Extreme rich condition

[Perry Mitchell]

Originally Posted by XfireZ51

So Todd, are u saying that the sensor values we read at initial Power Up, not engine start, may not be the actual values for the sensors at that moment, ie TPS?

Also, how is the motor going Closed Loop w no X-counts coming from the right side?

Did you ever get a response regarding the motor going closed loop without a proper signal from the O2 sensors?

[Marc Haibeck]

Hi Perry,

I presume that the scanned data from the right oxygen sensor still shows zero volts.

Perform this simple test to verify that the wiring is correct. Back-probe pin C15 on the ECM and connect a volt meter. Ground the meter on the negative battery terminal. Turn on the ignition without starting the engine. With a battery voltage of about 12.5 volts, the voltage on pin C15 should be in the 350 to 425 mv. range. After about 60 seconds the sensor will warm up and start reporting oxygen. The voltage should go down to about 90 mv. after about three minutes.

The left sensor on pin A16 should do the same thing.

[Perry Mitchell]

Thanks Marc. I will do that test today and report back.

[XfireZ51]

Originally Posted by Perry Mitchell

Did you ever get a response regarding the motor going closed loop without a proper signal from the O2 sensors?

I did get a response from one of the tuning gurus on Third Gen.


I think that it can. The ECM usually just looks at the O2 sensor voltage for closed loop determination. That is either lower then a set value (200 mV) or higher then a set value (700 mV).

Because until in closed loop with prop gains there may not be x-counts.?

I have had instances where one of the O2 sensors would report a string of 0 volt readings, ie during cruise, and would still stay in Closed Loop. However, it could exit Learn mode after a certain period of time.
One of the reasons I switched from Bosch sensors. I don?t have that issue w the AC sensors.

[Perry Mitchell]

Marc. I did what you said and here are the results. I connected to the purple wire at pin C18 on the green connector and got .550v which declined rapidly to .160v in 1 minute. Then it slowly decreased to .084v in 3 minutes. Then I connected to pin A16 in the gray connector for the left sensor and got .570v which dropped to .160 in 1 minute and settled at .074 in 3 minutes. There was some variation in these numbers each time I did the test. Do they sound about right?

[Marc Haibeck]

Your test results show that the sensors are wired correctly and that the sensors are reporting reasonable oxygen levels.

Let's put the odd right oxygen sensor voltage scan data aside for now.

Image 257 shows the engine in closed loop, running rough evidenced by the 50 kpa manifold vacuum and running very rich on the right bank.
Left BLM125 + INT96/256 = .86 or -14% fuel trim.
Right BLM133 + INT192/256 = 1.27 or +27% fuel trim.
You are observing excess fuel in the exhaust which is consistent with the system adding a huge amount of fuel on the right bank.

Image 258 shows the engine in open loop with normal 42 kpa manifold vacuum. The fuel trim looks reasonable.
Left BLM120 + INT128/256 = .97 or -3% fuel trim.
Right BLM140 + INT128/256 = 1.05 or +5% fuel trim.
You are observing that the engine runs okay with no smoke in open loop.

I wonder if the ECM is malfunctioning due to noisy power? You should followup on the low system voltage reported in the scan data in post #81. The PID shows 10.7 volts. I suggest getting the system voltage to better than 12 volts with the engine running.

Check the following:
- The ECM grounds on pins B6, B17 and C12 should run directly to the engine block. They need to be direct runs with nothing else connected to share a ground on those wires.
- The ECM battery feed pin B11 should be a direct run to the battery positive terminal. Nothing else should be connected to it. It should not go to a terminal block and then to the battery. The wire should be 14 gage if less than three feet long. 10 gage if up to 10 feet long.
- The battery should be fully charged. You should not be jump starting the engine due to a discharged battery.

[Perry Mitchell]

Hello Marc
A lot of information there. Thanks for taking the time to post it for me. Did you read the post where I stated that the right O2 sensor that I purchased had the pigtail wiring incorrect? The black wire was in the wrong location in the connector. I have not performed another scan since I corrected their mistake but was corrected prior to performing the O2 sensor tests that you provided. I hope to do another scan today.

As far as the low battery voltage is concerned, I need to figure out why the alternator is not charging. It could be the way it is wired to the trunk mounted battery or the way it was reassembled after being apart for polishing. Shouldn't be to difficult to correct. I have always kept the battery charged and never had to jump start the car. I was surprised to see the low voltage when we performed the scan. That is when I discovered the problem.

My chores today are to follow up on your ECM wiring requirements. I really appreciate your and others help with my problems.

[Perry Mitchell]

I want to resurrect this topic as I think I?ve got things sorted out and would like the opinion of the members who gave me so much information in the past. I had to replace my alternator because the existing one seemed to have failed. I also managed to get the cooling system completely filled by using a vacuum system to get the water pump completely filled. I have attached pictures of my existing tune and would like your input. The engine starts very well and now seems to idle very well in both open and closed loop. The exhaust seems to have only minimal smoke. I think I got it. What do you guys think?

[-=Jeff=-]

Glancing at the BLM it is 115, you want it close to 128. 115 is rich and the ECM is pulling fuel

[Perry Mitchell]

Originally Posted by -=Jeff=-

Glancing at the BLM it is 115, you want it close to 128. 115 is rich and the ECM is pulling fuel

Oh great. How do I fix that?