Fighting lean idle, sputtering, popping

[Shigun]

So I'm pulling my hair out trying to figure out this issue. First off, the engine:

S14a SR20DET
2871r
555cc Injectors
Walbro 255
Z32 MAF
Vented to atmosphere BOV, does not seem to be leaking
RS Enthalpy ECU
NKG BKR6E spark plugs gapped at 0.28", I'm installing some new ones to 0.30"
Boost level is ~10-12PSI on wastegate
Let me know if any more information is needed

When I first got the motor and got it up and going, I had a nice 20 in/Hg vacuum, car ran and idled good, no problem.

Over a span of time the vacuum at some point dropped to about 15 in/Hg, and I've developed an issue where on start, hot or cold, the car will have a very poor, sputtering idle. In addition, I can hear the exhaust popping every now and then when sitting and idling.

The car itself acts like it wants to die, but if I tap the throttle, it will bump up and idle fine until I let off the throttle. Wideband is reporting anywhere from 17-20 at idle, 14-15 cruising, 11-12 at WOT.

Checked timing in timing mode and it's right on 15, but as soon as I plug in the TPS again it goes up in the 20-30 range. When driving around, it usually stays in that range, sometimes dropping down to the 17 range, very very rarely in the lower area of the teens. It almost never actively gets anywhere near 15, even when idling.

I built a boost leak tester and found a few issues here and there that I fixed, but none of them really seemed to have any effect at all on this.

When the car starts stumbling and wanting to die at idle, the vacuum will start dropping rapidly down to the 10in/Hg and below area.

Any time when I am actively driving it, I can't tell that there is any issue just from how it responds and acts.

I've uploaded a data log from a normal driving session I did, though there is one point where I got stuck behind somebody going stupidly slow, so you'll probably notice that. It's pretty large, about a 20 minute log with 69505 lines, so it takes a short bit to load.

https://docs.google.com/spreadsheets/d/1Kd6p5uAFINg6V7was4P0ya1AGjvsmWCYhiaY0hl4PMM/edit?usp=sharing

I'm not 100% certain on the general voltage range and responsive properties of the O2 sensor, but it looked like it was a little odd in that it would go to 0 at times. I also noted at idle that I can unplug the O2 and there is 0 change at all, but the consult reported a constant, if I remember correctly, approximately 0.31V.

Any input at all would be incredibly appreciated, and if there are any questions, let me know and I'll answer anything I can.

[Shigun]

Bump, still having this issue, any help would be appreciated.

[Croustibat]

It looks like you have a leak when vacuum is high, which is what happens with leaking BOVs. Actually they all leak at idle, the vacuum pulls it open and unmetered air goes through the system.

There 2 fixes for that:
1/remove it
2/recirc it

The third option is to deal with it and hope it will never suck enough dust to damage your engine (hope is not something you should count on with engines IMHO but to each their own)

[Shigun]

It looks like you have a leak when vacuum is high, which is what happens with leaking BOVs. Actually they all leak at idle, the vacuum pulls it open and unmetered air goes through the system.

There 2 fixes for that:
1/remove it
2/recirc it

The third option is to deal with it and hope it will never suck enough dust to damage your engine (hope is not something you should count on with engines IMHO but to each their own)

I actually spent a metric fuckton of time last night sitting down with the FSM and looking over my engine. The guy who originally helped me out with the motor as I was learning was a little off on some of the workings of the motor, so there are some issues here and there.

One such instance is that the valve cover breather was hooked up to nothing. When I created a port and connected it to the intake (custom intercooler and intake piping), that instantly helped idle and vacuum levels (I would normally sit at 15in/hg, I now sit at a healthy 20in/hg).

I'm already planning on going and getting a piece of steel tubing to weld in to create a port to recirc the BOV.

Thanks for responding though, greatly appreciated!

[Croustibat]

That was quite some leak, i am surprised the car even worked.

The reason it was a problem is this : there is a one way valve in the intake manifold that opens on vacuum and closes on pressure. It connects the manifold to a valve cover breather and allows oil vapor recycling. If some breathers are open, it will suck air from outside, then unmetered air in the system, you know the drill.

[Shigun]

That was quite some leak, i am surprised the car even worked.

The reason it was a problem is this : there is a one way valve in the intake manifold that opens on vacuum and closes on pressure. It connects the manifold to a valve cover breather and allows oil vapor recycling. If some breathers are open, it will suck air from outside, then unmetered air in the system, you know the drill.

Yep, basically exactly confirms what my research was saying. I was always looking at it and other pictures going "this doesn't seem right, they always have this connected to something else, and it feels like it's alternating between pulling in and pushing out air."

The PCV line was connected, and the line at the back of the manifold closest to the firewall that goes from valve down to block was connected, but this one wasn't. Time and research later and, voila, engine is running much better.

Last thing is the stall when coming to a stop, but we've already established that I need to recirc, which I'm going to be doing today.

Doesn't help that I have the S14A SR20 as well, so while 99% of the information I find is for the S13 SR, it doesn't always apply in the same way, lol.

[Croustibat]

The stall when coming to a stop is likely due to the BOV, but you can fix it by modifying the tune, on the fuel cut map (what is usually called "fuel cut" is when TP reaches TTP max, the map i am talking about is the one telling the engine to cut the fuel when gas pedal is released and RPMS are dropping, then enables fuel again when reaching a lower RPM. All you need is to set this threshold higher). Or you can set a higher idle speed. Rpms will drop too, but it should not stall.

[Shigun]

I'm not sure that I can modify the tune, given it's an Enthalpy tune (correct me if I am wrong).

[Shigun]

Wow, recirculating made such a difference. I have to test with when it's cold as well, but it drives so much better now. I still hear a bit of a pop from the exhaust at idle, not sure what's up with that yet still. Any potential thoughts for it?

It is probably good to note as well that my exhaust is a 3" downpipe with a 2.5" crossover to a 3" catback, so I don't know if that is going to have an effect on this (though I doubt it). This is a pretty odd motor swap and the body that it's in has the exhaust tunnel on the passenger side, so I had to cross over under the tail of the transmission. I'm looking into getting the exhaust redone to go down the driver side under the car, but have to relocate the fuel lines a bit.

[Croustibat]

You cannot modify the tune if you don't have the tools, so for now don't touch it. If it was made for these exact AFM and injectors, it should be ok.

The thing is, when recirculated, a discharge valve still leaks; but it does not matter, as the air that goes through has also gone through the MAF.

A pop at idle can really be tons of things, from a little too lean fuel map, worn sparkplugs or wrong gap, an exhaust leak, worn valves ... .28/.30 should be ok for spark plug gap though. Maybe you can try a colder index for the spark plugs, but i would not worry too much if i were you.

[Shigun]

Yeah, I got this particular enthalpy ECU used from a user because it was, literally, the exact same as the setup I was going for, so I didn't have to worry about a retune.

If I was to take a guess, it's probably either too lean of an exhaust leak, as at idle I'm right around the 17-18 range according to my wideband. Normal driving is fine (14-15), as is WOT (11-12). As well, my exhaust is somewhat shitty with the crossover under the transmission, I need to get it redone to go straight back, just haven't had time to go and get it done.

I'll look into getting some BKR7E plugs...with the issues I've had over the past few months, it probably wouldn't be a bad idea to throw in some new ones.

[Croustibat]

dont worry about the exhaust, as long as it does not leak it is fine. I made the same hp with the stock exhaust and a boost controler than people made with straight 3" ones, and it got better spool. It was a little slower to rev north of 5000rpm though.

Leaner at idle could also be caused by higher latency injectors. At idle, latency is longer than the open time. if your injectors are a bit slower than the intended ones, it could be caused by that.