yes another P0171 and 900 RPM thread that needs your help

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Any codes after? Your LTFT seems to spike a bit above +10 and seems to be mostly positive especially when accelerating.

You could check your fuel pressure before the fuel pressure regulator. If pressure is low, it would make sense that it's running lean and it's trying to add more fuel. It's a little pricey so would be worth testing before just throwing a new one on.

As for the fuel pump, I would hope that you got your ACDelco from a reputable retailer rather than eBay or Amazon as fake parts have been flooding those places. A CCC pump could have been slapped into an ACDelco box. They are actually made by Bosch and still have that sticker on them.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Any codes after? Your LTFT seems to spike a bit above +10 and seems to be mostly positive especially when accelerating.

You could check your fuel pressure before the fuel pressure regulator. If pressure is low, it would make sense that it's running lean and it's trying to add more fuel. It's a little pricey so would be worth testing before just throwing a new one on.

As for the fuel pump, I would hope that you got your ACDelco from a reputable retailer rather than eBay or Amazon as fake parts have been flooding those places. A CCC pump could have been slapped into an ACDelco box. They are actually made by Bosch and still have that sticker on them.
I did check it, it's up above.
20230317_173130.jpg

20230317_173101.jpg
One is ignition on the 50 is engine on at idle.
Don't think I ever charged the filter.
And it's a 2004
Been driving with it for 2 years no codes.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Been driving with it for 2 years no codes.
Now I'm confused. Are you or not getting a P0171 and high idle speed?

What I meant checking the fuel pressure before the regulator would be to disconnect the fuel line at the rail and check the pressure directly from that line, taking the regulator out of the equation. You would then get the full pressure from the pump. If you get similar pressures, then it's your pump. If it's higher, I would suspect the pressure regulator.

And yes, I would FIRST replace the fuel filter.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Was referring to driving for 2 years with this pump. Yes I have the code and the 900. But was teying to make sense of why the pump would be part of this since it's been working fine right before I took the head off, and changed a broken manifold.
Wgen all of it went back all hell broke loose, well mainly P0171 which I never head. I used to have the P0420 and that was due to the gas tank inlet pipe leaking. Because of that about 8 years ago I had a meltdown in my cat, and it took me 14 hours to come back from Lake Tahoe to Los Angeles going 30 mph maximum speed. Theough all that P0171 was not present and am sure the car was running as lean as it gets.
It just doesn't make sense. The LTFT is all over the place. Just drove a 2012 Mercedes 350 and the LTFT is at 12 or 13 cruising and goes to 7 under load but no code. That is lean. This mustbe a Chevy deal. These cars have the qeirdest issues.
But then again all cars have something crazy.
I will change the has filter and tey to see how I can check the pressure before the regulator. My old regulator was leaking gas and I had no code. So the regulator is new but I don't think it's AC Delco. That could be a problem. Car running great.

Wanted to know if the the middle muffler that has a leak could be plugged up. By tapping on it like I said it sounds full in the front end where the leak is and different towards the back. Could that mean it could be plugged up?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Possible. A backpressure test would confirm this. It would also come with low power and poor MPG.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Poor MPG I have but also have power. I am trying to justify the fluctuations în FT's
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Backpressure could do that by diluting the intake charge by keeping more exhaust in the cylinder. Just a theory on my part.
 

mrrsm

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Well... Next... I'd want to poke an Index Finger at:

(1) Replacing the Air Filter.

(2) Using an Inexpensive Two Channel PICO-Scope Model # 2204A or an Eight Channel Hantek Model # 1008C Oscilloscope and perform an On-Screen "Parade" or what is called "A Picket Fence" array of the Secondary Ignition Coils Side-By-Side in order to observe ALL of the COPs performing On Screen and look for any differences that bear out having any artifacts that suggest any LEAN Conditions.

Observe Some "Known GOOD" Secondary Ignition Wave Form Artifact Identifiers:

WAVEFORMBASICS.jpg

LEAN Conditions caused by a Failing Intake Manifold Gasket. Note the Height of the KV-Line AND the Height of the Shortened Burn Time Climbs upwards as its duration shrinks due to Lean Conditions:

SECONDARYIGNITION PICKET FENCE.jpg

(3) Examine THIS Classic Image for One Problem Cylinder vs. ALL Six COPs being fully functional to compare one against the other and determine if anything looks "Ugly"...

SECONDARYIGNITION PICKET FENCE1.jpg

In a different example, Back Probe a Specific Suspect COP and observe what the Secondary Ignition Spark-Line does by Shortening when attempting a "Snap Throttle". If that Spark Line Climbs precipitously (angling Down and to the Right) adjacent the High KV Line as the Burn Time SHORTENS...

SECONDARYIGNITIONEXTRESISTANCE.jpg

...then suspect an Ignition Problem that is EXTERNAL to the Combustion Chamber such as an Aging Spark Plug or a Failing COP (Coil On Plug). Look for any Carbon Tracing on the Spark Plug AND on the Rubber Insulation Boot.

THIS condition spells a BIG Problem for the Coil On Plug.. NOT Caused by IT ...but Caused by the LEAN Conditions placing the COP under Great Stress to Fire The Spark Plug!.

But if the KV-Line Shortens and the Spark Line Shortens, Tilting Upwards while the Burn Time extends further to the Right, then Suspect an In-Cylinder Problem such as a Sluggish or Stuck EFI:

SECONDARYIGNITIONCLOGGEDEFI.jpg
 
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mrrsm

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Oct 22, 2015
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The "Known BAD" Wave Form Examples listed above are Generic ...but apply in almost all situations. The focus at GMT Nation is of course involving GM and GMC Vehicles and the Wave Forms may appear different for other Makes and Models. FYI... I own (...and use) ALL of the following Oscilloscopes and "O" Scope--DMM Combos:

(1) PICO-Scope Model #2204A (via Laptop) 2 Channel
(2) Hantek Model #1008C (via Laptop) 8 Channel
(3) Autel Maxi-Scope Model #MP-408 (via Laptop) 4 Channel
(4) Hantek DMM- "O"-Scope Hand-Held Portable Model #2D82AUT0 2 Channel
(5) Yeapook 7" Touch Tablet Oscilloscope 2 Channel
(6) Snap-On Portable Graphing DMM Model #MT-2400 2 Channel via KV Unit

If you want more On Topic Oscilloscope Diagnostic Information and Training Examples as well as Links to the FREE Software... Please Visit THIS Thread:

 
Last edited:

gica

Original poster
Member
Dec 25, 2012
135
Cali
The "Known BAD" Wave Form Examples listed above are Generic ...but apply in almost all situations. The focus at GMT Nation is of course involving GM and GMC Vehicles and the Wave Forms may appear different for other Makes and Models. FYI... I own (...and use) ALL of the following Oscilloscopes and "O" Scope--DMM Combos:

(1) PICO-Scope Model #2204A (via Laptop) 2 Channel
(2) Hantek Model #1008C (via Laptop) 8 Channel
(3) Autel Maxi-Scope Model #MP-408 (via Laptop) 4 Channel
(4) Hantek DMM- "O"-Scope Hand-Held Portable Model #2D82AUT0 2 Channel
(5) Yeapook 7" Touch Tablet Oscilloscope 2 Channel
(6) Snap-On Portable Graphing DMM Model #MT-2400 2 Channel via KV Unit

If you want more On Topic Oscilloscope Diagnostic Information and Training Examples as well as Links to the FREE Software... Please Visit THIS Thread:

I have to tell you I am a dyi mecanic enthusiast, owned a bodyshop back in the days. Nowadays I fix my own and my family's vehicles. What I really like doing is buying tools. That is a bad habbit. I do that for electronics repair, auto repair and boat repair. On occasion I might have everything to do home repairalso. Plus fishing gear all you can eat. It a problem at this point and the wife is in therapy hahaha.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Ok so P0171 came back, so did the 900 RPM and on the info center I get really bad mpg. The leak on the middle muffler is loider after the smoke test. I have to do exhaust pressure test. I already changed the air filter. Waiting on the fuel filter.
And what hapenned the website account was suspended 2 days ago than yesterday the whole website was off.
 

mrrsm

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Oct 22, 2015
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Here is another "Spot-On-Topic" Thread describing the P0171 WITH the 900 RPM issue... with more insights from "The Roadie" and Other Members:

 
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budwich

Member
Jun 16, 2013
2,027
kanata
test your MAP using a vacuum pump using your data reader to get the resulting info that the pcm sees.
 
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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
And what hapenned the website account was suspended 2 days ago than yesterday the whole website was off.
Check this thread. There was a glitch in the matrix.

 
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TollKeeper

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Dec 3, 2011
8,045
Brighton, CO
Check this thread. There was a glitch in the matrix.

Neo matrix GIF on GIFER - by Landanius
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Here is another "Spot-On-Topic" Thread describing the P0171 WITH the 900 RPM issue... with more insights from "The Roadie" and Other Members:

Thanks, the fill tube is new, the charcoal chanister is not.
Here is another "Spot-On-Topic" Thread describing the P0171 WITH the 900 RPM issue... with more insights from "The Roadie" and Other Members:

Here is another "Spot-On-Topic" Thread describing the P0171 WITH the 900 RPM issue... with more insights from "The Roadie" and Other Members:

Thanks, the fill tube is new, the charcoal chanister is not. I changed the purge valve
Recently due to the P0420 code. It tyrned out to be a leak in the fill tube to the tank. I bought a special adapter tgat took care of the code after many years of pain inthe rear like this one. Funny because the tank fill up gives me an oposite impression from that thread. My code came when tank was close to empty. I just filled it and nothing yet. Still waiting for the fuel filter. Don't think ot will do anything though.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
test your MAP using a vacuum pump using your data reader to get the resulting info that the pcm sees.
Can you elaborate? So take it out connect the vacuum pump and pump it with engine on or off, scanner on on values live data? How much air?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Thanks, the fill tube is new, the charcoal chanister is not. I changed the purge valve
Recently due to the P0420 code. It tyrned out to be a leak in the fill tube to the tank. I bought a special adapter tgat took care of the code after many years of pain inthe rear like this one. Funny because the tank fill up gives me an oposite impression from that thread. My code came when tank was close to empty. I just filled it and nothing yet. Still waiting for the fuel filter. Don't think ot will do anything though.

P0420 has nothing to do with the evap system. Basically means your cat isn't working (likely) or possibly an issue with your O2 sensors (less likely). To properly diagnose this, you would need to check and compare live data on both sensors. The upstream should be cycling while the downstream should be relatively flat indicating it's cleaning the exhaust. If it's cycling like the upstream, almost identical, the cat is dead.

Since the evap system was worked on, maybe the evap is leaking vacuum causing the P0171?

I think the fuel pressure is a red herring. It was worth chasing however, when mine was outright leaking with low pressure, it never threw a code so...

And since the head was rebuilt, it might be worth it to check the compression.
 

budwich

Member
Jun 16, 2013
2,027
kanata
Can you elaborate? So take it out connect the vacuum pump and pump it with engine on or off, scanner on on values live data? How much air?
engine off / key on. Use a hand vacuum pump. You change the vacuum by small amounts going from 0 inhg to say 20 which is basically a "normal range" for intake vacuum. The MAP should respond / agree with the vacuum pump's gage. IF it doesn't, then it is likely some issue with this area.... wiring, sensor, pcm, etc.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
engine off / key on. Use a hand vacuum pump. You change the vacuum by small amounts going from 0 inhg to say 20 which is basically a "normal range" for intake vacuum. The MAP should respond / agree with the vacuum pump's gage. IF it doesn't, then it is likely some issue with this area.... wiring, sensor, pcm, etc.
Ok I shall try it thanks
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
P0420 has nothing to do with the evap system. Basically means your cat isn't working (likely) or possibly an issue with your O2 sensors (less likely). To properly diagnose this, you would need to check and compare live data on both sensors. The upstream should be cycling while the downstream should be relatively flat indicating it's cleaning the exhaust. If it's cycling like the upstream, almost identical, the cat is dead.

Since the evap system was worked on, maybe the evap is leaking vacuum causing the P0171?

I think the fuel pressure is a red herring. It was worth chasing however, when mine was outright leaking with low pressure, it never threw a code so...

And since the head was rebuilt, it might be worth it to check the compression.
Sorry I wrote the wrong code P0440.
You're right P0420 is the cat
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Wrong code notwithstanding, the rest I wrote is valid and should be checked.
 

gica

Original poster
Member
Dec 25, 2012
135
Cali
Also the fuel pressure regulator is not an AC Delco. Don't know if that makes a difference. The original started to leak badly so I bought it off the market. I think it was before the work on the head and it did not throw codes.
 

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