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Strange new acceleration issue - input appreciated


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Also, you are able to keep it at WOT at lower RPM just fine. Something unique is happening at that engine speed. An inlet/post-MAF tube getting sucked shut would explain it and has been reported before. It also makes sense that when he lifts off the throttle he can recover, up until it happens again.
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What about mounting a vacuum/boost gauge to measure the pressure before the throttle or turbo? Keep an eye on it while re-creating the problem. If you suddenly get vacuum from boost or zero then we have some new clues to go on.
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What happens if you go past the RPM at partial throttle so the event doesn't occur, and when you are past that threshold (4700 rpm or whatever it was) THEN go WOT? Does the event occur instantly?

I attempted this test this morning. WOT, lift to 80-85% throttle past the trigger range, then 100% throttle and it does occur although at varying RPMs (5800 as well as 6200RPM). Then did again and once the event triggered lifted briefly and then WOT again and it was immediate (slightly higher RPM than first event in this pull).

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There's a little flex in both the post maf tube and the inlet towards the turbo - hard to imagine either getting fully sucked closed. I can try popping the airbox as described, what will this do though? Point out a restriction in the stock box under load? I doubt my stage 2 VF40 is asking for more flow than stock can provide (with a clean AVO panel filter).
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Sometimes a change to the system can give new clues. I did find a grounding error on the ECU of a vehicle once when I did measure the signal between ECU and ignition - the instrument I used introduced enough change to the signal to hide the fault making the engine run smoothly - and a short time of thinking about Kirchoff's laws made me consider the grounding of the ECU.

 

So introducing an error into the system (even if it's a small one) may be enough change to either make the problem worse or make it disappear.

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Thanks Tony - appreciate your input as well as others here. I'm going to do some more trial and error. I get what Nils is saying and think I'll just unplug the MAF and do a pull. Also removing the resistor for the EGT. See if I can get the ECU to learn something new and then put things back in place.

 

I still don't understand why when the event occurs I'm going full vac according to MRP and the BPV isn't releasing. After inspection the intake tract looks well sealed, all my vac lines are zip tied or using corbin clamps, no leaks between the turbo and TB, new fuel pump, fresh plugs, good compression and outside of this bizarre dump it does at WOT at high load, the car runs great. Even tossed some seafoam into the tank and sucked some in the vac lines to clean those areas out.

 

I'll report back after pulling the MAF cable and doing a pull, and pulling the resistor in the EGT.

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A new idea is that it's the turbo that is starting to give up. Not easy to verify unless you swap turbo.
This has been rolling around in my head throughout troubleshooting the problem. Especially with the increased oil blow by. It hasn't even been a year before this warranty replacement VF40 was installed.

 

I was planning a BNR 16G this year, looks like I'll be doing that ahead of schedule as it's killing me not knowing what's causing this event. It's easy to drive around it, but I don't like to know there's something negative going on with the car. Especially if it's something that can manifest into a greater issue.

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So what's the theory regarding the turbo? I'm not seeing how you could go full vac suddenly if the throttle is wide open, even if something crazy happened like the turbo seizing up momentarily.

 

Wastegate?

"Bullet-proof" your OEM TMIC! <<Buy your kit here>>

 

Not currently in stock :(

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Update:

 

Well things have progressed. Now the event occurs at about 5K RPM anywhere from 50% throttle input to 100% WOT when in boost, where before it was totally isolated to WOT (had tested previously and I could be up to 90% throttle input and no event up to redline).

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Would like to see a log of it happening under other throttle % conditions, if you can.

 

My money is still on the inlet. Could have been exacerbated by you groping it during the inspection?

 

By the way, the P/Ns for the throttle body components are:

O-ring - 16175AA331

Bolts - 010406500 (qty.4) [Tightening torque = 6 ft-lbs]

Throttle body Assembly - 16112AA020

TB Hose #1 - 21204AA830

TB Hose #2 - 21204AA900

Hose Clamp - 092313102 (qty.3)

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I wasn't hard on the inlet and had the area well lit when I inspected. I tried to make it flex but didn't shift it around. I'll do a couple pulls and log and report back. Inlet (OEM) would probably be cheaper than a TB to replace and can't hurt even with future mod plans.

 

Thanks for digging up p/ns as well!

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