GloverEggs

Have a 2005 Suburban 5.3L flex Fuel engine. About 80,000 miles on rig. About two weeks ago it started to misfire. I had run the tank very low and had just filled it up. Always makes you wonder when something starts the next day after that. Well first thing I found out was that the suburban does not have a changeable fuel filter. It finally started to throw codes with a check engine light so I checked them out using a ELM-327 bluetooth OBD-II reader. I was getting P0131: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1) (Powertrain, Generic), P0171: System Too Lean (Bank 1) (Powertrain, Generic), and P0300: Random/Multiple Cylinder Misfire Detected (Powertrain, Generic). I double checked the mass airflow sensor and the air filter. Both looked great and brand new.

By this time, the suburban was starting to backfire and run extremely rich. You could smell gas when it was running. The fact that an O2 sensor was showing a lean condition when excess gas was present indicated to me that the sensor was probably bad. I also figured that issues with the fuel filter would cause errors to both banks equally. Well long story short. I bought a Bosch 15284 O2 sensor to replace the front driver's side sensor. When we put that sensor in, the signal to 0.1 V on both Bank 1 sensors 1 and 2. When we returned the original sensors, 1#1 (bank 1 senor before cat) read at 0.1V while 1#2 (bank 1 after cat) read at 0.1V until the engine was rev'd up then it would go up and come back down as the engine slowed. Still way too much gas. Well maybe both bank 1 sensors were bad so I picked up a Denso 234-4668 O2 sensor. When this is installed it shows 0.1V. We then unplugged 1#2. With it unplugged, it shows 0.44V (which I assume is good that it is reverting to the norm). We then unplugged 1#1. It then showed 0.44V. Still lots of excess fuel being pumped into the system. With both sensors unplugged, the OBD-II reader was not providing fuel trim values. They had been running normal on bank 2 but had been about 25% to 30% on bank 1. Based on the smell, it was at least that bad with both sensors unplugged.

We are now thinking of moving the bank 2 sensors over to bank 1 and vise versa to establish that it is a sensor problem and not a wiring problem on bank 1. However, we are scratching our heads with the gremlin causing the problem. I have only had the rig for about 1.5 months and have put about 3k on it. It has run great both on and off road until now. If we have to take it to a shop, we will, but we are also very competent mechanics. Unfortunately, mechanic is the key word. This is all electronic/computer crap. Any help that people can provide would be appreciated.

in2pro

Everything was working fine prior to fill up?
Does you scanner tell you what the alcohol content is?
Have you checked the fuel pressure itself?
I suspect a fuel injection issue, all those o2 sensors just don't up and stop working like that...
I would also try getting fuel from another station as it could be bad fuel...

GloverEggs

Everything worked perfectly prior to fill up. I know that usually "bad gas" isn't but that was what I originally thought. I then started thinking about low tank maybe dirty gas and plugged fuel filter, but can't check/change that. However, as I started to think about it more, if I had a general fuel problem, it would be affecting both banks, not just bank 1.

I can't tell alcohol content with the scanner. But supposedly this engine can handle up to 85% alcohol, right? I have never tried it.

Is there a way to check the fuel injectors individually?

in2pro

The issue with alcohol is that the engine can be confused, thinking it has E85 when it doesn't....
Its a shot gun approach, but you might try disconnecting the battery for several minutes and then try everything again....

GloverEggs

Actually already did that. The battery was weak when we bought it and the windshield wiper reservoir was leaking so changed the battery and the washer pumps last weekend prior to working on this issue. The battery was out for about a day.

tech2

what are the fuel trim values on both banks with everything plugged in? post ltft and stft for both banks at idle and at 2500rpm.

GloverEggs

Bank 1 Long Term = 25.0
Bank 1 Short Term = 14.78
Bank 2 Long Term = 5.47
Bank 2 Short Term = 0.78

We swapped left and right bank o2 sensors today. Reading in essence did not change. To me that indicates that I have a wiring or computer problem. What is the suggested next step to determine what is wrong?

tech2

there is probably nothing wrong with the 02 or 02 wiring.

what do 02 sensors detect...oxygen content in the exhaust stream. your engine is misfiring. all the 02 are going to see is oxygen from an unburned fuel mixture, not unburned fuel. the 02 are perceiving a lean condition and enriching the fuel mixture.

you have to fix the misfire first. If you have a scan tool that has a misfire counter, look and see if all the misfires are on one bank. I would check for a clogged cat on the misfiring bank. hammer-fist the cat; does it rattle? run the engine with the pre cat 02 unscrewed from the exhaust pipe to bypass the cat.

if that is ok do a compression check.

GloverEggs

I am going to look at these as soon as I can. I hate short days. I leave in the dark and get home in the dark!