Here are some readings taken live during a 30 minute highway drive. I included a range of values and a range of the most commonly seen values where I thought appropriate.

ECT 194

STFT B1&2 Complete range (-10 to +25) Both banks had very similar readings. Increased under acceleration and rarely went negative unless I was coming to a stop light.
LTFT B1&2 Complete range (0 to +25) Both banks had very similar readings. During highway crusing the LTFT stayed at +25 with the STFT ranging around +10 to +25.

MAP (inHG) Idles around 13.2 Range (+5 to +28) Increases under acceleration and decreases during deceleration.

MAF varied from (0 to 4) and increased under acceleration and decreased under deceleration.

Spark Advance (-10 to 41) Increased during light throttle cruising. Decreased during acceleration. Generally stayed in the (30-41) range and predominately at 41 during flat land highway driving.

o2 varied from .0x to .9x sensor 1 & 2 were constantly moving between that range.


Other than the high fuel trim readings does anyone see any other issues? I'm not sure what the common ranges for these are on a properly running Blazer. Let me hear some thoughts if you see readings or hear symptoms that lead you to believe it might be a certain part. Right now I'm still leaning toward replacing the fuel pump.

Edit: Or if you see any reading that can help me to rule out certain common problem areas. Such as, does the MAP reading imply that I probably do not have a vacuum issue? Does the spark advance imply that my distributor is working correctly? Thanks

 

Hi, I am new to this forum but I'm having the exact same problem with my 2000 blazer 4.3.
My fuel-trim numbers almost duplicate your's exactly and I have already replaced my fuel pump and regulator within this past week. My fuel pump numbers were almost exactly as yours and that's why I chose to replace my pump; with a Delphi. I also chose to use an AC Delco fuel pressure regulator.
I don't have the AIR pump on mine and I haven't been able to locate any vacuum leaks. I'm stumped! I use an AUTOENGINUITY scanner on my laptop and I'm able to see the live data. My fuel trims are still very high both long and short term. I can make a vacuum leak and watch the number increase rapidly and, when I put the vacuum hose back on, they decrease. However, they're still in the positive area and upwards of 20% long-term. I used some propane in a bottle to go around the intake manifold as I just had it off yesterday; nothing changed number-wise with the addition of the propane.
I will glady share any information and provide more specifics so perhaps we can all learn something. This is a great site and I'm glad to be a new member! PEACE

 

notnoah's, unless you have removed the AIR pump, you likely have it as it was a requirement for all US & Canada based vehicles in 2000. Regardless, you are welcomed to follow along in this thread.

The options are summed up as the following. The PCM think more fuel is being injected than actually is (clogged injectors affecting both banks equally). The PCM thinks less air is being pulled into the engine than there actually is (vacuum leak or a problem with the crankcase ventilation system being allowed to pull in outside air bypassing the MAF sensor). The PCM is seeing skewed O2 sensor information possibly from an exhaust leak on both banks (unlikely). Something is causing the spark to be too retarded or advanced to support proper combustion resulting in too much free O2 in the exhaust (very odd occurrence)...

Looking back at a scan from my old Bravada, hot idle at ~650RPM, ECT at 194F, MAP readings were in the 10-11 inHg range, MAF was in the 0.60-0.62 lb/min range, IPW's were in the 3.8-4.3 millisecond range with a LTFT average bank to bank of ~+8% at that particular instance, IGN ADV bounced between 13 & 22 during this time span as well.

 

Thanks for the response! First thing that jumps out at me was the fact that, when I looked for the AIR system per your previous suggestion, there isn't one; with no lines plugged or removed and no pump set-up present. On both sides of the bottom radiator area, just to the left and the right of the remote oil filter, are 2 things that look like just like some sort of coil. There are wiring harnesses connected to them and they're riveted to the cross member that supports the radiator. They are both yellow and the wiring harnesses are prefessionally wrapped as though they're factory. There is nothing else connected to them besides the wiring harness.
I purchased the truck from a really nice guy from Texas and they have emission testing required upon renewal of registration. There are no check engine lights related to anything besides lean bank 1 and bank 2 and the emission-pass stickers are still on the windshield. I have to assume that there in no AIR system. And, if there was, where would the AIR lines plug in at the manifold? Thanks again for your valuable information; I've read some of your posts and they're detailed and professional.

 

Just for some additional information... The new fuel pump I put in was a Delphi FG0052 and, the pressure at the schrader valve, measured 60psi with pump running and about 55psi when it stopped; it will not go above 60psi at ay point. The Blazer idles at about 52psi. These reading were the same as the Airtex pump that I replaced. When I took a reading directly after the fuel filter it read around 95psi and then dropped steady to around 75psi. The fuel filter was replaced about 60 miles before I replaced the pump. That is why I put a new regulator on. However, even with the the new regulator, the new pump provided the same readings at the schrader as before replacing it. The only difference was when the pump stopped and the pressure began to drop to its lowest reading, the pressure began to rise to about 58psi and then stopped. Does this sound like a bad new Delphi pump? Thanks...

 

notnoah, when I said you could follow along in this thread, I meant that if something posted to help the original poster helped you, great, but please do not start asking questions in someone else's thread. It has the tendency to divert attention from the OP and often results in confusion for all. If what has been posted does not help you and no other threads of similar topic help, please create a thread of your own to discuss your problem citing references to other threads if you can.

But to answer your question about the fuel pump, sounds perfectly normal to me. The 52psi running is somewhat troubling though.

 

Sorry, didn't mean to upset anyone. My Blazer troubles mirror that of the original person who posted and my numbers are almost identical as well. His original question had to do with whether or not he should be looking to replace his pump. I did that procedure and my lean bank 1 and bank 2 problem remains. Therefore, it seems as though he might have something else going on besides the pump or the regulator; I replaced both without solving my-- and/or possibly his-- difficulties. Perhaps my information, and questions, could help him solve his issues as well? Or at least not feel the frustration alone...

 

No one is upset. In my experience here and on other forums, the intentions of the 2nd person in a thread with the "same problem" and the direction a thread takes after more questions get asked by said 2nd person are rarely the same and very often, things go sideways detracting from the OP's original problem... We can see how this one plays out though. It isn't my thread, just trying to watch out for the interests of the OP.

But anyway, I laid out the scenario's for what could cause a lean condition throughout the engine. Time to dig into it.

Have either of you tried blocking off the fresh air tube to the back of the intake duct work above the throttle body as well as disconnecting and plugging the PCV valve from the driver side valve cover, putting a small filter on the line to the passenger side valve cover? This would eliminate a possible source of outside air into the engine that the MAF sensor would not see. The same can/should be done with the other vacuum powered accessories; HVAC/4wd & brake booster (only when idling, do not drive down the road without knowing what to expect from the brakes without power assist from the booster).

Do either of you have the ability to do an injector balance test? This can be used to let you know if all of the injectors are distributing the same amount of fuel into all of the cylinders. One or more injector that is spraying incorrectly on each bank could cause reduced engine performance along with a lean condition due to improper fuel atomization.

 

Thanks for your understanding and I'll do my best to remain true to the OP.
I have not tried plugging the PCV vacuum source on the intack maifold yet nor have I tried blocking the fresh air port to the back of the air intake duct-work. Just to be sure, that is the large plastic hose that connects the intake duct-work to to the passenger side valve cover, correct? (I am unaware of any other vacuum line going to the passenger valve cover.) Are you then suggesting that I connect the 'pcv' hole on the driver side valve cover to the 'breather' hole on the passenger valve cover via a small filter?
I have already disconnected the vacuum line to all of the vacuum powered accessories by plugging that small line before the one-way check-valve; that didn't change any of my o2 or stft readings.

I did do a injector balance test and all 6 injectors went from 60psi at pump engagement down to around 48psi after hearing them clicking a few times. All 6 were less than the 1.5psi difference from their averages.

 

On the PCV system, put a small filter on the line that runs from the passenger side valve cover to the plastic intake duct on top of the throttle body, plug the port on the intake duct, plug the line from the intake manifold to the PCV valve leaving the PCV valve installed in the valve cover.

Don't forget about the brake booster. It is a potentially large vacuum leak, but should manifest itself as a braking problem prior to becoming an engine problem.

1.5psi isn't enough to worry about on a balance test so that checks out fine as far as the injectors doing what they are told to do.

Do you have the ability to monitor the O2 sensor trace either with an oscilliscope (my preferred method) or with your scan tool (hopefully your scantool has a pretty good refresh rate). If so, what is the min & max voltages from the B1S1 & B2S1 sensors?