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  1. #1
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    900 T16S Vert, 900 mix n match
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    Question C900 LH2.2 ECU Pin Out Question.

    I'm upgrading from 8v to 16V and everything's gone fine until I tried to check out the fuel pump relay operation in advance of firing her up this weekend coming.

    I've decided to use the 2 relay's that came with the 16v injector loom and ECU rather than use the existing 8V fuel pump relay...plan is to leave in situ but cut the Grey/Red fuel pump feed after the 8V relay output, cabin side of the bulk head connector (upper white one - think it's connector 152?), and run the T16 fuel pump relay pin 87B 12V output back to the fuel pumps in place of the 8v relay feed.

    Here's the snag.....everything's working fine bar the fuel pump realy getting an earth from pin 17 of the ECU...I checked the relay (and it's operation and resistances, and open and closed operation etc when feeding the actuator connections with 12V across it....nice click and works fine....managed to try it in another T16s....relays are fine.

    The fuel pump relay actuation voltage is getting a good 12v from the main relay alongside it via the overboost fuel cut of switch .....at this point ignition is on (fed off a green/white tap off in the fuse box) and the main relay is being activiated via the ECU...just not getting a ground for the fuel pump relay - Purple wire is good from relay to 25 way plug at ECU ........( so can't get the 12v feed to pin 30 across the relay to 87B and thence to the pumps.)


    That's the prelude to the Question.......

    What conditions need to be met to trigger the ECU to ground out pin 17 or can I just ground the pin 17 and be done with it............rather not go that way as it seems pin 17 on the ECU is there for a reason and just using the 8V fuel pump relay in the fuse box seems wrong...sure Saab put those 2 relays in there for a reason when they went ECU injection.

    Any guidance greatfully recieved,
    SteveI

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    Last edited by SteveI; 03 October 2013 at 17:44. Reason: can't speel.

  2. #2
    Sam Carlson
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    The ECU has to be receiving an RPM signal to ground the fuel pump relay and start the pump. You have to either be cranking the engine or the engine has to be running. If the ECU is getting an RPM signal (I think it gets this from the EZK in an N/A car, or straight from the ignition module in a turbo car), it will ground the relay. If it isn't, I'd think it would also not be spraying fuel either, so the car would not run.

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  3. #3
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    Thanks for that Sam...your absolutely on the ball. I've not connected the RPM signal (blue wire that also feeds the tacometer) from the ignition amp yet or tried cranking the engine as it's been fully rebuilt and not prep'd for the first turn over yet.

    Again, many thanks.
    SteveI

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  4. #4
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    Ok..next question folks moving onto the AMM now (Bosch -005)

    Checking the burn off funtion for the AMM.....the books say 4 seconds after switch off (engine at normal temp and after 2500 rpm or more) there should be a voltage of about 5v for 1 second.....to 'clean' the air flow filiment by heating it til it glows and thus removing any crud that's stuck to the wire (I assume crank case venting will cook oil onto the wire and the aim is to routinely vapourise it off?)

    I'm not seeing this either as the wire glowing inside the AMM or if a peel back the boot on the AMM 6 pin plug and put a DVM across the two relevent 2 pins.....I have continuity back to the ECU pin 8 from the AMM pin and a good ground on AMM pin....also the 4 seconds after switch off there's a nice solid 'click' sound but not sure if it's inside the ECU or one of the co-located relays.



    Do I need to satisfy another criteria to see this burn off function happen?

    I've ordered up a replacement / spare AMM as I'm still running over rich and sooting up the plugs but trying to check everthing else while I'm waiting for it!

    Thanks in advance.
    SteveI

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  5. #5
    Sam Carlson
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    '90 900 LPT with a flat-nose conversion
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    Burn-off voltage should be between terminals 1 and 4 on the AMM plug (I think they are numbered on the AMM itself).

    Is the coolant temperature sensor (NTC sensor) plugged in and does it have a good connection and test OK for resistance? That can cause over-rich running and possibly prevent burn-off.

    Is the check engine light illuminating? If so, you may have an issue with the Air Mass Meter itself. Does it run the same with it disconnected? If so, further proof the AMM may be bad.

    I have also heard the relay click after shutdown. I always assumed it had to do with the burn-off function, because it seems to click right when burn-off happens, but it could be coincidental. I will have to check my electrical diagrams to see if it's involved at all. I thought it had to be revved to 3000rpm, not 2500, but I may be wrong. Rev it higher?

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  6. #6
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    Thanks Sam....I'll try again reving over 3K.

    I checked the NTC resistance and it looks to be OK..and varies in the right direction as the engine heats up.....maybe I'll measure resistance at the ECU pins rather than just across the NTC itself in case I have continuity issues post laying the loom in but it was OK when I checked the loom on the bench.

    Check engine light is not wired up yet....would that circuitry missing make a difference?..I assumed it was just a tell-tell that supplied a ground under fault / initial switch on.

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  7. #7
    Sam Carlson
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    I don't know if it makes a difference whether the check engine light is wired up or not. I know it does go on before startup. The reason I asked was because the check engine light will illuminate when the air mass meter or NTC sensor is unplugged. This could aid in diagnosis. I don't know any other faults that cause a check engine light on LH 2.2 ECUs. The light doesn't care about the oxygen sensor, and it obviously won't work if the cam hall sensor/EZK is disconnected. Kind of useless, I know.

    You have a tremendous amount of fortitude and patience going ahead with this very tedious project. I admire it.

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  8. #8
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    In hindsight and the damage to the bank account the sensible thing would have been to rebuild the 8V but a 16V came along complete with loom so was tempted into this folly!

    The change from 8v to 8vT with APC went really well and I learned alot but the really, really long term aim would be to go T5 so getting there via T16 and learning how all that works along the way is the plan.

    Thanks for the guidance BTW......when the rain lets up I'll go wire in the CEL and recheck the NTC at the ECU end.

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  9. #9
    Sam Carlson
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    Thinking further, I believe the CEL being wired up would not affect anything. I know this because I've "fixed" people's cars by pulling the bulb!!

    You would gain a diagnostic aid by having CEL present, though.

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  10. #10
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    Just a quick update to close this one down....checked the NTC and the relevent pins at the ECU end...all OK.

    Bit the bullet and splashed out - so sourced a replacement AMM this week and set it to default / initial setting (380ohms across pins 3 and 6) and threw it in.....dah nah! Fueling sorted and running like a dream......need to set the CO2 on a proper machine and tweak the idle etc but she's running, boosting up to the red (I retro fitted a turbo dash with boost gauge) and she's not sooting up the plugs now.

    Thanks everyone for the help with the electricals ...8V Mechanical CIS to 16V Bosch ECU ..Done.

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