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2004 XT 5 MT
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14 Posts
Discussion Starter #1
I have been battling this problem since I rebuilt/modded/upgraded my 04 XT MT. From 3200 RPM to 3800 RPM, at low load/in vacuum I have a lean spike that I was only able to cure by adding load to the load compensation table for that range. The issue is present in both open and closed loop fueling. See attached log

I do not have any boost/vacuum leaks, I have new plugs, a new AME FP, a new Subaru MAF sensor I even put the original airbox back on to ensure it wasn't a MAF scale issue. I think it could be a fuel delivery issue. What could be the main cause of this issue? I feel like the load compensation table is a band-aide to an underlying issue. Any input would be greatly appreciated. below are the mods I have done as they relate to fueling.

AEM FP
Aromotive FPR
injector clinic 1000cc top feed conversion
parealell fuel lines
new MAF sensor
Stock airbox
new fuel filter
 

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Super Moderator
2018 X3 M40i / 2014 VW Passat TDI SEL
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1,618 Posts
pay real close attention to your fuel pressure. I had lean spikes with surging which was a problem with harmonic pressure waves causing spikes all over the place. Lots of dampers fixed my problems.

Does it look like this?

Or this?
 

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2004 XT 5 MT
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14 Posts
Discussion Starter #3
@Scooby24 Unfortunately I have a liquid filled gauge so to see any oscillations I would have to hook up a different gauge (which I am not against doing). did you use sock subaru dampeners or did you use aftermarket? I was looking into these as they have a vacuum reference.
 

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Super Moderator
2018 X3 M40i / 2014 VW Passat TDI SEL
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I had to go with aftermarket as the subaru dampers didn't resolve it. I had to put dampers on the inlets for each rail to fix it. Injector Dynamics I believe came out with a solution at some point as I don't think I was the only one with problems. My theory is that such large injectors needs such rapid and fast duty cycles for lower fuel needs that they cause pressure waves in the lines that needs much more dampening than you might expect.
 

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'17 Imp Ltd wagon CVT
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1,172 Posts
For me, addressing the issues you speak of consisted of both tuning and mechanical approaches.

By far, the largest component to making this load-range issue go away was a mechanical change, but it wasn't changing or adding fuel line dampeners like most. Using a suggestion in the forums specific to my engine, I added a foot and a half of fuel line at the inlet to the regulator... an insult to my modding sensibilities in its crudeness... and it made an immediately noticeable difference. I was amazed. To make the added line virtually unnoticeable I coiled the line below, out of quick sight, and secured it loosely. Loosely, because its purpose was, of course, to become a pulse dampener for the fuel line. With steel in all but the very short connections of flexible hose between the chassis lines and engine fuel line dampening has been left to little, partially effective but limited in range, OEM dampeners. Apparently, however effective the OEM system is in general their mechanical range doesn't deal with all resonances. The factory tuning compensates for some of this inadequacy with the load compensation tables, among other things. But the elephant in the room is the imperfect mechanical dampening, which, in my experience, was largely solved by a simple length of fuel line.

Unfortunately, that left the OEM load comp tuning over compensating for the new fuel line reality. So that had to be addressed as well, one of the tuning parts. Discussions of this abound, at least elsewhere than this forum. Since no one had/has definitive LC table modifications my tuning took a while, but eventually after many iterations the LC tables were optimized.

Finally, both fueling and AVCS were similarly addressed... much leaner fueling produced more power and a happier datalog, while also reducing shock waves in the fuel lines thus also smoothing the transitional load range in question. Most tuning advice encourages a fat, rich, fuel curve that supposedly mitigates engine knock... but I believe as do others, and supported by data and experience, that too much is a bad thing, ring land failure being one. Those of us who chose to tune properly instead of throwing a quick and dirty excess fuel substitute at it, got both a stronger better running engine as well as a less knock prone and safer engine.

In other words, fixing the subject fueling issue is not as simple as throwing a couple parts at it. In fact, it's not the only modified tuning issue that falls into the same category... that is, modifying the engine's components and getting a tune for them...and continuing to use seldom addressed tuning tables which no longer apply. The normal big tables like load, boost, fuel timing etc are obvious, as are things like injector tuning, and some AVCS for example... but even here there are applicable tables rarely if ever addressed that directly affect driving a street machine totally unrelated to the WOT, graph making, dyne spinning pro tuner's work.

Assuming, hopefully, that you do your own tuning, keep at it. Sadly, there are fewer tuning resources today than ten years ago, but they're there. I found forming relationships with others who were successful extremely fruitful, both in ideas as well as references.
 
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2004 XT 5 MT
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14 Posts
Discussion Starter #6
@Fate I have read the posts about the 1m fuel line extension on NASIOC and iwsti. I tried it but it did not seem to make a huge difference (perhaps I didnt give it enough attention). I have played with my AVCS table, per injector trim and primary ignition timing in that area to try and resolve the issue. The only thing that has helped has been the LC table. I am doing my own tuning, but that is not to say I am necessarily good at it! I will be ordering 2 Radium dampeners tonight. I will update this post when I get them installed.
 

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Super Moderator
2018 X3 M40i / 2014 VW Passat TDI SEL
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I will say I tried the long inlet hose as well..the theory is the same...longer hose dampens the line...however in my case it wasn't good enough. It did help...and I tried adjusting LC tables as well but the harmonics aren't consistent and the surging never went away. When I got the dampers on and the fuel pressure was stable, I think all I did was zero out the LC table...ran perfectly afterwards and there was zero surging or hesitation, and long/short term fuel trims suggested I wasn't seeing spikes in those rpm ranges anymore.

Just in the videos above you can HEAR the difference the steady fuel pressure made. It just idled amazingly. I recall taking it out for the first drive afterwards and being blown away with how smoother it ran and how different it sounded overall. It's certainly not something that was placebo, lol.
 

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2001 Forester STi 6spd with MapDCCD
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4,672 Posts
Turn your Aeromotive FPR up to say...46 or 48psi and using the Injector dynamic sliding scale tables (through cobb) , adjust as necessary with all background information for min pulse widths and latency settings.

Let me preface this by saying that the 'Infamous' lean spot on subaru's is almost always a symptom of the OEM fueling layout, which in short, causes a starvation on the passenger side fuel rail at low loads (on all port injection, sub 2014 EJs). I spent literally the first half of my tuning experience thinking that it was something that could be tuned out or somehow fixed, and yet almost every time i was met with the same result when using the same parts. After analyzing lots of data, it was very obvious that the ECU was indeed trying to correct it, but after playing with a dual wideband setup (one for each bank of cyls) it became clear that the passenger side was momentarily being starved of fuel. You can try adjusting for individual cylinder IPW compensations and overall CL load targets, but its a minor bandaid at best that made 2 and 4 pig rich and 1 & 3 marginally better. The issue was always resolved by going to a larger fuel system.

With that being said, even with some setups running ID1000s and a proper regulator, i have gotten the rare incidence of it still exhibiting such features after a proper tune with very small AF correction swings. In such cases, the solution that worked best was raising the FPR from the stock 43.5 up to something like 46 or even 48 in some cases, and re-tuning based on the rise in pressure. The results were pretty satisfactory with a stop to the lean spot occuring.

So, why does this lean spot still occur after upgrading? Depends on the quality of parts used. In the case of the ID1000s that still experienced issues after swapping, i suspected it had something to do with the fact that the lines were split using a "T" fitting and not a recommended "Y" fitting to split fuel between left and right rails. The "T" fitting likely had some pretty violent turbulence in terms of how well it would flow compared to a less abrupt "Y" fitting that many other kits utilize.


Just some thoughts from my recent field notes for you.


-Mikey
MKtuned
 

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2004 XT 5 MT
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Discussion Starter #9
@MikeDrives1 I am at 58 PSI and still seeing the issue. I installed 2 Radium fuel dampeners and the lean spot literally moved 1000rpm up. .. from starting at 3200 before to starting at 4200rpm now. The positive side is I am never in this RPM range under light load. One thing I will try is changing out my fuel distribution block (essentially a 'T') to a Y fitting set up. That will be the least expensive part of this whole issue!!
 

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