900 Turbo 16s intermittent cough

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Thread: 900 Turbo 16s intermittent cough

  1. #1
    Saab Junior
    Join Date
    Jan 2004
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    Dorset, UK
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    34

    900 Turbo 16s intermittent cough

    Here's the info:

    MY93 900SE body, added T16S engine (and running gear). All work done by an independant Saab specialist.

    The story
    Car starts and runs fine except an intermittent cough. It can be under light throttle or full throttle at various revs. The cough is like a drop in power as if there is no throttle. It can be a single one or a splutter of two or three. I cannot make it happen at will and its always such a suprise I don't have time to see what the boost guage is doing. Oh it also packed up on me and was diagnosed as failed fuel pump. Nice trip in an RAC truck after 2.5 hours at -5C waiting with no engine. The fuel pump was replaced - still coughing It does it from cold or when warm.


    I've tried.
    Plugs were the corret NGK, but I put new ones in anyway (7mm gap). Ouch said the autofactor when he was charging me!
    I changed to super unleaded and thought the cough was not so severe (it had felt like whiplash on ordinary unleaded). Still there in frequency though.
    I went to Shell Optimax and it was a noticeable softer cough, more an ahem, but still similar frequency.
    The end of my mechanical tinkering...

    The garage have:
    Replaced fuel pump
    New fuel filter
    Adjusted air mass meter (was rich)
    Replaced FPR with 3 bar one from 900i
    New Distributor cap
    Changed injectors
    Changed coil
    Boost Control valve appears OK

    It still coughs, but it took 33.8 miles to do it after I left the garage, then did it about 15 times in the next 60 miles. The car feels really smooth and responsive with plenty of whoosh except for this cough which tends to make me nervous about overtaking. I appreciate why their road test didn't find it!

    Additional
    I am not boosting into the red with fall back only about 3/4 through the orange. Garage has suggested staying away from optimising boost till we sort the problem.

    Any ideas please? I've had the car a month and its incredibly frustrating and time consuming to keep taking it to the garage. They are incidentally being very understanding.

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  3. #2

    Re: 900 Turbo 16s intermittent cough

    Can't think of anything right now except to ask if the specialist has tried pulling any fault codes from the fuel injection ECU (I'm assuming it's a Bosch LH). That the problem diminishes with higher octane fuel also implies there could be something not right with the timing. But that's just a passing thought really.

  4. #3
    Saab Junior
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    Jan 2004
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    Dorset, UK
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    34

    Re: 900 Turbo 16s intermittent cough

    Thanks for the lead. I had a look under the bonnet, can't see the fuel suply lines like on my old 8 valve, its all wrapped in a big loom, but there is a thingy with wires that seem to go to the injectors (looking from the front of the car it is just infront of the injector rail) and it is stamped Lucas and Saab. I can't see any big box saying Bosch as in the 8 valve - is there any other way of telling which injection system it is? A brief glance at the Haynes says it should be Lucas - does this capture fault codes? I will mention timing too - it goes back on Wednesday.

  5. #4

    Re: 900 Turbo 16s intermittent cough

    Depends on what year the T16 donor car was from. If it would still be running the original N/A fuel injection, it'd be wonder the car's not running properly...

    The fuel injection computer is located in the right side kick panel (footwell area) - you will have to remove the door weatherstrip (partly) and the carpet retaining strip (three screws). Then you peel back the carpet to find the ECU.

  6. #5
    Saab Junior
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    Jan 2004
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    Dorset, UK
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    Re: 900 Turbo 16s intermittent cough

    Thanks Eric - the donor car was a 1993 900 SE. I will get them to check. What should it be running - Bosch LH or the Lucas and which one? I assume its not just a matter of switching the box..

    I would have thought that they would have married the fuel injection to the engine - but you never know - roll on Wednesday

  7. #6

    Re: 900 Turbo 16s intermittent cough

    If the donor T16 was the same year as your recipient 900 SE('93), it should have the Lucas CU14 fuel management system. Look for a Bosch 3.0 bar fuel pressure regulator on the fuel rail (not a surefire method as 3.0 bar has been also used by the Bosch systems on normally aspirated 16v models and is a popular fuel upgrade for Bosch systesm on T16s, but conversely if it's 2.5 or 2.8 bar chances are the fuel system is an older Bosch LH 2.2 or 2.4).

    Just realized there's a better way of looking what kind of fuel system you have: the orientation of the air mass meter (first thing after the air filter box). If it's horizontally mounted (i.e. in line with the turbo intake pipe) it's a Bosch system, if it sits vertically it's Lucas (right, fellows?)...

  8. #7
    Saab Junior
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    Jan 2004
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    Dorset, UK
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    Re: 900 Turbo 16s intermittent cough

    Hello again Eric,

    I found the air filter and there is a block shaped gubbins coming off it vertically in line before the pipe shoots off at a right angle and under the pipe from the intercooler towards the Turbo. Attached to the this block thing is a flat rectangular box oriented thin side vertically with "LUCAS 5AM 73350A 1991" on the side.

    There is a brass coloured device that could be the FPR labelled made in Germany and 3.0 bar on it at the bulk head end of the injector rail. They put this on last week as part of the try all avenues approach - see list in original post. Not sure what the old one was (I think 2.8).

    Does it look like I have a mixed injection system?

    What now?

    Jan

  9. #8

    Re: 900 Turbo 16s intermittent cough

    That's all correct for this specific engine and year.

    If the former fpr was indeed a 2.8 bar, you have swapped an incorrect part for a correct one. Shouldn't hurt.

  10. #9
    Saab Junior
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    Re: 900 Turbo 16s intermittent cough

    well thats getting there slowly.

    So we are left with checking the timing and error codes from the FI?

    Yesterday I noticed that the exhaust was blowing a little at the junction of the Turbo outlet and down pipe - could that be it.

    Also the symptom does seem to occur more under hard acceleration and also up hill.....

  11. #10
    Wastegate
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    Re: 900 Turbo 16s intermittent cough

    Sorry,

    Only just got around to reading this post.

    It's sounding very much like my old C900 Carly which would do exactly that, and sometimes for 2-3 minutes!

    That was finally tracked down (after many many trips to the garage!) to being faulty earths.

    After all the earth points were cleaned up it ran much better.

    The main earth points are at the end of the injection rail near the thermostat, and by the bottom of the radiator by the battery tray.

    I also had a faulty EGR valve on the underside of the inlet manifold which would mess up the fuel setting at idle when tuning so it ran wrong when revving...

    Andrew

  12. #11
    Saab Junior
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    Re: 900 Turbo 16s intermittent cough

    Thanks I will suggest earthing to the garage.

  13. #12
    Saab Junior
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    Re: 900 Turbo 16s intermittent cough

    Seems the garage do earthing as the first thing when fitting the FI.

    No fault codes available from the Lucas FI - apparently it only activates the CHECK ENGINE warning light.

    The engine and associated systems came from a car that was running great!

    Ignition timing rechecked. OK

    They are starting from the beginning again and going through everything as no ideas left. They and I are a tad frustrated. Whilst a E 900i is wheels and dry I do miss my

  14. #13
    Saab Junior
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    Re: 900 Turbo 16s intermittent cough

    Anyone have any idea no matter how bizarre?

  15. #14
    Turbo Talker
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    Re: 900 Turbo 16s intermittent cough

    An intermittent fault like this is really hard to pin down
    I would seem that it is an electrical contact that is usually ok but sometimes is broken
    hence the coughing

    To find it you need to either find it when it is dodgy (unlikely ) or work through the ignition system/fuel system with a fine tooth comb
    checking connections /checking earths/checking wiring looking for corrosion util you get the problem
    A real pita but there is no other way....

    good luck

  16. #15

    Re: 900 Turbo 16s intermittent cough

    QUOTE Jan95aero:

    I changed to super unleaded and thought the cough was not so severe (it had felt like whiplash on ordinary unleaded).
    End quote.

    Have you checked the overboost cutout switch? Its behind the glove compartment and only requires that you tighten a screw or bridge the wiring. Maybe I've picked up your symptoms differenly but if you are thrown forward as if to nearly bite the steering wheel, then this could be the simple cure.

    hth

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