Poor Gas Mileage and Idle

[sohcsol]

A buddy of mine has been having some problems with his explorer lately and I'm trying to help him chase down the problem. He's had no luck so far, so I'm coming to you guys. By the way, I'm an import guy so take it easy on me. The explorer is a 91 4x4 with a v6, unmodified.

The problem started with a surging idle and a check engine light. The check engine light was for the o2 sensor indicating the engine was running rich. So rich that the exhaust leaves huge black marks on the pavement when it's warming up. MPG dropped significantly. The plugs were pretty much black when removed. The Intake Air Temp sensor was also covered in black debris.

He changed the plugs, o2 sensor, Intake Air Temp sensor, and Coolant Temp sensor and those haven't really affected anything. There is still a CEL, but I'm not sure what code it is.

After searching this forum, we checked the FPR. The small diameter vacuum line that faces the firewall is dry; no fuel leakage, so I assume the FPR is good...? I also read a post about similar problems and the guy determined the ECU was bad and replacing it fixed things..? This guy doesn't have a ECU that is known to be good to switch out, so I'm looking for other ideas first. Thanks.

 

[Vanquish502]

First of all, get the code(s).

Take the truck to a local parts store(Whatever they're called in the US) that has the free code reading.

Thank you come again

 

[alexefron]

check the codes, also cleaning the maf could help, but im guessing something else is going on there too. most auto part stores will do it for free. when you get the codes come post them. what kind of black are we talking about on the plugs exactly (oil, carbon, etc.)?

 

[savagefan]

Just because the vac line from FPR is dry, don't assume the unit is good. After checking codes, test fuel pressure.

 

[Maniak]

And test the TPS (thats free).. If the tps voltage jumps around, it will confuse the computer as it tries to compensate.

There are threads on testing the TPS, including one that talk about how to adjust it (e.g. drill out holes to move it to get the optimum settings)

~Mark

 

[sohcsol]

The codes that the computer is sending are :

42: O2's always indicataing rich, no switching detected

72: MAF/MAP/Baro insufficient change during goose test


Also, one of the vacuum lines coming off the air box housing is not going to anything...There is the small line with a boot and the 3/8" hose line, it's the hose line. Appears to go down below the battery somewhere but can't determine where or even what that line controls. Thanks again for any help.

 

[savagefan]

It's for the thermactor or whatever Ford calls it to supply heated air to your air box.