Code 34, Code 34 Help

[gtcobra302]

Hey
I have a 1991 Mustang Coupe former FHP car with a 5.0 odviously. It is bone stock, absolutely nothing done to anything. Its auto and it gets crappy gas mileage. Like 11 to the gallon if that good. My 1989 GT with work top to bottom gets at least 18 and it runs low 12's. The car runs great except of course for the gas mileage. The only code that shows up is code 34, which is " Canister or EGR valve control circuit or EVP voltage high". Does anyone know what causes this and would that cause bad gas mileage?
ANY HELP WOULD BE GREATLY APPRECIATED
thanks

 

[jrichker]

Code 34 Or 334 - EGR voltage above closed limit - Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover. Prior to re-installing see if you can blow air through the flange side of the EGR by mouth. If it leaks, there is carbon stuck on the pintle valve seat, replace the EGR valve ($85-$95).

If the blow by test passes, and you have replaced the sensor, then you have electrical ground problems. Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the black/white wire and the negative battery post. It should be less than 1 ohm.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter.

Let’s put on our Inspector Gadget propeller head beanies and think about how this works:
The EGR sensor is a variable resistor with ground on one leg and Vref (5 volts) on the other. Its’ resistance ranges from 4000 to 5500 Ohms measured between Vref & ground, depending on the sensor. The center connection of the variable resistor is the slider that moves in response to the amount of vacuum applied. The slider has some minimum value of resistance greater than 100 ohms so that the computer always sees a voltage present at its’ input. If the value was 0 ohms, there would be no voltage output. Then the computer would not be able to distinguish between a properly functioning sensor and one that had a broken wire or bad connection. The EGR I have in hand reads 700 Ohms between the slider (EPV) and ground (SIG RTN) at rest with no vacuum applied. The EGR valve or sensor may cause the voltage to be above closed limits due to the manufacturing tolerances that cause the EGR sensor to rest at a higher position than it should.

This will affect idle quality by diluting the intake air charge

 

[jammer84_03]

jrichker.....i just wanna shake your hand sometimes and give ya an atta boy...lol you rock on all the diagnostic stuff.... - james

 

[Paul Perreca]

he's the mustang peoples champ lol