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Author Topic: 1.8T/09A rock crawler in some kind of open loop / limp mode  (Read 4304 times)
1.8tcrawler
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« on: September 16, 2021, 09:40:02 AM »

Hi All,

New here and new to VW. I recently finished building a completely one off rock crawler in my garage. It is powered by a AWP 1.8T with a 09A Tiptronic trans behind it, both from a 2003 Jetta.

It crawls rocks great, but power falls off very quickly above 2500rpm or so. It is geared very low so 180hp should have no trouble getting up and moving and spinning the tires a little. The ECU was flashed by someone local and had the immo removed, doesn't appear to have anything else done as I get several codes for EVAP, airbag crash sensor, lack of gauge cluster, lack of ABS module, downstream O2 open circuit, etc. The trans has only one code for lack of communication with ABS module and near as I can tell, is working and shifting exactly as I'd expect it to.

  • When I log throttle % in VCDS, the actual throttle % is about 1/3 of what I am requesting with the pedal. With ignition on and engine off, the throttle plate moves from 0 to 100% as I'd expect.
    When I data log in VCDS, the requested boost is 1000mbar across the board and the actual is around 1350 max (like 5-6psi).
    When I watch my vacuum gauge running off the FPR, I see 20in vacuum at idle and when the MAP is seeing 5psi, the gauge is just about reading zero (not actually getting into boost).
    Clamping the boost reference line to the wastegate makes no difference in the amount of boost.
    I have a fuel pressure gauge right at the front of the rail and it is reading 40-45psi under all conditions.
    When I log lambda in VCDS, the requested is 1.000 all the time and actual drops to around .85 once I am off idle.
    In OBD section of VCDS, I see the fuel system readiness says open loop due to a fault.

I have run out of people willing to help me with this and most blame it on the transmission. Whether that is true or not I don't think I have confirmed. I'd like to get into using Nefmoto and Tunerpro to try to figure this out on my own. I am hoping someone here can help me with where to start Smiley

I am going to order this cable as I see a recent post with someone saying they recently purchased it and it worked for them.
https://www.amazon.com/gp/product/B07X5VQ5DC/ref=ox_sc_act_title_1?smid=A2XHF1TEX86Y60&psc=1

I read the S4 wiki and I have no interest in tuning for any more power than I have, just turning off as much stuff as possible the ECU may be looking for that's already there. In addition, if there is something telling the ECU to go into this weird open loop limp mode I seem to be seeing, I am hoping I can override that in some way or tell the ECU to ignore it.

Cable will be here Sunday, and I hope to start playing around with it then. If anyone has any suggestions on where to start aside from deleting all the emissions stuff, I would love to hear it.

I attached a pic of my buggy and the engine codes I am seeing.

Thanks in advance!!!



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fknbrkn
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mk4 1.8T AUM


« Reply #1 on: September 16, 2021, 10:31:33 AM »

Throttle % are non-linear to pedal; its lower due to boost request lower than wastegate spring pressure
evap and o2 codes are the reason of open loop fueling

all this codes could be easily removed
as for low boost request - log 120s groups (didnt rember exactly where it is) - torque reduction request from transmission

ps
that shit looks awesome
pm me, i can do that stuff for free.. just for fun  Grin

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BlackT
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« Reply #2 on: September 16, 2021, 12:03:37 PM »

Cool stuff,  Shocked Shocked
Send trans DTC
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1.8tcrawler
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« Reply #3 on: September 16, 2021, 07:42:31 PM »

Thanks for the kind words, guys. It's a lot of fun even as it is.

log 120s groups (didnt rember exactly where it is) - torque reduction request from transmission

Good call! It looks like I am definitely hitting torque reduction right when it feels like it's falling on it's face. Now I need to determine what is causing that. The only code I'm getting from the trans is no communication with ABS module. Would that really cause that much of a power cut?

Will I be able to tell the ECU to either ignore this? Or bypass it in some other way?

Thanks for the help...

Trans DTC and log from tonight attached.
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Sandstorm3k
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« Reply #4 on: September 18, 2021, 05:47:24 AM »

Very cool stuff, should be easily solved with some help of fukenbroken  Smiley
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