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Gutless at low RPM

Discussion in 'Z32 Technical' started by tuff, Apr 15, 2018.

  1. tuff

    tuff Member

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    Ok i admit defeat, I've got a bit of an issue and im now chasing my tail.

    Bought a zed recently (Brock32 old car) that i have just completed an engine swap on as it had spun a bearing big time. The motor i have fitted has had a recent rebuild, turbos appeared to be in the same condition. The compression was up around the 165-170 mark across the board when tested.

    The car has all deletes done, massive 125mm thick core FMIC, s2 ptu, 480cc injectors, nismo fpr, pod filter and Nistune, 14psi tune.

    Now here is my problem. Car idles like a dream, has a fair bit of top end power but is gutless under 3800rpm, and almost feels like it has a stumble or miss up in the rev range. I've had a few of these now and it definitely feels like it is majorly lacking down low. Absolutlely zero codes coming up but it did have the power cont fuse blown which i sorted.

    In troubleshooting i have checked amd replaced the fpr and set base pressure as it was dodgy (slightly better), replaced tps as it was an n/a item and out of spec, done a fpcu bypass to make sure it wasn't a dicky fpcu, done a smoke leak test, zero leaks, injectors all appear to be firing fine and coils all within spec. No miss at idle etc. Only thing I will be doing tomorrow is to pull plugs and put some coppers in, the irridiums looked fine but i dont know how long they have been in for.

    I suspect it might be in the tune. The car was originally tuned as an auto with medium sized smic, where as now it has the massive fmic and manual, plus it was tuned about 7 years ago from what i can find.

    Any other thoughts on things i should be looking at? My plan is to get it retuned once this is all sorted.

    Thanks
     
  2. tuff

    tuff Member

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    Also checked base timing is set at 15 degrees
     
  3. Madcow

    Madcow Active Member

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    Check for air leaks and vacuum leaks.

    Also check for boost rags.
     
  4. tuff

    tuff Member

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    Did a smoke test at 10psi, no leaks evident I'll check for rags tonight, i definitely removed ones i fitted but you never know what previous owners have accomplished
     
  5. zx299

    zx299 Well-Known Member

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    Is your VTC functioning ?
     
    kickerzx likes this.
  6. J3bba

    J3bba He Who Struggles

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    Tune sounds about right. If there was something blocking the air ways it would be gutless all along the rev range. Have you got a fuel pressure gauge? If the fpr isn't working properly it could be dumping too much fuel in down low sapping power?
     
  7. WazTTed

    WazTTed Grease Monkey

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    Did you check the turbos on that motor you put in ? Possibly sticky ?
     
  8. tuff

    tuff Member

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    Turbos spun freely by hand and had no evidence of touching housings, minimal freeplay, pretty much looked like they had been rebuilt. Yep have a gauge on it, ill reset fuel pressure tonight to match the upped pressure from the fpcu bypass, it jumped up 10psi base so I'll tweak that back down, that could be part of the problem, if fpcu wasn't cutting it and now bypassed, it definitely feels better after the fpcu bypass. Might throw amother fpcu at it as i hate running oem pump flat chat, fucking noisy things
     
  9. tuff

    tuff Member

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    I'll hook conzult up tonite and have a look at the maps but I've got no fuckungidea what im looking at
     
  10. tuff

    tuff Member

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    Ok so changed to copper plugs at 0.9mm, plus swapped afm and pod, all of a sudden idle is shit and popping away, iridiums looked fine and all the same. Made no real difference to power. Changed fpcu to another unit, again not much difference. Reset ecu and swapped fuel pumps over and adjusted base idle up a touch to 46psi. Seems to be running a lot better and more power...... but..... now hicas light is coming on, heavy power steering and no friggin fault codes with it. Reservoir is full, swapping caps made mo difference. Im wondering if the speed sensor might have something to do with it. Conzult and data scan show the speed signal to ecu about 10% lower than vehicle speed on speedo and gps speed, i wonder if that is on its way out and is causing some of these issues.

    I'll do a boost leak test tomorrow after work to determine if I've got any leaks under boost, smoke test showed nothing but with a bit more pressure i might have some leaks i couldn't find
     
  11. tuff

    tuff Member

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    Also has a illumi dash so it might be causing some issues so that might swap out to see if its a culprit
     

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