2003 Explorer Sport started hard, popped, died, restarted runs rough and terrible. | Ford Explorer Forums - Serious Explorations

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2003 Explorer Sport started hard, popped, died, restarted runs rough and terrible.


New Member
October 11, 2015
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City, State
Year, Model & Trim Level
2003 Ford Explorer XLT Sp
Yesterday afternoon I went to start my 2003 Ford Explorer Sport (4.0 SOHC, Automatic, 2WD, 160,000 miles) and it popped; smoke came from under the hood.

I assumed it was electrical; however, there are no noticeable charred wires or melted components. Upon opening the hood, there was some smoke coming from the intake inlet near the filter housing. I assume it was a backfire.

I started it again, but it wouldn't stay idling and required fancy footwork to keep the motor running between 1,000 RPM and 3,000 RPM. There are no audible knocks. There is no coolant in the oil. It just runs awful.

I disconnected the MAF sensor. Started the vehicle and it maintained an idle with raucous and regular throttle surge between 1,000 RPM and 3,000 RPM.

Unfortunately, I have to work until Thursday, so I don't have a lot of time to investigate. I hope that someone has some insight to the issue.

Has/does your engine have timing chain noise (either at startup, or while running)?

A backfire is usually caused by a timing problem. On the 4.0L SOHC engine this can be caused by one of the timing chains jumping a tooth (AKA jumping time) which unfortunately is fairly common for this engine. I would do a compression test on both banks to see if any valve damage has occurred. If is has your engine is pretty much junk, but even if it hasn't you're probably looking at major repairs.

The best way to proceed is with proper diagnosis. The 4.0L SOHC engine is most prone to jumping time at startup. That was the death of my first SOHC engine. That engine had terrible chain rattle during startup. 2000StreetRod is very knowledgeable on the SOHC engine. Perhaps he can suggest some other possibilities.

My '94 Explorer (different engine) used to occasionally backfire at startup and blow a vacuum line off the tee on the firewall. It would then run much like you're describing. Check all your vacuum lines.