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Old 31st October 2010, 22:12   #1
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Default Knocking engine problem (need clarification)

Hello Everyone,

I've been running my baby (mm550xd ex-army) since march 2009 and completed 23000 Kms in it. Its my almost daily drive to office which is about 24-28 Kms away. recently had starting problems.. got starter checked and carbon brushes n plate replaced (I'm no technical expert and this was all done by a close family friend whos a mechanic). Starter now works perfectly fine but another problem crops up. Its was diagnosed by my friend as a hand pump problem because the oil keeps flowing back after having pumped oil manually, and somehow (by bad luck) while trying to fix the hand pump we managed to spoil the thread and the entire hand pump head in the process (leading to airlock) , So changed the handpump head and replaced old filters with new ones and tried starting again. Jeep started with difficulty and once it started it gave this crazy knocking sound which got a bit scary. I was then told that I need to get the Nozzles serviced/overhauled coz the knocking was most probably because of a nozzle problem. So, went to a serciving centre, got the nozzles checked and found out they were jammed (after opening them up found some kinda impurity in the valve which i suspect might have been aluminium pieces from the cross threaded pump head and somehow got into the nozzle). So got them cleaned and tried firing the engine again. It ran smooth for sometime but the knocking started again. Got the nozzles checked again as per my mech friend's advice and this time had to overhaul the nozzles so did whatever was advised. and now it starts fine, no knocking anymore.
However, I go to work the next day in my jeep and about half way I hear the knocking sound again, on hearing it I let ease off on the throttle (as advised beforehand by my friend) for sometime then the knocking disappears. This has happened a couple of times now. So I'd be grateful to have any advise/inputs/clarification from friends/experts here if I should take any measure(s) for the best of my Jeep. And I took the Jeep out today for a short drive but it was running perfectly fine with no issues.
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Old 31st October 2010, 23:02   #2
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is it coming from GB or engine area?
please check the engine & GB rubber mountings.

may be engine+GB+TC assembly starts to vibrates due to warn out rubber bushes/mounts.

Last edited by jeepster : 31st October 2010 at 23:03.
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Old 1st November 2010, 11:14   #3
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Hi Johanes,

Inspect the Rocker Arm Assembly.

Regards,

Arka
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Old 1st November 2010, 12:32   #4
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Quote:
Originally Posted by ex670c View Post
Hi Johanes,

Inspect the Rocker Arm Assembly.

Regards,

Arka
I think the thread initiator is not too familiar with the finer nuances of English, and that's okay. From what I have read in his first post I would guess there is not a knock as in rocker arm knock. My guess is that he has an air leak somewhere in the fuel system since that is where the proximate problem took place...I think. The subsequent attempts at fixing it temporarily bled the system which then started leaking again since the small leak was not fixed. I would check everything around the manual fuel pump and the fuel filter gaskets....and the fuel pump.

Last edited by DirtyDan : 1st November 2010 at 12:37.
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Old 1st November 2010, 22:13   #5
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Thank you all for your valuable inputs,

@Jeepster, I'm 100% sure its not Engine/GB mounting/bushes .. they have been checked and are good.

@arka, I guess if its the rocker arm then the knocking problem would be quite persistent but in my case it is not.. as per you troubleshooting guide I think it would be an injector problem.. maybe some kind of impurity got into the injector

@DirtyDan, Yes Air leakage from the manual fuel pump was the issue earlier but that problem has already been solved.. and there are no leaks at all now..

Well, went to work in my Jeep today (drove around 80Kms) and no knocking at all, I'm so happy and hope it doesn't bother me anymore.

Anyways, I'll keep the jeep running and see how things turn out
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Old 7th November 2010, 12:05   #6
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You have said that there were metal flash around the nozzles when you cleaned them. I suspect that the fuel lines are contaminated with metal pieces as a result of a micro leak (old rusted metal). Micro leaks are extremely difficult to trace normally, but contribute to the problem, especially after a longish run at high speed when more fuel is required and pressure in the line is higher. It is best to get a pressure test done on the whole line, especially if the lines are very old (ten to fifteen years). Better still change the whole fuel line.

Some times there can be knocking due to bad fuel, as kerosene is used to adulterate the fuel. Even moisture ingress can create a havoc.
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Old 7th November 2010, 17:29   #7
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@Ajoy, Thanks for you valuable advice. I have been running the jeep daily now and I've noticed that the knocking rarely comes, and even when it does it doesn't last more than a couple of minutes, i just have to ease the accelerator and the knocking stops. Anyways, I can't just take things for granted and once my office workload gets a bit lighter and get to take leave, I'll be getting the entire fuel line and sysstem thoroughly checked/serviced.
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Old 8th November 2010, 10:15   #8
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Quote:
Originally Posted by johannes View Post
@Ajoy, Thanks for you valuable advice. I have been running the jeep daily now and I've noticed that the knocking rarely comes, and even when it does it doesn't last more than a couple of minutes, i just have to ease the accelerator and the knocking stops. Anyways, I can't just take things for granted and once my office workload gets a bit lighter and get to take leave, I'll be getting the entire fuel line and sysstem thoroughly checked/serviced.
If you are getting knocking under hard acceleration, it points to pre ignition. The reasons may be

Fuel with either lower cetane value or contamination with naphtha. Find a reliable source of diesel, empty your tank and fill it with fresh fuel.

During overhauling the engine, the head may have been shaved a bit too much, and coupled with a thinner head gasket, resulting in higher compression ratio, that too would require higher cetane value fuel. You can get the compression checked for each cylinder easily in most of the work shops.

The engine is overheating (cooling passages blocked?). Then the knocking will never be in the first few kilometers.
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Old 8th November 2010, 10:53   #9
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In case it helps someone else : My Jeep has suffered from engine knocking only twice till date. Either time, it was due to adulterated diesel filled from a highway pump.
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Old 17th November 2010, 08:42   #10
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From what you say your problem is caused imo not by fuel quality,rockers,or the compression ratio.

It is caused by faulty fuel delivery.Maybe the injectors need to be checked again and make sure you have clean fuel filters.

If the injector spary pattern is temporarily incorrect due to dirt or foreign particles it would cause the engine to knock.
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