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Thread: Z30DT all symptoms of dodgy SCV... BUT....

  1. #1
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    Default Z30DT all symptoms of dodgy SCV... BUT....

    Hello peeps! Been lurking for a while & decided to share this:

    DON'T THROW THE BABY OUT WITH THE BATHWATER JUST YET

    OK, I seem to have had most of the symptoms of failing SCV: loss of power, hesitating around 2000rpm, error codes: rail leak or rail pressure control valve malfunction, injection system malfunction, P0093... all sounding scary.

    First time, changing the fuel filter helped a lot - it was black all the way up: figure blocked filter - not enough fuel under load. Makes sense. Then the problem came back, so out with the filter - this time it was only black 30% up the filter element. Hmmm. Problem did seem to go away, though.

    Problem back the other day: now quite bad. I recorded some data with OPCOM - plotted desired rail pressure and actual rail pressure VS time. It showed sudden and large deviations: pressure rising, wanting 80MPa, suddenly falling to 15MPa.

    Anyway, I took the top off the fuel filter assy and noticed that the filter housing body was not brimming full of fuel, but about an inch down. So I topped the filter up, put the pipes back on and finally topped it up through the 'bolt hole' at the top, put the bolt back in and.... THE CAR WAS BACK ON FORM

    OP COMMed the desired vs actual rail pressures and the graphs were an exact match. Cool!

    So, as these cars do not have a separate lift pump, but rely on the fuel being sucked up right from the tank, it seems like I have a small leak that's allowing air in. This air would collect at the highest point: the fuel filter housing. Once sufficient, this would mean the fuel pump starts to recieve air and fuel, causing pressure drops, especially when a load is placed on the engine - only enough fuel is pumped by the high pressure pump to supply the engine: that's what the SCVs do. It makes sense that the ECU interprets the pressure drops as a leak in the high pressure side and throws the codes.

    Reckon this is definately worth a try before binning a big chunk of change on fuel pump bits... certainly buys a few at the bar.

  2. #2
    Regular Member Celes's Avatar
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    Vehicle : Opel Signum

    Trim : Sport

    Engine : 3.0 CDTI

    Year : 12/03

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    I'm experiencing the same symptoms on my Y30DT. I'll change the fuel filter again as I was planning, but this time I'll top the housing up using your method...through the bolt hole I'll clean the filter housing as well, just in case

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    Try to press the top of the filter down with one hand to get a seal between the top and bottom parts of the filter whilst you're filling it , otherwise the fuel will leak out before it reaches the top of the bolt hole. Maintain this pressure until you've got the bolt tight, so have the bolt and torx bit driver within reach. It's a bad design - you should be able to tighten the assembly up, then top the filter housing up through a separate bleed screw.

    Maybe an inline electric lift pump is the way forward, as trying to find a tiny air leak 'in' is sooooo much harder than finding a diesel leak out. Anyone done this mod?? Would be so much easier to bleed if there's positive pressure in the system.....

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    Holy ****!!!!!!

    I have a z30 dt, and for the past week have been having stuttering and power loss and sometimes limp mode.
    I thought it was scv's but as a safeguard changed my fuel filter, ( which was only half full of diesel) and gues what . . . . 350 miles later I have no problem!!!!!

    So sounds exactly the same prob and solution

    I also had error code P0093 - larger system fuel leak

    Nick
    Last edited by s2yob; 27th June 2011 at 08:35. Reason: Missed words

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    Regular Member Celes's Avatar
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    Vehicle : Opel Signum

    Trim : Sport

    Engine : 3.0 CDTI

    Year : 12/03

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    Needless to say I spilled about a gallon of diesel all over the engine tying to fill the housing up through that small hole lol

    The car was good yesterday. Going to find out soon enough if it's still having problems with cold starts today...

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    Regular Member Penfold101's Avatar
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    I was having the same problem which kept being fixed temporarily by changing the fuel filter. What I eventually did, after changing the housing and it making no change, was to remove the housing altogether from the car.

    Remove the top from it, and top it up on the level so it's brimmed right to the top. Put the lid on tightly and then refit to the car. When you put it back in , you may notice that it doesn't sit perfectly level.

    I believe what's happening is that when you fill it up on the car there's an air pocket being left at the top which gradually gets worse and worse due to the engine LP pump sucking fuel through instead of there being a positive pressure form the tank.

    When I did this the hesitation problem vanished for well over 10K miles and only just started to reappear before I sold it.

    That's my advice anyway...

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    Quote Originally Posted by s2yob View Post
    Holy ****!!!!!!

    I have a z30 dt, and for the past week have been having stuttering and power loss and sometimes limp mode.
    I thought it was scv's but as a safeguard changed my fuel filter, ( which was only half full of diesel) and gues what . . . . 350 miles later I have no problem!!!!!

    So sounds exactly the same prob and solution

    I also had error code P0093 - larger system fuel leak

    Nick
    It ocurred to me that when you're changing the filter and then filling the filter body up with fuel, you're doing 2 actions... so I tried only doing one of them and the problem disappeared. IF it was an SCV problem, it would still be there - the SCV's don't 'know' what you've done to the fuel filter or whatever... so if they're knackered, they're knackered, no matter how clean your filter is, or how full the filter body is. I reckon there may have been a few cases for a lot of panic (and expense - hopefully under warranty) for a poor design.

    Celes - I find it helps to get some sort of jug with a narrow spout (and a steady hand -!-) to avoid getting too much diesel everywhere - still get some, though

    Penfold101 - thinking the same RE: low pressure on the fuel supply line.

    Must admit, this is the first diesel arrangement that does not keep some sort of postitve pressure on the fuel supply, be it gravity or a low pressure pump. Is this just cost cutting, or a genuine reason? Other than selling us new fuel pump bits, because the 'diagnostics' say one thing, but it's just fuel starvation (in some cases)

  8. #8
    Regular Member Celes's Avatar
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    Vehicle : Opel Signum

    Trim : Sport

    Engine : 3.0 CDTI

    Year : 12/03

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    The new fuel filter did NOT help much. The car was mighty fine yesterday after the filter change, but struggled to start this morning, also no power and all other SCV failure symptoms.
    Massive drop in fuel pressure under load, Rail Pressure Neg. Deviation fault code, I think it was P0190 but not sure. I'm baffled......

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    Have you ruled out whether you have a filter half full of air again?

  10. #10
    Regular Member Celes's Avatar
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    Vehicle : Opel Signum

    Trim : Sport

    Engine : 3.0 CDTI

    Year : 12/03

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    I've replaced the filter on this engine about 10 times now (counting the old 3.0 too) and never had problems after the replacement.

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