Curing Low Rev Stumble By Replacing Crank/Cam Sensors?

[RallyMachine]

Has anyone replaced these sensors (with no active/current CELs) in an attempt to fix the 2250-2500rpm stutter?

 

I was just talking to a coworker who drives a bone stock LGT wagon who has a similar low rev stutter and he mentioned these sensors as a possible suggestion...

 

Also does anyone see anything wrong with aftermarket replacements? They are far cheaper than OEM but these seem to be pretty critical components to engine function lol.

[covertrussian]

I have a strict no aftermarket sensor rule* when it comes to any engine components. They simply don't last, build quality on them is usually sub par.

*Only exclusion is O2 sensors, but even those I will only buy Bosch or Denso.

 

Can you describe the stutter a bit better, when does it actually happen; from dead stop, or while rolling, partial throttle or full throttle? Have you checked for vacuum leaks & turbo inlet holes?

[RallyMachine]

Yeah makes sense to me... I'm running a denso aftermarket o2 but that's it and from what I understand denso is the OEM anyway.

 

The stumble is always in vaccuum and happens randomly under light to moderate throttle in low gear when climbing past ~2250rpm. It's very minor but almost feels like a mini-misfire. Just general not smooth. But again it doesn't do it every time or almost never in higher load/gear situations.

 

I have watched my wideband and when it happens it maybe rises a couple points to 15.0 but nothing that would make me think that it is a fueling issue/misfire. I'm not sure if it's a tune issue or a hardware issue... Definitely no vacuum leaks as I just tested everything a month ago or so.

[Max Capacity]

russian, didn'tyou zero out some of the timing tables ? didn't that fix this issue ?

 

I know my Tuner has tuned it out of my cars.

 

FWIW, my aftermarket front O2 lasted 2 years. The rear aftermarket is still going strong 4 years later.

[covertrussian]

I'm running the Denso O2 sensor myself, but like you said it is the OEM part.

 

What tune are you running on your car? What you might be hitting is the closed loop to open loop portions of the map (which btw did you disable closed loop to open loop delay?)

 

russian, didn'tyou zero out some of the timing tables ? didn't that fix this issue ?

 

I know my Tuner has tuned it out of my cars.

 

FWIW, my aftermarket front O2 lasted 2 years. The rear aftermarket is still going strong 4 years later.

 

Yes sir, right here, it could be that but that wouldn't cause the mixture to lean out.

[firehawk618]

There's a LONG thread about this exact issue, I will link it shortly.

 

 

EDIT:

 

http://legacygt.com/forums/showthread.php/stumble-cruise-only-218669.html?t=218669

[RallyMachine]

Hmmm sounds like his is more at highway cruise...mine is low gear, low revs.

 

Mine is very intermittent... I almost always feel it at least once on my commute, but it doesn't happen every time I pass that rev range. Definitely seems like it is at light loads only too. Also my CL/OL delay is set by revs and throttle position. So 1st gear changes to OL at 5000revs OR 90% throttle, 2nd gear 4500rpm or 80% throttle etc etc for example. So I am in CL the entire time this happens...

[covertrussian]

What rpm and gr/s are you in when it happens?

 

When was the last time you cleaned the maf btw?

[chato]

I get it around 2200rpm at under 1/4 throttle.

[RallyMachine]

^^what he said. Not sure about g/s

 

Probably a couple months since cleaning the maf.

[firehawk618]

I get it around 2200rpm at under 1/4 throttle.

 

 

 

Same here.

[covertrussian]

What tunes are you guys running on? I was trying to replicate it and even on stock drive by wire map I still didn't see it.

 

Actually thinking about it, there is a good chance you guys might be hitting the AVCS emissions hole.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/05LGTStockAVCS.png~original

 

The ECU should interpolate, but it might not be doing it efficiently due to instant drops on stock AVCS map. In theory at 2200 you should be at 7* avcs advance, but it could be going from 15 to 0* which is a huge jump. If your still running the stock one, try running this map and see if it helps (it will help with MPG's too, gained me about 1.5mpg).

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS10.png~original

[robinlsb]

Clean the MAF???

[firehawk618]

Clean the MAF???

 

My maf is brand new.

[FknBoss]

That makes sense russian. Why would they have put that dead spot there?

[firehawk618]

What tunes are you guys running on? I was trying to replicate it and even on stock drive by wire map I still didn't see it.

 

Actually thinking about it, there is a good chance you guys might be hitting the AVCS emissions hole.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/05LGTStockAVCS.png~original

 

The ECU should interpolate, but it might not be doing it efficiently due to instant drops on stock AVCS map. In theory at 2200 you should be at 7* avcs advance, but it could be going from 15 to 0* which is a huge jump. If your still running the stock one, try running this map and see if it helps (it will help with MPG's too, gained me about 1.5mpg).

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS10.png~original

 

 

Wow that table *stock* is all over the place.

 

Thanks for sharing this potential solution

[RallyMachine]

I just checked mine and it looked my tuner removed that dead spot in my tables, so that's not the issue with me

[covertrussian]

That makes sense russian. Why would they have put that dead spot there?

 

The common thought is it's there to reduce emissions. I personally think it's there to reduce gas mileage so the car does similar to other AWD turbo cars

 

I also run 15*, here is an example map for a stock car with catless up pipe. This usually will get me 28+ mpg.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS15v11.png

 

I just checked mine and it looked my tuner removed that dead spot in my tables, so that's not the issue with me

 

Are the degrees fairly consistent or does it jump around? Look at your timing map too, make sure it's fairly smooth with no big timing drops.

[RallyMachine]

Yes AVCS table is smooth... How much is too big of difference in timing? Mine change with g/s but are basically the same through the rev range if load is constant (definitely more resolution in the higher load cells though).

[covertrussian]

I usually try to avoid timing cliffs so to say, I try to not do more then 6* between cells when possible (on my Nissan's). I haven't really touched the Legacy timing map, but looking at the stock table I do see a bunch of big timing changes .

 

If you guys could log your g/rev and tell me exact rpm and g/rev range where it happens we should be able to better pin point it.

[firehawk618]

I also looked at my tables, my tuner also smoothed it all out.

[FknBoss]

The common thought is it's there to reduce emissions. I personally think it's there to reduce gas mileage so the car does similar to other AWD turbo cars

 

I also run 15*, here is an example map for a stock car with catless up pipe. This usually will get me 28+ mpg.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS15v11.png

 

 

 

Are the degrees fairly consistent or does it jump around? Look at your timing map too, make sure it's fairly smooth with no big timing drops.

 

28mpg holy fawk. Send me that map and tell me how to upload it lol.

[Max Capacity]

I also can get close to that if I keep it out of boost and drive 68-70mph on CC.

 

My Spec B has gotten better mpg at certain times. Again it depends how you drive.

 

Granted this is just highway miles.

[covertrussian]

28mpg holy fawk. Send me that map and tell me how to upload it lol.

 

It's fairly simple, all you really need is just update your AVCS map to be similar to above. You can also find some base tunes that I linked in my build thread.

 

I also can get close to that if I keep it out of boost and drive 68-70mph on CC.

 

My Spec B has gotten better mpg at certain times. Again it depends how you drive.

 

Granted this is just highway miles.

 

Yup this is with me going 70mph, but constantly playing with cruise control (my car refuses to stay at 70mph, it's 69 or 71 so I play with it until it reaches 70 every time I have to get off cruise for slowing down). In the colder weather I couldn't get above 25mpg with stock AVCS map.

 

 

 

 

Anyway back to the stumble, if AVCS map is smooth, timing map is smooth, I would start looking at it as a mechanical issue.

[RallyMachine]

Just wanted to share something that might be relevant to this thread.

 

Replaced my MAF sensor today and while I was in there I pulled out my crank position sensor for shits and grins based on this thread:

http://forums.nasioc.com/forums/showthread.php?t=2127497

 

Low and behold this is what mine looked like. I just wiped it off and have yet to drive it but I was surprised at how much dirt that had accumulated after 104k miles. Just a public service announcement... I'll follow up if there is any improvement or not.

 

http://i266.photobucket.com/albums/ii273/themadtestpilot23/Mobile%20Uploads/image_zpsdedb6150.jpg