Ok. I bought a 1 owner 2000 blazer with 88k on it. I didn’t get but a mile from house and check engine light came on. Codes were the 2 for lean bank 1 and lean bank 2. I’m sure the original owner had issues as he recently spent $2200 at a shop for new fuel injectors and then a new fuel pump. He mentioned to me during the test drive that in mornings, truck would hesitate a little until it warmed up real good. Anyway, I had a friend check fuel pressure and it was around 55 or 56 I believe. I made the decision to put an AC Delco pump in it in case they used a cheap one. After testing brand new pump, the fuel pressure was exactly the same. We then tested the fuel trim levels. Seems the short trim levels were spot on but long term were over 25 which is causing check engine light to come on. When engine is hot it runs great on hwy doing 70 or 80. When cold it hesitates. Also when hot, from a dead standstill flooring it, it seems a bit sluggish. So, if my catalytic converter is bad, could that cause high long term fuel trim numbers to be so high? I hate just throwing parts at the truck. It’s beautiful and I want it to run good. Any help or suggestions would be great. Thanks y’all.

 

hi welcome to the forum

 

You always add short term and long term fuel trims together for a given bank observing the sign (+/-). I assume that your scanner is giving you a net positive (+) 25 for that total on each bank? If so, then the PCM is adding fuel to compensate for a lean condition. If the LTFT number is most of the total then that just means that you have the problem most of the time.

What can cause a lean condition:

Inadequate fuel supply - pump pressure, fuel filter, injectors, regulator, hoses.
Unmetered air - air entering after and not measured by the MAF, such as a vacuum leak.
Bad MAF
Bad O2 sensor
Stuck EGR valve if so equipped
Bad ECT sensor
Exhaust leak

Did you do the leak down portion of the fuel pressure test?
Have any of those sensors been replaced recently?
Do you know how to evaluate those sensors using the live data portion of your scanner?
Fuel trims at idle and again at 2500 will help to determine if you have a vacuum leak.

George

 

fuel pump and injectors have been replaced as stated in original post. I had a mechanic check everything on this truck and all is normal except for fuel trims. There are no vacuum leaks and today, I even replaced the catalytic converter with no change. I got 4 to 5 miles from the shop and check engine light came back on with same 2 lean codes. I’ve never dealt with anything so frustrating in all my life. 🥵

 

I can help you but we need to work through the potential causes, regardless of how new the parts are. I gave you the list of potential causes, the list is manageable. There are two choices - analyze, identify and repair or the parts cannon.

Again, what are the results of the fuel pressure sticky instructions, both pressure and leak down? Since your still having problems, that repair and the needs to be verified.
Do the STFT and /or LTFT change when the fuel system goes into closed loop as the truck warms up? Do the trims change at 2500 rpm?
Do the fuel trims straighten out when you unplug the MAF while its misbehaving?
Do you have the ability to monitor sensors on a scanner in live data?

If your not into this level of detail and analysis, I understand and you can pursue a different route. If you want to analyze your problem and get it fixed, ill be glad to help but we need to answer these diagnostic questions.

George

 

So, my friend had a code scanner and diagnostic tool. He actually is a mechanic. He is stumped too. He did leak down test and everything you mentioned. All sensors are working just fine. No vacuum leaks or exhaust leaks. We replaced the catalytic converter and no change too. The ac Delco fuel pump we put in has same exact results as one that we removed. Truck will stumble when cold but once at normal temp it runs great but still has the lean codes. Next week we are going to redo the spider injector assembly and intake gaskets and all of that. We are just getting very frustrated. This is a beautiful truck with only 88k and I love it!!

 

Sounds like you have a plan, hope you get it figured out.

George

 

Hey george
this morning I started blazer up and as always, it sounded just fine. I tried to spray all around intake again with no change in how engine is running. Figured I’d do it when cold but results are the same. While running, I unplugged the mass airflow sensor. The truck stopped immediately. Is that normal? Not getting misfire code just still lean bank 1 and 2. It’s driving me crazy.

 

Mine didn't quit when I unplugged that MAF sensor. Chasing a problem like that is annoying, hope you get to the bottom of it soon.

 

Shut it off, clear the codes, and then start it up with the maf unplugged. Go for a drive and let us know the LTFT’s and codes after your drive.