2003 5.4L 4x4 - low RPM shudder / hesitation / poor MPG

[Eric M]

Recently purchased a used 2003 Exp Eddie Bauer, 4x4, 5.4L with 181k miles.


Recent maintenance:
- plugs and coils
- all EGR related components
- cleaned MAF
- fuel filter
- changed all fluids to spec


Problem:

This began after I changed (drain & fill) the tranny fluid so I am hoping it isn't the dreaded situation of changing the tranny fluid on an old tranny leading to tranny failure (yes, this does happen sometimes). I used Mercon V.

So, when the car is at full operating temperature, it shudders/hesitates in all gears *only* in the 1500 - 2000 rpm range. Beyond that no problem, except that it does shudder a bit when manually activating and deactivating the overdrive switch at highway speeds. Right as this problem occurred, my mpg went from 12-13 in the city to 9-10.

Prior to the fluid change, tranny shifted perfectly.

Anyway, the car starts easily, idles perfectly, and throws no codes when idling and when driven at highway speeds.

I know that asking about this is a shot in the dark as there are a number of things that could cause these symptoms. But I thought I'd see what y'all have to say! Thanks!

 

[bigdogchrisl]

Vacum leak probably hairline intake crack...

Sent from my SM-N970U using Tapatalk

 

[Eric M]

Vacum leak probably hairline intake crack...

Sent from my SM-N970U using Tapatalk

Excellent suggestion. I'll check it out. Thanks.

 

[bigdogchrisl]

Excellent suggestion. I'll check it out. Thanks.

NP, had it twice, once on the Expy once in a Lincoln with the 4.6

Sent from my SM-N970U using Tapatalk

 

[Eric M]

NP, had it twice, once on the Expy once in a Lincoln with the 4.6

Sent from my SM-N970U using Tapatalk

A follow-up question: where was the crack on your manifold? I have dealt with internal cracks on my Crown Vic's manifold, which caused coolant loss. The Expy leaks no coolant. So, I'm guessing the crack could be on the upper/visible part of the manifold? Thanks.

 

[bigdogchrisl]

Yes, it was actually from the fuel rail mount. Apparently someone tightened tge rail too much and cracked it. JB Weld held it for over 75,000 miles until it failed again over cylinder 1 - requiring replacement

Sent from my SM-N970U using Tapatalk

 

[Eric M]

Yes, it was actually from the fuel rail mount. Apparently someone tightened tge rail too much and cracked it. JB Weld held it for over 75,000 miles until it failed again over cylinder 1 - requiring replacement

Sent from my SM-N970U using Tapatalk

Perfect. Thanks again.

 

[Expedition007]

A plug or coil could still be bad. Your description sounds like an ignition miss. I would be getting a scan tool on it that can measure misfires while driving it. Find out what cylinders are misfiring and then swap coils from a misfiring cylinder to one that was not. See if you can move the misfire to a new cylinder. If that doesn’t move the problem, then move onto plugs. I replaced my plugs with Motorcraft plugs, but within a few weeks I had misfires again. There had been a batch of marginal plugs with many dead on arrival.

 

[bigdogchrisl]

A plug or coil could still be bad. Your description sounds like an ignition miss. I would be getting a scan tool on it that can measure misfires while driving it. Find out what cylinders are misfiring and then swap coils from a misfiring cylinder to one that was not. See if you can move the misfire to a new cylinder. If that doesn’t move the problem, then move onto plugs. I replaced my plugs with Motorcraft plugs, but within a few weeks I had misfires again. There had been a batch of marginal plugs with many dead on arrival.

Agreed, especially under load. But since it didn't sound like there were codes and given that you have to push the vacuum lines out of the way to check/fill tranny - seemed more likley to me he either knocked off, loose or cracked it when playing
With the tranny. That's how Charlie Sheen got in trouble...

Sent from my SM-N970U using Tapatalk

 

[Eric M]

A plug or coil could still be bad. Your description sounds like an ignition miss. I would be getting a scan tool on it that can measure misfires while driving it. Find out what cylinders are misfiring and then swap coils from a misfiring cylinder to one that was not. See if you can move the misfire to a new cylinder. If that doesn’t move the problem, then move onto plugs. I replaced my plugs with Motorcraft plugs, but within a few weeks I had misfires again. There had been a batch of marginal plugs with many dead on arrival.

Thanks for the info. I have scanned it multiple times while driving and have not had a single misfire code or any other code. If a plug was bad, wouldn't a code definitely be thrown? I am almost to the point of bringing it in to have a professional-grade scanner hooked up to it, before disassembling and examining the intake manifold.