2003 4.0 SOHC Explorer problem - timing chain(s)? | Ford Explorer - Ford Ranger Forums - Serious Explorations

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2003 4.0 SOHC Explorer problem - timing chain(s)?


New Member
July 6, 2015
Reaction score
City, State
Haverhill, MA
Year, Model & Trim Level
2003 Ford Explorer
We have an '03 with 128K on it, went through a toll gate and no acceleration after, ran like crap. Made it to next exit, stalled and wouldn't restart. Rode flat bed of shame home. No breathing through engine 15# back pressure, cats totally clogged. Replaced Y-pipe and cats. Now runs, but runs poor and both cats heat cherry red within a minute. Removed harmonic balancer and crank trigger, keyway appeared okay. 0" vacuum at idle and 10" at 4000 rpm. Pulled low oil pan cover off, no plastic bits evident but 4.0 has split oil pan with casting above 10mm bolted on shallow pan under oil pump pickup. Diagnosis is engine mechanical or timing issue would need to disassemble to verify. Compression tested one cylinder each bank, values were good.

Has anybody run into these symptoms? What course of action to take?


"I'm counting to 3, then I'm getting your dad."
Elite Explorer
March 16, 2013
Reaction score
City, State
Woodstock, GA
Year, Model & Trim Level
04 Ford Explorer 4.6l
Clogged cats can burn a hole in the plastic intake. What are your short and long term fuel trims?