DAM drops very low only in the summer

[Oberon]

I hope someone can give me some ideas of what else to check on my car as I am at a loss. To start, my issue is my car drives great all winter long. Once the weather starts getting warm my DAM drops, 90+ humid day the DAM can get to almost 0 (.068). If the next morning it is cooler (low 60's) the DAM will start to work its way up again till the heat hits. This is all normal driving very limited boost. Fall weather hits with consistent < 60 F temps and DAM will eventually work its way back to 1 and be fine till later spring.

 

Now as to what I've checked and or replaced. First I'm running stage 2 Cobb OTS 91 map. Running 93 good quality gas. My car has 153k miles on it with Invidia catted down pipe and Borla exhaust.

 

Jan 2019, replaced head gasket, spark plugs, clutch, timing belt and radiator. Summer 2019 replaced all 4 coil packs. Spring 2020 replace up stream O2 Sensor. Recently cleaned MAF though will do it again to make sure. Just had compression test done Cylinder 1 was 145 PSI, Cylinder 2 & 4 150 PSI Cylinder 3 155 PSI. The spec says they should be 171 PSI, so tad low but expected with 153k miles. I was more expecting one to be much lower than the rest given the issues I'm having.

 

Intermittently I will see Feedback Knock less than -2.8 but not often, the DAM drops when Fine Knock learn stays negative. Once the temps drop and stay below about 60 it all goes away.

 

I do think I need a new turbo, could that cause this? I see TD boost error ranging from -8 to +24. When the weather is cooler and I feel safer doing a hard pull in 3rd gear there is TD boost error around 2-4 with >10 PSI boost. In general I've never driven my car hard. But figure with over 150k miles my turbo is likely at the end of it's life. But how do I test it? Could their also be issues with the waste gate? Smoke test last year showed no leaks and had this same issue last summer.

 

Am I way off about turbo? I'm at a loss what to test and don't want to spend money randomly replacing things. I'd like to keep the car a while longer especially since the new Legacy so far stinks, now if they come out with one that is a manual and more power I'm in!

 

Thank you for any help anyone can provide. I can provide data logs if anyone wants to see them.

[stewdogg]

Is the Invidia down pipe and exhaust the only upgrades you have? All stock other than that?

 

Seem to me like all your issues are coming from the same place.

 

Any check engine lights on?

Any abnormal engine noise?

[Sarang]

DAM dropping is not always a bad thing - It means that your ECU is trying to make sure you don't blow the engine.

I would have mine drop in the hot part of the summer - July and August mostly. Running 95 or 100 octane would fix that, which led me to believe that knock is just hard to avoid on 91 when it's 100+ out.

Remember that the OTS maps are very conservative since they have to be safe on everybody's engines with downpipes from all manufacturers. Have you considered an etune? That would be specific to your engine, mods, and other factors.

[cww516]

I've noticed the same thing on the OTS stage 1 91 map, usually anything above the low-mid 80s will cause it to drop for me at anything over 2-3 pounds of boost. Given my complete lack of tuning experience, I would ass-u-me that the temperature compensation tables in the map could be tweaked to help with that (and with Cobb being in Texas, they probably had an opportunity to refine the high-temp end a little), but as long as it comes back up, DAM dropping isn't really a bad thing. The e-tune suggestion isn't a bad one, either- Cobb didn't make a downpipe for the 5th-gen GT, so they didn't really have a set configuration to test with when building that map like they did with the stage 1 maps.

[Oberon]

As far as mods the down pipe and exhaust are all I've done. I do use a K & N air filter instead of the OEM one. Anything else I did was breaks and suspension related. Basic Stage 2 setup. I'm using Cobb's OTS stage 2 91 Map normal wastegate. I use the best gas I can find locally 93 at a Sunoco.

 

My concern with the DAM drop is that it seem a bit excessive now. It use to drop to .812 in the summer maybe .75 then go back to 1.00 on a cool morning. My drive home yesterday it dropped to .128. This morning was still in the mid 70's and high humidity so it only got up to .5. That seems sever to me, but IDK. It does seem to be better on a low humidity day but I'm in upstate NY so those are rare. You can feel and hear the difference when the DAM gets below .75.

 

I contacted cryo tune about an e-tune

https://www.cryotuneperformance.com/etuning

Thinking that the issue may be my tune and read the same in forums. Dave wrote back to me saying the DAM drop was a concern and that Cobb's OTS tunes are decent they would be concerned with doing a tune for my car. Dave recommended I get a compression test which I did and nothing was way off. He didn't think a tune would help which surprised me.

Should I contact a different e-tune place Cryo tune was highly recommended?

 

Thanks for the comments!

[coco26]

Dave is right. OTS tunes are "safer" (meaning less likely to knock) than a normal tune because they have to work for every car. He could make you a tune, but it would be less powerful than what you have, so you might as well go back to a stage 1 OTS or stock tune.

 

I'd look more into what might be making your specific engine knock so much, like abnormally high intake temps, excessive carbon buildup in the cylinder, running lean, etc.

[Oberon]

I do watch my intake temp and datalog it. on a hot 90+ F day with >75% humidity the intake temp gets up between 120-130 at slow speeds or stopped. It drops down to 110 range when I get up to 60 mph. Is that to much higher than ambient temp?

 

How do I check for excessive carbon buildup in the cylinder or running lean? What should I be looking for? I'm noticing these DAM drops with normal driving with limited boost.

 

Sadly with the down pipe if I try to run a stage 0 or 1 map I get a check engine light because of the lower O2 sensor. However it takes a bit so I have tried and still see the DAM drop in hot humid weather.

 

Thanks

[pinesol]

I had somewhat similar problems that I wasn't sure were problems prior to tearing my engine apart recently. My compression numbers were good, but DAM would drop occasionally; I didn't think too much of it. My plan was to pull the heads off to do head studs when I did my timing belt, but once I got the heads off it was clear that I had some actual issues. Burned valves, likely due to bad valve seals and just a ton of gross carbon/sand-like stuff on the piston. That said, the cylinder walls were in really good shape and it all cleaned off pretty easily, as you can see by the after picture.

Edited July 21, 2020 by pinesol

[coco26]

What pinesol said is what I mean my excessive carbon... if you have a borescope, you can look inside at your pistons, which could be an indicator of the condition of your valves.

 

You can check if you're running lean by either taking a look at your fuel trims, or checking the color of your spark plugs.

 

Those intake temps are normal for out-of-boost driving.

 

Also, even though you're getting 93 octane, is it from a reliable station? I've gotten gas from cheaper stations (walmart, grocery store brands) that not only pull power because of knock, but physically make the engine run rough.

[Alexmed2002]

Also, even though you're getting 93 octane, is it from a reliable station? I've gotten gas from cheaper stations (walmart, grocery store brands) that not only pull power because of knock, but physically make the engine run rough.

 

I'm also curious if this was an issue. Maybe the idea that cheaper gas really is bad actually played a part?

[Oberon]

I thought about the gas too because at one time I was getting cheaper 93. I looked into the best places locally for gas and I go to a Sunoco near my house for my gas now. The only change I noticed is my gas millage improved a little but sadly the knocking/ DAM drop didn't go away, maybe not quite as bad as last summer and this summer has been a hot humid one here but still bad drop.

 

I'll look into the carbon build up and try to see if I am running lean. Do I watch the AFR to tell if I am running lean? What should the numbers be for my car?

 

Thank for the help, this is great things I had no idea to look into.

[Oberon]

My AFR when I have 0 or less boost seems to me to be much to high. It is 15-20! Now since I'm using the OEM O2 sensor and not a good wide band is this accurate? I thought anything over 14.7 was lean. Now when I do have boost the AFR drops down to under 13 and goes down as boost goes up which I believe is what I want from what I understand.

[Sarang]

It should be fairly accurate when not under boost. Mine hovers around 14.7. 15-20 sounds like a leak somewhere. That means that your engine is getting more air than the MAF says that it should, which means a leak between the MAF and the intake valves. The fact that it's worse under vacuum means that it's likely between the turbo and the intake valves, maybe even between the throttle and the valves.

Can you post a log?

There's a little hose that plugs into the intake manifold behind and under the center that pops off on my car. Have you looked for that? It's the boost reference line for the BPV. You'd probably have to remove your TMIC to see it.

[Oberon]

Paid better attention to the AFR while driving it goes above 15 when my foot is off the gas. Moment i give the car any gas it drops down below 14.7, is that normal? I attached my datalog from my drive home, normal driving. it just rained a little and temp dropped to low 70's so DAM actually improved a bit but still much to low.

 

I need to get back under and look but I think my down pipe is cracked at the weld before the CAT, couldn't see very well. Really hate to have to buy another one if I can even find the same one, if it is cracked may be able to weld it.

Data log afternoon 7-22-2020.csv

[Sarang]

That sounds normal. When coasting with your foot off the gas and the in gear, it should turn off the injectors. This results in a small amount of plain air being pumped through the motor with no gas being injected, so an AFR of ~20 means completely lean.

 

Something's going on. You're getting a bunch on knock under boost and that DAM is really low. One of the places it dropped fast was under moderate load, above 2500 RPM, and barely positive boost. It might be fine to drive it gently, but I would stay out of boost.

 

I do wonder if you have a boost leak. It seems like your AFR should be richer for that section where you're above 8psi.

 

You also seem to be running rich at low load under vacuum. I'm not sure why that would be.

 

At this point, if it were me, I'd take it to the shop. I'm not sure what the next step in diagnosis is.

[Oberon]

Good to know thanks.

 

I noticed the same with the DAM, drops most under moderate load, like going up an incline, my drive to work is quite hilly.

 

I have actually taken it to a shop, but what should I have them test? The shop I usually go to or even local dealer (they did the head gasket what a nightmare dealing with them), take it for a drive and don't notice anything. All the issues show up in the data logs, with out the data logs, unless like me you drive the car daily you wouldn't notice the engine sounding different, the whole feel of the car is off.

 

The show I go to near my job listens to me and will look at anything I ask.

 

Boost leak sounds like what I was thinking but how to test for it, is the turbo just going? Wastegate gunked up?

 

I tried to contact dyno shops, sadly none near by and they weren't very good with communication. The one that got back to me said they would want my car for like 3 days and they were way out in the country 70+ miles from me so not even near a place to rent a car.

 

Thanks for the help and feedback.

[coco26]

I don't have much to add to what Sarang said, other than I agree with investigating a boost leak. You should have been fully spooled long before you got to 3600 rpm at 90% throttle, but your boost error is still saying underboost by about 6 psi. That being said, I think the wastegate duty cycle on my car is a good bit higher than your 30% at that point, but that could just be a feature of your tune.

[stewdogg]

I agree, you need to look for a boost leak. Stop thinking the turbo is shot and concentrate on a boost leak. A bad turbo isn't really a thing on the 5th gens (that I have seen) and if they do go it's usually the bearings. Have you looked around to see if anything is apparently out of place with the turbo system? There are a handful of things that seem to create a boost leak in these cars, that others have experienced around here as well. I would start looking at those things and go from there. Maybe you can find it without taking it to someone?

 

I go through this with my car once in a while and have to figure it out. I monitor fine knock learn, feedback knock and DAM (with 3 others that don't matter for this). Seems like with a boost leak I have seen the fine knock creep up when hitting any kind of boost.

How long have you driven the car with low DAM? I always stop driving mine when the DAM drops, till I figure out the issue. In the very least I stay out of boost and that is difficult, so not the best option for me.

 

 

Can you do any of the work yourself? I kinda feel like you have to do some of your own work on a higher mile turbo car. It's already too much money for the go fast and look pretty parts.

[Sarang]

I don't think this is your turbo going. You're having AFR issues, which might be leading to issues spooling up. I would think that if your turbo was going, you'd have OK AFR but not spool up.

 

I would check for a boost leak. Look for the little boost reference hose on the back of the intake manifold that I suggested before. Make sure the vacuum/boost lines don't have pinhole leaks. You can literally just blow into them and feel if they're leaking.

[Oberon]

I will definitely start looking for a boost leak. I will look myself and talk to the mechanic across the street from where I work, easy to drop the car of and walk to work come back later, especially if he waits and has it up when I can take a look better.

 

For me the DAM drop goes away when the cooler/colder weather hits. It started late last summer, as I started looking into what the cause was it gone by mid fall. No issues till the weather got warmer this spring. Even a cooler morning the DAM will work its way back up.

 

I try to drive with little to know boost, when I have any I'm going up a steep hill but keep the RPM lower and take it slow. Sadly I don't have another option for a car why I really want this fixed.

 

I'll see what I can do this weekend.