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  1. #26
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    Originally posted by Richie
    Yes, 2 plugs.

    The reverse sensor is just beside the reverse switch that does your reverse lights and is found on the top of the gearbox (F28)
    That explains that one, I've only got an F20

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  3. #27
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    Originally posted by Cemesis
    The boost does take longer to reach its peak, you can feel it. If you run 8psi in 1st gear then it takes less time to reach 8psi in 2nd gear than if you run 4psi in first and then want 8psi in 2nd.

    Maybe you can't feel it in the Cav but you can feel it in the Astra.

    Lets look at it a min -

    1st gear - your turbo is spinning away at '000's of RPM's but only producing 4psi as the ECU is opening the wastegate (via amal valve) to restrict it.

    You put the clutch down, the excess boost is blow out the dump valve so you have no boost in your inlet tract and switch to 2nd gear.

    2nd gear, you engage it and put the throttle down. The wastegate snbaps shut and the car boost to 11.75psi (standard car for easiness).

    The boost drops to 8.8psi and the ECU tries to keep it here by operating the wastegate as mentioned abovel


    You push the clutch in and the excess boost is blown out the dump valve leaving no boost in the inlet tract (same as changing from 1st to 2nd)



    You engage 3rd and floor it, the wastegate snaps shut and the boost builds.


    etc etc etc.



    Both times you are left with NO boost in the inlet tract and the turbo is building the boost again.



    Mebbe yours is smoother as its got an Apexi ??
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  4. #28
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    Mine uses the first gear switch, thanks to ste_sa for suggesting it to me in the first place

    So am I correct in assuming that the reverse gear boost inhibitor switch has been chopped off my loom or modified somehow? I presume it's just left 'open'.

    Hey, I bet closing the two of them together gives the ECU something to think about.... lmao

  5. #29
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    Originally posted by Tricky
    Of course it comes in slower if it's going from 4psi to 8psi.... it's got to pick up an extra 4psi from somewhere!!!
    I mentioned this above. Its not building boost from 4psi, its building boost from a vacuum as the boost is blown out the dump valve when the butterfly closes.
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  6. #30
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    i get it richie,just need andyk now on them wire colours

  7. #31
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    Originally posted by Richie
    I mentioned this above. Its not building boost from 4psi, its building boost from a vacuum as the boost is blown out the dump valve when the butterfly closes.
    You ain't seen the speed I change gear though have you son lmao lmao lmao
    Last edited by Tricky; 05-11-2002 at 17:14.

  8. #32
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    Shaggy/Tricky - if there is a problem with the reverse or 1st gear switches (the ones giving low boost) then you will either -

    1 - Run constant low boost

    2 - get an ECU code up telling you there is something wrong with the 1st gear or reverse gear switches.



    If none of these happen with yours then you're fine.


    Shaggy - this will not cause the violent boost cut so this aint your problem. If swapping the amal valve pipes around (like in pic) does not sort it then fit a boost aguge to see what boost you're running.



    If the car is running excess boost then the car will cut the ignition to protect itself. This feels like a misfire.
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  9. #33
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    ive swapped the pipes on the amal valve havent tested it yet but i hope it works,thanks for the help guys

  10. #34
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    The 1st gear limiter wires are found at the front of the F28

    The are in black shouding although the wires underneath are-

    brown
    brown/red

    If you connect them together boost will only be limited in reverse

    100% sure

    Although im not so sure about the reverse wires

    black/yellow
    black/white

    If the speed sensor wires arent connected at all what happens?
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    If its a NOVA I might know. Ive tried/fixed everything.
    Nova 280+ bhp and a quaife straight cut gearkit + ATB and water injection and 6 pot calipers that wont fit! Now I have a power steering setup for my nova!
    I also own a Citroen Xsara VTS

  11. #35
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    so how do i wire a high/low boost switch in,can i cut into a wire at the amal valve???

  12. #36
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  13. #37
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    look along the ecu loom above the box there are 3 two pin connectors

    1 female
    2 male

    one male connects to the reverse switch

    one male connects to the 1st gear switch (if fitted)

    the female on the ecu loom has the reverse lights from the car loom pluged into it.....

    if the speed sender isn't connected then the ecu doesn't know how fast you are going.... of cause if u have the first gear boost limit on and are doing 100mph the ecu starts asking questions

    with f20 reverse works the same.... (ecu loom into rev switch... lights into ecu loom) 1st needs a loop of wire in it to run full boost....

    but not if a phase kit is fitted cause it removes the 1st gear limit
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  14. #38
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    Originally posted by Richie
    1st gear - your turbo is spinning away at '000's of RPM's but only producing 4psi as the ECU is opening the wastegate (via amal valve) to restrict it.

    You put the clutch down, the excess boost is blow out the dump valve so you have no boost in your inlet tract and switch to 2nd gear.

    2nd gear, you engage it and put the throttle down. The wastegate snbaps shut and the car boost to 11.75psi (standard car for easiness).

    [Snip]


    Both times you are left with NO boost in the inlet tract and the turbo is building the boost again.
    Fraid the previous gears boost will affect the next gears boost. Boost is proportional to turbine rpm, the wastegate controls turbine rpm, the amal valve controls wastegate position.

    The turbo will have to spool up more when going from 4psi in 1st to say 8psi in second.

    I mentioned this above. Its not building boost from 4psi, its building boost from a vacuum as the boost is blown out the dump valve when the butterfly closes.
    While the dump valve is operating it should be atmospheric pressure or slightly above. If it's dropping back to vacume you need to learn to change gear quicker. lmao

  15. #39
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    The point I am making is that when you press the clutch to change gear, the excess boost is dumped out the DV.

    This brings the boost to virtually nothing so you arent building the boost from 4 to 8psi when you change from 1st to 2nd, you are boosting from around 0 to 8psi.


    Going by whats said by some ppl, if you were simply boosting from 4psi to 8psi (4psi cause by boost limit) then does this mean you are boosting form 8psi to 8psi when changing from 2nd to 3rd ??


    Thats why, when you change gear, the boost guage shows the boost building.
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  16. #40
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    Fair point, but we can somewhat ignore the 'fill time' of the inlet tract. This will be very quick indeed. The main 'lag point' will be the turbine needing to spin up to a higher rpm.


    Although, engine rpm will have dropped due to changing gear, so air consumption will have also dropped so may negate the above... dunno lmao

  17. #41
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    Originally posted by shaggy
    so how do i wire a high/low boost switch in,can i cut into a wire at the amal valve???
    Not sure if this will give the same effect as the 1st gear switch does. The effect of having the 1st gear switch wired in is you get no overboost like you do in the other gears. I'm not sure you'd get the same effect with doing what you're suggesting. I'm also thinking that you'd need something more sophisticated than messing with the amal valve, I think I'm right in saying that the 1st gear limiter runs a completely different map in the ECU? Feels that way anyway. Anyone?

    Anyway, shaggy, did your amal valve fix work then or not? I'm tellin ya lmao lmao

  18. #42
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    No, the boost limiter (1st and reverse) simply make the ECU limit the boost to 4psi which, as well as getting rid of overboost, is lower than normal boost to.

    Normal boost is 8.8psi which is more than double the limited amount.

    Thats why it feels slow.
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  19. #43
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    Your logic regarding the first two gears is correct Richie but in practice the car is faster in 2nd gear without the first gear limiter.

    I tried two runs down my road with the boost set to 0.8 bar. One with a disconnected limiter and one without. On the run without I got wheel spin in both gears and on the run with I got wheelspin in neither.

    I couldn't explain it at the time but I remember in a post from ages past that AndyK came up with a theory that the turbo wouldn't be spun up as much when chaning to 2nd.

    It made sence at the time.
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  20. #44
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    tricky i dont know i still havent driven the car yet but will post as soon as i do cheers.

  21. #45
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    Originally posted by ste_sa
    look along the ecu loom above the box there are 3 two pin connectors

    1 female
    2 male

    one male connects to the reverse switch

    one male connects to the 1st gear switch (if fitted)

    the female on the ecu loom has the reverse lights from the car loom pluged into it.....

    if the speed sender isn't connected then the ecu doesn't know how fast you are going.... of cause if u have the first gear boost limit on and are doing 100mph the ecu starts asking questions

    with f20 reverse works the same.... (ecu loom into rev switch... lights into ecu loom) 1st needs a loop of wire in it to run full boost....

    but not if a phase kit is fitted cause it removes the 1st gear limit
    cant find them connectors anywhere the git,not sure about boost the gauge only shows 5psi so will turn it up a bit.

  22. #46
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    Your loom might have been modified. Or a favourite place to run the redundant wire/connector when the C20LET is in a 2WD car is up in between the n/s suspension turret and the n/s inner wing.

    What car have you got anyway???

  23. #47
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    astra gsi

  24. #48
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    are they near the reverse light plug in the loom,i can see that but no others.

  25. #49
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    Erm.... is your loom a proper LET item or a GSi one that's been modified??

  26. #50
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    think its a proper let,but not sure it was already converted.how can i check???

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