T

Datalog Throttle Fluctuating_car went into limp after this pull

The Sasquatch

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Mar 28, 2024
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Lambda, Vanos, throttle position, boost, all look a mess but not familiar with interpreting logs. Any ideas?!

Symptoms


1) When accelerating the car doesn't pull cleanly/consistently, there is some easing and re-surging when accelerating. This actually happens most noticeably under light acceleration. Log illustrates this.

2) Idle also has a bit of vibration/tends to be sometimes a hundred revs or so lower than 650 per minute.

3) Throttle response is a little sluggish

Car has new:
Coils
Plugs
Crankcase Breather
Intake hose
Vaccum tested several times (now solid)
Air filter
Sports Cat
Intercooler

Running stage 0
 

The Sasquatch

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Mar 28, 2024
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Codes thrown after pull:

2CF4 - Oxygen Sensor before catalytic converter, dynamics slow response

2D2F - Oxygen sensor before catalytic converter, dynamics multiple fault

Car has high flow downpipe fitted but is running MHD with 'aftermarket DP' selected in tune. Could this be an issue?
 

ShocknAwe

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Jan 24, 2018
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I see overboost and big correction cyl, 5. Tune details? Throttle changes could be closures.

Vanos looks ok in terms of request and effort, exhaust a little off.

Are your O2 sensors reversed?
 

The Sasquatch

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Thanks for the response.

Tune above was stage 0, MHD V1.6.

I tried flashing V1.8 stage 0 today as I read the boost control is more refined. Also cleaned the charge pipe pressure sensor - which was dirty.

Car has high flow cat and FMIC fitted.

Interestingly the O2 sensor codes didn't appear - I drove the car for nearly an hour to see if it would generate a code but no codes were produced. The throttle closures however are still there.

O2s were fitted by a garage so I expect they would be correct but can't say for certain if these are correct or not? Could this be a cause of throttle closure?

Here's the latest log from today, V1.8, stage 0 (MHD), and after cleaning the charge pipe sensor:

Any ideas what might cause corrections/throttle closure?
https://www.spoolstreet.com/[GRAPH ... series="3,14,23,24,27" zoom="-1,65"][/GRAPH]
 
Last edited:

The Sasquatch

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Thanks for the response.

Tune above was stage 0, MHD V1.6.

I tried flashing V1.8 stage 0 today as I read the boost control is more refined. Also cleaned the charge pipe pressure sensor - which was dirty.

Car has high flow cat and FMIC fitted.

Interestingly the O2 sensor codes didn't appear - I drove the car for nearly an hour to see if it would generate a code but no codes were produced. The throttle closures however are still there.

O2s were fitted by a garage so I expect they would be correct but can't say for certain if these are correct or not? Could this be a cause of throttle closure?

Here's the latest log from today, V1.8, stage 0 (MHD), and after cleaning the charge pipe sensor:

Any ideas what might cause corrections/throttle closure?
https://www.spoolstreet.com/[GRAPH ... series="3,14,23,24,27" zoom="-1,65"][/GRAPH]
Wastegate also looks all over the place?
 
Last edited:

wheela

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Jun 4, 2021
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Other than the over-boost & oscillation, it looks pretty normal for the stock tune. Stage 0 is the stock tune, so there should be no differences in boost control between 1.6 and 1.84 (thatb would only apply to stages 1 and above).

The overboost and oscillation could be from the combination of stock tune and your downpipe. With a high flow downpipe, the turbo will respond quicker and make more boost at given conditions vs. how the DME is expecting the turbo to behave.

Take a look at load request% and load actual% You'll see that the overboost causes load actual to exceed load request. The DME closes the throttle plate in response (to keep load actual from exceeding load request). The throttle closures all align with the boost & load oscillation.

Not sure about the O2 sensor codes? I'm not 100% sure as I haven't ran the stock tune with my downpipe, but I don't know if MHD automatically disables the downpipe codes when running stage 0 (stock tune) like it does with the other tunes. I think there's check boxes to select when flashing, you may want to try re-flashing stage 0 and checking how those check boxed are set up - try to select an aftermarket DP option.
 

The Sasquatch

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The load request vs load actual you mention is very interesting and makes sense.

Double checked the map and ‘aftermarket Dps’ definitely selected. Could the larger FMIC cause the overboost?
The only other thing fitted to is a K&N panel filter - standard airbox, etc.

I just flashed stage 2 (also with aftermarket DPs selected) to see if it would produce a different result but closures are still present. Would this suggest a hardware issue was causing the overboost?

Here’s the stage 2 comparison I just ran this evening:



Wastegate is very spikey but not sure if this is a normal response to the issue rather than cause?
 

Attachments

  • 2024-04-03 21_16_08 98G0B v1.84 stg 2 91_95.csv
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wheela

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Jun 4, 2021
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I don't think the intercooler or k&n filter are to blame for the overboosting. I don't believe I've seen any stock turbo n55 logs consistently over-boost like that. I noticed you started your log very low, and stopped pretty early, it would be good to see what boost does out to over 6k rpm. I'd not start lower than 2500.

How long have you had the car? I wonder if the turbo isn't stock?

Edit: Or any work done on the turbo lately? Potentially a mis-adjusted wastegate actuator? With the motor off, it should fully close with 5.9 in-Hg vacuum applied to it. If it's fullt closing with less vacuum, it could cause overboosting.
 
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wheela

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Another thought. Did this start when you got your DP installed? If they oriented the DP clamp incorrectly when they installed your DP, it can interfere with the wastegate actuator rod (see circled area in pic below). If that's happening, and blocking your wastegate from fully opening, that could also be an explanation for the overboosting.
 

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    Screenshot_20240403_224528_Gallery.jpg
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The Sasquatch

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Thanks for the feedback. Good questions...
Can't say if the turbo isn't stock but the intercooler, etc was stock so I'd expect it to be - but would have to check.
Interesting info on the wastegate actuator. I believe this did start after the downpipe was fitted so sounds like it could be a cause. I'm going to arrange to have the wastegate actuator either reset or replaced so I can see if this solves it.

Only other thought is the O2 sensor codes that it was generating on the V1.6 stock map (with DPs selected). But more confusing that the O2 codes aren't being generated on the V1.8 stock map (with DPs selected).