LS1 keeps throwing P0171 & P0174

[Reaper]

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 VZ 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 while back 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 crap. Inspecting the break shows a crack that had been there quite some time and it finally let go at around 190,000km. 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
7. Installed new 02 sensors - better but still throwing codes although more infrequently now.
8. Plugged in a Vac gauge which seems to read normal to me (see toob: https://www.youtube.com/watch?v=EkQq...ature=youtu.be). Not in the vid I ran the car up to 3000 and held it there. Vac went up and stayed at around 23(?) steady.


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 tube that runs from the rocker cover vent to intake makes no difference to the idle quality. I have inspected the hose and as far as I can tell it's fine.

A lot of people have suggested a vac leak but I'm near convinced that is not the answer because:

1. Visual inspection of all lines (there are not many on this motor) shows all to be fine and in great condition
2. Vac gauge reads normal. If there was a leak of any consequence I'd suggest it would jump around or read low.

Aaaaaaaaaaaanyway.... I'm out of ideas so help is appreciated.

 

[Deuce]

Have you run a compression test on all cylinders?

could a completely unrelated issue of a dribbling injector be messing with your sh!t?

 

[Reaper]

Have you run a compression test on all cylinders?

could a completely unrelated issue of a dribbling injector be messing with your sh!t?

Yeah I did a leak down test after I did the valve spring - all ok. I'd have thought worn ring's or something would manifest itself in lower manifold vac and if the valve was damaged things would go all over the place. A dud injector is a possibility but...

Both banks throw lean at the same time. If it were an injector, or even a few I'd think it'd throw one bank and/or the other but at different times even if they were only a few seconds apart.

 

[SS-REX]

Is there a way of telling your MAF sensor is working properly?

Here's a thread i found sounds similar but i think he had a vac leak?.

http://forums.justcommodores.com.au/lsx-development-modification/112732-car-running-lean.html

 

[Reaper]

Yes I have cleaned the maf with electrical contact cleaner. Beyond that I have nfi how to check if it's measuring correctly or not

 

[SS-REX]

Yes I have cleaned the maf with electrical contact cleaner. Beyond that I have nfi how to check if it's measuring correctly or not

I don't know if this will give you a detailed result but it gives general idea if your is working. DTC P0101 - How to Service LS1 MAF - My Pro Street

 

[ari666]

step one: grab a 6 pack of stella's (the imported ones, with the little "brewed in the UK" sticker on them, not that aussie brewed ****)
step two: bring it to my shop
step three: we plug in HpT scantool and check all the sensor functions
step four: drink some beers
step five: fix whatever issue it has
step six: avoid booze busses on the way home.

 

[HamaTime™]

step one: grab a 6 pack of stella's (the imported ones, with the little "brewed in the UK" sticker on them, not that aussie brewed ****)
step two: bring it to my shop
step three: we plug in HpT scantool and check all the sensor functions
step four: drink some beers
step five: fix whatever issue it has
step six: avoid booze busses on the way home.

 

[Deuce]

A dud injector is a possibility but...

Both banks throw lean at the same time. If it were an injector, or even a few I'd think it'd throw one bank and/or the other but at different times even if they were only a few seconds apart.

Ahh, so a fuel issue could be the cause. Therefore a fuel pump or fuel filter could affect both banks at the same time?

The fact that the code is for lean exhaust not rich exhaust, I would say fuel starved rather than air starved or air rich is the cause.


Unless you forgot that you bolted forced induction on??

 

[Reaper]

Ahh, so a fuel issue could be the cause. Therefore a fuel pump or fuel filter could affect both banks at the same time?

The fact that the code is for lean exhaust not rich exhaust, I would say fuel starved rather than air starved or air rich is the cause.


Unless you forgot that you bolted forced induction on??

Yes - for sure. Both are new however (genuine items)