Troubleshooting Low Vac, raised AFRs?
#1
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
Having some weird symptoms that I can't seem to troubleshoot myself.
Finalized and dyno tuned my t25 turbo build a month ago and only have tweaked the cruise fuel cells since. The car was running great and was consistently getting 19 in/Hg of vac at idle, and something similar at cruise. AFRs were all right where I wanted them as well, idling ~14.5.
Really have no idea what caused the issues since I just mildly changed some fuel cells and then the issues occurred a week later.
Now the engine pulls 10-14 in/Hg at idle and cruise, doesn't increase vac on decel, and idle AFRs seem to have increased and are inconsistent. Occasionally it will idle at ~14.7 after a drive, but usually is idling ~15.7. Keep in mind I've left the idle cells locked and untouched since original tuning so don't think its a change of tune.
I went ahead and tested compression and got the same numbers as before the turbo went on. All solid. Only other thing I can think of is a vacuum leak, but I can't find one anywhere and my RPM's haven't increased.
Attached is a datalog from my warmed up commute to class, AC on the whole time. Current tune attached as well if it helps. If your more experienced eyes can see something I don't, it would be much appreciated as id like to have this car running as good as it can.
Finalized and dyno tuned my t25 turbo build a month ago and only have tweaked the cruise fuel cells since. The car was running great and was consistently getting 19 in/Hg of vac at idle, and something similar at cruise. AFRs were all right where I wanted them as well, idling ~14.5.
Really have no idea what caused the issues since I just mildly changed some fuel cells and then the issues occurred a week later.
Now the engine pulls 10-14 in/Hg at idle and cruise, doesn't increase vac on decel, and idle AFRs seem to have increased and are inconsistent. Occasionally it will idle at ~14.7 after a drive, but usually is idling ~15.7. Keep in mind I've left the idle cells locked and untouched since original tuning so don't think its a change of tune.
I went ahead and tested compression and got the same numbers as before the turbo went on. All solid. Only other thing I can think of is a vacuum leak, but I can't find one anywhere and my RPM's haven't increased.
Attached is a datalog from my warmed up commute to class, AC on the whole time. Current tune attached as well if it helps. If your more experienced eyes can see something I don't, it would be much appreciated as id like to have this car running as good as it can.
#2
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
My OCD would drive me to put a Mityvac on every vacuum line and magnifying glass every vacuum hose connection point for irregularities. Then I would but a small clamp on every one of them. Check the intake manifold and throttle body very carefully for cracks. Tighten and/or replace gasket on TB. Check torque on IM nuts/bolts. Snug down all your intercooler piping. I discovered multiple tightening opportunities after a long day at the dyno and one blown off vacuum line just a couple of weeks ago.
#5
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
MAP should be correct. It's running off the FPR line and the boost gauge is running from the cruise control line. I believe MAP was 42 kpa which was consistent with the 12inHg on the gauge.
#7
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
Ok, this issue really has me confused. After more looking, pinching lines, and trying to leak test, I couldn't find any vacuum leaks. AFR's were sitting at ~16.0 for idle as well today so im really lost as to what's happening. Specifically regarding the AFR's raising, should this be a symptom of a vacuum leak?
#9
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
Ok, so I went ahead and tried a smoke test with a fat cigar with no luck yesterday. Also am confident of no exhaust leaks and AFR values are correct...
Went ahead and completely retuned my CL idle to perfection since it was a little off before due to a misadjusted idle valve. Wanted to see if it helped at all.
While messing with everything, I noticed the MAP sensor is now miraculously reading 27 kpa on TunerStudio which is perfect. AutoMeter gauge still reads ~12 inHg however. Really odd since it seems to display boost fine. Guess ill recheck all its connections and look for kinks.
Went ahead and completely retuned my CL idle to perfection since it was a little off before due to a misadjusted idle valve. Wanted to see if it helped at all.
While messing with everything, I noticed the MAP sensor is now miraculously reading 27 kpa on TunerStudio which is perfect. AutoMeter gauge still reads ~12 inHg however. Really odd since it seems to display boost fine. Guess ill recheck all its connections and look for kinks.
#10
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
Guess it wasn't a tuning issue after all...
Car was running great for the last week with ~28kpa idle, but then while testing some stuff, I went ahead and used my launch control for maybe a second tops (spark cut, -2deg, 4k), and noticed idle kpa was sitting ~40 again.
immediately went and played with all the vac lines to see what would change the kpa but no lines affected it. I'm just very confused as to where this leak could be but it definitely was reopened by the 2-step. Any last ideas before I torch the car?
Car was running great for the last week with ~28kpa idle, but then while testing some stuff, I went ahead and used my launch control for maybe a second tops (spark cut, -2deg, 4k), and noticed idle kpa was sitting ~40 again.
immediately went and played with all the vac lines to see what would change the kpa but no lines affected it. I'm just very confused as to where this leak could be but it definitely was reopened by the 2-step. Any last ideas before I torch the car?
![vash](https://www.miataturbo.net/images/smilies/vash.gif)
#12
Junior Member
Thread Starter
iTrader: (1)
Join Date: Dec 2018
Location: Dallas/Fort Worth
Posts: 311
Total Cats: 100
![Default](https://www.miataturbo.net/images/icons/icon1.gif)
No cat and I know only bad things come from it... it just gives me a fuzzy warm feeling inside.
In other news, I've actually solved my own issue and realized I might be the most oblivious person I know. Over the 3 weeks I was troubleshooting the issue, I never noticed it was directly related to the AC being on... To be fair, for the last week I left it off while I was touching up my tune, and flipped it back on right before testing the two-step. The whole time, it's literally just been that the AC uses vacuum when on. That and the hose to my gauge is kinked or something which also threw me off.
The relationship with my car is such a love/hate cycle...
In other news, I've actually solved my own issue and realized I might be the most oblivious person I know. Over the 3 weeks I was troubleshooting the issue, I never noticed it was directly related to the AC being on... To be fair, for the last week I left it off while I was touching up my tune, and flipped it back on right before testing the two-step. The whole time, it's literally just been that the AC uses vacuum when on. That and the hose to my gauge is kinked or something which also threw me off.
The relationship with my car is such a love/hate cycle...
Thread
Thread Starter
Forum
Replies
Last Post