Can a bad fuel pressure regulator cause misfiring? We have replaced the plugs and wires and coil pack and we are still getting the misfire code. Is it possible the fuel pressure regulator is bad? Its a 99 Ford Taurus. Thanks.
If excessive fuel pressure were the cause of a misfire, you would have other symptoms to go along with it. I would expect to see a check engine light throwing out a rich exhaust condition on banks one and two. I would also expect to see a lot of black smoke from the exhaust.
A failed fuel pressure regulator will almost always cause the above symptoms, but I don't think I have ever seen one cause a misfire without any other symptoms. So I would most likely rule out a fuel pressure regulator for the time being.
A lack of fuel pressure can cause a misfire. But I wouldn't suspect a fuel pressure regulator as the cause. I would suspect a plugged fuel filter, a kinked fuel line, or a failing fuel pump. I would test the fuel pressure with the engine running and see if you have between 35-45 PSI. If you do, then your fuel pressure is fine.
Since you didn't say if the misfire code is isolated to one cylinder, or if it is the P0300 random misfire, I am not sure where to take you for the diagnosis. If it is isolated to one cylinder and you have replaced the ignition components, and you are sure the cylinder has good compression, I would start looking at that cylinder's injector. You could test it with an ohmmeter to see if it has 11-18 ohms of resistance through it. If it doesn't, then you know it is bad. Unfortunately if it tests between 11-18 ohms it does NOT necessarily mean it is good. It could be plugged or leaking. You would almost have to replace it to eliminate it as being bad.
FPR-800 fuel pressure regulator
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