TBI Code 44 Lean Exhaust Help Needed

[kwissman]

I have been getting an intermittent Code 44 Lean Exhaust on my 91. It seems to come on when it gets up to temp and will go on and off with varying times that it is on. The engine is stock with the exception of long tube headers. I put in a heated 3 wire O2 sensor last year when I did the headers. The light came on right after filling up with gas and the Idle was erratic and very rich.

So far I have done the following things with no luck:
1. Replaced fuel pump with one for a 96 vortec 350. I was planning to replace it since I did not trust it. No Change
2. Replaced Fuel Pressure regulator. Checked and adjusted fuel pressure. I currently have it set to about 15psi and it runs rich enough that I get black smoke at idle. I just did this last weekend.
3. Checked for Vacuum leaks with carb spray. No leaks found.
4. Checked EGR with a vacuum pump. It opens and closes. Not sure of what else to check on the EGR.
5. Changed out fuel filter. It had maybe 500 miles on it and when I dumped it out it looked like the gas was darker than normal. No change.
6. Checked wiring on the O2 sensor and could not find anyting wrong. It is getting the 12v. I don't have a way to monitor the O2 voltage while it is running.
7. Checked Injector spray pattern and it looks good at idle and off idle.
8. I tried the Affordable Fuel Inj troubleshooting and after I turn it off and restart it the light is not on. The engine goes into closed loop, so it says the problem is intermittent.
9. I have run the gas low and added Heet to remove water and FI cleaner and it still is happening. Filled up last weekend

Questions
1. Can an O2 sensor just intermittently go in and out of band and still work sometimes?
2. This started about 5 minutes after I filled up with gas before a trip. Could I have water in my gas causing this problem?
3. What other tests can I do on the EGR to see if that is possibly causing my problem?

Any other ideas other than replacing the basically new NTK O2 sensor.

Thanks
Kent

 

[AKbigsub]

I have the same code. I have an exhaust leak I have to repair before I dive too deeply into further diag. I will interested to hear what you find.

 

[HarryH3]

2. This started about 5 minutes after I filled up with gas before a trip. Could I have water in my gas causing this problem?

This is quite possibly the "problem". I had the same thing happen with my '87 K5 years ago. Stopped and bought gas near Pensacola, FL, then just a few miles down I-10 the truck started running like crap. I stopped in some little town and bought a fuel filter, but changing it didn't help. I kept driving until the tank was about half empty. I filled up again and within 2 miles the truck was running perfectly again.

I would not spend much time or money on "fixing" this until you've had a chance to burn off some of that gas and put in some fresh stuff (from a different station!).

 

[Thunder]

Have you checked the:
TB gasket for leaks?
Pulled off the EGR valve and clean it? It may be stuck slightly open.
15 PSI FP will give you a rich idle and can make it run a little rough at idle.

 

[kwissman]

Thunder,

I have checked the TB gasket for leaks with carb cleaner.

I have not pulled the EGR. I guess I need to do that this weekend. If I push it open it dies. Are there any other ways to check the EGR.

The only reason that the Fuel pressure is at 15 was to see if that was part of the problem. I am going to turn it back down.

Thanks and I will check those this weekend if I have time.

 

[kwissman]

The problem is still there. I did not get to mess with it last weekend, but I found a little blurb on testing the O2 sensor with a torch, so I am going to try that and run a new wire for it. The existing wire goes up behind the engine and I would rather have it run under the dash and then down with the ground and power wires.

I am also going to turn down the fuel pressure as it is way too rich at idle.

 

[Cricket]

You might also consider checking for exhaust leaks ahead of the 02 bung.

 

[blazup1x]

Check your Ignition Module.

 

[wheels87k5]

How does it run under load? Does it only run erratic at idle?

The problem I had was when it was at partial throttle. It would idle good until you put it in gear, then it would stumble. Put it back in park or neutral and it would idle good again

The EGR was the culprit on my 87 Blazer.

To test the EGR: Pull the EGR soleniod line off at the EGR...Plug the line connected to the EGR solenoid. If vehicle performance improves, then it's either the soleniod or EGR.

EGR may not be your problem, but it's easy to test if it's a similar setup as mine.

 

[kwissman]

O2 Sensor was Bad

I fixed the problem. Once I bench tested the basically new NTK 3 wire O2 sensor I found that the voltage was going from -0.65 to +0.23. The zero must have shifted or something. I replaced the O2 sensor and ran a new wire for the O2 inside the cab and out with the other wires and it is now running fine.

I just need to fix the shaking at 60+ MPH.

 

[kwissman]

Testing O2 sensors on the workbench.

Here is the process that I used to bench test the O2 Sensor.

Use a high impedance DC voltmeter as above. Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.

ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don't miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.