Could use some help before I drive my truck off a cliff. 2002 Chevy Blazer, 152k miles runs like a champ. Last year I replaced all 3 O2 sensors and the y-pipe as the cat was getting clogged. Over the last few day I have been getting a p1133 which is bank 1 sensor 1 slow response. First thing I did was reset it and it came back on in a few days. Ive swapped bank 1 and bank 2 to isolate the sensor and the code comes back on bank 1 still. Using ScanXL I can watch and compare the sensor and its switching. ScanXL reports the avg about the same as bank 2. Fuel trims and all good under 10% both short and long term. Any suggestions. Its driving me crazy. Wiring issue maybe????

 

Good job with the O2 swap, it definitely confirms a problem in bank 1, and eliminates the possibility of a bad O2 sensor.

Sounds like a heater circuit problem to B1S1, possibly a poor connection. If the ground or B+ circuit for the sensor were totally open, P0135 would set in memory. Check B+ and ground connections for the sensor and make sure the sensor and vehicle harnesses are not damaged, (pinched etc). A voltage drop test at the sensor might reveal a problem. Does your ScanXL have graph capabilities? If so, compare B1S1 and B2S1. That would confirm the slow response time on bank 1. If the ScanXL lists O2 cross counts, compare B1S1 and B2S1.

Other possibilities are:
Have you tried cleaning the injectors?
Has the injector upgrade been done? (eliminates the poppet valves and relocates the injectors to the intake ports)

 

Yesterday I checked the wiring at birth the pcm side and the sensor side on both banks. No issues found. Voltage measurements were the same from bank 1 to bank 2. Bank 1 is definitely not switching and does not drop as low in Voltage compared to bank 2. Bank 2 reguraly gets below 200mv while bank 1 does not. Today I an going to check fuel pressure leak down to make sure there is no leaks. Any other suggestions.

 

Ive check the fuel pressure and it hold 58psi for over 15 minutes without dropping at all. I am running out of ideas.

 

Are the bank 1 fuel trims slightly negative?

If B1S1 O2 voltage doesn't get as low as B2S1, all it would take is for one injector, (or poppet nozzle) on bank 1 to not seal completely, and B1S1 O2 voltage would not get down low enough. It may or may not show up on a leakdown test because it checks the entire system for leaks. Injector balance test momentarily opens each injector for a given amount of time, making it a better choice. If your ScanXL can't do injector balance, an option would be to pull the nozzles out of the intake, activate the fuel pump, and check each nozzle for leakage. It's not as precise, but it's worth a try.

Usually if a bank 1 injector or poppet leaks, it sets P0172, but if the leak is small enough, it may not. In which case the P1133 shows up, until the leak gets worse.

Have you tried cleaning the injectors?
Has the injector upgrade been done? It eliminates the poppet valves and relocates the injectors to the intake ports. One of the reasons for upgrading, is the poppet valves are prone to getting gummed up and leaking.

 

I've done the leak down test and the fuel pressure is rock solid. Over 20 minutes and no drop in pressure. As far As I know the fuel system is stock. No modifications. I just rechecked everything wiring wise and cannot find an issue. Should I pull the upper plenium to check the spider. Also. What is the upgrade u speak of.

 

Just did some research and no it does not have the upgraded injectors and it is a "W" engine so I'm assuming it would be possible. I just don't wanna throw the money at it if it isn't the problem.

 

The only way to tell if your engine has the injector upgrade, is to remove the plenum and look. Here's a link for it: Delphi Fuel Injector FJ10565: Choose the best Fuel Injector at Advance Auto Parts Amazon, Ebay, and a ton of other places online have them for substantially less.

IF an injector or poppet are leaking, causing the P1133, the leak has to be very small and the leakdown test probably won't detect it.

Are the bank 1 fuel trims slightly negative?
Have you tried cleaning the injectors?
Is your ScanXL capable of doing the injector balance test?

 

As far as the injector balance test I cannot do that. The long term fuel trim on bank 1 is slightly negative while bank 2 is slightly positive. Both are under 5% . The o2 on bank 1 seems to switch more under a greater load then at idle. Might pull the intake and check but I'm not sure what else it could be. Thank you for the help by the way. I am very car savvy and have a lot of repair experience and this one has got me stumped.

 

Negative trims on bank 1 confirms that it's running slightly rich, and that the PCM is adjusting the pulse width, (less than 5%) on the injectors to compensate for it. Less than 5% ain't squat though. Just for grins and giggles, did you check voltage drop at the B1S1 B+ heater feed? You don't need to start the engine, but the ignition must be in the run position. We already know the problem is not in the O2 sensor pigtail, so checking at the connector, (one test probe on each side of the connector) will give accurate results. On your 2002 it should be a light green with white stripe wire.