Can someone assist here? I have a '99 5.4 Lariat 4WD. When normal 2WD driving mode (electronic switching txfr case), and making a turn either slowly or from a stop, the engine starts to make a diesel noise. It really sounds like a diesel on turning. Anyone ever heard of this or have had this problem? I haven't tested this in 4WD mode 'cuz the majority of my driving is in 2WD.
Any help would be appreciated. My next step is to take it to a dealer to fix.

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...my first "big" truck
'99 Ford F-150 Lariat
4WD, 4DR...absolutely stock (I guess)

 

My 99 Supercab with a 4.6 does the same thing when using 87 octane and the engine is at full operating temperature. When I use 89 octane I rarely ever hear it. Probably not a big problem to fix, I just haven't bothered.

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1999 F150 XLT 4X2 SuperCab
- 4.6 (Romeo)
- Oxford White/Gold
- BodyGuard Bedliner
- Prime Designs Deflector
- Ventvisors

No Door Cracks, No Engine Mods, No Problems

 

Excellent suggestion. Duh...why didn't I think of that before. I'll burn this tankful of 89 and put in some higher octane gas. I'll let you know the results. Thanks again (as I hit my head, yell an expletive followed by D'OH!)

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...my first "big" truck
'99 Ford F-150 Lariat
4WD, 4DR...absolutely stock (I guess)

 

When you are turning, are you cranking the wheel all the way to the locking point or no? It could be the power steering pump? Dont know just a suggestion

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1997 F-250 LD XLT 4x4
All-Star Bed Liner
5th Wheel Hitch
Soft Tonneau Cover

 

Mine makes a similar noise like mentioned early when I turn either way and the steering wheel is approaching the stop. It is the power steering. Took me a few times to realize what it was. I don't know if a higher octane gas would help. I put Chevron Supreme in my truck and got pinging and what sounded like valve clatter. I have since put regular in it and haven't had pinging since.

99 F150 XL
4.6L
Manual
Bone Stock (not for long)