New head gasket failure
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  1. #1
    VIP Sponsor David Cavanagh's Avatar
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    Default New head gasket failure

    This is doing my head in.

    My wife Laguna, (2 litre 8 valve) burnt out an exhaust valve a few weeks back. Easy job, pull off the head replace the valve jobs done.

    Problem is when the engine starts is screaming at full revs as soon as it fires, full 6,000 rpm. I've checked everything, butterflies are staying shut so it has to be a vacum leak between the throttle body and the head.

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    I've checked and triple checked all the vac lines, I've clamped them all so no air can get through (there's only 5 of them) and it still screams so it must be the manifold not sealing on the head.

    I've had the manifold off a dozen times and looked for and cracks and distortion and there's nothing. I've changed the manifold gasket and its the same, yesterday I swaped inlet manifolds off the R19 I'm driving, now it has the 19 manifold and its still the same, all day yesterday swapping manifolds and all I ended up with was 2 dead Renaults.

    I'l starting to think its sucking air somehow around the head gasket but that would be imposible wouldn't it?
    It has compression, we know the sound of an engine when cracking that has a compression leak, that chuffing noise of leaking compression that it had with the burnt valve. I've spun the motor over without the coil plugged in and it sounds fine so there's plenty of compression (although I haven't tested it).

    I've pulled off and swaped everything I can think of, I've had extra pairs of eyes working with me in case I'm missing something obvious and there's nothing wrong anywhere.

    The head gasket is the only thing left, yes its on the right way up I'm always careful to check that and the head is flat but can a new gasket suck air but not let compression out?
    David Cavanagh

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  2. #2
    1000+ Posts robmac's Avatar
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    Valve/s jammed open? Perhaps an exhaust valve Cams wrongly timed?

    Seem unlikely 'tho.

  3. #3
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by robmac View Post
    Valve/s jammed open? Perhaps an exhaust valve Cams wrongly timed?

    Seem unlikely 'tho.
    I've thought of all that but it wouldn't have compression and wouldn't start.
    David Cavanagh

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  4. #4
    1000+ Posts Fordman's Avatar
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    Wow, coming from you Dave, there's something really weird there, because obviously you've checked all the right things.

    In my opinion, a head gasket could not let in enough air to run on, without serious compression leakage, or water pouring out, and it would have to be leaking on all cylinders to run like that wouldn't it?
    Probably along your line of thought, how can it run at high rpm if the throttle plate is closed? Does it run a cold start circuit of some kind? Early EFI engines had an air bypass valve that opened when cold to allow air past the throttle plates, sort of like a carby choke needs the throttle opened a bit to run on the rich choke mixture. If it has something like that it could be stuck open.

    However, under no load conditions, it doesn't need the throttle to be too far open to run at high rpm. Have you tried putting it in gear (I guess its an auto) as soon as engine fires? (Obvious danger involved, dont want to see the car leaping across the road!). Just a small piece of old gasket material jammed in the throttle may be enough - is the throttle really closing right down? Have you tried completely blanking off the air intake orifice? That would rule out any kind of leakage past the throttle area.

    And the "black magic" part - the ECU - is there some kind of reset required? If you haven't already, try disconnecting the battery for a while, that sometimes does wonders. Are there any fault codes?

    Good luck.
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  5. #5
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by Fordman View Post
    Wow, coming from you Dave, there's something really weird there, because obviously you've checked all the right things.

    In my opinion, a head gasket could not let in enough air to run on, without serious compression leakage, or water pouring out, and it would have to be leaking on all cylinders to run like that wouldn't it?
    Probably along your line of thought, how can it run at high rpm if the throttle plate is closed? Does it run a cold start circuit of some kind? Early EFI engines had an air bypass valve that opened when cold to allow air past the throttle plates, sort of like a carby choke needs the throttle opened a bit to run on the rich choke mixture. If it has something like that it could be stuck open.

    However, under no load conditions, it doesn't need the throttle to be too far open to run at high rpm. Have you tried putting it in gear (I guess its an auto) as soon as engine fires? (Obvious danger involved, dont want to see the car leaping across the road!). Just a small piece of old gasket material jammed in the throttle may be enough - is the throttle really closing right down? Have you tried completely blanking off the air intake orifice? That would rule out any kind of leakage past the throttle area.

    And the "black magic" part - the ECU - is there some kind of reset required? If you haven't already, try disconnecting the battery for a while, that sometimes does wonders. Are there any fault codes?

    Good luck.
    Its a manual actually.
    Tried it with the cold start sol blocked off and as is now it has the one off the 19 so count that out also.

    The cars is on jack stands so no danger of it leaping forward and I tried reving it to free up anything in there, even dismantled it when the manifold was off.

    I told her I dont see a problem because thats how she drives it anyway, the speed is coverned by the gears. Thats when the fight started.
    David Cavanagh

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  6. #6
    Contented Peugeot Driver addo's Avatar
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    Is it a "slip and grip" cam pulley? Are there similar timing belts with different tooth counts?

  7. #7
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by addo View Post
    Is it a "slip and grip" cam pulley? Are there similar timing belts with different tooth counts?
    No its all key way. Thats the thing, its such a simple engine you can't go wrong. Even if it was tooth out it would run badly but it wouldn't do this.
    David Cavanagh

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  8. #8
    1000+ Posts Wildebeest's Avatar
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    Dave,
    In the back of my mind I recall something like this happened to a Renault 19 I was road testing. Throttle stuck, high revs etc. Had to restrain it by holding it on the brakes until back at the workshop.
    There were two things I recall although they both may be desperates in your example.
    [1] A braided earth cable from the cyl head to the firewall had pulled out of its crimped lug.
    [2] One of the engine cable harnesses passed very close to *1 plug lead. This was relocated.
    The engine revving problem went away.

    The State Service manager at the time for Volvo and Renault asked me to do a report on this. This subsequently found its way into a Dealer Service Bully. A gold watch soon found its way.....in my dreams.

    Anyway Dave, this may be of some help.

  9. #9
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by Wildebeest View Post
    Dave,
    In the back of my mind I recall something like this happened to a Renault 19 I was road testing. Throttle stuck, high revs etc. Had to restrain it by holding it on the brakes until back at the workshop.
    There were two things I recall although they both may be desperates in your example.
    [1] A braided earth cable from the cyl head to the firewall had pulled out of its crimped lug.
    [2] One of the engine cable harnesses passed very close to *1 plug lead. This was relocated.
    The engine revving problem went away.

    The State Service manager at the time for Volvo and Renault asked me to do a report on this. This subsequently found its way into a Dealer Service Bully. A gold watch soon found its way.....in my dreams.

    Anyway Dave, this may be of some help.

    I've checked the earth straps, all look fine.

    wiring loom sitting close to a plug lead? Doesn't make sense to me, if the plug lead was earthing out wouldn't it just make a miss fire.
    David Cavanagh

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  10. #10
    Fellow Frogger! G4ME's Avatar
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    Take your foot off the accelerator when you start it.
    That's it for my wisdom :-)
    ...Paul
    There is a law against doing more than 100kmh...there's no law on how fast you get to 100kmh!!!

  11. #11
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by G4ME View Post
    Take your foot off the accelerator when you start it.
    That's it for my wisdom :-)
    ...Paul
    Why didn't I think of that. Paul your a legend.
    David Cavanagh

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  12. #12
    1000+ Posts jo proffi's Avatar
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    What about removing the brake booster line and replacing it with a compressed air line, introducing a small amount of air pressure and listening or soaping up the likely suspects, looking for bubbles.

    Its a lot more peacfull chasing a leak that way then with the motor screaming at 6000rpm.

    Jo

  13. #13
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    Does the Laguna have an idle air control valve like a 19 does? Could be the hoses there..

  14. #14
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by jo proffi View Post
    What about removing the brake booster line and replacing it with a compressed air line, introducing a small amount of air pressure and listening or soaping up the likely suspects, looking for bubbles.

    Its a lot more peacfull chasing a leak that way then with the motor screaming at 6000rpm.

    Jo
    Problem is I don't have a compressor at home, yeah I can't do any checking with a cold engine screaming at 6 grand. 3 or 4 ok I can unplug, crimp whatever but at 6 on a cold engine, not good.

    Spiz,

    It has the same idle valve as the 19. Already unplugged it, blocked off the hoses and eventually fitted another one.
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  15. #15
    VIP Sponsor David Cavanagh's Avatar
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    You know guys, come to think of it there is a small amount of water running down the block above the bellhousing. I thought it was from the thermostat housing just above it but the more I think about it the more it could be coming from the head gasket. If it is that means it mustn't be sealed correct?
    David Cavanagh

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  16. #16
    1000+ Posts jo proffi's Avatar
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    Ok, no compressor. What about your mouth??

    6k rpm air is a fair bit of a leak, and should show itself quickly.

    Jo

  17. #17
    VIP Sponsor David Cavanagh's Avatar
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    Quote Originally Posted by jo proffi View Post
    Ok, no compressor. What about your mouth??

    6k rpm air is a fair bit of a leak, and should show itself quickly.

    Jo

    Yeah it should be easy shouldn't it, thats the annoying part. I'll take home a rad pressure tester tonight and see if bubbles come out from under the HG. Otherwise I'll get G4ME to come round for a beer and he can blow down it, he's full of hot air. Hmmm maybe not he'll just get it pregnant.
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  18. #18
    Too many posts! JohnW's Avatar
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    Wow. This is one right up there! It obviously isn't one of the things you've checked over and over again. Trouble is, it is so rare to have to touch a modern engine we don't have much experience with the nasty little things that go wrong.

    "Only 5" vacuum lines!!!!!

    As an ignoramus regarding modern sensor systems, I just wonder if there is a damaged or disconnected device or its wiring, that was displaced when the head came off? Or something disconnected in the wrong order or wrong way.

    Maybe it thinks it has full throttle in some bizarre way.

    I drove past you late last week and again on Saturday going back to catch a Perth flight but didn't have time to drop in and say hello. I recall when I did drop in a couple of years back you had a Scenic with the opposite problem - simply wouldn't fire at all and was to be wrecked instead.

    I'll follow this one with a lot of interest.
    JohnW

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  19. #19
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by David Cavanagh View Post
    Yeah it should be easy shouldn't it, thats the annoying part. I'll take home a rad pressure tester tonight and see if bubbles come out from under the HG. Otherwise I'll get G4ME to come round for a beer and he can blow down it, he's full of hot air. Hmmm maybe not he'll just get it pregnant.
    I'd struggle to imagine an air leak that isn't as obvious as hell if it is big enough to give 6K revs . I guess you are having the same struggle. But ignorance at my end is considerable on this one!

    Can you test the integrity of the head gasked one cylinder at a time when the valves are shut on each cylinder?

    I presume you'll retighten the head and see if the drips stop too?
    JohnW

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  20. #20
    Tadpole
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    I'd isolate all hoses going to the inlet manifold. I cant remember the Lagua 4 cyl but do they have the idle speed control Bosch Motor like the 19's? If so make sure there is not a dirty great hole in the hoses. Try blocking it off if in doubt! Is the motor behaving ok and not stuck wide open? Again a simple test, remove it from the equation complety, block off the downstream fitting below the throttle and see if it changes things.

  21. #21
    Contented Peugeot Driver addo's Avatar
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    I still remember my Xantia engine starting and running with no inlet manifold. The fuel feed line coincidentally squirted into a cylinder!

  22. #22
    1000+ Posts 504-504-504's Avatar
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    Is it running on all cylinders?
    Fitted up a Bellett with sidedraught weber, crossover manifold and extractors years ago.
    It would run happily on 2 cylinders if you removed a pair of plug leads.

    Removing plug leads in turn might help to localise the problem.

    Paul

  23. #23
    Too many posts! JohnW's Avatar
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    Quote Originally Posted by addo View Post
    I still remember my Xantia engine starting and running with no inlet manifold. The fuel feed line coincidentally squirted into a cylinder!
    You know, there's a book in a collection of these stories!
    JohnW

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  24. #24
    1000+ Posts jo proffi's Avatar
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    Quote Originally Posted by addo View Post
    I still remember my Xantia engine starting and running with no inlet manifold. !
    And i remember a corolla starting and running with no driver.....


    Jo

  25. #25
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    Get rid of the fuel supply, disconnect pump.
    Then spray Aerostart at various places around the engine, you will soon find where the air is being sucked in.
    Graham

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