S15 SR strange lean issue

[zombiewolf513]

Hey, so I've searched and searched but can't find anything that really describes the same problem I'm having.

Setup:
Stock S15 SR
NGK BKR6EIX plugs at .031" gap
FMIC
Tial Q
Wideband and Boost gauges
3 inch exhaust from elbow back
Somehow I've been running a re-manufactured 1996 type x ecu

Problem:

At idle my AFR is between 14.3 and 14.7, Vacuum stays steady at 20 inHg, RPMs between 810-830.

Occasionally on cold starts at idle my vacuum will quickly jump to 10 inHG then go right back down to 20inHg and hover around 18-20 inHg a little bit. It'll do that maybe once or twice every 30 seconds.

While under load, if in vacuum and accelerating at partial throttle (normal take off from idle or just speeding up a bit), the wideband will jump to 17:1 and I get about 70% power loss. It'll stay at 17:1 until I start picking up a bit then it'll slowly work it's way down to around 14.5:1.

While I'm cruising at a steady speed it'll stay between 14.5-16.

At WOT it'll jump to 17:1 and by the time I've hit my boost limit of 10lbs, it'll have worked its way to 12.8-13:1.

I did the swap at the beginning of January and everything ran beautifully. Then these issues started happening about 3 weeks later, and since they started they've been slowly getting worse and worse. I've changed the plugs and cleaned the IACV with carb cleaner and it helped a little with the WOT thing, but not much.

Any ideas? I'm thinking some sort of strange vacuum leak, TPS, IACV, VTC, or clogged injectors, or some sort of combination.

Thanks!

[KiLLeR2001]

Fuel pump, injectors, fuel pressure, you need to check all these things. I'd also run a step colder on the spark plugs (7). Also make sure your timing is not too advanced.

[zombiewolf513]

I'll look into all of that tomorrow, I'm also going to check for vacuum leaks.

[zombiewolf513]

I've come up with a pretty good theory of what could be happening.

I have a hole in my intercooler/charge piping.

My AFR is solid at idle, my theory fits this because if there is a hole in the charge piping and the throttle body is closed, I'm only drawing in a small bit of air anyway and it is being regulated by the IACV, hence the small amount of hunting I see in my boost gauge when the engine requires more air making that small hole a temporary vacuum leak.

Then I run lean as shit under partial throttle because the throttle body opens making that hole in the charge piping a HUGE vacuum leak, causing such a lean condition and hesitation.

In WOT, it runs lean then as I hit boost it settles out because the hole stops being a vacuum leak but instead becomes almost a negligible boost leak.

Come to think of it, I did slam my front end really hard one night pulling out of a gas station. Cracked the intercooler maybe?

[KiLLeR2001]

Vacuum/boost leak = running rich because you are losing air into the atmosphere instead of it entering your engine. So imagine the same amount of fuel being present but only getting 85% of your air. Thus, a rich condition.

[KaminaSan]

A boost leak becomes a vacuum leak when not in boost. An example would be a hole in the intercooler. When boosting, there is positive pressure, pushing air out, making it run rich because of the extra fuel.

When cruising that hole sucks in air making it run lean.

I can tell you this because I developed a boost leak and my boost afr went from 11.1 to 9.9 AFR WOT. Meanwhile my cruising AFRs went from 14.8 to 16, and my idle would sometimes go up to 17.5:1, causing random slight hesitation under light throttle.

BOOST LEAK TEST

[zombiewolf513]

A boost leak becomes a vacuum leak when not in boost. An example would be a hole in the intercooler. When boosting, there is positive pressure, pushing air out, making it run rich because of the extra fuel.

When cruising that hole sucks in air making it run lean.

I can tell you this because I developed a boost leak and my boost afr went from 11.1 to 9.9 AFR WOT. Meanwhile my cruising AFRs went from 14.8 to 16, and my idle would sometimes go up to 17.5:1, causing random slight hesitation under light throttle.

BOOST LEAK TEST

:s101: :coold:

[zombiewolf513]

Didn't really get to do the boost leak test, but here's what I've done and what happened (helped a little with WOT and partial throttle, but most of the problems are still present):

What I did:
Re adjusted and retightened all FMIC fittings. Tightened up the fitting around the BOV (it was a little loose). Removed MBC. Added a bottle of injector cleaner. Cleaned MAF. Recalibrated wideband.

What happened:
-Idle, still perfect.
-1st gear... WOT yields almost instant 11 AFR above 2500 RPM. Partial throttle throws AFRs in the 16 range then it'll settle out to 14.5 pretty quickly. Cruise stays at 14.5.
-2nd gear... WOT yields 15 until 3000RPM when AFR starts to work its way down to 12.2 at 5000RPM, then it'll shoot down to 11.2-12 at 5500, then some backfire as I engine break. Partial throttle under 2500 RPM will lean to 17 and sometimes (I'll explain the sometimes) work down to 14.5 unless I'm at -5inHg or above, above -5inHg and AFR stays at 14.5. Cruise stays at 14.5-15
-3rd gear, pretty much the same as 2nd gear.
-4th gear, pretty much the same but if I accelerate from a coast it'll jump to 16 then quickly go to 14.5
-5 gear is the same as 4th.

I unhooked my vtc solenoid and tested everything out, but it all just felt the same.

Things I noticed:
-If I engine break from boost I'll go all the way lean, then with partial throttle it'll shoot to 17 and hang there, engine break to boost will go 14.5 then drop like I described for any given gear.
-If I go WOT in 1st,2nd, or 3rd I overboost to 10psi (no boost controller hooked up).
-I noticed that if I rev lightly, my BOV partially opens while the throttle body is open. I disconnected the BOV and it didn't change much of anything except I think it opens itself at 10psi of boost @ 6500 RPM causing me to run so rich I basically lose all power.

This is frustrating. I'm running the fuel pressure test and boost leaks test tomorrow morning.

I'm starting to think this ***mysterious*** ECU is fucking all sorts of shit up.

[zombiewolf513]

Unplugged the o2 and drove around, all problems went away. Time for an O2 replacement.

[KiLLeR2001]

Hmm, usually when the O2 goes bad you'll run rich all the time. Hopefully replacing it fixes your problems!

[zombiewolf513]

We'll see. If it doesn't I may just keep it open loop and run an AFC