What are signs of a failing turbo?

Hey guys, I have a 06 OBXT 5MT with 137k on it. I picked it up with 134k, and slowly doing all maintenance to it. First thing I did was the T-belt/H2o pump and associated seals/hoses along with the P/S pump all OEM. I had a fluctuating temp gauge and ended up doing the upper hose and both coolant caps.

 

Drove the car to work yesterday and on the way home everything seemed fine. I still think the temp gauge moves a little towards hot but barely. So on the way home I noticed the car lacked power. When I changed gears and started to accelerate the car would kind of hesitate and feel like it has a restriction then all of a sudden it takes off and I hear the turbo spool. I didn't want to cause any further damage so I drove home and parked it.

 

Do you guys think this is a failing turbo? No check engine light but, I am going to check with my AP if there are any. Oh btw I have a stage 1 tune on it. Any ideas or suggestions to what I should check? TIA for any help......

Is it making any noises or throwing any codes? Also what’s coolant temp reading on your access port when it’s moving towards the hot. A few things can cause your hesitation including a failing coolant temp sensor.

A failing turbo will sound like metal on metal or a you would have no boost. It sound like the car is pulling timing for whatever reason when the turbo is spooling up.

 

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Next time I drive it I will connect the AP. I usually don't drive with it. I am not getting any noises and it spools great, matter of fact most of my driving is with the radio off just to listen to the turbo spool. Just for peace of mind I previously acquired a VF52 and just waiting for JMP to give me the go ahead to ship it to him for a rebuild. This is my first Subaru, not new to turbo cars, but I am still learning this platform.

A failing turbo will sound like metal on metal or a you would have no boost. It sound like the car is pulling timing for whatever reason when the turbo is spooling up.

 

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A blown turbo will still make a boost. My car had a severely blown turbo, about 1/4" play and fins contacting the housing as well as a cracked housing by the wastegate opening and it still made 11 pounds of boost.

 

The only thing i can say for knowing if your turbo is blown is noise. If I revved my car to 2000 rpm and held it for a second and let off i could hear a rattle as the RPMs dropped. im thinking that sound was the turbo wheels hiting the housing

 

I dont know if you filled the car up with gas before the problem happened, but a bad batch of gas would cause it to pull timing due to excesive knock from a lower octain fuel

 

I dont know what parameters you can view on Cobb but if you look at your feedback knock correction that will tell you if your car is pulling timing. It would alos beworth looking at your IAM (Ignition Advanced Multiplier) If everything is normal when the car is at operating temp your IAM should be 1

Edited August 5, 2020 by samuel082799

A blown turbo will still make a boost. My car had a severely blown turbo, about 1/4" play and fins contacting the housing as well as a cracked housing by the wastegate opening and it still made 11 pounds of boost.

 

The only thing i can say for knowing if your turbo is blown is noise. If I revved my car to 2000 rpm and held it for a second and let off i could hear a rattle as the RPMs dropped. im thinking that sound was the turbo wheels hiting the housing

 

I dont know if you filled the car up with gas before the problem happened, but a bad batch of gas would cause it to pull timing due to excesive knock from a lower octain fuel

 

I dont know what parameters you can view on Cobb but if you look at your feedback knock correction that will tell you if your car is pulling timing. It would alos beworth looking at your IAM (Ignition Advanced Multiplier) If everything is normal when the car is at operating temp your IAM should be 1

I was referring to a turbo in which the turbine shaft has snapped as a failed turbo. Yes, a failing turbo will still make boost but if the shaft snaps it is not possible. My old turbo had a seized wastegate actuator causing the car to severely underboost under load but the shaft never went out.

 

Either way a turbo which has failed or is failing will make noises when revved at park or while building boost.

 

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I was referring to a turbo in which the turbine shaft has snapped as a failed turbo. Yes, a failing turbo will still make boost but if the shaft snaps it is not possible. My old turbo had a seized wastegate actuator causing the car to severely underboost under load but the shaft never went out.

 

Either way a turbo which has failed or is failing will make noises when revved at park or while building boost.

 

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The parameters of the AP does not go that far in depth. I did drive the car yesterday and it does not hold back as bad as the other day but it still hold back. I’m at half tank of fuel so I will wait till quarter tank and run some fresh gas and an additive to see if it helps. Turbo spools good, no noises parked or driving. I do have knock summary of 27 after about 20 mins of driving. I do have a #4 cylinder giving me knock feedback. Doesn’t seem turbo related however. Will take a look at #4 coil/plug this weekend.

Your saying hesitation... Could this be translated to a stumble?

I had similar situation as dwmccauley01 in that the stock turbo wate gate seized open. Did cause a CEL each time it could not maintain any boost. After this it was repaired replacing the hot side with a working unit. It finally bit it with squeeling before heat soak upon initial startup. Replaced with a 16G and haven't had an issue with Turbo since. Tuned at that point of course.

 

Now for the hesitation... Look at your Oil Control Valve parameters on the AP. THe OCVS is one part that will go south and cause stumble. I had several attempts farting around other things and the fix was these two 100 dollar parts replaced stumble gone. THis was always off idle accelerating from a intersection or the girls school parking lot. Never while driving after rolling.

Your saying hesitation... Could this be translated to a stumble?

I had similar situation as dwmccauley01 in that the stock turbo wate gate seized open. Did cause a CEL each time it could not maintain any boost. After this it was repaired replacing the hot side with a working unit. It finally bit it with squeeling before heat soak upon initial startup. Replaced with a 16G and haven't had an issue with Turbo since. Tuned at that point of course.

 

Now for the hesitation... Look at your Oil Control Valve parameters on the AP. THe OCVS is one part that will go south and cause stumble. I had several attempts farting around other things and the fix was these two 100 dollar parts replaced stumble gone. THis was always off idle accelerating from a intersection or the girls school parking lot. Never while driving after rolling.

 

 

I will check the AP for those parameters and give it a try. This hesitation(which could be called a stumble) happens when I accelerate and at idle. I did notice it at idle when I got the car but it never effected anything else. So I wonder if I may have 2 separate issues going on here. The hesitation while driving would only happen when I accelerate then it would go away. As another member stated and what it felt like was timing being pulled(maybe knock) and then it releases. The last time I drove it it was not as abrupt but the car did not feel a peppy as before. And I am only getting 8psi at full throttle in 4th.

 

Is there an on car test for the OCVS, such as resistance? Or can I use the AP and it give me an indication to look at the OCVS? I will attack this this weekend to see what i can come up with. Still have the same gas from the last time, once I reach quarter tank I will put fresh gas and see if that helps as someone suggested.

Monitor your DAM. If not at 1.00 your getting nock and pulling timing.

OCVS just start going bad, cleaning may help but meh, the solenoid just stops working correctly after time and heat cycles. I'm convinced they should be part of the timing belt service. I'm on my third set at 230k +.

 

8lb of boost just don't sound right. Are you using a cobb tune or custom?

Mine is custom tuned and running 15lb creeping to 16 when I'm not looking.

There was another discussion about the stumble while driving related to the vac source for the fuel regulator being better from the BOV tube as opposed to the intake on #4 cylinder. Also changing the length of one of the fuel hoses to help alleviate this for some.

Make sure there are no vacuum leaks. DAM below 1 is an indicator you might. Or just a bad batch of fuel. I've seen both happen.

Ok will monitor the DAM. I recently had a timing belt service but didn't replace the OCVS. I think with the mileage I will replace them just for peace of mind.

 

8lbs is low as when I did the Cobb tune I believe I was somewhere around 12ish pounds.

This is the generic Cobb Tune. I will search for the vac source thread and the fuel hose length and see what I come up with. I will check for leaks as well. What is a good method of finding a vac leak. Doing it from the intake hose with a gauge or smoke tester? Thanks for your input everyone, I appreciate your help.

Took the car out on a short drive, thought I would be able to drive longer but the skies went completely black from the thunderstorm coming.

Knock sum >> 0/28 count

DAM>> 0.000(driving/idle)

Coolant temp>> 200F (sitting at light)

Roughness Cyl 4 >> 0/2

Boost(vac) @ idle>> -9.4psi

Does this give an indication of where to look other than the infamous #4 cylinder?

Well I'm not sure how your DAM is 0 but you shouldn't have roughness on any cylinders so I would check spark plugs and possibly the coil

 

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Took the car out on a short drive, thought I would be able to drive longer but the skies went completely black from the thunderstorm coming.

Knock sum >> 0/28 count

DAM>> 0.000(driving/idle)

Coolant temp>> 200F (sitting at light)

Roughness Cyl 4 >> 0/2

Boost(vac) @ idle>> -9.4psi

Does this give an indication of where to look other than the infamous #4 cylinder?

 

That doesn't seem like enough misfire on 4 to worry about, when I got ringland failure I got it on 2 at first and it was missfiring bad and would actually throw a code for it every once in a while. Then cylinder 4 went soon after and the car would idle so ruff, you didn't need a computer to know something was wrong [emoji23].

 

As far as the vacuum goes my boost guage measures boost in psi and vacuum in in.Hg and at idle it sits at 20 in.Hg.

 

To my knowledge DAM is the same as IAM. Dynamic advanced multiplier vs ignition advanced multiplier. In your ecu/tune there are two ignition tables there is primarily ignition timing, and a knock control table. Your base timing table for the most part is 6 degrees of timing shy from the max the engine runs during normal operation. And the knock control table has the extra 6 degrees in it.

 

So when you first start your car your IAM or DAM should be at 0.500 meaning that is multiplying the value in your knock control table by .5 so it is adding in 3 degrees of timing vs the 6 it can add in. Once the engine operates for a little while and it doesn't see any knock the DAM goes to 1 meaning it is adding in that full table of timing.

 

If a serious knock event occurs (more than 3 knock sums at once) it will automatically drop the IAM to .5 in order to pull timing and keep the engine from getting damaged from continuous knock. Then if the car sees no knock after a little while it will go to .75 and then 1 if everything is good.

 

I figured I would explain why it is that you should be looking at your DAM or IAM, so you know that for some reason your car is running as little timing as it can due to detonation or knock.

 

Idk if the turbo would have anything to do with that directly. When my turbo was blown I could remove my intercooler and see a puddle of oil in my throttle body coupler (I'll put a picture) I had an AOS at the time so the oil was definitely coming from the turbo. That would be an easy way to check your turbo health is to check for oil there. If there is no oil I wouldn't worry so much about the turbo.

 

If there is oil getting into the combustion chamber that will lower the octane causing pre detonation, but this could also be caused by bad gas.

 

If you really want a good idea of your engine health you should do a compression or leak down test. If you have ringland failure you will have low compression on that cylinder. If it's valves you will have no compression.

 

I have a video on compression test if you want to see how I did it I can post the link

 

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That doesn't seem like enough misfire on 4 to worry about, when I got ringland failure I got it on 2 at first and it was missfiring bad and would actually throw a code for it every once in a while. Then cylinder 4 went soon after and the car would idle so ruff, you didn't need a computer to know something was wrong [emoji23].

 

As far as the vacuum goes my boost guage measures boost in psi and vacuum in in.Hg and at idle it sits at 20 in.Hg.

 

To my knowledge DAM is the same as IAM. Dynamic advanced multiplier vs ignition advanced multiplier. In your ecu/tune there are two ignition tables there is primarily ignition timing, and a knock control table. Your base timing table for the most part is 6 degrees of timing shy from the max the engine runs during normal operation. And the knock control table has the extra 6 degrees in it.

 

So when you first start your car your IAM or DAM should be at 0.500 meaning that is multiplying the value in your knock control table by .5 so it is adding in 3 degrees of timing vs the 6 it can add in. Once the engine operates for a little while and it doesn't see any knock the DAM goes to 1 meaning it is adding in that full table of timing.

 

If a serious knock event occurs (more than 3 knock sums at once) it will automatically drop the IAM to .5 in order to pull timing and keep the engine from getting damaged from continuous knock. Then if the car sees no knock after a little while it will go to .75 and then 1 if everything is good.

 

I figured I would explain why it is that you should be looking at your DAM or IAM, so you know that for some reason your car is running as little timing as it can due to detonation or knock.

 

Idk if the turbo would have anything to do with that directly. When my turbo was blown I could remove my intercooler and see a puddle of oil in my throttle body coupler (I'll put a picture) I had an AOS at the time so the oil was definitely coming from the turbo. That would be an easy way to check your turbo health is to check for oil there. If there is no oil I wouldn't worry so much about the turbo.

 

If there is oil getting into the combustion chamber that will lower the octane causing pre detonation, but this could also be caused by bad gas.

 

If you really want a good idea of your engine health you should do a compression or leak down test. If you have ringland failure you will have low compression on that cylinder. If it's valves you will have no compression.

 

I have a video on compression test if you want to see how I did it I can post the link

 

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@samuel082799 that would be great if you can post a link. I asked for a leakdown/compression test when I got the T-Belt done but the shop was too busy to do it. I wanted to know what was going on with Cyl #4. It make sense what the DAM/IAM does and the way you explained.

 

I definitely believe timing IS being pulled. When I briefly drove it tonight I can hear the turbo spool but the car wasn't moving any faster. The more I accelerated, the turbo spooled, the car hesitated then I would feel it pick up speed.

 

I will go over to my buddy's and do some work on it this weekend. He has an oscillioscope and can do a relative compression test. If I find a low cylinder then I can do the static compression/leak down tests. I will also pull the IC and see if I find any oil in there as well.

 

Thanks for stirring up the juices, that video link would be helpful. I think I will get some new plugs and swap the left side bank coils to see if that knock follows to the next cylinder.

Sounds like you got a plan [emoji106]

 

 

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If you can data log you should post up some data. It could be beneficial to see how your boost, rpm, and AF sensor #1 correlates with the timing pulled and cylinder roughness. Plugs and testing of the blocks health is always good to do but i dont think an issue with your air fuel mixture has ruled out. Only getting 8lbs of boost at WOT can cause enough of a rich condition for detonation.

 

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Sounds like you got a plan [emoji106]

 

 

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Yea, my buddy is pretty good with diagnosing and I am mediocre at best. So between us hopefully we figure things out.

If you can data log you should post up some data. It could be beneficial to see how your boost, rpm, and AF sensor #1 correlates with the timing pulled and cylinder roughness. Plugs and testing of the blocks health is always good to do but i dont think an issue with your air fuel mixture has ruled out. Only getting 8lbs of boost at WOT can cause enough of a rich condition for detonation.

 

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With the AP I can configure 6 parameters. My boost vac is still at 9/10 at idle which I know it should be around -20inhg. I will drive using boost,AFR,DAM,RPM, roughness #4 when I drive to my buddy's garage. I took it on a good 25 mile road test this morning and here's what I got.

All of this at idle

Boost -9.46psi

Coolant 205F

Knock Count 27 count

DAM 0.750

Roughness #4 0/2

With the AP I can configure 6 parameters. My boost vac is still at 9/10 at idle which I know it should be around -20inhg. I will drive using boost,AFR,DAM,RPM, roughness #4 when I drive to my buddy's garage. I took it on a good 25 mile road test this morning and here's what I got.

All of this at idle

Boost -9.46psi

Coolant 205F

Knock Count 27 count

DAM 0.750

Roughness #4 0/2

 

 

On the ap, under tune/adjustment, see if retarding your timing by a degree each run will correct your issue.

Your vacuum at idle is prefect. Which leads to no leaks.

 

 

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With the AP I can configure 6 parameters. My boost vac is still at 9/10 at idle which I know it should be around -20inhg. I will drive using boost,AFR,DAM,RPM, roughness #4 when I drive to my buddy's garage. I took it on a good 25 mile road test this morning and here's what I got.

 

All of this at idle

 

Boost -9.46psi

 

Coolant 205F

 

Knock Count 27 count

 

DAM 0.750

 

Roughness #4 0/2

I would log feedback knock correction instead of knock sums. Knock sum just count how many times the engine reads knock but alot of times it is just noise. Feedback knock correction will show you when and how much timing is pulled if the engine detects significant knock. If your FBKC is at 0 than your not really knocking.

 

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Ok, I will go out for a drive tonight and monitor these parameters and see what I get. I need to get some plugs to replace while I am in there.

Try to see, if possible, at what point in the powerband you're getting the most feedback correction.

 

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To add to this, I'd also monitor fine learned knock correction (flkc). This is a learned timing pull due to a past knock event. It may not even be knocking when you see it post a -number but it's pulling timing preemptively in case an event is about to reoccur at that point where load/throttle pos/boost/etc.are the same as when a knock event occurred in its memory. If the number it pulls starts to decrease closer to zero that means it isn't seeing knock and giving timing back slowly. If you datalog you can see if there is a trend as to where its pulling timing. Also monitor AVCS L&R at least for one pull to see if they are way out of sync. Best way to see this is datalog but real time monitor will give you a rough idea.

Try to see, if possible, at what point in the powerband you're getting the most feedback correction.

 

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It seems to be happening just around 1500-2k and as I build up speed if feels like the car goes faster in increments if that make sense. As I accelerate the car seems like it is jerking(timing being pulled) trying to build speed, the turbo is however spooling strong as I can hear it. I will check using the AP.