Persistent p0172 and p0175

budwich

Well-Known Member
hmmmm.... you might want to do the key on, engine off obd vacuum reading a few times over the next few days or hours. That seems like a significant difference on the "baro". You can pull your filter for a "short while" to see if it makes any immediate difference on the air flow readings... maybe.
 

TJBaker57

Well-Known Member
You can also install any of dozens of free smartphone apps that display the sensor data from your phone and can quickly see current barometric pressure to compare to your MAF/MAP sensor KOEO reading. Pressure data is generally reported as millibars or hPa so the conversions are straightforward.

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MBS1994

Well-Known Member
Key on and engine off baro was 82kpa, map 11.89 psi, and no vacuum on torque.
 

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MBS1994

Well-Known Member
Something that has been bothering me. After I welded my y pipe again and replaced my exhaust manifold gaskets my check engine light was off for about 5 start ups and maybe 30 miles, it showed my map as a pending so I cleared it and it hasn't came back. It wasn't till after that the p0172 and p0175 showed again as pending. So I replaced my o2 sensors and reconnected my battery it immediately had the codes as pending. I noticed when I went to do my o2s my header bolts weren't very tight. Could they be working loose from heating and cooling and throwing the codes? I just dont get why it was so quick to have the codes this time compared to last. Oh and second thing not sure if it's abnormal or not but I took off my air filter and the idle was very jumpy
 
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MBS1994

Well-Known Member
So I unplugged the maf again and checked fuel trims to see. How it is normally is ltft on 1 and 2 is -15.63 and maf unplugged is +12.5 ltft bank 1 and +8.59 Ltft bank 2. Found it a little odd that both banks match exact on rich but has a +4 difference on positive. I also found a old thread from me when it turned off when I found a o2 sensor loose and a cracked line from the driver side valve cover to the intake manifold but it only stayed off long enough for emissions.
 
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MBS1994

Well-Known Member
The tuner is going to take another look at my tune if my fuel pressure is okay. So far everything seems like it's working proper
 
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MBS1994

Well-Known Member
Found a vacuum leak at where the oil fill tube(not sure the actual name) seats into the valve cover, and either the intake manifold gasket or the passenger valve cover couldn't tell for sure. Could this be causing the problem? A response would be well appreciated
 

christo829

Well-Known Member
Hmm..could you post some images of those leak locations? I'm running the 4.2, so hopefully one of the members with the 5.3 can help nail that down.
 
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MBS1994

Well-Known Member
For sure on the thick line under the fill tube and somewhere between the thin lines going back. The valve cover and the intake manifold are real close so it was hard to tell. The passenger side does run slightly richer than the driver where the two confirmed leaks are. Has me thinking the intake manifold leaks effecting both sides and then the fill tube leaks putting it slightly richer on the passenger. Btw not my motor just for the example
 

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TJBaker57

Well-Known Member
Found a vacuum leak at where the oil fill tube(not sure the actual name) seats into the valve cover, and either the intake manifold gasket or the passenger valve cover couldn't tell for sure. Could this be causing the problem? A response would be well appreciated

How were these detected?
 

Mooseman

Moderator
The metal tube that's pointing forward should have another plastic tube attached to it that goes up to the intake resonator. It supplies fresh air to the PCV system. If you don't have a hose connected at the intake resonator, you will have unmetered air coming in past the MAF.
 
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MBS1994

Well-Known Member
The metal tube that's pointing forward should have another plastic tube attached to it that goes up to the intake resonator. It supplies fresh air to the PCV system. If you don't have a hose connected at the intake resonator, you will have unmetered air coming in past the MAF.
The hose is there. It was further back just didn't find a good pick from top side. Its somewhere from the middle to the back.
 

budwich

Well-Known Member
plug the tube and hose for now and see what happens... they are basically emissions "stuff" which won't do much in the short term.
 
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MBS1994

Well-Known Member
So replaced the oil fill tube, cleaned my injectors, and replaced my intake manifold gaskets. Knock on wood I think its fixed. Also idle is steady as can be, no stutter what so ever. I'll need to do some driving but that is my idle. lt was sitting at -9.38
 

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MBS1994

Well-Known Member
Still no codes, pending or confirmed, but haven't driven it to much still but has gotten a couple warm ups. I'm still a little hesitant to call it fixed/solved yet since they've haunted me for so long. Hoping to go driving today and see if anything shows. Will report back soon.
 
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MBS1994

Well-Known Member
Still at it. Sorry for the slow progress. Still has a vacuum leak, removed the intake, cleaned the hell out of the heads, and reseated it, and still can't tell exactly where it's from, gonna enlist help from a extra set of eyes. Bought a fuel pressure gauge and when it's running it's at 58psi, I turned off the car and it dropped to 55 and held for 5 minutes(checked on a work break so I didn't have very long to wait).
 

Mooseman

Moderator
Have you tried using carb cleaner to track down the vacuum leak?
 
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MBS1994

Well-Known Member
Wait so I have a question on all this. I kept reading that a vacuum leak could cause a rich condition because it's unmetered air getting into the motor and with all my maf, map, etc working properly it dumps extra fuel to try and reach balance. But if that were true I could pull just about any vacuum line and I should see even more of a rich condition in theory. I know from pulling vacuum lines my trims lean out so the opposite. So with my fuel pressure seaming to be fine wouldn't this almost single out the tune as the issue? And also thinking about it where both sides are running rich that would also make me think tune.
 
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budwich

Well-Known Member
you could be right BUT... you make the statement "with all my maf, map, etc working properly". You know that for sure?

Further related to your "premise" of pulling a vacuum line. Are you saying when you pull a vacuum line, you see a change in the vacuum being monitored? or you are just "proposing" that is what happens? Basically, what is your vacuum reading before you pull "any vacuum" and what is it there after?
 
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MBS1994

Well-Known Member
you could be right BUT... you make the statement "with all my maf, map, etc working properly". You know that for sure?

Further related to your "premise" of pulling a vacuum line. Are you saying when you pull a vacuum line, you see a change in the vacuum being monitored? or you are just "proposing" that is what happens? Basically, what is your vacuum reading before you pull "any vacuum" and what is it there after?
As far as the maf, map, etc goes they've been replaced and I was going off GMs parameters to set the codes and all readings are in spec to not set the code.
No to the vacuum reading but that's a good idea. I was just going on the thought process that if a vacuum leak was making it run rich then pulling a vacuum line would make the rich condition worse but instead my trims go more positive.
 

budwich

Well-Known Member
As far as the maf, map, etc goes they've been replaced and I was going off GMs parameters to set the codes and all readings are in spec to not set the code.
No to the vacuum reading but that's a good idea. I was just going on the thought process that if a vacuum leak was making it run rich then pulling a vacuum line would make the rich condition worse but instead my trims go more positive.
but I think you misunderstand... especially related to your earlier post 198. The "conditions" that you were looking at, are operating parameters that have to exist for the test to run and set the DTC IF it exists. Those are NOT the conditions that set the code itself. I think that is what tjbaker was indicating.

Hopefully, your thought about the "vacuum test" is good... but also your thought about the "tune" might be valid especially if one knows what was actually "tuned"... meaning does the tune "hone" a "speed density run" (ie. MAP heavy) or improve the "blend". Further, you have indicated in the past about "wiring issues" to the sensors (for what ever cause). The "fix" of those might not be totally good electrically across all operational ranges, in terms of current / voltage which the sensors rely heavily on (ie. consistency, well regulated).

can you please restate what your ltft is before and after removing any vacuum line.
 
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MBS1994

Well-Known Member
So I redid my wire fix job on my map and temp sensor as they were rush frustrated jobs. I took it to the store today because I haven't driven it in a while and no more pending p0172 and p0175. They were pending on thanksgiving after car work and I haven't touched or driven it till today. I doubt it's fixed but just found that interesting and quietly hoping. And also yes I can soon on the trim numbers
 
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MBS1994

Well-Known Member
Seems off to me no?
 

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MBS1994

Well-Known Member
I'm pretty solid on it being my throttle body. I had a bad from my wife's 6.0 tahoe that I slipped my harness onto and my tps would drop down and then slip it back on mine and it would pin to the 30%. If my thought process is right even once now couldn't my throttle body be bad and its telling the ecu it's under load so it's putting in more fuel than necessary so creating the rich condition?
 

budwich

Well-Known Member
I don't think so.... This is "key on, engine off" data. I think that the tb has a "relaxed" position and an enerigized position (ie. running). You can readily confirm by looking at the data at idle. You should see the tb sitting at in and around 20 for a "normal" idle. IF that is not the case, then perhaps you do have a TPS issue.

As for the fuel level, are you saying your tank is empty, half full, full and that indicator is not correct?
 
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MBS1994

Well-Known Member
I don't think so.... This is "key on, engine off" data. I think that the tb has a "relaxed" position and an enerigized position (ie. running). You can readily confirm by looking at the data at idle. You should see the tb sitting at in and around 20 for a "normal" idle. IF that is not the case, then perhaps you do have a TPS issue.

As for the fuel level, are you saying your tank is empty, half full, full and that indicator is not correct?
So it was the 29.8 at idle with the old throttle body and with
I don't think so.... This is "key on, engine off" data. I think that the tb has a "relaxed" position and an enerigized position (ie. running). You can readily confirm by looking at the data at idle. You should see the tb sitting at in and around 20 for a "normal" idle. IF that is not the case, then perhaps you do have a TPS issue.

As for the fuel level, are you saying your tank is empty, half full, full and that indicator is not correct?
So with the old one it was 29.8 at idle, the spare one drops below 20. I just checked with key on and engine off and it sits at 30. I am going to compare it to the tahoe just for reference.
No I was confused on the fuel level input on if it meant that was the fuel it was putting into the motor. Also going to compare it to the tahoe. I know they are different platforms but at least for some sort of reference
 
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MBS1994

Well-Known Member
On difference I really see between the 2 is "absolute pedal position d and e" both mine are 20% and the tahoe is d 19% and e 9%. I can not for the life of me find what these are, I google it and it brings up throttle position sensor so I'm hoping it's that but I don't know. My engine load is also 4% higher but I don't think to much of that. Anyone know what the "absolute pedal position E" is?
 

budwich

Well-Known Member
I can't make sense of your posts which seem to be "broken up" a bit.

The post that you have attachments for and show the throttle position circled is not "at idle" but is just a key on. You seemed to then indicate that this was the "old one" at idle... ???? It is not IF that is the data attachment that you posted... the rpm on the engine is "0"... engine is not running.
Please confirm what you are seeing / doing.
 
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MBS1994

Well-Known Member
I can't make sense of your posts which seem to be "broken up" a bit.

The post that you have attachments for and show the throttle position circled is not "at idle" but is just a key on. You seemed to then indicate that this was the "old one" at idle... ???? It is not IF that is the data attachment that you posted... the rpm on the engine is "0"... engine is not running.
Please confirm what you are seeing / doing.
I got a new phone so I lost all my data logs from car scanner, that was the last log i posted on this thread before that. I must have over looked the rpms because I'm grasping for straws here because I'm at such a loss. I do apologize for overlooking that. Do you have any idea what that absolute pedal E is? The only other thing I can even think to compare the two cars on is vacuum to see if there is much difference.
 

budwich

Well-Known Member
I don't lnow what absolute pedal e is for. Not sure it matters. BUT you are indeed "wandering". There were things that were suggested herein both by you and others... an example, you mentioned about pulling a vacuum line and seeing if your "claim" about it changing trims was accurate and also if it was seen (ie. vacuum value changed in step). Was that done? what was the result?

Further you just posted in #229 that the codes are gone... so what are you actually chasing. Still further, those codes don't show up immediately... the PCM needs to see the condition (trims over / under a certain value) for 2 minutes or more at a time. Hence, you need to monitor your trims to see if they are "wandering" in a certain direction.... NOTE: it is the LTFT that is important NOT the STFT.
 
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MBS1994

Well-Known Member
First two are with a vacuum line pulled and last two are some driving. I noticed that it only seems to be bad at idle. When I'm driving all my numbers go way closer to 0 but I so much as slow down for a stop light and they tank negative fast, especially when I put it into park.
 

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budwich

Well-Known Member
OK... that is a good basis for understanding what happens with a vacuum line pull and as expected ("extra air") so the system seems to respond there in. Idle will be most impacted as the extra air will cause richness which will cause running slow a problem.
Now you need to provide exactly the same type of data for a run with everything plugged together with little to no leaks (as far as you can determine). Then you can compare data to determine what your next step might be. I am somewhat concerned about the variance of the LTFT... I would expect them to be more like the end of the second chart somewhat "flat" / stable. Were you pounding on the pedal on the front part of the second set of chart (ltft).... even opening and closing the throttle plate / pedal?
Good info
 

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