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Hi All.
Looking at a Holden(Chev) Cruze 2011 with p0171. Fuel trims at idle are Lt 30 St 9. At higher revs, these numbers come down to an acceptable level. So thinking vacuum leak I put a smoke machine on. Found a leak near the throttle body. Fixed that and checked fuel trims again to confirm fix. Numbers were the same so ran smoke machine again. No smoke was seen anywhere but the gauge was still showing a large leak. I don't have much experience with the cruze so am wondering could I have the smoke going into the wrong port. It is the port that connects with a corrugated hose to the turbo which from my understanding is the pcv.
You mentioned the turbo, so can I figure this is the 1.4L engine? There's only two options on the US market Cruze, not sure what options you run into. :silly:
With the engine idling and no loads, what's the TPS percentage?
My first thought is a ruptured PCV diaphragm in the valve cover, underneath the stupid little engine cover. With the engine idling, check the round part of the valve cover for a small rectangular port. Cover it with your finger to confirm the vacuum leak. You can also watch the trims at the same time for improvement.
Hi Tyler.
Yes sorry 1.4L turbo engine. Have checked the pcv diaphragm and that is fine.
Throttle Position at idle is 4.26% Rpm 698 MAF 1.75g/s MAP 44Kpa. Engine Load 17%
At 3000 RPM Throttle Position is 25.3% MAF 7g/s MAP 29.6Kpa Engine Load 19% LTFT 5.1% STFT -3.5%.
One thing I have noticed is the O2S1 only fluctuates between 100mV and 660mV.
MAF signal is frequency based so the 4 Volt test @WOT is no good but I did have a good looking frequency ramp @ WOT.
Max g/s @ WOT was 100 which to me seems to be in the ballpark.
Redid smoke test using the brake booster port on the manifold with the same result of no visible smoke but still plenty of flow/no pressurisation.
The other thing I noticed is that there is no misfire at idle.
Hope this helps.
Did you have anything sealing the intake at the air filter box when smoke testing? If not, that may explain why you're not building any kind of pressure. If your smoke machine didn't come with the right size of plug, you can always do what I do and put a plastic bag over the air filter box connection. Reinstall the intake tube and snug the clamp. Bam! Instant seal.
If you still don't find any leaks, try disconnecting the purge valve and recheck trims. These valves are known for flowing incorrectly when commanded open, and GM's definitely like to run the purge at idle. The command is fairly low, but if the purge valve is opening more than it should, then that'd amount to a vacuum leak.
Whilst smoke testing I used the plastic caps that came with the kit. Not a perfect seal so also sealed intake with rubber glove. Have reset fuel trims but they slowly build back up. Will try the purge valve. Have also smoked the brake booster so all good there. Won't see the car for a few days will keep updated. Thanks
Tyler You called it mate. Purge valve. Disconnect the purge valve and trims start to fall away to a more acceptable level. Not perfect mind you but to a level that won't set a dtc or damage the car. Looking at all the data and there is no way I could have picked it but a push in the right direction and a simple unplug it test and Bob's ya aunty.
Cheers mate.
vb4me wrote: Tyler You called it mate. Purge valve. Disconnect the purge valve and trims start to fall away to a more acceptable level. Not perfect mind you but to a level that won't set a dtc or damage the car.
Nice! GM just can't seem to get purge valves right. If you end up replacing it, let us know where you end up with trims?
Looking at all the data and there is no way I could have picked it but a push in the right direction and a simple unplug it test and Bob's ya aunty.
Cheers mate.
vb4me wrote: Tyler You called it mate. Purge valve. Disconnect the purge valve and trims start to fall away to a more acceptable level. Not perfect mind you but to a level that won't set a dtc or damage the car.
Nice! GM just can't seem to get purge valves right. If you end up replacing it, let us know where you end up with trims?
If I see the car again I will do. I generally only diagnose but occasionally I will do simple repairs
Looking at all the data and there is no way I could have picked it but a push in the right direction and a simple unplug it test and Bob's ya aunty.
Cheers mate.
:lol: :lol: :lol: Haven't heard that one before!
Bit of an Australianism I suppose. Old Pommy saying twisted a bit Lol
vb4me wrote: Update for you Tyler. Purge valve replaced and fuel trims absolutely spot on. Purge valve was actually stuck partially open.
Fantastic to hear, thanks for the update!
I'm still not sure why this didn't set a P0496. I was very close to not mentioning the purge valve at all, because the P0496 detection strategy is usually excellent at catching stuck valves. Now I know better. :silly:
Hi vb4me,
Just wondering if you are based in Melbourne. I own a 2011 Holden Cruze SRi-V with P0171 issue on and off every few hundred kilometres.
Cheers
Reinstall the intake tube and snug the clamp. Bam! Instant seal.
I was very close to not mentioning the purge valve at all, because the P0496 detection strategy is usually excellent at catching stuck valves. Now I know better. :silly: