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Evo 8 VERY low boost/spool- almost 5psi at 6krpm, not boost leak or iwg
I've googled around, searched evom, and done what I found in those but now I'm stumped. I haven't found a thread similar to this issue, so if one exists I'm sorry for starting another!
My '05 Evo VIII is almost completely stock except a K&N filter and HKS Hi-Power catback. It has almost 160k miles on it. I've owned it for 3 mostly drama-free years.
I started having an issue a year ago where it felt like I wasn't getting full boost (maybe 17 out of the stock ~20), but the car was still pretty fast and I couldn't do much with not very much diagnostic info. A few months ago it got much worse steadily and quickly, and will now not boost hardly at all. The boost gauge jumps from -20 to 0 super quick, but above 0 it is very sluggish, boosting 1-2 psi by 3krpm and doesnt reach peak (4.5psi) until 6000rpm. It also feels like it revs really slowly. It is also throwing EGR flow code (I have the TB capped off but haven't flashed out the EGR stuff yet) and Boost system code. I've been getting the EGR code since before this issue.
I read that it could be IWG preload, stuck wastegate, or the hoses between turbo/IWG/boost solenoid. Since it boosts under wastegate spring pressure and the car is getting up there in miles, I suspected a worn out wastegate instead of just preload (the stock one also looked to be just about adjusted to max). Today I replaced the IWG with turbosmart IWG75 (stock 10psi spring), all the hoses with OEM replacement from dealership with the restrictor pills in place, and made sure to check that the wastegate flap moves freely when I made that switch. Doing all of these had no effect.
I also checked the turbo for shaft play- it has no front-back play and a tiny, almost unnoticeable amount of side/side play and there is no scuffing or evidence the impeller wheels have touched the coldside housing and there are no nicks in the blades or anything. It spins freely.
I have done a boost leak test to 30psi and it holds pressure without a peep.
Early on, I would always get P0420 cat inefficiency CEL and I eventually ECU-flashed that out of the picture thinking the rear o2 was bad (and because I want to wire in a wideband in that ECU spot so I can log it, when I put a bung in my downpipe). I also had a period of time (before I learned the car very well) that it was running rich for a long while due to spark plugs "blowing out" and from a boost leak, but both of those were fixed a while before this issue.
So my question is: what could cause such low spool/peak boost? And what could make it gradually fail over time, and end up less than wastegate pressure if the wastegate is ok? Given no other input, I would be trying a test pipe next to check if my cat has gone bad (it revs slowly in addition to not boosting, which seems could be backpressure related). I feel like that could be another rabbit hole though and I have no clue what I'd try next. I trust the experience of the members here above my own limited experience.
Diagnostic-wise I have boost gauge, obd reader, boost leak tester, and tactrix. I do NOT have wideband o2 yet.
This is just a shot in the dark, but perhaps a fuel pump or filter. If it is not getting enough fuel the feedback loop should basically detune the crap out of it to keep it safe. Not sure if it could go that far but possibly. I have seen clogged cats cause issues like this before just not on an evo. If your exhaust is plugged up it would not be able to pump out the air it needs to. Try just unbolting the cat and running straight pipe for a run if you can perhaps.
I really think you need to get a wideband on it and check commanded versus actual on AFR.
Take a look at your fuel trims if you can and see if they are way high. If they are really high (positive) then a clogged cat or fuel system issue would not be unlikely. If they are really large negatives then you may have a MAF sensor issue or something along those lines.
Thank you so much for your response! That does make a lot of sense. I'll log a few pulls today and post results.
Another thing that corroborates what you said that I forgot to mention (thinking it was taken care of) is a few weeks ago it started hesitating hard (felt like fuel cut?) when it started into low boost. I cleaned my air filter and MAF and it fixed that issue 98%, but I'll pay careful attention to that in the logs.
So I logged a short run (after letting it warm up a bit) and found that
1) my fuel trims used the low (3.906) or mid (2.343) values
2) 0 counts of knock in "knocksum" column but ~22 counts in knocksum3e at any rpm. (if this is the real value, I assume based on this alone, I need to park the car until I get this fixed)
I'll keep looking at the log and googling around as much as I can, but I'll upload it still. You guys can probably detect the problem in a few seconds =p
What mods do you have? Something is screwy with your log and it is not recording load correctly. You probably have to record one of the other load parameters instead of 1Byte.
This also says that your injectors are at 22% duty cycle at a MAP of 36PSI, so something is way off here I would guess. Your log should look more like the one I attached here which records across the map, not just in the 0 load column. This is just an old log so don't read too much into the values.
Also if you haven't read it, read up on Merlins Evo Tuning Guide. Ton of great info there on just about everything and will help you with logging and figuring out what it should look like.
I unfortunately can't help much off the log you sent though.
Mods-wise, it's just a K&N filter and catback exhaust, everything else stock. It was originally a sea-level car, but it's at +4400ft now (not that that'd matter much on more modern cars). The max my boost gauge reads right now is 5psi at 6k so I'm not sure why MAP is so high. Thanks for pointing me in the direction of Merlin's guide!
Because the fuel trim is so high, miles are high on the car, and because it can't hurt to have a backup if it doesn't turn out to be the issue, I've got a fuel pump/filter on order and will have them put in after work tomorrow.
Your turbo is dead (like previously pointed out). I had a similar problem on an evo 10, turned out half the exhaust wheel was missing. Didn't smoke, nothing looked off, just no power and superslow boost.
Since my last post I ordered a HFC since my cat has been throwing the CEL almost since day 1 (everything stock, no mods reason for it to be throwing code) and I figure it's better to have one anyway and completely rule that out. If in doubt, replace things that are small upgrades? The only reason I decided to pull the trigger on that instead of suspect the turbo immediately is in addition to no spool, it is also underperforming even for a non-turbo car.
If the cat doesn't do it (I don't have high hopes) then I will pull the turbo and check it out. Eventually (within a couple years) I want to do a 2.4 long rod setup and aim to get 700+ awhp- if the turbo is bad, I assume it wouldn't be prudent to go straight to the turbo I'd use on that setup, even keeping it on a leash until the supporting mods are done (I'd imagine it'd spool super slow and not be fun to tune down). I guess I'd do an FP Green JB (to be cheap- $1100 vs $2500) until I do the rest.
Your 10# spring is the weakest that Turbosmart offers for that actuator. I think there are two stiffer spring options(16#, 22#??). Try a stiffer spring. 10# is just about like stock.
Sparky- yes, we do have emissions testing in UT. From my experience, they really only go off of a visual inspection and if it throws a CEL- they don't do sniff tests.
Lonestarr- When I looked around it during wastegate actuator swap, I checked as best I could for cracks without removing anything. There are no carbon deposits in the area or exhaust leak sounds, but I'll drop my downpipe and remove the turbo/WG to check it out around the time I do the cat and will post findings here (this week/weekend hopefully).
At this point I'm almost hoping my turbo is trashed so I have a wife-viable reason to drop money on an FP green =p
Apr 25, 2015, 05:29 PM
