Engine Surging and Running Rich

Posts specific to the 2.0 litre Turbo engine

Re: Engine Surging and Running Rich

Postby dr20t » Sun Apr 26, 2015 9:49 pm

Yeah they're quite loud (especially if you have a stock / quiet exhaust).

Given map reading is off, I would check the vacuum hose to the map sensor for cracks, including the canister that is in line with the map sensor and vacuum nipple on front of intake manifold. These commonly work themselves loose so check those and again check all vacuum hoses

I wouldn't see Subaru in my humble opinion. They know nothing and will conduct a bunch of frivolous and expensive tests at your expense.

Mick
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Re: Engine Surging and Running Rich

Postby Corbin » Mon Apr 27, 2015 3:42 pm

Okay I'm unsure of whether a MAP reading of 5psi at idle is normal or not. Relative pressure would mean that the MAP-BAP = ~-10psi which is normal, correct?

Specialist assures me the problem is not a vacuum leak as it is running rich at all times.

I did reset the ecu today and noticed that fuel leaning #1 and fuel correction #1 are at 0 after the reset, though this is only idling and light revving while stationary. I assume this will change when the car transfers to open loop.

Possible O2 problem?

Any idea what I should be logging or monitoring in order to help diagnose the issue more?
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Re: Engine Surging and Running Rich

Postby dr20t » Mon Apr 27, 2015 5:08 pm

Yes a variance of 5psi at idle is substantial and indicates a vacuum leak or faulty map sensor. Check the things I suggested above.

Af learning and correction only happen in closed loop not open loop.

Learning takes some time to see values so no need for concern there

However af correction should be real time adjusting (assuming you're live logging this and not just a snapshot). If you're not seeing any values when live logging then this indicates faulty 02 reading. Check wiring to it first (the foremost one on your dump pipe about 20cm's down from the turbo) and if that seems all ok then order new 02 sensor

My tip if you're changing 02 is to use the updated one which can be sourced from garage88.
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Re: Engine Surging and Running Rich

Postby Corbin » Mon Apr 27, 2015 6:09 pm

Thanks so much for your help dr20t.

I'm not sure I understand what you mean by a variance of 5psi. Would you explain what the value should be?

I had meant to say that the fuel corrections would revert when transferring to closed loop. My bad. Unfortunately the car won't be seeing much time on the road for a little while as...

I backed into my brother's car in the driveway. Apparently bull bar + slowly moving car = mass damage. Couple this with my engine troubles and it's fair to say I'm a bit sick of this car. :cry:
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Re: Engine Surging and Running Rich

Postby dr20t » Mon Apr 27, 2015 9:34 pm

Anytime mate

And sorry to hear of your misfortune

What I meant by 5 psi variance is - at idle, vacuum should be around -10psi. If you're seeing -5psi (variance of 5psi), either you have an intake leak, or your map sensor is out of whack.

Above values are manifold relative pressure. Ie relative to atmospheric pressure.

Hope this helps. If you cant drive the car, check your 02 sensor via voltage/resistance (either romraider or multimeter/ohmmeter).

Keep us posted on how you go

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Re: Engine Surging and Running Rich

Postby Corbin » Tue Apr 28, 2015 12:16 pm

Aaaand I seemed to have confused myself. The values I was referencing were absolute pressures. Relative hover around -10psi.

On the way to the repair shop today to get a quote ( :shock: ) I managed to pull a few datalogs. I was hoping someone with a bit more experience than me could help interpret them.

I logged a cold start, acceleration, country road cruise and warm idle.

Unfortunately the forums won't let me upload .csv files however they can be accessed on my legactgt.com thread. (http://legacygt.com/forums/showthread.p ... ost5134727)

Any help would be appreciated,

Thanks again,
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Re: Engine Surging and Running Rich

Postby Corbin » Fri May 01, 2015 8:35 pm

From looking at the logs myself I have gathered that the A/F learning and correction #1 at cruise seem to wander around the negative values before reading a continuous stream of 0 values before returning to the negative values. Is this normal for the values to read 0 while at cruise?

The A/F sensor is reading predominantly 0.76 lambda with the resistance sitting mostly on 31 ohms moving only 3 or 4 ohms in either direction on occasion (at idle its a constant 31 ohms).

Any help in interpreting this data would be greatly apprectiacted!

Thanks,
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Re: Engine Surging and Running Rich

Postby dr20t » Sat May 02, 2015 7:45 am

Sorry I tried opening on my phone and couldn't.

If what youre saying is correct then it seems normal correction.

When it goes go zero it indicates your ecu has switched to open loop fueling (ie no reliance on 02 sensor for reaching target afr)

I still believe its accelerator pedal related
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Re: Engine Surging and Running Rich

Postby liberty254 » Sun May 08, 2016 1:34 pm

Did you find out what the issue was. Experiencing singular thing. Idling at -8psi vs target of -10 and running rich. Vehicle surges at 3000-4000 rpm in gear 3 & 4. LV attached
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