Running WAY TOO Rich
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From: Edmond
Running WAY TOO Rich
Just completed a rebuild of a 5.0 on a 1991 F-150. The engine started up with no real problems on the first attempt, but it is running VERY rich. Wondering if it might be a TPS or MAPS sensor problem. Has a brand new O2 sensor and EGR valve. I didn't change anything on the throttle body during reassembly, but did give it a good cleaning before putting it back on the upper intake. Someone told me the problem sounded like a bad ECM, but I would think that the ECM fault would make it not run at all. Anyway, I would be willing to try whatever you guys think to get this one solved..... 
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From: Langhorne, PA
If you sprayed the throttle body with TPS attached, it could have hurt the TPS. Test and adjust the the sensor according to haynes, I think that one gets an adjustment.
Did you do anything to the Fuel injectors? Replace them with new ones maybe?
Did you do anything to the Fuel injectors? Replace them with new ones maybe?
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From: Edmond
The injectors were replaced with some that were reconditioned. The codes that came up were coolant temp related, but I thought that they were due to the engine being below op temp when the codes were taken at Autozone. I thought the guy missed a code 95 (ECM and elec fuel pump), but he said I had "heard it wrong".
I did spray some cleaner into the throttle body during the cleaning, so I'll check the TPS with an ohm meter. Thanks for the ideas; I'll keep trouble shooting........
I did spray some cleaner into the throttle body during the cleaning, so I'll check the TPS with an ohm meter. Thanks for the ideas; I'll keep trouble shooting........
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From: Southern USA
auto zone in texas tells me they only check obdII on Fords.??? i guess they have diff. equipment at diff stores. did you run it enough for the ECM to settle in? might try resetting it. on my '91, i just take off the small black ground wire that bolts to the side of the fender, by the hood hinge assy, that way you dont loose your radio settings......i would also dbl check all vacuum lines, esp the one to the fuel press. regulator. these plastic line are known for getting brittle over the years, you may have accidently damaged one and not aware of it. hope to be of some help.....paul
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From: Edmond
I pulled the vacuum line from the fuel pressure regulator and it didn't seem to make any difference to the idle operations???? The line seems to have vacuum, so I wonder if the regulator is stuck wide open. Wouldn't that make the engine run pretty rich all the time? As far as I know, there isn't a practical way to check the regulator with standard tools that a "hobby" mechanic would have in his tool inventory......
Let me know you thoughts....
Let me know you thoughts....
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From: Concord, NC
If you can check fuel pressure, that would give you a good indication. Pulling the vacuum line on the regulator would show you if the diaphragm was torn, which apparantly it is not, otherwise you would have fuel in the vacuum line. The regulator would have to be stuck closed to increase the pressure, which would make the truck run rich. Double check that you have a good vacuum going to the MAP sensor, and that the sensor is plugged in and operating correctly. Make sure you have good voltage on the VREF wire, first, and then check the MAP wire with the engine off - it should be 2.5 volts. MAP sensors rarely go bad, it's usually something else.
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From: Edmond
OK.... I replaced the TPS nad the coolant temp sensor based on the codes and WALLA.... the truck runs like a well oiled machine!!!! Thanks to all of you for your help and your encouragement..... Hope I can return the favor some day too.
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