'94 F-150 with a 351, suddenly seems to be running on 6 cylinders

Asked by Jul 29, 2015 at 06:06 PM about the 1994 Ford F-150 XLT 4WD Extended Cab LB

Question type: Maintenance & Repair

My '94 F-150 with a 351, suddenly seems to be running on 6 cylinders. Mechanic is
blaming bad fuel pumps, but truck runs exactly the same off either tank, starts right up &
idles so I disagree about fuel pumps. We hooked a gauge to the test valve on the fuel
lines & it reads 35-38 when truck was running. I'm thinking ?injectors? we replaced fuel
filter & cap & rotor. Any ideas for diagnostic or repair?

6 Answers

47,665

Are 2 spark plugs wires switched?

47,665

Switched, meaning on the wrong plugs. That would do it.

47,665

Injectors seldom go bad 2 at a time.

No, unfortunately... It happened after the truck was run on the rear tank tell empty and started to die before quickly switched to the front tank. It was driven 3-5 miles after that, parked and the next time it was started it began showing these issues...

18,790

First eliminate a possible spark problem with the plugs, wires etc. If your vehicle fuel injected. If so you could have sucked up some crud from an empty tank and fouled an injector. Also, change the fuel filter.

So I have now replaced the plug wires as well and very little if any improvement. I did run a diagnostic: ER test: Code 172-HEGO shows system always lean Code 213-Spout circuit open EO test: Code 172-HEGO shows system always lean Code 452-Insufficient input from vehicle speed sensor I can't imagine the O2 senor causing all of this... Now where to begin??

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