I have 30psi at fuel rail before start up then 65psi after start up. When I unplug the vacumm line to the fuel pressure regulator the pressure doesnt change. Should it? What kinds of driveability issues would this cause.
Vacuum should make the pressure go down and unplugging the hose will make it go up. During coasting, intake manifold vacuum is high which tugs harder on the molecules of fuel at the tip of the injectors. To prevent a rich coast-down condition, pressure is dropped so the difference between the two forces acting on the fuel molecules remains constant. If the regulator doesn't respond to changes in vacuum, the higher pressure will cause an excessively rich mixture any time other than moderate to hard acceleration. You might see black smoke from the tail pipe and fuel mileage will decrease.
March, 7, 2011 AT 7:59 PM
Best advice i've gotten so far thanks I have been having hard shifting if I am not under moderate acceleration from first to second but when I give it a little more throttle than im used to it shifts normally it feels like the rich condition is causing the timing to be off and making the shifts harder than normal. Also throwing a code p0102 MAF signal low. I just replaced the fuel filter which had some junk in it im thinking that something may be in the fuel pressure regulator also is it possible to clean this out or is replacement the only option $80 factory only item it seems.
March, 7, 2011 AT 8:31 PM
Your Engine Computer constantly runs tests on the various sensors. To do that it has to compare some to each other. In this case it may be expecting to see a given amount of air flow through the mass air flow sensor based on the position of the throttle position sensor and engine speed. The fault code isn't saying the MAF sensor is defective, just that it doesn't believe the values it's reporting. That would agree with a vacuum leak or leak in the fresh air tube. A vacuum leak will also cause engine speed to increase but under load there will be reduced power. That means you have to press the gas pedal further than normal. That will affect shift timing and harshness. Besides a vacuum leak, the MAF sensor element could be dirty. Bug juice and other dirt insulates it. The sensor works by warming up a heating element, then watching to see how much the air flow cools it. If dirt insulates the sensor, it won't cool enough making it look like less than the actual amount of air is entering the engine. Some sensors, such as on Corvettes, run a very high current through them to burn any dirt off about 20 minutes after the engine is stopped. I don't know if Ford does anything similar, but to be safe, don't spray any cleaner into the sensor for a good hour or two after stopping the engine.
March, 7, 2011 AT 9:07 PM
Thanks again. Is it possible to clean the fuel pressure regulator or if it is not responding to vacumm pressure does it need to be replaced? There is quite a bit of vacumm pressure at the hose but unplugging it did not affect the fuel pressure at the schradder valve.
March, 7, 2011 AT 9:28 PM
GM has a really huge problem with the pressure regulator leaking fuel into the vacuum hose. I have never seen a defective regulator on a Chrysler product. I have found one split ten cent o-ring that caused a loss of pressure right after the engine was stopped and resulted in a long crank time to get it restarted. I am not aware of any unusual history with Ford regulators. It does sound like the return port is blocked but I think it would be more likely the steel return line to the tank got crushed or the rubber return hose between the engine and body is kinked. 65 pounds seems to be too high and is about the most a good fuel pump can produce. You might consider removing the rubber return hose where it goes to the body, then see if fuel flows from it. If that lets the pressure drop, you'll know the regulator is okay.
March, 7, 2011 AT 9:32 PM
Forgot to mention that I never autopsied a failed regulator. It would seem debris that is large enough to plug the outlet port wouldn't be able to make it through the fuel filter. I never heard of cleaning a regulator.
March, 7, 2011 AT 10:14 PM
Yep your right again I cleaned it and it made no difference still shifting hard under normal or slow driving conditions again I have that MAF code p0102 that keeps popping up could it have an effect on hard shifting under normal driving. If I drive it just a little harder than usual it shifts normally but if I drive normal (slow) it shifts too hard and if I really get on it it seems to shift ok but seems not to run as well as usual feels like its loading up with fuel after shifting to seccond seems like a bog for acouple of seconds before it spends all that fuel then halfway thru 2nd gear clears up and acellerates like it should till it goes into third. Again I appreciate your help it seems you know what is going on and any advise is helpfull at this point. I am pretty good with older engines but this OBD2 controlled engines drive me crazy I wish I could just deal with spark or fuel again LOL.
March, 7, 2011 AT 10:31 PM
The higher fuel pressure will not cause a shifting problem directly but it will cause a change in the "personality" of the engine. You will be holding the gas pedal in different settings. When the pedal is down further, as in harder acceleration, the transmission will up-shift later and with more force. The clutch packs apply harder and faster to reduce the slippage that takes place until they are fully applied. Under light throttle up-shifts, the clutch pack engagement is softened to give a smoother, more comfortable shift. I don't know how you found the fuel pressure staying too high so quickly but I suspect that is the cause of the change in shifting characteristics. Solve the fuel problem and I'll bet the shifting goes back to normal.