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Electronicals / Forscan Expert
Joined: Fri Nov 24th, 2017
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Theory and root cause analysis:
Truck misfires or stalls due to loss of compression on 1 or more cylinders.
Why? Exhaust valves aren't seating all the way.
Why? Hydraulic lash adjusters have pumped up during high revs.
Why? Valve spring force is less allowing HLA to pump up higher than normal.
Why? Valve height is taller allowing for less valve spring force.
WHy? Valve seats are recessed causing taller valve height.
Why? Valve seat material has worn away from high millage.
I've justified the theory by paying for a 1 month subscription to IATN to see what actual technicians have seen. There are many that had the same exact symptoms and all had recessed valve seats. Good thing about IATN is it filters out all the armchair quarterback mechanic responses. Worth the $20 bucks to see the knowledge base.
It's a very hard diagnosis and the only way I can see diagnosing it is to rev the crap out of the truck and have it die and immediately do a compression test. The dollar bill over the exhaust also is a big indicator. If you had access to scope and an amp clamp you would probably see the ignition wave form show a low compression situation on the rev. Exhaust pressure transducer readings I would think would also show this.
This is exactly like the Vulcan 3.0 issue that ford had a tsb for but the 3.0 is a pushrod engine and doesn't have the same HLA setup like the LIMA. So those usually have constant low compression.
I also don't believe there was a TSB for this since it mostly occurs on really high millage vehicles.
So hopefully tonight or tomorrow I can confirm my theory/hypothesis.
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2000 XLT 2.5L A/T 2WD
Mods:
Power Windows/Locks Mirrors using OEM harness and parts
Explorer Sportrac White Face Cluster
Explorer OHC and Auto-dim Mirror
Auto Door Locks
Full HID Projector Retrofit