Txdragon

Really odd, but this just occurred today. I've had no problems with my tune til now. I am at idle and pegged out lean. Like, to the point of engine stumbling. When I hit the gas, it does ok. Driving, it's good, within range; but at idle. Nope. Scary lean. Please tell me this isn't ANOTHER failing fuel pump? What's the deal?
Tuning with Neptune, have adjusted no settings other than about 1.25 degrees of timing advance earlier today throughout my whole map. I have VTEC currently disabled, and have since my second day (I have driven 25 total miles with no issue before this).
D16Z6, Skunk2 rods, NPR pistons, Skunk2 IM and 70mm TB, OsideTiger 440cc injectors, walbro 255 high pressure pump, CXRacing T3/T04E .63 A/R turbo. 38mm wastegate 8psi spring, manual boost controller bringing boost down to 5psi.

I have tried the obvious in adjusting my idle A/F zone with ZERO success. I can hit the gas in idle and make adjustments just fine. I have tested this way to see if maaayyybe my O2 went bonkers, but I can lean or richen everywhere but idle. My first thought is fuel pump, and I have no other suspects yet. Help!

JRCivic1

How about an exhaust leak between the engine and the wideband O2 sensor ???

motoxxxman

I would guess this too. Or it's misfiring, possibly has compression issues, or those injectors that I've never even heard of are simply garbage. Check valve lash adjustment too; if it's out of spec it can cause some pretty severe misfires.
Fuel pump is fine. If the pump was dying, it would affect higher rpm and higher throttle, not idle.

I'm curious though. you say you have an 8psi spring in the wg, but are using a manual boost controller to bring the boost down to 5psi. please tell me how you're doing that, because it's physically impossible. boost controllers can only raise boost, they can't lower boost

2x0

In to find out what the problem is. Seems strange that adjusting your idle fuel value make no difference. Have some compensation factor out of whack? If running in closed loop what do your s.trim and l.trims look like while this is happening?

Also, if something is causing a misfire, wouldn't that put more unburnt fuel into the exhaust and cause a rich AFR?

Txdragon

Brand new spark plugs installed with the rebuild. NGK Gapped at .029. Unless the misfire started at that very instant. Valve lash was checked and adjusted before i installed. I've been working on tracking a smoke issue and have determined it is my valve stem seals, according to symptoms, next time i build a block, i'm going to do the head too. Lesson already learned there, brother. I was actually about to head to the parts store to pick them up after being called to tell me they arrived and discovered my posted issue. I've not had issues with a misfire the 25 miles so far that i've put on this build. Compression loss is unlikely, but already considered and I will be getting a compression tester at some point today. I don't remember the numbers offhand, but post build, they were certainly over 160 across the board. What's the point about the boost controller? Ask how any boost controllers work, I can't explain it. **shrug** I don't design these things. I can go from 1-30 psi, according to the manufacturers claim. I've certainly been higher than 8, and all the way down to 1. I am adjusted, right now, to 5 psi, or As of my last adjustment, I am just simply not pressing the gas pedal hard enough to give me more than 5. It doesn't really matter much because I am not going, and do not want to go higher than 5psi at this moment and the part that should not possibly work, is placebo enough to work for me.. I monitor manifold pressure as read in Neptune anyways, so I know where I am boosting, regardless of where I have whatever set.. As for the injectors, look them up. Plenty folks have used them successfully and use them still. They have been around a while.

Txdragon

I would expect a misfire to cause fat A/F rather than leaning out as well. I didn't adjust any aspect of the tune other than give about 1.25 degrees of advance in my timing map. From 3500rpm at med load, to WOT. So it's extremely unlikely anything budged. To test on a changed-by-fat-finger on the keyboard, I loaded my startup tune and had the same results, pegged lean at idle, good with gas pedal. This tells me it's a hardware issue (being the car). As for my tune in progress, all my values are still exceptionally conservative.

Txdragon

I will look at this today. Why though would it be lean only at idle though if this is the issue? Shouldn't it actually be worse under load?

Txdragon

To test the idea of an exhaust leak, I will move my sensor from its current location to my DP elbow. It currently resides at my test pipe. If the exhaust leak is causing the lean read at idle, is it a safe assumption that the engine itself is ok and it is only a false reading due to said leak? Since it would be a false reading only, driving wouldn't be an issue? I know datalogs would give inaccurate data at idle and so on but, engine shouldn't go boom since it's NOT actually running 19 afr at idle? All I know right now is this seems like another temper tantrum because I am fixing to replace the valve stem seals. My Honda curse strikes again.. lol

motoxxxman

You'll figure it out eventually, but boost controllers do only raise boost. you can't reduce boost below the wastegate spring pressure rating. If you have an 8psi spring installed, it's impossible to bring it lower by using a boost controller [when at wot].

Misfires always read lean on the wideband, not rich. O2 sensors are called o2 sensors because they read oxygen content, not fuel content, in the exhaust. When a misfire occurs, there is unburned oxygen in the exhaust, higher oxygen content, so it reads lean.

Exhaust leak reads lean for the same reason; fresh air is able to get into the exhaust; extra oxygen, so it reads lean. Reason it can show leaner at idle only is because there is very low exhaust volume, and the exhaust pulses are slower. In between positive exhaust pulses are negative exhaust pulses, which will suck fresh air into the exhaust. At higher rpm and higher throttle, there is more exhaust volume, and the pulses change, which gives less time for fresh air to get sucked in through the leak..

As you said, try moving the wideband to the bung closer to the engine, as long as it places the sensor before the exhaust leak if you do have an exhaust leak. That should tell you everything. If it still reads lean there, then you have a misfire.

Txdragon

Wonderful info here! Now about a potential misfire; why would this not cause higher rpm trouble? Shouldn't it read lean throughout the drive? Why still would it be only at idle?

boosted94gsr

Txdragon

Everything is prone to failure. I've had some ID injectors crap out on me. Also had an AEM and a Walbro fuel pump die unexpectedly. These injectors have so far served me well.

2x0

I, too, have never heard of these injectors. I wouldn't jump to conclusions in saying they are bad, but it can easily be checked by swapping in some different ones and updating the tune to see how it idles. Just to rule that out as a potential cause.


Right, right. I know I've been told this before, just couldn't remember the reasoning. Makes sense. Thank you

Txdragon

Turns out I lost my second O2 bung screw. This created the exhaust leak pre-wideband sensor. I am capping it shortly and will then be hooking up the laptop to see if this eliminates my lean idle. Cross your fingers, folks!

Txdragon

Problem resolved! The issue was the exhaust leak. Lost that O2 bung cap evidently somewhere on my return trip from the parts store yesterday. Just replaced it and she is idling at a comfy 13.5 afr. Thanks for the insight and help!!

2x0

Glad to hear it wasn't a misfire, or something worse