02 blazer bank 1 and 2 lean codes

We recently replaced the blown 4.3 in my wifes blazer with a low milage JY 4.3 and on startup we had lots of misfire codes. Changed the distrubutor and they went away. Drove it around for a while and got P0171 and P0174 Bank 1 and 2 lean codes. We cleaned the MAf, the code came back. Finally it went away for about 1 1/2 weeks. The other day it came back on, but I noticed something. It happened when I started the blazer with the air conditioning turned on. Took it to my son at work and we hooked up the snap on reader. The air conditioner adds 4% to load when turned on. This moves it to another cell in the fuel map. Could those cells have inadequate fueling stored for that load? Everything else looks pretty normal, but the O2 sensors might be a little lazy. I should mention that the truck sat for 9 months with the battery disconnected between motors. If I leave the air off, we don't seem to get the code. And the fuel pressure is dead on at 55 psi.

The fuel trim at idle with AC on drove me nuts when tuning! I get 3% even in a V8.

There's not a big difference in O2 switch points, may be just enough? Could change the tune and adjust Stoich to 14.13 for the E fuel. For a test you could fill up with Non Ethanol and see if the issue goes away?

Those codes are set to 2nd trip emissions. So 2 restarts and 2 fails to report.

http://www.gearhead-efi.com/Fuel-Inj...1&d=1376751950

When we looked at the stored codes with the SnapOn scanner, it was adding 23% fuel to banks 1 and 2 when the codes were set. That yielded 14.6 AFR. I have no way to tune it, so I am just trying to figure out if I have a bad part somewhere, or the software is just being stupid.

IIRC the lean codes are set from fuel trim but I don't know what exactly the code looks for. The 14.6 that the scanner shows is just what is set in PCM as desired or Stoich AFR, it's not actual.

But WOW 23%? What does it do on a normal day without AC? Either way that is BIG trim! Stock vehicles are not that far off.... half of that yes... and if you make one change to the tune to Desired AFR to 14.13 that goes away...

Did your son look up TIS to see if that calibration was ever updated?

23% indicates an issue. 10% is max acceptable, and that's at the limit. You're probably at 14-18% without A/C. Lazy sensor, maybe. Air leak from hose or big honkin' elbow at TB not connected? Fuel pressure on low side of stock? Lazy O2 could do it but I wouldn't suspect the sensor if it was switching properly while the trim as at 23% lean.

Note regarding the fuel pressure. Almost always, the pressure as tested is on the low side of stock. I almost always bump it up if I have the intake apart. The regulator is in the manifold and can be adjusted using a tamper proof torx bit. You may be able to get to the adjustment without complete manifold disassembly.

23% is Huge. I would suspect a vacuum leak or fuel pressure or injectors or bad fuel or a tank of E85.

Jeff

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Originally Posted by 1project2many

23% indicates an issue. 10% is max acceptable, and that's at the limit. You're probably at 14-18% without A/C. Lazy sensor, maybe. Air leak from hose or big honkin' elbow at TB not connected? Fuel pressure on low side of stock? Lazy O2 could do it but I wouldn't suspect the sensor if it was switching properly while the trim as at 23% lean.

Note regarding the fuel pressure. Almost always, the pressure as tested is on the low side of stock. I almost always bump it up if I have the intake apart. The regulator is in the manifold and can be adjusted using a tamper proof torx bit. You may be able to get to the adjustment without complete manifold disassembly.

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My stock engine ran 15+ sometimes without any problems.

I would say its an unmetered air leak as well.

He would have to remove the plenum and I would recomeend installing the fuel lines to the regulator and adjusting the pressure with the pump running and a pressure gauge attached.

I think unmetered air leak is a possibility. We can't find it, but we only sprayed a little brake clean. I guess we will have to get serious about trying to find an air leak. as for fuel pressure, 55# running isn't enough for a completely stock 4.3?

Something has changed in brake fluid and even starter fluid that they don't work for finding vacuum leaks anymore. To prove... just spray some in intake and engine does not raise RPM...

Now try a propane torch! If it finds a vacuum leak the RPM will rise!

Yeah, That was what I was going to try, just need to get a propane torch.