1999 Ford Taurus Code P0172 and P0175 Runs rich bank 1 and

HPHILLIPS

MEMBER
1999 FORD TAURUS
6 CYL
FWD
AUTOMATIC
105,000 MILES

This problem is driving me crazy. I overhauled the engine but it took me over a year. Now it runs fine, compression is over 150 on all cylinders, but this code won't go away and I can't pass emissions to get a new tag! As I said it runs fine and no black smoke from the exhaust. The manifold vacuum is a bit low at 15 but I cannot find a leak. Sometimes I get an ignition misfire code but it may be be because it runs so rich. Plugs are all black though #2 is slightly less so. I thought I had found the problem because though I have voltage to the mass airflow sensor it reads higher while running than the manual says it should, only slightly lower than when running. So I had a bright idea and I separated the hose between the MAF so that some of the air bypassed the sensor. I did not get the codes this way while running in the driveway. Also the maniflold vacuum came up to just under 16. I am guessing it was still a bit rich or maybe went lean but not enough to set off the computer. I am guessing the IAC has to crack open a bit more causing the low manifold vacuum. I cannot find any component that measures the vacuum pressure so I think I am done looking for leaks. Could the computer have lost the correct settings or something?

Oh, I replaced the MAF but it does the same exact thing. But when I replaced it, there was a warning that the warranty was void if I did not reuse a rubber seal on the connector. Apparently that went missing during the rebuild somehow. Can this be because of a stupid dust seal? I hate to drag it into a shop and have them do a $100 plus diagnostic and then find out it is because of a $5 part.

BTW is there an OBD tool that will tell me how rich lean, and the tables etc without costing an arm and a leg? I guess I could spare a few fingers.

8 Replies

RASMATAZ

MECHANIC
75,992 POSTS

OBD2 P0172 & P0175. Is a typical symptoms of an engine that is running rich (too much fuel, not enough air) are poor fuel economy, elevated emissions (Carbon monoxide or CO), and engine may have rough idle or surge condition.

Possible causes include a bad O2 sensor, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.

HTH-Good Luck

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Thursday, August 7th, 2008 AT 12:23 AM

MERLIN2021

MECHANIC
17,250 POSTS

Also the only sensor that uses vacuum to operate is the MAP...I agree on all the others Raz listed so test pressure like this....
https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
You can rent the test gauge at Autozone.

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Thursday, August 7th, 2008 AT 2:35 AM

HPHILLIPS

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10 POSTS

I replaced the fuel regulator first thing, forgot about that. I cannot actually check the pressure as this uses a small fitting and the tester won't fit between it and the alternator with the adaptor. There is no MAP on this car. How do you check for a plugged fuel return line, is that the one the regulator is on? I don't think the manual says which is the return. Also I had to install the camshaft position timing by eyeball as I could not find the special too. Could that have anything to do with this? Also the airfilter is new, and just to be sure I tested it with the MAF disconnected from the air box. But if I disconnect the MAF from the intake hose I don't get the run rich codes. I put some fuel injector cleaner in the tank, I suppose the old fuel could have clogged them up, but wouldn't that cause it to run lean not rich? Also both the ambient and coolant temperature sensors are working and correct.

Also if the fuel pressure is too high, how does the computer manage to correct the rich condition when the MAF is bypassed?

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Thursday, August 7th, 2008 AT 7:07 AM

MERLIN2021

MECHANIC
17,250 POSTS

The pcm uses an average if the maf is unplugged, so your problem may be the MAF if it clears up when you disconnect it. There is an adapter For Fords and other cars that don't even have test ports, it's installed at the filter. The line coming out of the FPR is the return, test it by blowing into it, and removing the gas cap, listen at the tank. Check for kinks in the line. If you don't show CPS codes, you may have nailed it pretty close by eye!

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Thursday, August 7th, 2008 AT 2:28 PM

HPHILLIPS

MEMBER
10 POSTS

I did not unplug the MAF, rather I simply pulled the hose off between the MAF and the throttle body. The hose will push itself right back on so I stuck a screwdriver between the hose and the MAF so that some of the air bypassed it. After that I REPLACED the MAF, but the new one acts just like the old one so back to square one. I am thinking that maybe the reference table memory got lost or scrambled while the computer was down without power for a year. Thats another reason I don't think its the pressure regulator or plugged return line, because the system was able to correct the problem if less air went through the MAF.

I worked as a mechanic for a while but that was in the 70's. What is a FPR? I doubt I can afford any special diagnostic tools as I am not a hobbyist nor a professional, I just like to have a project once in a while.