fid

iTrader: (18)

I will try to be as direct as possible to keep reading limited.

Setup That Matters:
-HKS Intake With Apexi Filter (New)
-Stock Cams
-FIC 850's (NEW)
-Battery In Good Shape
-Walbro (New)
-Stock Replacement Front O2 Sensor (New)
-Perrin Fuel Rail

Problem:

After extensive mapping and playing with the injector latencies and scaling I cannot get the car to idle anything below 16.0:1. The car will cruise fine hanging between 14.7 and 15.2. I changed to FIC's from PTE 780's in which I had the exact same problem with and started throwing parts at the problem trying to fix it. When logging the idle I noticed that the injector pulse width will not change not matter how much I increase the latencies (locked in at 1.28ms). It will start off in open loop rich of course but once it drops back into closed loop it idles lean. I can pull the O2 sensor harnass and get the car to idle pretty much right on stoich but not with O2 sensor feedback. I would think if my latencies weren't in check they would be exposed when the O2 sensor is unplugged and the fuel delivery is strictly operating off the numbers given.

Any help/suggestions is welcomed and thanks in advance to all . Happy Thanksgiving also .


UPDATE:

Finally hunted down this sucker after throwing plenty of parts at it. Turns out it was two things.

1) There was a pinhole (looks like they pulled up to quick when they stopped welding) on the bottom side of the O2 bung on the O2 housing. You couldn't see it from the top or the bottom of the car with the housing on. Pulled it off and saw it after close inspection. I must have missed this when porting the housing and examined it .

2) The test pipe to cat back flange gasket totally blew out and was leaking pretty good. Replaced the gasket and it sealed up nicely. Only thing that baffles me is that once I replaced this gasket (even after re-welding the O2 housing) then it idled fine. Meaning the rear O2 sensor shouldn't be giving any feedback for idle enrichment, just emissions. Maybe my understanding of the rear O2 is wrong.

Now the car idles dead on 14.7 but is throwing a code for fuel trim because of me trying to compensate for the leak. I am in no way new around working cars but it just goes to show you that even someone more familiar with tuning and auto mechanic can miss/overlook the simplier solutions to the problem. So in all this what I tried:

-Messed with latencies and scaling
-Changed injectors
-Checked for boost leaks
-Changed front O2 sensor
-Plugged up exhaust to find rear exhaust leak
-New plugs for good measure

If I were to do it again I should have started with doing all the things that didn't involve throwing parts at the problem. Instead I let my ego get in the way thinking that there was only a few thing it could have been. For future members that may be finding this using the very valuable search button I would recommend hunting down your lean idle issue by (assuming your cruise A/F seems close, if not check oyur latencies):

1) Log your fuel trims and making sure your latencies/scaling are all where they should be. If your fuel trims are within check it is more then likely your problem lies somewhere eles.

2) Do a boost leak test. Unmetered air will cause a irraditic idle mixture.

3) Check for exhaust leaks from the O2 housing all the way back to your last exhaust flange. You can cap your exhaust like I did to listen for majors leaks (helps if you have second person). And check all of your flanges for obvious signs of a leak like black sout buildup around the gasket or on the mating surface itself.

4) Next I would measure the voltage output from the front O2 sensor. Narrowbands operate on a small voltage (0-1.5V). If the sensor is outputing 0V then you know what your problem is.

5) Pull your injectors and visually inspect. You could get them cleaned and flowed by someone like RC Injectors or another reputable company. If you have another set of injectors, dial them in to see they fix the problem.

Just a few things to get you started on diagnosingyour lean idle issues. Hope it helps alittle .

tephra

iTrader: (6)

what are your fuel trims telling you?

in evoscan log "Fuel Trim Low" and "Fuel Trim Mid"

Low is your idle trim, Mid is your cruise trim. You want them both as close to 0 as possible - +/- 2% is ok.

fid

iTrader: (18)

Honestly, I haven't even bothered logging them since all my changes (extreme or not) have netted the same result. I will log them and report back. Do you have any ideas why my idle pulsewidth wouldn't change when prompted? Thanks for he response.

Charlie_B

iTrader: (1)

Could just be an exhaust leak throwing off the wideband. If your trims are within spec, your fine.

Ive got a BR DP (the one w/o the donut gasket), and I idle between 15.5-16.3. I know it leaks a little, can see the black soot when I take it off. But the WB shows 14.7 at cruise. So I just figured that the leak only affects it at idle.

fid

iTrader: (18)

UPDATE:

Finally hunted down this sucker after throwing plenty of parts at it. Turns out it was two things.

1) There was a pinhole (looks like they pulled up to quick when they stopped welding) on the bottom side of the O2 bung on the O2 housing. You couldn't see it from the top or the bottom of the car with the housing on. Pulled it off and saw it after close inspection. I must have missed this when porting the housing and examined it .

2) The test pipe to cat back flange gasket totally blew out and was leaking pretty good. Replaced the gasket and it sealed up nicely. Only thing that baffles me is that once I replaced this gasket (even after re-welding the O2 housing) then it idled fine. Meaning the rear O2 sensor shouldn't be giving any feedback for idle enrichment, just emissions. Maybe my understanding of the rear O2 is wrong.

Now the car idles dead on 14.7 but is throwing a code for fuel trim because of me trying to compensate for the leak. I am in no way new around working cars but it just goes to show you that even someone more familiar with tuning and auto mechanic can miss/overlook the simplier solutions to the problem. So in all this what I tried:

-Messed with latencies and scaling
-Changed injectors
-Checked for boost leaks
-Changed front O2 sensor
-Plugged up exhaust to find rear exhaust leak
-New plugs for good measure

If I were to do it again I should have started with doing all the things that didn't involve throwing parts at the problem. Instead I let my ego get in the way thinking that there was only a few thing it could have been. For future members that may be finding this using the very valuable search button I would recommend hunting down your lean idle issue by (assuming your cruise A/F seems close, if not check oyur latencies):

1) Log your fuel trims and making sure your latencies/scaling are all where they should be. If your fuel trims are within check it is more then likely your problem lies somewhere eles.

2) Do a boost leak test. Unmetered air will cause a irraditic idle mixture.

3) Check for exhaust leaks from the O2 housing all the way back to your last exhaust flange. You can cap your exhaust like I did to listen for majors leaks (helps if you have second person). And check all of your flanges for obvious signs of a leak like black sout buildup around the gasket or on the mating surface itself.

4) Next I would measure the voltage output from the front O2 sensor. Narrowbands operate on a small voltage (0-1.5V). If the sensor is outputing 0V then you know what your problem is.

5) Pull your injectors and visually inspect. You could get them cleaned and flowed by someone like RC Injectors or another reputable company. If you have another set of injectors, dial them in to see they fix the problem.

Just a few things to get you started on diagnosingyour lean idle issues. Hope it helps alittle .