" after doing all the timing, top end, etc. The only things I haven't inspected are motor mounts, torque converter, nor pressure plate. Either I'm going crazy or there is something there. I've owned the truck since new in 2004.

 

I thought of it, but there are no other signs of a broken torque converter. Nothing slips, transmission changes gears really smooth, after 700 miles transmission fluid still looks like a new.

No one comments, except my brother in law. He is the only one that feels those vibrations too, but he is a qualified mechanic so he takes care about a details like that. I also own a Mercedes-Benz with a gas engine and it idles so smooth that I can't even tell if the engine is working without looking at a tachometer.

I've noticed something in the past few days, especially with the colder weather. It seems like the heating system isn't as robust as it should be. Even with the temperature set to 90°F, the cabin gets warm but not quite as hot as I'd expect. In my other cars, cranking the HVAC up to 90°F would make it nearly unbearable to stay inside for long; I usually reserve that setting for quickly drying out the cabin in the autumn or winter. Both the water pump and thermostat are brand new (Motorcraft for both), and there are no apparent leaks. However, I'm wondering if there might be a blockage in the radiator. At lower RPMs, could the water pump be struggling to push water through, causing vibrations?

 

Hi, I've been pretty swamped lately, but finally got around to tackling the truck problem last weekend. I use it as my daily driver, and unfortunately, it's still acting up.

Gotta own up to my goof – turns out those annoying vibes are due to misfiring. Why did I think my engine was misfire-free? Well, the ECU is cool with it as long as it stays below 2% of the total cylinder firing. No codes, and the MIL light stays off. My old scan tool couldn't handle live data, but with a different one, I dug up more info. Looks like an issue with the electrical system, likely the charging system. I've been keeping tabs on live data and noticed something interesting: before each misfire, the ECU tells the alternator to drop the voltage by 0.5v for a hot second, and almost every time it does, bam, misfire. Check out the chart from FORScan I attached to see it visually.

FORScan Chart: [url=https://i.imgur.com/ocU4fsR.png]LINK

System voltages:

• Battery after an overnight chill: 12.07 volts
• System voltage at idle in park, regular electric load: 14.07 volts (with occasional dips to 13.5v, like the chart)
• System voltage at idle in drive or reverse, all electric bells and whistles: 12.1 volts (lights, defroster, the whole shebang)
• System voltage at 2000 RPM, any gear, any voltage: 14.1 volts (with occasional dips to 13.5v, like the chart)

While installing the engine, I moved the engine ground strip to the front from the back. Did some resistance checks, and all seems good:

• Negative battery terminal to engine block: 0.01 Ohm
• Negative battery terminal to engine heads: 0.01 Ohm
• Negative battery terminal to alternator housing: 0.01 Ohm
• Negative battery terminal to ECU: 0.01 Ohm

Thinking my next move is grabbing a new alternator and battery to see if that shakes things up (or hopefully not). But, before I kiss another $400 goodbye, keen to hear your thoughts on this head-scratcher. Why does the ECU keep telling the alternator to play with the voltage like it's some kind of charging cycle or maybe interference? Appreciate any insights!

 

Can't see the graph, but now that you have live data, are the misfires concentrated on one or two cylinders, or completely random?
I Would try to eliminate them first and see if the voltage isn't dropping while the misfires occurring rather than the other way way around.