Question1991 Ford Taurus, 3.8 V6, Auto Transmission with 130k miles. The car intermittently bucks at cruising speeds between 45 and 65 only, this problem appeared suddenly and did not develope over time. The engine runs as smooth as glass at idel and under acceleration. The check engine light is NOT on. The following repairs have been done within the last 15k miles: plugs and wires replaced, distributor cap and rotor replaced, fuel filter, PCV valve and all fuel injectors replaced, EGR valve cleaned, O2 sensors replaced, air filter replaced, throttle linkage cleaned and lubricated. Dry gas is added on a regular basis along with Cheveron Techron Fuel System Cleaner at every oil change. I checked the spark plugs today and they are all in normal condition and gapped to ford specs. Any suggests as to what might be causing this problem. Thanks, Zach
AnswerHello and thanks for the question...I'll try to help.
It sounds like the vehicle has been taken care of very well. I would suggest that the fuel pressure is taken a look in to. The spec. that I've always followed is that the pressure should be at 38-41 PSI at Idle or with the key on and enigine off.....and approximately 60 PSI with the vac. regulator unplugged, engine running. Unplugging the regulator with the engine running, simulates wide open throttle, where there is an loss of vac.
Other then that, I would have the computer system looked in to even though the check engine light isn't on. There still might be "soft" faults stored in the computer system memory.
Also, go back over the compete tune up. Check for ignition wires that might be chaffed or leaking spark to a ground. Condition of the cap and rotor. Ignition timing.
Also, does the engine reach proper opperating temp.? Has the cooling system been changed as well as the thermostat?
Hope this helps,
Erik
