MY08 with Stage 2 Tune, but MAF g/s seem low

OzRex08
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MY08 with Stage 2 Tune, but MAF g/s seem low

Postby OzRex08 » Wed Oct 21, 2015 8:40 pm

Hi all,

I thought I'd throw this one out there after having a bit of a look through the forum for an answer...

I am currently using a stage 2 map for my 08 rex that I got from the RR site and it's been going well. However, I have seen other rex's logging much bigger g/sec numbers and was wondering if my mine was low and how I would go about diagnosing what could be the cause. The most I get on 3rd gear pull is 193 g/s, I currently have the following mods installed:

- Ultrex TBE
- K&N Panel filter in stock box
- Mishimoto Induction Hose.
- 1 restrictor pill removed (Actuator side)
- 1 restrictor pill hole enlarged to 1.0mm (from 0.8mm)

The tune is aiming for 17psi on the TD04, and it reaches full boost by around 3000rpm. I was experiencing boost creep issues previously so that's why I enlarged the restrictor hole size.

I have checked for leaks pre and post turbo and there does not seem to be any present. Could a dirty / faulty MAF sensor be the cause? Or perhaps the car needs a compression test???

Any ideas would be welcome.

OzRex08
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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby OzRex08 » Thu Oct 22, 2015 10:56 am

It's quite possible that atmosphere and altitude are skewing the numbers. 650m above sea level and intake temps were around 31C yesterday with a fairly high humidity.

According to this site: https://wahiduddin.net/calc/calc_hp_dp.htm

My engine is probably running at about 88% of rated HP.

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Subey
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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby Subey » Fri Oct 23, 2015 1:58 pm

MAF g/s is a direct lookup on MAF voltage so either you have compensations that reduce the reported MAF (i.e. temp compensations), a dodgy/dirty MAF, a leak or really are only hitting 193g/s. On a 2.5L that is low.

Following some logic.
- A leak pre-turbo would mean air is being sucked in through that instead of past the MAF = low MAF reading

- A leak post-turbo would mean boost is being lost and your turbo would be working harder to get to your target, which would = a high MAF reading

- A dirty MAF would probably read high, I don't think they fail in new age imprezas in a low read manner and it would probably run like garbage off boost too

- Not hitting target boost due to mechanical issues (e.g. wastegate, solenoid of boost line) would = a low MAF reading

So take your pick. I'd check hoses/lines then clean the MAF and see how you go from there.

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Subey
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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby Subey » Fri Oct 23, 2015 2:04 pm

I'd log MAF voltage, load (g/s), manifold pressure absolute, target boost, rpm, max WGDC and WGDC.

That'll tell you if you're not hitting target boost and what your load looks like. No need to log MAF g/s, you can calculate g/s it = (rpm*load)/60

In your example if you hit a max g/s of 193 then that is likely to be around 6000rpm. Working backwards you have a load of (193*60)/6000 = 1.93. A 2.5L will have a higher airflow than a 2L at the same boost level due to larger displacement cylinders so careful comparing a 2L to yours.

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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby OzRex08 » Fri Oct 30, 2015 6:08 am

Hey,

Thanks for the replies. The following morning when it was a bit cooler I did a run and logged a few g/s higher. Unfortunately, on the way home I hit a Roo and have been dealing with that.

While I mentioned that there was no apparent leak from before the Turbo, the Mishimoto induction hose never did sit flush with the Turbo right from the first moment I installed it (no matter how hard I pushed on it). So perhaps that is something to look at again. I have emailed Mishimoto, sent some pics and asked them if I should have to trim the end so that it sits flush all the way 'round on the Turbo inlet. They are stll getting back to me on it.

As I've managed to get most of the dings out, and repair the bracket that holds the bumber to fender I'll get out (a bit later in the day) and do another log with MAF Voltage etc.

Cheers

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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby OzRex08 » Fri Oct 30, 2015 1:37 pm

Hi Subey,

Here's a log done around lunch time today.

http://www.wrxenhanced.com/logs/romraiderlog_20151030_125025.csv

From what I can see, it looks like my Max WGDC is holding back my initial WGDC in places. I can fix that by increasing the Max table. Engine Load seems to max at around 2.84 g/rev but not sure whether this is normal either. The road was a flat as I could get it, but it's rare to find a flat road around here.
:)

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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby Subey » Fri Oct 30, 2015 6:19 pm

Changing out of the restrictor pill in the boost line has caused your boost solenoid settings to not work as they were originally tuned to. Looking at this, the tuner reduced WGDC over 5800 to combat the boost creep you were seeing.

You need to either get a 3 port solenoid and retune boost or to revert to the stock pill.

Image

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Re: MY08 with Stage 2 Tune, but MAF g/s seem low

Postby OzRex08 » Fri Oct 30, 2015 8:03 pm

Hi Subey, thanks for taking a look. I happened to find the missing restrictor pill (0.8mm) so I reinstalled it on the actuator side. I'll need to do another run and see how it goes. I'm thinking that if my MAF scaling was out, this could also account for the low g's/sec, but to tune this properly I'll need to install a Wideband.

Thanks again.

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