PO171 & PO172...system to lean bank 1 & bank 2

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#1
have a 2001 Chevy Silverado,1500,2wd,4.3,VIN "W" in the shop with a PO171 & PO172...system to lean bank 1 and system to lean bank2.....I don't know if the codes were already there, but I did a complete tune up....and changed the fuel injectors to the updated one like the one in the pic....I sprayed carb cleaner around the intake and didn't see any change in the vacuum readings...which are between 18 & 20...fuel pressure is supposed to be Key On Engine Off 55-62 psi ...fuel pressure is 50PSI...and 49PSI when running....STFT-47-50..LTFT-25....I am thinking maybe a weak fuel pump but I don't want to drop the tank and replace it unless you guys think this is my problem....thanks for any help on this.......Jim

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billr

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#2
Well, what about the FPR? Is it one that you can see if fuel is going back the return line, at that pressure that is below the normal "cracking" pressure?
 

billr

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#4
How about voltage right at the pump, can you check that easily? On my 1500 Express van the FP connector is accessible without lowering the tank.
 

billr

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#5
Also, how about disconnecting the inlet line to the fuel filter and test for fuel pressure there, "right at the pump"? On the Express the filter is also pretty easy to get to.
 
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#7
wouldn't the LTFT be + if there were a lean condition... the PCM ADDING fuel to compensate for lean? I am not thinking backward on the - vs + fuel trims am I?

What is fuel pressure leak down...

How are the 02 sensors reading?

After you changed FI you have given it some run time ... thinking the STFT will react and change befor LTFT
 

billr

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#8
I think he is saying short is +47 to +50, long is +25. Hyphens (which I love to use) are kind of multi-purpose and can be ambiguous.
 
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#9
"PO"172 in my book say that the system shows too rich on Bank 1. PO 171 says the system is showing too lean on bank one, as Jim says. I don't know if that is what Jim meant when he wtote it.

So with po172 bank 1 is really showing rich. then the computer is working properly trying to cut back the fuel because of the Rich running condition on back one, and setting code po171. It seems to me that you have a rich running condition, not a lean running condition.

Am i right or wrong on that?
PO173 is running lean on bank 2.
 
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#10
You are right....sorry about that....STFT+47-50...LTFT+25....I am glad you guys are here to straighten me out...I think I am just getting burnt out on this..I was trying to remember the codes..without looking.I know it said sytem lean bank1 and system lean bank2...Hope this helps...I will check more and let you know...Jim
 
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#11
??? sorry I am confused -again- happening alot lately

P0171 - that is a lean code bank 1
P0174 - that is leam code bank 2
and the STFT is +47 LTFT is +25
 

billr

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#12
As I understand it, the trims are rich trying to compensate for lean codes, right? Time to get back to the low fuel pressure... sorry, Jim, but I think you are going to have to spend some time underneath there!
 
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#13
sorry I am confused -again- happening alot lately

P0171 - that is a lean code bank 1
P0174 - that is leam code bank 2
and the STFT is +47 LTFT is +25

Yes Kev....that is the right readings....PO171 and PO174...i just took the fuel filter off and hooked my fuel pressure gauge to the line...when I turned the key on the gauge went to 100 PSI...then went down to 65 pretty quick....then down to 45 in about 3 or 3 minutes....I am going to put the filter on and check it again and I will get the O2 sensor readings....Jim
 

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#14
Did the vehicle come in for a tuneup or for the CE light?

Why were the injectors replaced?

Since you did a complete tuneup, I assume the fuel filter was replaced.......

So fuel pressure is definitely low,,,,,surprised it starts, that low......

Here is the rub........we don't know what the fuel pressure was BEFORE the unit was replaced......

Need to check if you are getting full voltage to pump.....this will need a double setup......you will need a test light(load) plugged in the harness connector, and a voltmeter across the test light......having just one or the other, will not show you how much voltage is going there.......not sure if this setup has the Ground on the chassis nearby....have seen some bad grounds causing voltage drops....

Another thing to check is pressure with the return blocked.......if there is a rubber return line, it can be clamped....if steel or plastic, a special line with a shutoff valve has to be used.......just turn key to on......if pressure does not go above the 50 psi you had before, then it is the pump(if it is low, cycle the key).......if it does go well above 50psi, and then you release the clamped return line or open the valve, and it drops to 50 psi, you are not going to be happy.....
 
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#15
Thought the 02 readings would help make sense out of the - fuel trims AND a lean code - Now that we cleared up the + or - numbers as well as the correct codes.

I think the fuel pressure is where to look now... are you "T"ed into the fuel line or dead heading to the gauge? 100psi sounds deadhead,..
I have the sick memory that there is no fuel line schrader under hood.