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2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2)


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skippy
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Oct 18, 2016, 1:53 PM

Post #1 of 21 (1547 views)
2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

2001 gmc sonoma 4.3 4x4. It has kind of a rough spuddery idle, and spudders sometimes on acceleration. check engine light on with codes for system too lean bank 1 and bank 2. I CAN NOT find any vacuum leaks anywhere ive tried smoke and spraying carb cleaner. its also not losing any coolant or motor oil. I have replaced the EGR valve, MAF sensor, fuel filter, and also ran a fuel pressure test. The pressure might be a little low but remains pretty constant around 50 psi. Where do I look next??


(This post was edited by skippy on Oct 18, 2016, 2:05 PM)


kev2
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Oct 18, 2016, 2:37 PM

Post #2 of 21 (1537 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

50psi - I think that is to low - below spec lower end. Time permitting I will double check specs...


Hammer Time
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Oct 18, 2016, 3:03 PM

Post #3 of 21 (1535 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

Definitely below spec.
Spec is 60-66PSI and that is critical.



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skippy
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Oct 18, 2016, 4:16 PM

Post #4 of 21 (1528 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

so does low fuel pressure make sense with the given symptoms? ive been researching and it looks like ill have to pull off the plentum to get to the fuel pressure regulator. figured it wouldn't be a bad idea to go ahead and put a new spider injector assembly and then obviously clean it up and replace the intake manifold gasket. Opinions?? I really doubt that it is the fuel pump


(This post was edited by skippy on Oct 18, 2016, 4:42 PM)


Hammer Time
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Oct 18, 2016, 5:38 PM

Post #5 of 21 (1522 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

If you plan on just guessing and throwing parts at it, that's going to be real expensive.
You need to test things first.

Follow the return line back until you can find a section of rubber and pinch it off. Now check the fuel pressure again. If it doesn't spike way up. then change the pump. If it does, then look at the regulator.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
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Oct 18, 2016, 5:50 PM

Post #6 of 21 (1518 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

Ok I will check that. And the truck has over 170k miles so i don't mind replacing some other parts that are going to help the performance and efficiency in the process of trying to find this problem. And in the end I'll still end up paying less than I would have if i took it to these mechanics around here with there ungodly shop rates


Hammer Time
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Oct 18, 2016, 5:55 PM

Post #7 of 21 (1515 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

After you spend $50,000 in hand tools and another $75,000 in electronic test equipment, a few thousand more in never ending training, you can charge "ungodly" rates too.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
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Oct 18, 2016, 6:23 PM

Post #8 of 21 (1512 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

just saying im not going to pay anymore by throwing a few extra parts on that may be the problem in the process of finding it, than i would even if i just paid someone to diagnose it. I dont see any harm in that


Hammer Time
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Oct 18, 2016, 6:27 PM

Post #9 of 21 (1509 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

It doesn't always work out that way. I've seen many people spend $500-$700 in parts to avoid $90 in diagnostic fees.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
Novice

Oct 18, 2016, 6:35 PM

Post #10 of 21 (1506 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

Ill keep that in mindWink

You say if there is a spike in fuel pressure after pinching off the return line to look at the regulator. I know how to tell if the regulator has been leaking once the plentum is off, but what if there is no evidence of that?? any internal problems with the regulator i could test for? and what if it isnt the regulator or the pump at all??


Hammer Time
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Oct 18, 2016, 6:38 PM

Post #11 of 21 (1503 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

If the regulator was leaking internally, the fuel pressure will drop immediately when the key is shut off. If it's bypassing and going back to the tank, the pinch off test will show that.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Hammer Time
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Oct 18, 2016, 6:41 PM

Post #12 of 21 (1499 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

If the rest pressure leaks down it can also be the check valve in the pump.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
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Oct 18, 2016, 6:47 PM

Post #13 of 21 (1498 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

considering the pressure was pretty constant after the key shut off, what else could be wrong with the regulator? (assuming the pump is good)


(This post was edited by skippy on Oct 18, 2016, 6:49 PM)


Hammer Time
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Oct 18, 2016, 6:50 PM

Post #14 of 21 (1489 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

It could just be regulating at the wrong pressure but it's far more likely to be a bad pump. If you can't make it spike, then the pump is just too weak.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
Novice

Oct 18, 2016, 6:53 PM

Post #15 of 21 (1487 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

well i thank you sir, i will report back after some more informed testing


Discretesignals
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Oct 19, 2016, 4:20 AM

Post #16 of 21 (1463 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

Before going through all that, you really need to look at your fuel trims and freeze frame records to see what was going on when those lean codes set. You can also do a WOT test while watching the O2 sensors to determine if you have a fuel pressure issue. Pinching the return line off with the engine running to dead head the fuel pump isn't very friendly on the fuel pressure regulator. It could blow out the diagram in the regulator if the pump is good. If your going to dead head the pump, put your gauge inline with a shut off valve in series at the fuel filter and dead head the pump that way. Just heads up. Most cheap OBD2 scan tools with data stream capabilities will allow you to see O2 voltages, fuel trims, and freeze frame data.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Oct 19, 2016, 4:24 AM)


Hammer Time
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Oct 19, 2016, 10:53 AM

Post #17 of 21 (1451 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

All I told him to do is flip the key of for a second and look for a pressure spike.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
Novice

Oct 19, 2016, 2:21 PM

Post #18 of 21 (1445 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

well i went back out and decided to run the fuel pressure test again just to double check before i went any further. the check engine light shut off as i was doing that. I decided to take it for a drive and about 2-3 miles down the road once it was up to temp the CEL came back on. I'm thinking maybe O2 sensors since it kicked back on once it warmed up?? but i cant imagine those would be causing the low fuel pressure. Im gonna run a test on those as soon as i can get a reader with live data.

More info on the pressure test: when you flip the key on, just during the first few seconds that you hear the fuel pump running, the pressure is point on at 60. as soon as you stop hearing the fuel pump it drops to 54. start it up and its around 49 - 51 dial is kinda shaky. during the revs it will drop low to mid 40s and then back up to 49 - 51 when you let off. shut off the key and it remains at 50 for a good few minutes before dropping really slowly over time.

On a side note it seems that i am getting really bad mpg's


Hammer Time
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Oct 19, 2016, 2:25 PM

Post #19 of 21 (1442 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

It sounds to me like you have a bad fuel pump. It should remain in spec at all times once built up. Make sure you change to filter along with the pump. It can't be the sole cause of the problem but it could lead to failure of the pump if it's plugged.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



skippy
Novice

Oct 19, 2016, 4:29 PM

Post #20 of 21 (1430 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

the parts store wants 280 for a new fuel pump. online i am seeing them anywhere from 55 to 360. any advice there on what to avoid? is dorman a good brand?


(This post was edited by skippy on Oct 19, 2016, 4:34 PM)


Hammer Time
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Oct 19, 2016, 4:49 PM

Post #21 of 21 (1419 views)
Re: 2001 GMC Sonoma 4.3. P0171, P0174 (too lean bank 1 and 2) Sign In

There are only 2 brands I would use........... Delco or Airtex



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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