Another A/F Learning 1 A & C High Thread...

Recently purchased the car with low/no compression on one cylinder and proceeded to rebuild the engine. Got it all together and got a break in tune from my tuner. After a bit of driving the A/F learning values are pegged. Do a leak test*, find a tear in the bypass hose. Great! I have an opportunity to put on the 08+ WRX tube. Spend my Sunday replacing the hose and check it again. "The" vacuum hose came off the back of the intake plenum. Pull the whole thing off and hairspray/zip tie every single connection. Fire it up, still pegs the A & C learns. Test again and find a small leak at the filter for the MAP sensor, looks like the body is cracked, can't seal it up but it's a slow leak.

Here's where things get a little strange for me. When I pressurize the system the valve for the evap system starts to hum or sing. I assume this is the valve fluttering and allowing pressure into the evap system**. If I clamp off the hose on the right (looking at the front of the car, the hose that goes to the evap line with the fuel lines) the humming/singing stops.

Other than that, I can not find any other leaks but the learning values sure indicate there's a healthy one somewhere. Is it possible or likely there is a leak somewhere in the evap system in the back of the car? Would the small pile of bubbles that formed on the filter be sufficient to cause it to add this much fuel? Is my testing procedure garbage?

NOTES:

* Built a tester with a ball valve, PVC cap, valve stem, and 0-30 PSI pressure gauge. Plug the cap into the inlet tube and slowly apply pressure, never going above 7 PSI internally.

** In the rebuild process I switched from side-feed to top feed TGVs and had to come up with something to make the fuel lines play nice. I found a set of hard lines from an 08+ WRX and installed those. The vacuum lines are not exactly the same but, as best I can figure, I've plumbed it to function the same way without the use of the T between the evap valve and the hard lines under the plenum.

I'm just gonna keep documenting this mess in the hopes it helps someone else one day.

Found a small leak on the filter for the MAP sensor. Bypassed that thing and replaced the evap valve while I was in there (mix up on my part when ordering from Subaru). A/F Learning 1A is still high but not as bad (it wanders around the mid 13s with the AC cycling on and off).

I've sprayed at least a half can of brake cleaner trying to find a spot that makes the motor surge but can't find one. Tried pinching off lines while watching the A/F correction but still no change... I'll test again tomorrow I guess.

I'm just gonna keep documenting this mess in the hopes it helps someone else one day.

Found a small leak on the filter for the MAP sensor. Bypassed that thing and replaced the evap valve while I was in there (mix up on my part when ordering from Subaru). A/F Learning 1A is still high but not as bad (it wanders around the mid 13s with the AC cycling on and off).

I've sprayed at least a half can of brake cleaner trying to find a spot that makes the motor surge but can't find one. Tried pinching off lines while watching the A/F correction but still no change... I'll test again tomorrow I guess.

What's your aftermaf tube (the one between the airbox and turbo inlet) look like?

I've been chasing high idle AF learning 1's on my car after I installed an AVO inlet and perrin aftermaf tube, which ended up getting a bit scrunched in order to fit with the bigass AVO inlet (haven't gotten a chance to adjust the turbo inlet's fitment a bit). I also did the TGV rings at the same time, but those don't seem to be an issue.

It doesn't seem to show any other signs of a vacuum leak, it's just screwy at very low airflow values. Idle is dead smooth, but my AF learning goes through the ceiling. Before with a completely stock (but kinda leaky intake), the car would sometimes stumble at idle, or have a random shudder.

My current theory is that the scrunched aftermaf hose messed up the airflow through the intake tube. What I think might be happening is that at low airflow values, the flow is not even through the MAF anymore. Air might be flowing faster along the edge of the MAF tube, and less of the air is passing the sensor. Once the engine starts gulping down some more air, everything goes back to normal. Basically I wrecked the MAF scaling.

Tomorrow I'm gonna fiddle with it and try to get the tube back on nice and straight to see if it makes any difference.

What's your aftermaf tube (the one between the airbox and turbo inlet) look like?...

I'm using the OE tube. I bought an aftermarket jobber but it doesn't remotely fit without some serious persuasion (sounds like you have a similar problem) so I opted to stick with the OE tube. It was the target of my merciless brake kleen spraying but didn't seem to have any effect.

Time to wrap this one up.

Finally took the car to the tuner (got my 1000 miles of break-in knocked out). He suspects that my MAF might possibly be slowly failing but tuned around it. Was strongly advised to watch things closely if I replaced it in the future. Learning tables are all where they need to be now and I'm a happy camper!

Yeah replace the maf

Ive had 2 go bad so far ( o5 lgt/97k)

Or go map sensor

Btw id def replace/ upgrade the turbo inlet

Its not fun but would you rather have it fail or break apart and then tank the turbo?

Yeah, It looks like I'm going to need a "bigger" MAP sensor anyway (tuner said the MAF was getting up to 4.85V at WOT but we're doing hybrid speed density so I think he misspoke).

Turbo inlet was swapped over during the engine rebuild. Very glad I did that while the motor was out and the plenum was off. Can't imagine trying to do it in the car...