LS1 - P0171 and P0174 both banks running lean
11-17-2014, 03:30 AM
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LS1 - P0171 and P0174 both banks running lean Hi all,
This is a bit of a saga but I'm fresh out of ideas so I hope you can help!
I have a late model LS1 fitted into an Australian GM car called a Holden Adventra (AWD station wagon) which till now has been great. The motor is 100% OEM stock and as far as I can tell has been looked after for all of it's life. My problems started a few weeks back and I'll try to summarize as follows:
Just sitting idling at the lights it broke a spring on one of the exhaust valves and of course it started running like a complete bag of crud. Inspecting the break shows a crack that had been there quite some time and it finally let go at around 140,000 miles. The motor has never been thrashed and serviced religiously - everything under the rocker covers was clean as a whistle. I replaced all of the valve springs and the car runs great (quieter and better than it ever has before) save 2 problems:
1. Cold start misfire for the first 10 min or so
2. Throwing P0171 and P0174 codes (always as a pair) during idle (eg sitting at traffic lights) or 0 throttle situations (braking usually at low speed - doesn't seem to happen ever above 30mph). This will happen even at normal operating temperatures. After the car is up to normal operating temp the idle will be perfect.
Things I have tried:
1. Cleaning the maf (no difference)
2. Replaced a broken exhaust manifold bolt (no exhaust leak but I dropped a spanner on it and broke the head off - another crack that had been there for quite some time)
3. Removed and replaced both my rocker covers checking the silicone 'o' ring for damage etc
4. Checked all vac pipes I can think of for cracks and splits etc (everything is in great condition on this car)
5. Sprayed aerostart (pressurised fuel in a can - great stuff) pretty much over the top of the motor (zero leaks found).
6. Performed a PCM idle reset procedure (Idle improved somewhat when cold - still throws codes as described above
One interesting observation I noted was when I sprayed aerostart down the intake duct (down steam of the maf) it made zero difference to how the car runs. I would have expected the idle to increase. NFI what to make of that
I also noticed that unplugging the PCV hose off the intake makes no difference to the idle quality. I have inspected the hose and as far as I can tell it's fine.
I have considered that I may have stuffed both the o2's when the valve spring broke but I'm unconvinced. It could explain the codes when hot but does not explain the idle problem when cold.
This is a bit of a saga but I'm fresh out of ideas so I hope you can help!
I have a late model LS1 fitted into an Australian GM car called a Holden Adventra (AWD station wagon) which till now has been great. The motor is 100% OEM stock and as far as I can tell has been looked after for all of it's life. My problems started a few weeks back and I'll try to summarize as follows:
Just sitting idling at the lights it broke a spring on one of the exhaust valves and of course it started running like a complete bag of crud. Inspecting the break shows a crack that had been there quite some time and it finally let go at around 140,000 miles. The motor has never been thrashed and serviced religiously - everything under the rocker covers was clean as a whistle. I replaced all of the valve springs and the car runs great (quieter and better than it ever has before) save 2 problems:
1. Cold start misfire for the first 10 min or so
2. Throwing P0171 and P0174 codes (always as a pair) during idle (eg sitting at traffic lights) or 0 throttle situations (braking usually at low speed - doesn't seem to happen ever above 30mph). This will happen even at normal operating temperatures. After the car is up to normal operating temp the idle will be perfect.
Things I have tried:
1. Cleaning the maf (no difference)
2. Replaced a broken exhaust manifold bolt (no exhaust leak but I dropped a spanner on it and broke the head off - another crack that had been there for quite some time)
3. Removed and replaced both my rocker covers checking the silicone 'o' ring for damage etc
4. Checked all vac pipes I can think of for cracks and splits etc (everything is in great condition on this car)
5. Sprayed aerostart (pressurised fuel in a can - great stuff) pretty much over the top of the motor (zero leaks found).
6. Performed a PCM idle reset procedure (Idle improved somewhat when cold - still throws codes as described above
One interesting observation I noted was when I sprayed aerostart down the intake duct (down steam of the maf) it made zero difference to how the car runs. I would have expected the idle to increase. NFI what to make of that
I also noticed that unplugging the PCV hose off the intake makes no difference to the idle quality. I have inspected the hose and as far as I can tell it's fine.
I have considered that I may have stuffed both the o2's when the valve spring broke but I'm unconvinced. It could explain the codes when hot but does not explain the idle problem when cold.
Last edited by RedHotMike; 11-17-2014 at 03:48 AM.
11-17-2014, 10:49 AM
#2
Are you certain the valve wasn't hurt when the spring broke? Also the PCV not affecting idle any...strange. Is there vacuum there? Maybe the inlet/vent didn't go back on in the same place when you pulled the valve covers? Where does that run to? May I assume you do not have IAC and have electronic throttle? At 140K I'd be planning to replace my O2 sensors soon anyway but not saying that's definitely the problem.
11-17-2014, 03:32 PM
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Thanks for the reply. In short no, I'm not certain the valve wasn't damaged when the spring broke however if it were slightly bent or whatever I'd have thought I'd only get a lean code on 1 bank and the misfire would at the very least stay around no-matter what the engine temp.
The PCV runs from the rocker cover to a port in the intake duct roughly 1/3 of the way upstream of the TB. You are correct that it is an electronic throttle on that motor
The PCV runs from the rocker cover to a port in the intake duct roughly 1/3 of the way upstream of the TB. You are correct that it is an electronic throttle on that motor
11-17-2014, 06:52 PM
#4
The part you are talking about is the vent(fresh intake air back into motor) I think. How is the other part(PCV/blow-by being sucked out of motor) run? Which of these were you referring to when you said you "took it off and idle didn't change?" Are you sure that is all sealed up? Do you have vacuum in both sides of the PCV system at idle?
Usually a lean condition is caused by the PCV system not properly pulling the fresh air from a metered(like between the MAF and the throttle body as you indicated) source. Acts like a vacuum leak because more air is getting into the motor than the MAF knows about and it doesn't tell the computer to throw more fuel in to compensate for said extra air. This is why I'm being very particular about the PCV and your indication that pulling the hose had no effect.
My questioning of the valve is not pointed at a specific symptom..but a funky valve can cause all sorts of fun. I am thinking that something got nudged or put back wrong during reassembly and the lean condition is likely unrelated to the spring issue. It's the simplest explanation and something I've done myself north of a million times.
Usually a lean condition is caused by the PCV system not properly pulling the fresh air from a metered(like between the MAF and the throttle body as you indicated) source. Acts like a vacuum leak because more air is getting into the motor than the MAF knows about and it doesn't tell the computer to throw more fuel in to compensate for said extra air. This is why I'm being very particular about the PCV and your indication that pulling the hose had no effect.
My questioning of the valve is not pointed at a specific symptom..but a funky valve can cause all sorts of fun. I am thinking that something got nudged or put back wrong during reassembly and the lean condition is likely unrelated to the spring issue. It's the simplest explanation and something I've done myself north of a million times.
11-17-2014, 09:04 PM
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The part you are talking about is the vent(fresh intake air back into motor) I think. How is the other part(PCV/blow-by being sucked out of motor) run? Which of these were you referring to when you said you "took it off and idle didn't change?" Are you sure that is all sealed up? Do you have vacuum in both sides of the PCV system at idle?
Usually a lean condition is caused by the PCV system not properly pulling the fresh air from a metered(like between the MAF and the throttle body as you indicated) source. Acts like a vacuum leak because more air is getting into the motor than the MAF knows about and it doesn't tell the computer to throw more fuel in to compensate for said extra air. This is why I'm being very particular about the PCV and your indication that pulling the hose had no effect.
My questioning of the valve is not pointed at a specific symptom..but a funky valve can cause all sorts of fun. I am thinking that something got nudged or put back wrong during reassembly and the lean condition is likely unrelated to the spring issue. It's the simplest explanation and something I've done myself north of a million times.
Usually a lean condition is caused by the PCV system not properly pulling the fresh air from a metered(like between the MAF and the throttle body as you indicated) source. Acts like a vacuum leak because more air is getting into the motor than the MAF knows about and it doesn't tell the computer to throw more fuel in to compensate for said extra air. This is why I'm being very particular about the PCV and your indication that pulling the hose had no effect.
My questioning of the valve is not pointed at a specific symptom..but a funky valve can cause all sorts of fun. I am thinking that something got nudged or put back wrong during reassembly and the lean condition is likely unrelated to the spring issue. It's the simplest explanation and something I've done myself north of a million times.
Just for interest, here is the offending valve spring when I removed the rocker cover. The motor is as clean as a whistle - no burnt carbon build up what so ever - approx 140,000 miles
Last edited by RedHotMike; 11-17-2014 at 09:54 PM.
11-17-2014, 11:03 PM
#6
I see that would be pretty hard to screw up. Where is the other part(PCV valve out to intake) of the PCV system? Valley cover or other valve cover? When you remove that connection in the pic, do you have any vacuum? What about the other side? In theory the intake(I mean the intake behind the TB, not the intake pipe between TB and MAF) should provide vacuum to create crankcase ventilation and the connection you are talking about in the pic vents fresh air back into the motor keeping it "clean."
11-18-2014, 12:32 AM
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There is suction from the pipe that leads to the rocker cover (thumb over the hose method) but no suction from the intake duct side. I thought the PCV was inbetween a metal plate attached to the under side of the rocker cover and the cast rocker cover itself (has the tube coming out of it which the hose slips over)
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11-19-2014, 12:10 AM
#8
PCV is positive crankcase ventilation..if we're sucking junk out of the motor, fresh air has to go back in somewhere. That somewhere is the pipe in the picture attached to the intake tube. There is the other side of things where said suction actually originates...usually the other side valve cover to intake -manifold- or valley cover to same(not visible in the pic you posted--the entirety of that bit in the pic is the fresh air side). If you have vacuum at the fresh air vent as you said though, the manifold to PCV side is likely working. Sorry if we're missing each other somewhere here..PCV is real simple once you get it but for some reason some folks(including me) are confused about it until the "aha" moment. So if this is all obvious to you, and you think that both the suction and fresh air sides of the PCV system are connected and working properly, we can move on.
Have you checked your fuel pressure? Fuel filter? What happens if you unplug the MAF altogether? Any difference? Strange that additional (artificially added)fuel behind the MAF had no effect as well. That tells me that maybe your vacuum leak test might not be accurate since you were looking for a change in idle characteristics right?
Have you checked your fuel pressure? Fuel filter? What happens if you unplug the MAF altogether? Any difference? Strange that additional (artificially added)fuel behind the MAF had no effect as well. That tells me that maybe your vacuum leak test might not be accurate since you were looking for a change in idle characteristics right?
11-19-2014, 12:46 AM
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PCV is positive crankcase ventilation..if we're sucking junk out of the motor, fresh air has to go back in somewhere. That somewhere is the pipe in the picture attached to the intake tube. There is the other side of things where said suction actually originates...usually the other side valve cover to intake -manifold- or valley cover to same(not visible in the pic you posted--the entirety of that bit in the pic is the fresh air side). If you have vacuum at the fresh air vent as you said though, the manifold to PCV side is likely working. Sorry if we're missing each other somewhere here..PCV is real simple once you get it but for some reason some folks(including me) are confused about it until the "aha" moment. So if this is all obvious to you, and you think that both the suction and fresh air sides of the PCV system are connected and working properly, we can move on.
Have you checked your fuel pressure? Fuel filter? What happens if you unplug the MAF altogether? Any difference? Strange that additional (artificially added)fuel behind the MAF had no effect as well. That tells me that maybe your vacuum leak test might not be accurate since you were looking for a change in idle characteristics right?
Have you checked your fuel pressure? Fuel filter? What happens if you unplug the MAF altogether? Any difference? Strange that additional (artificially added)fuel behind the MAF had no effect as well. That tells me that maybe your vacuum leak test might not be accurate since you were looking for a change in idle characteristics right?
11-19-2014, 04:29 AM
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do you have access to a scan tool? If you can look at fuel trims and o2 readings it will help tremendously.
You could need intake gaskets or have a cracked manifold, when everything heats up and expands the leak may seal up. It is something big if its affecting both banks. Check the obvious, any vacuum hoses, keep figuring out your PCV system, throttle body and intake gaskets and inspect the intake manifold closely. Clean your throttle body real well while your at it, oily carbon residue buildup on DBW throttle bodies can cause driveability issues.
You could need intake gaskets or have a cracked manifold, when everything heats up and expands the leak may seal up. It is something big if its affecting both banks. Check the obvious, any vacuum hoses, keep figuring out your PCV system, throttle body and intake gaskets and inspect the intake manifold closely. Clean your throttle body real well while your at it, oily carbon residue buildup on DBW throttle bodies can cause driveability issues.
11-19-2014, 05:02 AM
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do you have access to a scan tool? If you can look at fuel trims and o2 readings it will help tremendously.
You could need intake gaskets or have a cracked manifold, when everything heats up and expands the leak may seal up. It is something big if its affecting both banks. Check the obvious, any vacuum hoses, keep figuring out your PCV system, throttle body and intake gaskets and inspect the intake manifold closely. Clean your throttle body real well while your at it, oily carbon residue buildup on DBW throttle bodies can cause driveability issues.
You could need intake gaskets or have a cracked manifold, when everything heats up and expands the leak may seal up. It is something big if its affecting both banks. Check the obvious, any vacuum hoses, keep figuring out your PCV system, throttle body and intake gaskets and inspect the intake manifold closely. Clean your throttle body real well while your at it, oily carbon residue buildup on DBW throttle bodies can cause driveability issues.
I get that stuff will may seal as it heats up but that doesn't explain the P0171/P0174 when it's hot. Aaaaaanyway - I have a pair of o2's on order so at the very least I'll be able to eliminate that as a source of error (I hope).
11-19-2014, 08:19 AM
#12
Curious - what is the ambient temp during these "cold" starts? Since you're driving an Australian vehicle I'll take a wild guess and say pretty warm? I know even 100 degrees is cold for a motor...just might give us some more info to chew on.
Wonder if you might have a sticky lifter on cold starts? Maybe an oiling system flush might help. I know you said it's clean in there but this is something that can happen to well-maintained LS motors for not much reason it seems. I would think there might be a little noise with it but sometimes hard to detect at low RPMs with a misfire. Throwing stuff at the wall here.
+1 for cleaning the throttle body. LS motors put so much gunk through the PCV system without a catch can you usually end up with a half quart of oil and carbon/etc. in the intake even on a great motor.
I know you said you did an idle reset. Have you just pulled the battery cable and let the thing go dead for an hour or so? Maybe worth trying.
Wonder if you might have a sticky lifter on cold starts? Maybe an oiling system flush might help. I know you said it's clean in there but this is something that can happen to well-maintained LS motors for not much reason it seems. I would think there might be a little noise with it but sometimes hard to detect at low RPMs with a misfire. Throwing stuff at the wall here.
+1 for cleaning the throttle body. LS motors put so much gunk through the PCV system without a catch can you usually end up with a half quart of oil and carbon/etc. in the intake even on a great motor.
I know you said you did an idle reset. Have you just pulled the battery cable and let the thing go dead for an hour or so? Maybe worth trying.
11-19-2014, 05:06 PM
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Curious - what is the ambient temp during these "cold" starts? Since you're driving an Australian vehicle I'll take a wild guess and say pretty warm? I know even 100 degrees is cold for a motor...just might give us some more info to chew on.
Wonder if you might have a sticky lifter on cold starts? Maybe an oiling system flush might help. I know you said it's clean in there but this is something that can happen to well-maintained LS motors for not much reason it seems. I would think there might be a little noise with it but sometimes hard to detect at low RPMs with a misfire. Throwing stuff at the wall here.
Wonder if you might have a sticky lifter on cold starts? Maybe an oiling system flush might help. I know you said it's clean in there but this is something that can happen to well-maintained LS motors for not much reason it seems. I would think there might be a little noise with it but sometimes hard to detect at low RPMs with a misfire. Throwing stuff at the wall here.
+1 for cleaning the throttle body. LS motors put so much gunk through the PCV system without a catch can you usually end up with a half quart of oil and carbon/etc. in the intake even on a great motor.
I know you said you did an idle reset. Have you just pulled the battery cable and let the thing go dead for an hour or so? Maybe worth trying.
11-24-2014, 12:39 PM
#16
code P0171, P0174 I'm having the same problem. I have a 2003 LM4 (5.3) transplanted into a '39 Chevy. After driving a bit it will throw the same codes but doesn't effect the drivability. I also replaced the O2 sensors but did not help and retorqued the intake. Can't seem to find any vacuum leaks. I do have an oil leak that I can't find. Slight drip coming from the right side off the transmission oil pan. I'm assuming it's being blown back there but can't find where it's coming from. Reason I mentioned this is wondering if the two are connected in some way (PCV system). Lets keep looking for a solution.
11-24-2014, 03:27 PM
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I'm having the same problem. I have a 2003 LM4 (5.3) transplanted into a '39 Chevy. After driving a bit it will throw the same codes but doesn't effect the drivability. I also replaced the O2 sensors but did not help and retorqued the intake. Can't seem to find any vacuum leaks. I do have an oil leak that I can't find. Slight drip coming from the right side off the transmission oil pan. I'm assuming it's being blown back there but can't find where it's coming from. Reason I mentioned this is wondering if the two are connected in some way (PCV system). Lets keep looking for a solution.
11-25-2014, 04:01 AM
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How old is the MAF? cleaning doesn't always work. Im not one to just start replacing parts but without a scan tool to view the data we cant tell exactly whats going on. It will really nail this down. You will be able to tell what the MAF is reading so you know how much air the motor thinks its getting pre-throttle body. You can see the MAP sensor and see if you do actually have a vacuum leak and you can look at the fuel trims to see if they are compensating for a lean condition. Even some of the cheap parts store code readers will give you this data.
While it may seem far fetched you have to ignore your problem with the valve springs, diagnose as if somebody brought you the car to work on. Start from scratch. Still check the basics, regardless of weather or not you THINK something is ok. I have seen lots of bad parts straight out of the box.
While it may seem far fetched you have to ignore your problem with the valve springs, diagnose as if somebody brought you the car to work on. Start from scratch. Still check the basics, regardless of weather or not you THINK something is ok. I have seen lots of bad parts straight out of the box.
11-27-2014, 08:53 AM
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Are you certain the valve wasn't hurt when the spring broke? Also the PCV not affecting idle any...strange. Is there vacuum there? Maybe the inlet/vent didn't go back on in the same place when you pulled the valve covers? Where does that run to? May I assume you do not have IAC and have electronic throttle? At 140K I'd be planning to replace my O2 sensors soon anyway but not saying that's definitely the problem.