1995 Blazer... I had a SES code P1133 when it was -7 F yesterday. The idle was rough, but operable. Recently changed what I believe was a factory O2 sensor.

Now I have looked at the O2 sensor voltages and bank 1x1 jumps around every other half second between .01 and .09, O2 1x2 is steady at 0.75. Respectively FT 1x1 stays around 0 except at idle, and F/T 1x2 is always at +100.

Should I swap my second (after cat converter) sensor for one of the same brand? The one before the cat was recently replaced: Denso Oxygen Sensor - Direct Fit Part No 234-4012.

I could use some help with identifying what these banks mean as I don't have those pages of my service manual.

 

The surprise to me on this is your tossing a pre cat code when your #'s on the postcat look terrible.
You should only have two one pre and one post but they built the 95's with whatever they had around.


Think you need to take your egr valve off and clean the crap out of it.


Post cat o2's will give no drivability issues, like rough idle.


Sounds like you have a scanner, do you get anything like "open or closed loop, determined by o2 sensor" ?

 

The Fuel System Status: Closed loop, using O2 sensor for fuel mix

I'm using Torque app on android to get the data.

The SES light isn't on all the time, fuel trim 1x1 stays around 0.0, fuel trim 1x2 stays at +100, and O2 1x1 bounces all over 0.1 to 0.9, and O2 1x2 slowly climbs to 0.8 at idle but stays low while driving.

I think I swapped the erg valve 2 years ago from a position code, haven't seen that since, doesn't hurt to check.

 

That's what I mean the front one is reading correctly, there supposed to jump from zero volts to one volt very fast. When they start to slow down is when the code trips.


The back one is bad but it should not cause a poor idle. Remove the egr and clean it good with carb cleaner. Then start inspecting all rubber vacuum lines for cracks and leaks. If it started all of a sudden one may have just fallen off. There are a whole set of lines that go to the evap set up that are poorly engineered.


You will see a plastic reveres double L line coming from under egr up to the purge solenoid. It's on the port side of the motor. It cracks all the time.

 

I checked the EGR purge and vacuum lines and found nothing wrong. However, the EGR eventually threw a code for insufficient recirculation. I had changed that electronic egr valve before, so as I prepared to replace or clean that when on my way to do so things really changed. After arriving at the store to buy an egr valve gasket, it decided to take 3 tries to start. From then on multiple hard starts took place and its persistent now. At this point I questioned if the EGR would affect a cold/warm start, and skipped that work for now and performed a fuel pressure check which showed a pressure loss to 0 PSI after 10 minutes after the typical 2 second prime. Sounds like a bad fuel pump right? I mean I replaced it 2 times already with Spectra pumps, but this time I used an AC Delco pump. That didn't help fix it, same issue as before. Does it make sense to replace the SPI at this point? It appears that if I pick up a ACDelco 217-1431 it comes with a fuel pressure regulator already attached, is that correct? Also, should I pick up this ACDelco 17112705 nut kit and ACDelco 10105939 upper gasket? I've never taken any of this part apart before, so I'm not sure what typically might break when taking this all off. I have already checked the fuel lines for leaks and the fuel filter is new. Just looking for advice before plunging another $300 into this.

 

Couple things here... your engine has one injector, it is batch fired, (fuels each cylinder equally with each pulse). To be fully OBDII compliant, (yours is not) the PCM must be able to control fuel mixture on each bank, (left & right) seperately. With that in mind, there is only one upstream oxygen sensor on your engine, should show as bank one sensor one (B1S1). If fuel trim is zero, it means that the fuel mixture that the PCM is applying is correct. B1S1 is reporting correct, no worries. The downstream sensor, (B1S2) is checking the converter. If voltage stays low and constant while cruising, ideally ~.45 volts, the converter is working properly. No problems with either O2 sensor.

The fuel pressure leakdown is a problem. Check fuel pressure at the service port next to the distributor. Ignition in the run position, engine off, fuel pump running, pressure must be 55psi to 61psi. It must remain above 50psi for at least 10 minutes after the pump shuts off. Post the results.

If it fails one or both parts of the test, you'll need to check pressure and leakdown at the fuel filter outlet to determine if the problem is in the tank, or in the plenum. All pressure and flow must end at the tester, no fuel allowed to the engine. (let me know if you need a parts list to make an adapter) Pump running, pressure should be ~90psi and remain above 50psi for at least 10 minutes. If it fails one or both of these tests, the pump needs replacement. If it passes both tests, the problem is in the plenum.