MPG problems
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New User
Joined: Oct 2007
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MPG problems
Hey folks. new blood here. Have a Problem with MPG on a 1990 f150 XLT 302 auto. AOD. Just bought the truck and am only getting 9 mpg. Have checked codes and got code 33 and 42. 42 is for rich O2 sensor but that makes sense for the mpg. 33 is for egr not opening or not seating properly. Have GOT to improve this. hope someone can help
Mike
Mike
Senior User
Joined: Mar 2004
Posts: 491
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From: Boyd,TX
We get lots of threads about this. Tune-up, injector cleaner, filters, etc. As for your codes, try here
www.fordfuelinjection.com
welcome to FTE.
www.fordfuelinjection.com
welcome to FTE.
Lead Driver
Joined: Nov 2002
Posts: 9,557
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From: Concord, NC
You have to be patient...15 minutes isn't a long time on this board.
Here are a couple of things to check. I would start with the fuel pressure and the fuel pressure regulator. If the fuel pressure is too high, the computer may not be able to adjust the injector pulse width to compensate for the additional fuel and the engine will run rich all the time. The same can be said if the fuel pressure regulator has failed internally. Fuel will leak through the diaphragm into the engine vacuum line, introducing unmetered fuel into the inlet air, causing a rich condition, irrespective of actual injector duty cycle. You can check for this by pulling the vacuum line off of the fuel pressure regulator. If any fuel is present, replace the regulator. If the fuel pressure and the pressure regulator check out fine, have a look at the MAP sensor to make sure it is functioning properly and that the vacuum supply line to the sensor is air-tight.
Here are a couple of things to check. I would start with the fuel pressure and the fuel pressure regulator. If the fuel pressure is too high, the computer may not be able to adjust the injector pulse width to compensate for the additional fuel and the engine will run rich all the time. The same can be said if the fuel pressure regulator has failed internally. Fuel will leak through the diaphragm into the engine vacuum line, introducing unmetered fuel into the inlet air, causing a rich condition, irrespective of actual injector duty cycle. You can check for this by pulling the vacuum line off of the fuel pressure regulator. If any fuel is present, replace the regulator. If the fuel pressure and the pressure regulator check out fine, have a look at the MAP sensor to make sure it is functioning properly and that the vacuum supply line to the sensor is air-tight.
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Joined: Sep 2007
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Also with the egr valve code you may have to much exhaust gas in the intake and you can't burn all the fuel giving you a rich mixture code. Does the engine idle rough? Is the airfilter clean, not just dropped on the ground and put back in clean?! Is the truck lifted and you have not changed the gearing yet? Need more info.
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Blu,
I wouldn't say it idles rough but it does "wobble" between 650 and 850 rpm for about 10 TO 15 sec. after coming to a stop and putting it park, then it settles out to about 750rpm and idles smooth. There is no lift but I am running 31X10.50 tires on stock rims. The air filter has honestly not been checked yet. Will be handling that in the am!
I wouldn't say it idles rough but it does "wobble" between 650 and 850 rpm for about 10 TO 15 sec. after coming to a stop and putting it park, then it settles out to about 750rpm and idles smooth. There is no lift but I am running 31X10.50 tires on stock rims. The air filter has honestly not been checked yet. Will be handling that in the am!
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With the idle "wobbling" like that I would soak or replace the IAC in carb cleaner(just the mechanical end) for the idle hunting but that won't cause a fuel mileage issue going down the road. I would replace the fuel filter and air filters first, not enough fuel can kill fuel economy too.
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Senior User
Joined: Sep 2007
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From: Arizona
What blu said
Amen to what blu said. I was having all sorts of problems with my 92 f150 302, bad mpg, engine running lean, starting hard. The fuel filter was fully clogged and all that junk went into the engine. Fuel filter and air filter are cheap. After that maybe check the throttle plates for carbon build up and if its still a problem start pulling plugs and checking gap and cleaning them off, maybe oil is on them. I know with mine after putting the new fuel filter on it was a night and day difference.