Troubleshooting Low Vac, raised AFRs?
 

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.

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.

I'll go back and leak check as many possible places as I can more thoroughly. The leak would have to be post-TB though right? IC piping seems to hold boost fine, however.

I'd be looking for a post throttle vac leak, if the vac is low at idle.


Are you measuring vac from the map sensor, or a separate gauge?

I'd check a gauge to make sure it matches what the MAP sensor sees.
Just to rule out a dodgy MAP (since that would also cause mixtures to be wrong)

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.

Yeah, if both match (or close enough to) it's unlikely to be the issue.
I was more thinking if there was a hole in the MAP hose, or if the MAP itself was faulty and mis-reading.

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?

If you haven't done a smoke test, you can try that. I'd also check for exhaust leaks as that can cause inconsistent afr readings.

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.

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? :vash:

Do you have a catalytic convertor? Don't use two step....

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...

Sort of.

AC doesnt use vaccuum, but when the compressor is on the engine needs to open the idle valve a bit extra so that it doesnt stall with the extra load.

More air into intake manifold = less vaccuum.

ahhhh ok, shoulda made that connection when the idle AFR's went up with the AC on