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1G Bone Stock DSM Hitting Fuel Cut @ 4500RPM

Posted by radwoodtsi, Apr 18, 2020

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  1. radwoodtsi

    radwoodtsi Probationary Member

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    San Francisco, California
    Hey all,

    As the thread title says, I have a 92 TSi that is completely stock outside of a cat-back and high-flow(but still restrictive CA legal) cat

    My mechanic removed the airbox to get to the radiator overflow tank to clean it off and inspect it. That's all fixed, everything back together.

    Drove the car and it's hitting fuel cut at WOT/4500RPM.

    Boost spikes to 14 PSI+(on stock gauge) and it hits a brick wall. Feels like someone punched you.

    I checked all the vacuum lines and hoses. I found the intake boot was on but loose so I tightened up the clamp and its on there good now.

    The ONLY thing I found was a missing clip on the air intake canister. Could that be causing that drastic air change to cause the MAF to freak?

    It's going back Sunday because the mechanic is also a friend(and it happened after his work) but I want to arm him with any info.

    To be clear, no boost leak test done and when i say stock I mean stock. No gauges, no MBC, nothing. We don't have a leak tester and in CA, we're in lockdown. Not much is open.

    Would love advice.
     
  2. Sjd6795

    Sjd6795 Proven Member

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    Wilsonville, Oregon
    Could be dirty and clogged injectors, fuelpump, and filter.
     

    Street Build 489  11

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
    Sjd6795

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  3. 2gmitsueclipse

    2gmitsueclipse DSM Wiseman

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    Auburn Hills, Michigan
    I would pressure test the intake and inspect/test the wastegate actuator as starting steps in diagnosing your issue.
    Most hardware stores are open, so you should be able to buy what you need to build the intake pressure tester (blt). See the video below:



    You will also want to inspect/test the wastegate actuator to ensure it is operating correctly. Check out the video below:



    These would be my suggested starting steps. Post up your results when you get a chance.
     
    Last edited: Apr 18, 2020

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    1998 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM

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  4. radwoodtsi

    radwoodtsi Probationary Member

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    San Francisco, California
    I appreciate both of your responses. Pardon my naivety here but would a clogged or fuel issue of any sort cause overboosting? It absolutely feels like it is. And it's a very mechanical, abrupt, consistent SLAM when it hits 4500 RPM. It's very on the nose, very repeatable, and almost painful when it hits.

    Further, this happened RIGHT after the intake was removed. The FIRST time it went WOT after the intake snorkel was R/R it did it.

    Thank you, boost test for sure if possible.
     
  5. radwoodtsi

    radwoodtsi Probationary Member

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    Also, if it matters, it has 85k miles.
     
  6. Hickory-NC-2Ggsx

    Hickory-NC-2Ggsx Proven Member

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    I believe it has somthing to do with the maf being moved around. Id start with cleaning the maf connector and the maf itself then check the wires on the maf connector as well, then boost leak test it if no change occurs. Also check the line going to the wastegate.
     

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  7. Hickory-NC-2Ggsx

    Hickory-NC-2Ggsx Proven Member

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    I know you said that you checked the line but double check the one on the intake going to the turbo and wastegate. 1G_Turbo_Vac_Diagrams1.JPG
     

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    Mitsubishi Mighty Max
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    1997 Mitsubishi Eclipse GSX
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  8. radwoodtsi

    radwoodtsi Probationary Member

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    Thanks!

    I did double check that line and it's tight and uncracked all the way around as far as I can see without entirely removing it.

    Also unseated, cleaned and checked the MAF plug. It's pretty spotless. Wires are old but no corrosion and clearly pliable.

    This is super annoying.
     
  9. Hickory-NC-2Ggsx

    Hickory-NC-2Ggsx Proven Member

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    Alright then next do a blt. Because the turbo will be sucking more air in through the maf than the wastegate actually sees becuase its not holding it. Which will send it into fuel cut.
     

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    Mitsubishi Mighty Max
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  10. Sjd6795

    Sjd6795 Proven Member

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    I figured if its hitting fuel cut with everything being stock it could be clogged fuel system. I use to run 17 psi on my 1990 gst with open Downpipe 3" and 3" intake never once hit fuel cut.
     

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  11. JeffwithaG

    JeffwithaG Proven Member

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    Definitely suspicious that it happened right after the MAF and airbox were removed. I had a similar issue that was driving me nuts for 6+ months. I could gradually build boost but if I tried a WOT pull, it would buck, backfire sometimes, and hit fuel cut. I did a boost leak test, plugs, wires, PTU, more boost leak tests, tested coils, cleaned injectors, fuel rail, regulator, more boost leak tests, cleaned EGR valve all with no success.

    I read a few more posts that mentioned the Fuel Pump/fuel delivery. I did notice my car would sometimes take a few more cranks to start up after I had been driving it. I bought a Walbro 190, got it installed and I didn't have anymore fuel cut issues after that.

    This issue is so difficult to diagnose because it could really be a myriad of items causing it. You can get a boost leak tester from eBay for about $30. I feel like everyone is going to suggest a boost leak test first because it causes the exact issue you have described.

    Edit: I have a 2G GSX, stock T25 with a 3" turbo back exhaust and hard IC pipes (but hopefully the above info helps for a 1G also)
     

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  12. TheFlashDSM

    TheFlashDSM Supporting Member

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    over boost could also cause fuel cut. but u mentioned u weren't. double check the boost solenoid. i believe its under the maf on the lower part of the frame rail. make sure its plugged in, and that the hose nipples aren't damages. good luck
     

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  13. Steve93Talon

    Steve93Talon Proven Member

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    Post pics of the MAF (and try swapping it if you can find another unmodded one). You can also pull the lower honeycomb which was the old trick for raising the fuel cut threshold, though I'd probably figure out what changed first. You need to get a proper boost gauge to see what your actual boost is, the stock one is useless. It sounds like something with one of the boost solenoid vacuum lines. You could also jump a vacuum line from the J pipe nipple to the actuator to see if the issue goes away.
     

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  14. radwoodtsi

    radwoodtsi Probationary Member

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    It IS overboosting according to the stock gauge.

    Unfortunately the car is too clean and too original to install another gauge. It's probably the nicest DSM I've ever encountered. It looks brand new. I will definitely check those out, thank you.

    TY!
     
  15. radwoodtsi

    radwoodtsi Probationary Member

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    Also forgot to respond - that is mounted on top of the air canister and all connections look good.
     
  16. TheFlashDSM

    TheFlashDSM Supporting Member

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    your problem has happened to me. your over boosting and the ecu is fuel cutting. the maf from what i understand is not sink with fuel cut. double triple check vacuum
     

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  17. TheFlashDSM

    TheFlashDSM Supporting Member

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    @radwoodtsi. also double check you waste gate. it might be getting rusty and having trouble opening.
     

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  18. Hickory-NC-2Ggsx

    Hickory-NC-2Ggsx Proven Member

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    The stock boost gauge works off the maf, Thats why the gauge says its 14psi or more. And like i mentioned befor if there is a leak and the wastegate isnt seeing the actual pressure the turbo is making because its not holding it. Then the wastegatd is just going to stay closed and continue to flow more and more until it opens.
     

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  19. radwoodtsi

    radwoodtsi Probationary Member

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    Update: Ran the wastegate directly to the j pipe and it did the same thing.

    Also, in the process, a nipple broke off the BCS. So that's fun. Was pretty brittle but I also applied some unnecessary hand pressure.

    Looks like I'll be searching for a replacement
     
  20. Steve93Talon

    Steve93Talon Proven Member

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    If you jumped the actuator to the boost source on the j pipe and it's still overboosting (which you can't confirm unless you throw in a real boost gauge), then it's possible that the wastegate flapper is stuck shut. Can you put compressed air to the actuator and see if the arm swings open freely?
     

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  21. John Miller

    John Miller Proven Member

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    Check intake for any obstructions. Could be a dirty injector which could also lead to melting a piston so check them. Also dirty fuel pump sock
     

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  22. radwoodtsi

    radwoodtsi Probationary Member

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    Thanks for all the help guys.

    Had everything apart. Triple checked(with my mechanic) all vacuum.

    Did not do a vacuum test. It's Sunday and this mechanic starts his day at 7:45PM. May try but it seems less likely.

    In the process, we cleaned up the fuel filter(it was filthy). After putting everything back together, checking all lines, hoses, and plugs - it improved by moving the fuel cut to 5200 RPM from 4500.

    This leads me to believe it's fuel related or electrical in some way.

    MAF is clean. Wastegate moves freely. Did not get a chance to check injectors - wrapped at 1130PM.

    I ordered a fuel filter(dirty anyways) and a Walbro 190 just in case. It's worth it for $120 total.

    Considering the removal/reinstall plus fuel filter just moved the RPM - any other thoughts?

    Currently running on wastegate pressure. -BCS nipple broke off.
     
  23. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    In Link, fuel cut happens anytime the AFR's are leaner than 12.65 or something close to that. I know you are stock but it sounds like that is running lean still. You helped it by putting a new fuel filter on but no way to know if the fuel pressure is up to par or not. Your tests just lead me to believe lack of fuel unless you find out the wastegate is stuck or stiff, which WILL over boost the car.
     

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  24. pauleyman

    pauleyman DSM Wiseman

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    This is classic boost leak symptoms. stock gauge pegging out is very indicative of this. I would guess it's the most common cause of what you are seeing.
     

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  25. radwoodtsi

    radwoodtsi Probationary Member

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    I would agree 100%. I need to perform one still.
     

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