P0171, Too Lean, how to smoke test?
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DJRodriguez88
New member
borrow/buy/make a smoke tester.
I like to remove the MAF sensor just to avoid blowing smoke at it but that's probably not necessary.
There should be some different adapters so you have some choices as to an entry point for your smoke.
One is an inflatable bulb that you stick into your intake, inflate so it gets stuck, then it shoots smoke from the bulb into the system. This bulb can also be used in your tailpipe to check for exhaust leaks.
One is a rubber grommet type deal which you can stick into thicker vacuum hoses like the brake booster's hose.
If you find the general area where smoke is coming out but can't pinpoint the connection try turning off the smoke and spraying a bit of soapy water around areas that could potentially have a leak.
All that being said, you can usually find a vacuum leak by just inspecting all intake piping and vacuum hoses. If your brakes also feel a bit funny then it's probably a leak at the brake booster.
Also if you can't find a leak and you're still too lean you might want to start looking into fueling.
- the fuel filter is pretty cheap and easy to replace. If it's clogged it could be preventing proper fuel pressure.
- the fuel pressure regular and fuel pump are a bit harder to get at, so rule everything else out first.
- it's probably not the injectors because you would have a localized (cylinder specific) issue rather than a general lean condition
I like to remove the MAF sensor just to avoid blowing smoke at it but that's probably not necessary.
There should be some different adapters so you have some choices as to an entry point for your smoke.
One is an inflatable bulb that you stick into your intake, inflate so it gets stuck, then it shoots smoke from the bulb into the system. This bulb can also be used in your tailpipe to check for exhaust leaks.
One is a rubber grommet type deal which you can stick into thicker vacuum hoses like the brake booster's hose.
If you find the general area where smoke is coming out but can't pinpoint the connection try turning off the smoke and spraying a bit of soapy water around areas that could potentially have a leak.
All that being said, you can usually find a vacuum leak by just inspecting all intake piping and vacuum hoses. If your brakes also feel a bit funny then it's probably a leak at the brake booster.
Also if you can't find a leak and you're still too lean you might want to start looking into fueling.
- the fuel filter is pretty cheap and easy to replace. If it's clogged it could be preventing proper fuel pressure.
- the fuel pressure regular and fuel pump are a bit harder to get at, so rule everything else out first.
- it's probably not the injectors because you would have a localized (cylinder specific) issue rather than a general lean condition
Last edited:
jgue467
Senior Member
When i got an 0171 it turned out to be the large air tube between maf and plenum. It can be several other things just got lucky finding this one first.
The ribbed portions wouldn't leak when idling or smoke testing for some reason. But under load perhaps tiny cracks between those ribs did leak causing code to light.
Used this oem part for an '01 and no issues since then years ago. Luck all.
The ribbed portions wouldn't leak when idling or smoke testing for some reason. But under load perhaps tiny cracks between those ribs did leak causing code to light.
Used this oem part for an '01 and no issues since then years ago. Luck all.
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I replaced that after searching the forum and seeing your post. I also used carb cleaner and couldn’t find a vacuum leak anywhere, so I’m not sure a smoke tester would help? I bought the hose kit to replace some vacuum hoses anyway.
I’m going to clean the MAF again, but I also have a p0301 so it could be associated with a bad injector. It’s getting a new fuel filter Monday and I’ll run some redline through it, I won’t be able to do the injectors for a couple months probably.
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