wolverine8490

Just wondering if anyone could give me a hand figuring out what is causing my issues. Right now I have a hanging idle after reving the motor, and a very slight miss @ idle. I have a 91 GT that has been comepletly rebuilt to a 306 with the TFS HCI.I have the following codes:

CM
91 No HEGO switching detected always lean (left side).
34 PFE or EVP circuit has intermittently failed above the closed limit of 0.67 volts.


34 - I checked the voltage output of the EGR wire, and have .73vdc. I cleaned it already once. Is that out of spec?

91 - I checked to verify that the power and ground conenctions were good. I have ground and power to the O2 sensor. I have sprayed carb cleaner all over the engine to listen for vaccum leaks and have found nothing. Should I replace the O2 sensor, or is there something else I need to try. I have also verified that my fuel pressure is 40psi @ idle with the vaccum line disconneted.

mjr46

DID YOU inspect the egr valve to make sure the pintle is completely closed and or there is no ruptured diaphram in the valve...I use a vaccum pump to test the integrity of the egr valve and it's function.

wolverine8490

The EGRlooked as though the pintle was closing all the way. I did check to make sure it would hold vaccum, and it was holding well.

I also just checked the voltage of the O2's output and it is reading .15vdc with KOEO.

Joel5.0

Since those codes are CM codes......clear KAM (disconnect battery for 15 min.), check KOEO codes, start engine and take it to op temp, and run a KOER self-test.

wolverine8490

Cool. I will give that a shot tomorrow and post the results. Thanks for the help.

wolverine8490

Well, I cleared the codes and drove around for a while, and I have no CEL. Not for sure what that was all about, but it has seemed to have fixed the CEL issue. Thanks for the help.

Joel5.0

Never mind the CEL...... run the KOER, there are failure codes that will not turn the CEL on. FYI....the KOEO and KOER self-tests will "direct" you to the circuits to concentrate on fixing (narrow possibilities down) a problem....but are also used as confirmation tests of the repair work..... just a thought.

wolverine8490

Ok, I am walking out now to do the KOER. I will let you know what I find out. The car does still run like crap even though the light went off.

wolverine8490

Well, thats annoying. Here I thought everything was good. I forgot to mention that I am running an offroad X-pipe. Dont know if not having cats will throw any of this or not. Usually I know it throws codes without cats, but I didnt think it would on OBDI.

KOEO:

85 - Canister Purge Solenoid circuit failure. (This has been removed)

CM:

91 - No HEGO switching detected always lean (left side). (I tested the voltage @ .15vdc on the output. Also the ground and power leads cchecked out)

34 - PFE or EVP circuit has intermittently failed above the closed limit of 0.67 volts. (Voltage on the output of the EGR was .73vdc)

KOER:

41 - No HEGO switching detected always lean (right side). (I tested the voltage @ .15vdc on the output. Also the ground and power leads cchecked out)

91 - HEGO sensor circuit indicates system lean (left side). (I tested the voltage @ .15vdc on the output. Also the ground and power leads cchecked out)

34 - PFE or EVP circuit above the closed limit of 0.67 volts. (Voltage on the output of the EGR was .73vdc)

Joel5.0

Having the EVP above .69 vdc valve closed will cause code 34 ...... drawback = none, the EEC-IV deletes/bypasses the EGR function altogether.... driveability symptoms = none, provided the EGR valve is seating all the way down...... solution = leave it be if emissions are not a problem, or replace the EVP/EGR valve combo.....a "fix-it" hack would be to remove the EVP sensor and grind a little off its tip, this will cause the sensor to seat dow further and bring the closed voltage value below the .67 vdc failure code threshold.

41 & 91 = Both engine banks are reading lean all the time..... things to check:
[ul][*]HEGO ground wire attached to the rear cylinder head (driver side)....the wire is orange.[*]Any vacuum leaks/unmetered air condition = open breathers on valve covers with PCV valve functional, intake gaskets (upper & lower), throttle body, vacuum lines, faulty brake booster unit, PCV valve out of its nest behind the intake manifold, etc, etc.[*]Exhaus leaks = any leak in the headers will cause the O2 sensors to read lean.[*]Bad O2 sensors, if you want to check the O2 sensors real-time, follow the tests described in the following diagram..... NOTE: Even though a 4-wire O2 is shown in the diagram, the tests apply for the 3-wire sensors.....SIGRTN is not part of the tests.[/ul]