Here’s the latest reader question, along with my reply!
Cyril asks: Engine light started coming on and fuel mileage dropped to 14 MPG from 22 MPG. Local shop replaced the oxygen sensor and one other sensor but not the throttle position sensor. Engine light comes on intermittently. Should the TPS be replaced?
My reply: Before you have your mechanic replace anything else – and charge you for the parts and labor – I’d ask him to find out what’s wrong with your truck! It sounds as though he’s been guessing because if the light was coming on due to a problem with the 02 sensor (and the “one other” sensor you mention) replacing those items ought to have cured the problem. I would not replaced the TPS unless it needs to be replaced.
Proper diagnostics are in order. Your truck may be pre-OBD II (On Board Diagnostics). OBD II-equipped cars have a universal plug-in port, usually located under the dash, on the driver’s side, to the left of the steering wheel. This is where you plug in the code reader to obtain the trouble codes stored in the computer, which help you trace the problem. Pre-OBD II cars work similarly, but they do not have the universal port; you’ll need a shop that has the necessary equipment to deal with the Ford-specific system.
As an aside: Has your mechanic checked the catalytic converter? Given your truck is almost 30 years old, I’d be looking at that unless it has been replaced and the one on the truck right now is less than five years old. And I’d still check it.
A bad (partially plugged) cat could easily cause your mileage to dump as it has and also would trigger the check engine light.
Keep us posted!
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