Diesel start-up

Discussion in 'Engineers' Talk' started by jumboscruit, Nov 30, 2009.

  1. jumboscruit

    jumboscruit New Member

    Having trouble with my vans engine lately, it starts OK, runs for a few seconds, then starts "missing", then eventually runs OK. I have replaced all the glow-plugs, and am sure all the leads are in order.

    The van is a 1996 Renault "Extra" car-derived van, (based on the clio), with the 1.9 engine. I was thinking it a good idea to measure the current-draw of all the glow-plugs to make sure they are all operational, but not yet done this.

    Similar problems in the past, have always been rectified with new plugs, but not this time.

    Would I be right in suspecting the control unit? Perhaps the plugs are losing their supply too quickly, as I believe they should carry on heating even after the engine has started. The engine is approaching 100K so perhaps thats a clue.

  2. joinerjohn

    joinerjohn New Member

    Could be the injectors. Have you tried some diesel additive that cleans the injectors. Forte or similar??. As far as I know the glow plugs stop heating up once the light goes off on the dashboard
  3. jumboscruit

    jumboscruit New Member

    Funny you should mention the diesel additive, because this problem initially started just after I put some Redex injector cleaning fluid in the tank. Strange.

    In fact the same thing happened three years ago, with the same outcome. It's got to be a coincidence hasn't it?

    Not just that, but the recent MOT was only passed on the emmission test by the tester putting some "Wurth" fluid in too. What does that stuff do?.

    Maybe this stuff in the fuel has affected the injectors.
    Can't see how it could affect the glow-plugs though. Maybe it will clear as I put more fuel in the tank, without any additive.

  4. chippie244

    chippie244 Super Member

    If the engine starts it's NOT the glowplugs that are at fault.
  5. jumboscruit

    jumboscruit New Member

    Thanks for those replies. Having read my Haynes manual carefully, it looks like the problem is with the control unit, as the glow-plugs should carry on glowing at full heat for up to ten seconds after start-up. They must be getting shut off too quickly.

    It seems there are several devices, sensors etc. that determine how much, and for how long the plugs glow, the main one is engine temperature, so this problem will only become apparent on the first cold morning start-up.

  6. -chippy_john

    -chippy_john New Member

    Find somewhere quiet,

    turn the ignition key enough to illuminate the glow plug light on the dashboard (assuming there is one)

    now wait until the light goes out

    keep listening, something like 20 seconds later you should hear the relay turn off the glow plugs.
  7. jumboscruit

    jumboscruit New Member

    Thanks Chippy. Had a look at the relays, after getting unit out of van, and cleaned contacts. after refitting I put my clamp-on ammeter on all leads, and switched-on, found 51 amps flowing, sounds about right I thought. No sound though from the relays, they are inaudible.

    Glow-plugs must be shutting off too soon.I think there is a timer that is actuated as soon as the starter is off,(engine running) and plugs should carry on glowing for a further 10 to 15 seconds or so.

    They are not doing this, so its got to be a new unit I'm afraid. Lets hope it stays mild!


    ARDLUI New Member

    Could be air in fuel system,check joints and diesel pipework
  9. jumboscruit

    jumboscruit New Member

    Thanks, will try and see if I can locate any problem. The engine hasn't been doing very well since its MOT, and the testers had to do some adjustments to get it through.

    Perhaps I ought to check the fuel filter unit,to see if there is a problem there.

  10. Mr GrimNasty

    Mr GrimNasty Active Member

    'MOT' Oh **! The bounce off max revs as required for MOT can shag the engine. I'd find out exactly what 'Adjustments' they made. When was your cambelt last done? The MOT might have caused it to slip a few teeth and they may have try to compensate for that.
  11. chippie244

    chippie244 Super Member

    Grimbo, if the cam belt has slipped a few teeth the engine is fooked :)
  12. joinerjohn

    joinerjohn New Member

    My dad had a Peugeot 405 diesel,on which the cam belt slipped (due to the water pump coming loose) He managed to limp to the nearest garage. They reckon if it had slipped 4 teeth, he'd have been lumbered with a bill for a replacement engine. I do know some engines will stand around 6 teeth slipping, and have heard of some diesel engines that can stand the timing belt breaking and suffer no damage. Unfortunately I have a Peugeot with a diesel engine that ****** out oil faster than the Torrey Canyon but still keeps going. :)
  13. chippie244

    chippie244 Super Member

    On certain engines the valves wont hit the piston, but not many.
  14. Mr GrimNasty

    Mr GrimNasty Active Member

    "Grimbo, if the cam belt has slipped a few teeth the engine is fooked."

    No, depends entirely on degree of slip and engine design. It hasn't gone completely - obviously.

    Again depends on design, but a lot of diesels will 'run' with everything way out - but you get difficulty starting etc.
  15. daff

    daff New Member

    If the engine starts and runs normally without missing for say thirty second or more it is unlikely to be the glow plugs, the miss would be noticeable on start up . It is more likely that it is the non return valve in the filter head that is on it's way out and allowing some of the fuel in the filter to drain back into the tank. When the engine runs it will draw air until the fuel flow is re-established, this would account for your miss.
    If the return valve goes completely the the engine will stop when the pump empties and you will have to bleed it or crank start it if your batt will take it.
    Hope this helps.
  16. Screwedfix

    Screwedfix New Member

    sound to me like you need to get rid of the old thing, not worth messing around with matey, get yourself a decent motor
  17. jumboscruit

    jumboscruit New Member

    The cam-belt has about 22K on it,being renewed in march 01. As you can work out, I don't use the van very much.

    Seems the "missing" problem is hardly noticable if the ambient is above 10deg.C I'm sure its the control unit, as they work on temperature, giving longer glow-plug operation the colder the weather gets.

    Also suspect the cylinder head gasket is faulty, as its always blowing coolant. Been like that for at least nine years. Most of the coolant seems to live in the expansion tank, and the engine mostly full of steam!
    Mind you, the van still returns over 45 MPG, so can't be that bad.

    If it was a fuel problem, wouldn't it be there all the time, not just for a few seconds after start-up?

    I think it is really time to think of a new motor, as it can barely get past 50 MPH nowadays.

  18. daff

    daff New Member

    Regards the fuel problem, The fuel in the pump lines and filter can syphon back into the tank and is replaced by air. On start up the remaining fuel in the pump allows the engine to run until presented with the air void created by lack of fuel, depending on fuel loss the engine will miss or stop completely.once the air has cleared and fuel flow has been re-established the engine will run as normal. Unfortunately the whole cycle starts over again when the engine is stopped for extended periods. This is a common fault on diesel motors.
    I doubt your van would have passed the emissions test had the head gone. Your "steaming" problem might just be down to a closed faulty thermostat. Check for "milky" oil and /or "sludgy" water thats a reasonable guide to head gasket failure.
    Check for plugs- once you are sure they are all OK. Take a live lead from from the battery through a switch direct to the the glow plugs, disconnect the supply if you want from the control unit , make sure you insulate the live end though. switch on and start the engine, if it dose not miss you have your answer.
  19. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Have you got a vented fuel cap and if so, is the vent blocked ? Does it hiss loudly if you remove it after a journey ?

    It happens on petrol vehicles(not sure about diesel), but after stopping the engine, the vacuum in the tank draws fuel back through the pipes, creating that airlock.

    Mr. HandyAndy - Really
  20. daff

    daff New Member

    Mr Handyandy. With regards to the diesel engines there is a one way reed valve in the top of the filter bowl. when this fails it allows the fuel to drain back into the tank. The degree depends how far gone it is. Regards

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