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Cams unable to advance - how much power am I leaving on the table?


stocklgt
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Just recently rebuilt my motor, pertinent info below:

 

IAG Stage 2 tuff block

STI cast intake manifold

B25 heads

Kelford 264/260

BCP X500+

AMR FMIC

 

all new timing components, oiling components, avcs etc.

 

Broke the motor and cams in for 1200 miles, then car was tuned on 93; results were less than stellar. I don't remember exact numbers, but somewhere around 330 tqe 370hp. Granted heartbreaker dyno, but I had my heard set on 400+. The tuner stated that he could not get the cams to advance. I double checked with the builder who confirmed the correct AVCS cams were installed.

 

New AVCS solenoids were installed, so I don't think that is the culprit. What else could be causing the issue? Cam holes plugged?

 

Tuner says that right now it is not dangerous for the motor, but we should look to get it fixed in the near future. At the very least it is going to involve pulling the timing covers, but I'm not trying to make this a super expensive job to gain 5-10HP.

 

The main questions are:

1) How much power am I leaving on the table?

2) How dangerous is this to the longevity of the motor

3) What steps can I take to avoid a potentially costly repair bill

 

I want to get this fixed before I decide to get retuned on E85.

 

Thanks in advance for the help. Not sure if this is a tuning issue or otherwise, but decided since ultimately i'll be revising the tune, this is where it belongs.

Edited by stocklgt
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Possibly a mangled sprocket? https://legacygt.com/forums/showthread.php/help-request-avcs-related-problem-131462.html

 

 

It shouldn't be dangerous to the motor at all, assuming it's tuned correctly. I should mention, this sounds like either a mechanical problem (i.e. AVCS sprockets are actually seized and not moving, or similar), or an electromechanical problem (AVCS sensors or solenoids not sending/receiving the correct signals). I doubt this is a tune problem.

Edited by solidxsnake
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Possibly a mangled sprocket? https://legacygt.com/forums/showthread.php/help-request-avcs-related-problem-131462.html

 

 

It shouldn't be dangerous to the motor at all, assuming it's tuned correctly. I should mention, this sounds like either a mechanical problem (i.e. AVCS sprockets are actually seized and not moving, or similar), or an electromechanical problem (AVCS sensors or solenoids not sending/receiving the correct signals). I doubt this is a tune problem.

 

Thanks for the link to that thread, I thought about the sprocket issue but my tuner believes its related to the cams being plugged up. The AVCS sensors and Solenoids are brand new, and were tested and the electromechanical problem was ruled out (according to the shop).

 

As long as it will not damage the engine (the tune is pretty solid and is on the safe side at 19PSi) I am wondering if its even worth looking into. Tuner says I am leaving quite a bit on the table, but I'm wondering if they are trying to squeeze some more $$ out of me. I trust them, but every shop needs to stay above water, and since the E85 part of the tune was already paid for, they won't get any $$ from me just for a retune.

 

How much power do you really think i'm losing, or is it more effecting the RPM that boost kicks in? I believe I'm at full boost by around 3800.

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Thanks for the link to that thread, I thought about the sprocket issue but my tuner believes its related to the cams being plugged up. The AVCS sensors and Solenoids are brand new, and were tested and the electromechanical problem was ruled out (according to the shop).

 

That doesn't make any sense. The actuation mechanism is in the sprocket; the camshaft is completely solid. If the sprocket isn't stuck, sensors and solenoids are good, then it could be an OCV issue. Edit: On further reading... I think what I'm calling the OCV you're calling solenoids.

 

As for how much power you're leaving... not sure. You're likely sacrificing a little low-end torque and fuel economy, but I'm not sure a zero-advance intake ACVS angle will actually sacrifice much peak power. I don't know enough to say for sure, though.

Edited by solidxsnake
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Yeah OCV, solenoids are same thing different terminology. I'm really thinking i'll just leave it alone at this point, no sense in trying to figure it out for minimal if any gains. Forgot to mention, no codes popping up, so thats why I am thinking the OCVs are fully functional. I heard from some friends that oil viscosity could play a part in the OCV operation, but I really don't think that's the case, is it? I was more concerned it would damage the motor, but if the motor is safe and I want more power E85 is the ticket. I have meth installed but decided against using it for now because I do not have enough fail-safes in place.

 

Cobb really needs to hurry up with the flex fuel solution for these cars. I don't trust hijacking the IAT sensor with the DT kit.

 

Thanks for the advice.

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The only potential risk to the motor I could see is the AVCS suddenly working (or advancing erratically) and causing detonation due to differences in induction. It's definitely something I'd get fixed, or at least figure out. If you're sure your AVCS is completely stuck at 0deg, then I wouldn't expect the car to have any issues. I'd probably zero out the AVCS tables in the tune as well if you're going to leave it alone.

 

 

Is it both sides that aren't advancing? Or only left/right? If it is indeed both, perhaps there's an electrical issue?

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The only potential risk to the motor I could see is the AVCS suddenly working (or advancing erratically) and causing detonation due to differences in induction. It's definitely something I'd get fixed, or at least figure out. If you're sure your AVCS is completely stuck at 0deg, then I wouldn't expect the car to have any issues. I'd probably zero out the AVCS tables in the tune as well if you're going to leave it alone.

 

 

Is it both sides that aren't advancing? Or only left/right? If it is indeed both, perhaps there's an electrical issue?

 

Thats a question I have to ask Dave Brown. I really don't know, but sounds to me like your thought about an electrical issue is correct if both left and right are not advancing.

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You want to get a log of avcs vvt angles and the voltages too.

Mainly to see at what angle they’re locked, and secondly to see what happens during the avcs calibration process. The latter happens iirc on the second key-on after an ecu reset.

 

Graphing the angles and voltages will give some indication of the issue, eg which side/s are affected and, if so, how they’re affected. Obviously log other parameters to provide context ;)

 

Usually, if the fault is severe, both sides will become inactive.

That is, the ecu will give up avcs altogether.*

 

Before that happens, you should see the ecu trying to compensate for the issue, so look out for angle oscillation or similar behaviour from the voltages.

 

So after a second key-on, after ecu reset, log the calibration sequence, then hold 1700rpm for a minute or so, then log freeway cruise...

 

Please post a link to a log, I’m interested to graph it in mega log viewer. :)

 

As for the cause of the issue, there’s 2 main culprits outside of failing avcs ocv’s:

Lack of oil pressure, eg due to low oil, or a blockage of some sort eg sealant in the avcs manifold/s, crud in the ocv body or in iirc the cam itself, or the cam gear. Non avcs cam bolts or presumably cams would cause the issue too, natch...

 

Or the cam gear/s were incorrectly installed, eg the cam itself was held static whilst the cam bolt was done up... or the wee dowels at the cam/cam gear interface were misaligned. Hopefully not...

 

* In some circumstances there may be a contraindicative (to avcs) yet related cel: cam position over...

Therefore your diagnosis should include cam sensor logging and/or inspection.

As avcs can’t function without it.

 

Also confirm you have specifically R-199-B single avcs 2.5t camshaft set: https://www.kelfordcams.com/nz/camshafts/subaru/ej25-wrx-sti-with-avcs-2004-current/r-199-b-camshaft-set.html

And that the triggers and sensors are compatible.

If not, can sensor conversion is definely a thing.

Of course the latter can be ruled out as your car is running at least... ;)

Edited by bigBADbenny
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You want to get a log of avcs vvt angles and the voltages too.

Mainly to see at what angle they’re locked, and secondly to see what happens during the avcs calibration process. The latter happens iirc on the second key-on after an ecu reset.

 

Graphing the angles and voltages will give some indication of the issue, eg which side/s are affected and, if so, how they’re affected. Obviously log other parameters to provide context ;)

 

Usually, if the fault is severe, both sides will become inactive.

That is, the ecu will give up avcs altogether.*

 

Before that happens, you should see the ecu trying to compensate for the issue, so look out for angle oscillation or similar behaviour from the voltages.

 

So after a second key-on, after ecu reset, log the calibration sequence, then hold 1700rpm for a minute or so, then log freeway cruise...

 

Please post a link to a log, I’m interested to graph it in mega log viewer. :)

 

As for the cause of the issue, there’s 2 main culprits outside of failing avcs ocv’s:

Lack of oil pressure, eg due to low oil, or a blockage of some sort eg sealant in the avcs manifold/s, crud in the ocv body or in iirc the cam itself, or the cam gear. Non avcs cam bolts or presumably cams would cause the issue too, natch...

 

Or the cam gear/s were incorrectly installed, eg the cam itself was held static whilst the cam bolt was done up... or the wee dowels at the cam/cam gear interface were misaligned. Hopefully not...

 

* In some circumstances there may be a contraindicative (to avcs) yet related cel: cam position over...

Therefore your diagnosis should include cam sensor logging and/or inspection.

As avcs can’t function without it.

 

Also confirm you have specifically R-199-B single avcs 2.5t camshaft set: https://www.kelfordcams.com/nz/camshafts/subaru/ej25-wrx-sti-with-avcs-2004-current/r-199-b-camshaft-set.html

And that the triggers and sensors are compatible.

If not, can sensor conversion is definely a thing.

Of course the latter can be ruled out as your car is running at least... ;)

 

While everything you said is Swahili to me, im sure my tuner will understand what you are saying :)

 

Thanks for the advice. Im thinking it might be non-avcs cam bolts that are causing the issue now.

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While everything you said is Swahili to me, im sure my tuner will understand what you are saying :)

 

Thanks for the advice. Im thinking it might be non-avcs cam bolts that are causing the issue now.

 

:lol:

 

 

So let's restart with simple questions then: Can you log? If yes, what tool do you have to log?

Edited by xt2005bonbon
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Then, log L/R VVT (or called OCV on the AP?). And report what you see. What I usually look for is this:

--under load, the angle increases

--both L/R angles should be in sync within +/-1 degree for 99% of the time.

 

 

 

You do not want to see one OCV stuck at an angle at all time.

 

You do not want to see one OCV lagging behind another one (e.g. as you increase the load, both angles should increase in sync and around the same level)

 

And you should not see both angles stuck at zero either at all times. From what your tuner said, it sounds like they are both stuck at zero no matter the load. Verify that is the case.

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