Uh oh - IAM dropped to 0.375

[heiche]

I'll clean the MAF today and see what happens. Thanks for the idea fahr_side and xt2005bonbon, it's a freebie that I hadn't thought of.

 

Still running stock fuel pump and FPR.

[fahr_side]

Still running stock fuel pump and FPR.

Yeah. If you're running 17.5psi at 5k2 you're probably tapering off to what, 16.5psi at redline? If you're at sea level and running 11.2 AFR you're going to be around 95% IDC on that 16G (I ran that turbo for two years). The stock LGT pump is really working hard to feed the injectors at that rate and it wears out. As it wears, fuel pressure will drop off at high flow rates. Whether or not this is your problem I'd drop either a DW65c in there or a stock GRB pump. The GRB, with it's larger turbo and the same injectors, is expected to run at higher IDCs and has a pump that does about 20lph more than the LGT/WRX/FXT item does.

[xt2005bonbon]

Informative posts fahr_side

[heiche]

Yeah. If you're running 17.5psi at 5k2 you're probably tapering off to what, 16.5psi at redline? If you're at sea level and running 11.2 AFR you're going to be around 95% IDC on that 16G (I ran that turbo for two years). The stock LGT pump is really working hard to feed the injectors at that rate and it wears out. As it wears, fuel pressure will drop off at high flow rates. Whether or not this is your problem I'd drop either a DW65c in there or a stock GRB pump. The GRB, with it's larger turbo and the same injectors, is expected to run at higher IDCs and has a pump that does about 20lph more than the LGT/WRX/FXT item does.

 

I like the STI GRB pump idea. Hmmmm, might have to consider that one...

 

Regarding injector duty cycle, I usually see it peak at < 90%. I'm at roughly sea level. I always expected it to be a little higher as you estimated. Ah well.

 

Another thing I just thought of is that when I replaced my short block with an EJ257, doesn't it have a slightly smaller piston dome volume, and therefore a slightly higher compression ratio? Maybe since my timing advance was previously on the edge anyway, it is now a bit too much?

[fahr_side]

Your original shortblock was in fact an EJ257. Your heads are identical to the '04 STi items with the same 56cc chambers. The stock EJ257 pistons have a dish of -22cc vs the -24cc for the stock EJ255 items. Put together that gives you the usual STi CR of around 8.28:1...

I've worked on a lot of the newer motors with the D25 heads. Those are a bear because they have the smaller 50cc heads, and it seems only CP makes an EJ255-specific forged piston with a -24cc dish, so they always end up with STi pistons in them. Final compression then comes out to around 8.78:1. This sounds a lot, but the stock CR actually calculates out to around 8.6:1 rather than the 8.4:1 Subaru states. In practice, I've never had to reduce timing on any of these cars that I had tuned on a stock block after they fitted forgies. We always skim the blocks and heads to be sure they're flat, and usually use 1.00mm MLS gaskets to compensate for that.

 

Please, don't consider a fuel pump. Just swap the poor thing, you're wringing it's neck. If it can't keep pressure up when IDC is under 90% your fuel system is already failing. Did you clean the injectors when you had the manifold off? It doesn't hurt to run a pint of methanol through the tank once in a while.

[heiche]

You sir, are a wealth of information! And I appreciate it.

 

I could be wrong, but I thought my car (2005 USDM Legacy GT 5MT) was shipped with an EJ255? I could be wrong though! But if that's true, and I replaced the shortblock with an EJ257 (keeping the new oem pistons it came with), wouldn't it then have a slightly higher compression ratio?

 

Regarding injectors, I did pull them and have them cleaned last year. Thanks for the info on fuel pumps. A new fuel pump is quickly bubbling up on my toys-to-purchase list.

[compsurge]

fahr_side is simply stating that the only difference between the EJ255 on the 2005 cars and the EJ257 is the piston dish.

 

The stock fuel pump is questionably sufficient on the stock car because Subaru undersized the wiring. There is a thread on it relating to the "stumble" that so many of the cars. A proper gauge wire was used to replace/supplement the OEM wire and the stutter has been resolved on some cars.

[Mr.Goodbarf]

+1 on fuel pump upgrade. Im running a bnr16g as well. My tuner all but refused to tune my car without a new pump.

 

Apparently we are stuck with these shitty injectors though.

[heiche]

Side note: I did perform a "FPCM upgrade" when I first got the car. Replaced my FPCM with STi part 22750AA010, along with much (but not all) of the wiring being replaced by heavier gauge.

 

Now that doesn't help the smallish fuel pump itself, and smallish fuel injectors though

[heiche]

Ok, I have some improvement, but it's only been a day, so I won't spike the ball just yet.

 

I took my timing table and dropped ALL values by 3 degrees, and flashed that. After driving it "like it was stolen" a few times today, IAM has held at 1.000

 

My current thinking is that prior to my rebuild, I was seeing a little timing pull here or there, as the timing map was pretty aggressive. I since have replaced my short block due to a main bearing failure. Here's where it gets a little murky... I think the EJ257 pistons that replaced my EJ255 pistons cause a *slightly* higher compression ratio. So if I already had a little timing pull before the rebuild, now I have even more. And the ECU on Friday said enough is enough and slammed the IAM down to 0.375.

 

So by dropping the timing 3 degrees across the board, it's looking a lot better. Even though I am still seeing 1.4 degrees being pulled in a couple of spots, it's better than the 4.2+ degrees from last week (the math kinda works out there: 4.2 before, subtracted 3 degrees, now seeing 1.4)

 

Anyway, I'll beat on the car some more tomorrow and see what happens

 

http://www.btssm.com/scrnshots/scrnshot12iamBetter.png

[compsurge]

You have a leak.

 

That or your MAF scaling is off. Cell A indicates a leak is present. A very small leak can cause huge changes in airflow at idle, so there is likely a very small leak somewhere.

[heiche]

Agreed that cell A is off. Eventually C and D creep up too, although not as extreme as A. Did a pressure test (about 6 or 7 psi), plugging the intake hose at the airbox. It held pressure very well, even 30 seconds after the compressor was disconnected, it held pressure. So yeah, alternatives would be like you said, maybe MAF-related. I still have a hunch about fuel pressure too, and will be installing a fuel pressure gauge later this week to check out that possibility.

 

Thanks for your help. I'd like to get that LV closer to perfect At least IAM is back up to 1.000

[xt2005bonbon]

How many miles does your car have?

[heiche]

134k

[heiche]

progress update: still working on this, although IAM has been holding at 1.000

 

Dropping the timing across the board 3 degrees helped the IAM issue, although *may* be a band-aid. Time will tell if I can bring the timing back up to where it was some day.

 

I replaced the MAF with a new dealer item. fahr_side and xt2005bonbon were both suspecting MAF issues. My WOT calculated load went up 10%! So the old MAF *must* have been reading too lean. Now I'll need to tweak a few things to adjust for a suddenly over-rich WOT, and get that back in line.

 

Oddly with the new MAF, my fuel trim is still high at around +8% at idle (cell A). Maybe that's a separate issue. It would really seem like a vac leak, but I've pressure tested it a couple of times and everything is tight and holds pressure even after the compressor is disconnected for a bit. But this isn't a big deal... more of an annoyance.

 

fahr_side: my new fuel pump arrived (STi GRB). Hope to put that in this weekend. Whether it helps, or is just preventative maint, it sounds like a good idea.

 

I'll post an update in the coming days, but for now the IAM at 0.375 is a non-issue as it is back up to 1.000

[xt2005bonbon]

Good to hear. How much was the MAF? I may have to get one too

[heiche]

You need a MAF too? Sorry to hear that. I paid around $160 at the dealer.

[xt2005bonbon]

You need a MAF too? Sorry to hear that. I paid around $160 at the dealer.

 

Daaang. That's small little sensor is NOT cheap!

[FJuan]

I'm in the same boat with you guys, looking at a new MAF sensor soon, once I test a few more things. I feel like I chasing the same issues as you are heiche.

[compsurge]

I might be as well, though it's been like this since I got the car. Definitely air related, no leaks detectable...

 

Maybe I should try borrowing a MAF for a while to see if driveability improves.

[heiche]

you could have a MAF signal that's reading low. That will account for timing being high and fuel leaning out. Try cleaning the MAF sensor or swapping it for a known good one.

 

Just wanted to post that everything is well after 2 weeks. If anyone notices that their AFR continues to slowwwly lean out over time (weeks, months, years) and eventually timing pull events continue to increase at the same time, it could be your MAF degrading. Replacing mine with a new unit made my engine operate much better. Thanks again everyone for your help!

[xt2005bonbon]

mmmh. I may be suffering from that too then. However, the only way you could confirm that is by changing the part right? Tracking its voltage did not really show anything correct?

[heiche]

yes, as far as i know swapping it out is the test. watching the Voltage doesn't reveal anything unusual as the signal is only slightly low.

[compsurge]

Chime back in a few more weeks. Did you ever have an issue at 2000-2500 rpm and low load?

[heiche]

Chime back in a few more weeks. Did you ever have an issue at 2000-2500 rpm and low load?

 

It had issues all over the place Below is an LV back from Sep 5, when things were getting ugly, and I got concerned. Then a couple weeks later the IAM dropped.

 

http://www.btssm.com/scrnshots/scrnshot9b-BadLV.png

 

It got better once the MAF was replaced. Now the LV is back to normal