i've got a 1990 5.0.I've been trying to trouble shoot a rich fuel condition.I found that the crancase is under vacuum.If I disconnect the oil filler breather line at the air box you can feel vacuum on the line.I checked the pcv earlier and it rattles,If it was sicking open I suppose it would cause this.The only other thing I know of that would cause this is a lower intake gasket leak at an intake port.Any other possibilties?If it is leaking would that allow fuel to get in the crancase or since it's under vacuum would it simply suck air from the crancase into the intake?I think maybe the excess air being sucked into the intake is causing the computer to read high o2 and it is compensating by trying to richen the mixture.Does this sound likely?
Thanks,
Billy

 

cajunbronco, start your truck and pull the PCV out of the valve cover, go over to the airbox and pull the breather line off of the airbox and feel for vaccum now, there should be none to maybe a small amount of possible blowback out the tubing, if you still have suction, I would agree with you, Can I ask though, how are you coming to the conclusion of a rich fuel consumption. Is it just by fuel mileage, rough running, fuel in the crankcase, smells bad at tailpipe, codes being pulled? Tell us the rest of your findings.
Electric1

 

Electric1,fuel mileage is bad,gas smells like oil.All the sensors are new.Not throwing any codes.I replaced the fuel injectors and it seems to have helped.Mileage has gone up some and oil does not get dirty as quickly.But it still smells of gas.I pulled all the plugs and did a compression check,it was ok.All the plugs were rich to some extent,a couple of plugs showed evidence of oil fouling that had burned off.I attributed this to rings not being seated after recent engine rebuild. I understand that you should have slight vacuum at the airbox line from the oil fill,but if I plug it with a vacuum gauge it will go to 18",same as the manifold vacuum.It also has a mysterious idle surge which would indicate a vacuum leak,but it doesn't do it all the time.When I pulled the injectors and removed the plenum there was some oil in the plenum,another indication it may be sucking from the crankcase.Thanks for the help,I'd like to solve this problem before I wash out the new rings or spin a bearing,gas does not have good lubricating properties.

Billy

 

cajonbronco, you did not tell me yet that you checked the airbox line vaccum with the pcv unhooked from the engine, remember pcv is hooked to intake manifold, hence if you do not unhook the pcv from the valve cover and plug something into the valve cover as a plug,( so you can check just the inside of the engine) you will see 18" hg at the airbox, that is where the crankcase gets it fresh air for crankcase ventilation, now if you unhook the pcv from the valve cover and put a plug over the valve cover, with the engine running and you have 18" hg at the airbox then I would agree with you, then you have an internal vacuum leak, I need some numbers here to help you, you need to get a digital meter that show HZ, Probe the center wire of the MAP sensor at the right rear of the engine compartment, I believe the wire is green, Key on engine off, HZ on that wire should read 156 HZ, with the engine running, it should read 108 HZ or close to, If the MAP sensor wire is showing higher numbers idling than 108 then the MAP feed the engine computer more fuel, If the MAP reads less than 108 then the MAP feeds the engine computer less fuel, Also pull the vaccum line off of the Fuel Pressure Regulator with the engine running and see if fuel shoots out of the vaccum port of the regulator, you don't have to let it off more than just to see, By the way, what is your fuel pressure reading, should be around 35 PSI running, Let us know what you find, Electric1

 

Thanks for the info,when i checked the line at the airbox the pcv was still hooked up.I will plug the pcv line and check it again.I checked the fuel pressure regulator,unhooked vacuum line while running,no fuel present,fuel pressure went up from 36 to about 42 psi.I also hooked a vacuum gauge to it and it will hold vacuum,so I don't think the diaphram is busted.The map sensor is new,I will try to check it not sure if my voltmeter will read Hz or not.I've also tested the coolant sensor resistance,it's ok(new sensor as well)The air charge sensor is new,but I will check it also.The computer is not throwing any codes,is there a way to tell if the pcm is going into closed loop?I'm wondering if it could be a problem in the pcm.When I turn off the engine the fuel pressure does drop pretty quick to about 20 pis and then slowly bleeds off.I replaced the injectors thinking I had one or more sticking open.The fuel pressure still drops after turning the engine off.I guess it could be a bad check valve in the pump,but the truck is not hard to start after it's ben sitting for a while.The situation has gotten better since replacing the injectors,but the oil still smells a little like gas and the mileage has gone from about 8mpg to probably 10 mpg,still on the first tank after changing injectors.The only other thing I'm wondering is I've got some tapping in the valve train.If a lifter is not pumping up and a valve is not opening all the way,how would this effect mileage and fuel richness?
Thanks again,any and all opinions are greatly appreciated.

Billy

 

cajunbronco, let's go after the leak down in the fuel system, when you shut down the engine the fuel pressure should go from 35 to 40 psi, it should not drop, but what I am concerned with here is if the fuel is still might be leaking to the inside of the engine through a fuel injector, so to test for this, hook up fuel pressure guage, cycle the ignition key and the fuel pump will run for 2 seconds, pinch off with pinch off pliers the pressure side of the fuel feed to the engine(look for the braided lines or plastic lines) pinch it off carefully, not to hard or you can damage the lines, this stops the reverse flow back to the pump check valve, watch your pressure guage, if it still leaks down pinch off the return side of the fuel system from the injectors, this stops the flow out of the pressure regulator, big line is feed line, small is return, if fuel pressure still drops you have an injector that is not closing, if the fuel pressure does not drop after pinching off one or the other lines, not to worry, leaking into tank, could just make the engine a little longer in startup time and have a slight miss fire on startup. Now closed loop happens at I believe 130'F, from what I have seen two criteria are needed here, first oxygen sensor switches within 30 seconds of startup, switches what?, switches electrically from low .10 volts to .90 volts within 30 seconds after startup, Ford uses a heated oxygen sensor and it is fast, most new units function in less than 20 seconds, computer needs to see this then 130'F. Then it hits closed loop, when an oxygen sensor has failed in the startup mode, and most of the time it is the heater circuit in the sensor, the engine runs at a higher RPM cold for a longer period of time than when the vehicle was new. PCM's of this era are not usually a problem very few fail in these years for Ford.Let us know about the fuel leak off. Very important. Don't assume your new injectors are ok, not while you are having this problem. Let us know, Electric1