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I\'ve got a Land Cruiser with a 4.2TD (direct injection). When you toe it, it sounds like it\'s pinking, and as soon as you back off, it stops. They\'ve had big end problems with these, but I replaced all the shells last year. It\'s possible one of these has gone bad or spun, but before I drop the sump again, has anyone any other ideas? Can diesels pink?
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I don't think diesels pink as such but if the usual 'diesel knock' becomes too severe it could make a similar noise to pinking in a gasoline engine.
In cases like these too much fuel is injected too early in the compression stroke... so when the extra fuel is hot enough to burn, resulting explosion and pressure rise is big enough to causes the engine block to rattle.
Retarding the fuel injection timing should help it or it could be faulty injectors that are opening at too low a fuel pressure if it's on mechanical fuel injection. Any diesel engineers please correct me if i'm wrong.
Lack of boost pressure could also cause excessive knocking.
hope this is of some help
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I always understood that the crucial difference between diesel and petrol engines was that the petrol/air mixture was compressed and then ignited, whereas in a diesel only the air is compressed and then the fuel is injected right at the top of the compression stroke.
So unless the timing has been altered, there would be nothing explosive to pink with?
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Diesels can 'rattle' badly due to injection occuring too early and causing max pressure to be reached before TDC.
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If the fuel was injected right at the top of the compression stroke the fuel-air mixture would probably still be burning in the exhaust pipe if the engine would run atall. Fuel Injection usually starts maybe 20 deg before top of compression stroke to allow time for some fuel to evaporate and mix with air to form a combustible mixture.
It doesn't burn instantly for similar reason why dropping a lit match into a bucket of diesel wont make it burn.
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Thanks guys. It had a new set of injectors about a year ago (for a mere £1500/set), just because I figured that at 170K miles it was about due. It just so happens it's a bit smokey at times, especially at tickover, but it seems to come and go.
In theory the pump timing can't change, as the pump is gear driven, unless something goes wrong internally. I've spoken to a couple of pump rebuilders, but none fill me with confidence that it will come back any better than before it went in. The pump is a denso mechanical type. I would like to check the timing, but the main dealer doesn't have the SST to do it. I would imagine that if something goes wrong with the pump to alter the timing, then it run like a dog all the time.
Some of the later 24v engines with electronic control pumps have been known to blow holes in the pistons due to leaking (dual stage)injectors. So whether that can apply to earlier mechanical pump engines, who knows, I've certainly never heard of it before.
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Are you sure the pump timing can't be changed. On the gear driven pumps i have worked with injection timing can be changed by rotating a drive coupling or rotating the pump relative to the engine block.
If that's the case maybe you could mark the pumps position and try rotating it lock it up again and see if it gives any improvement. Just a thought. Perhaps there's been enough wear in the gears to change the timing.
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If the fuel was injected right at the top of the compression stroke the fuel-air mixture would probably still be burning in the exhaust pipe if the engine would run atall. Fuel Injection usually starts maybe 20 deg before top of compression stroke to allow time for some fuel to evaporate and mix with air to form a combustible mixture. It doesn't burn instantly for similar reason why dropping a lit match into a bucket of diesel wont make it burn.
You want max combustion pressure to occur at TDC or just after. On a Diesel, injection is usually about 15 deg. BTDC - this gives time for the flame-front to propagate out from near the injector and quench on the piston around TDC. Various techniques are used to introduce turbulence to speed this process up.
I'm pretty sure that injection timing can be altered on these mechanical set-ups. Might be an idea to find an appropriate forum and pose the question there.
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You want max combustion pressure to occur at TDC or just after. On a Diesel, injection is usually about 15 deg. BTDC - this gives time for the flame-front to propagate out from near the injector and quench on the piston around TDC. Various techniques are used to introduce turbulence to speed this process up.
That describes pre-mixed combustion in spark ignition engines. In the petrol engine, the combustion flame starts from a flame kernel at the spark plug electrode and propagates throughout the chamber. That's why it's started before TDC.
Diesel combustion is different because it doesn't occur in a pre-mixed homogeneous air fuel mixture. When there is sufficient heat in the air in the combustion stroke to vapourise the localised fuel spray, fuel ignites *Spontaneously* at many points throughout the mixture.
It is the steep rise in pressure caused by this event (pre-mixed combustion) that is responsible for diesel knock. After this more fuel is injected (well after TDC on the expansion stroke at full power) and burned as quickly as further air can be diffused into the mixture. Turbulence speeds this process up.
No quenching normally occurs at TDC. Peak pressure occurs usually 20 deg After TDC. for peak power output.
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Yes, you can actualy change the timing, but only by rotating the pump on it's mount against the block. You can't change it much, and it's never been touched. The pump drive is also keyed to the gear, so that shouldn't move either. I've just had an oil analysis done, and that showed absolutely no bearing materials present, so hopefully that rules out a big end problem, although if it was so bad it would have probably gone bang by now anyway.
I guess I need to get the injectors pulled and have the opening pressures checked as a starter, then get the pump in to be checked out.
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I pulled the injectors today, and one had leaked soot past the copper seat, and up the body of the injector until the O ring. Any ideas if this could cause the knocking/noise? Maybe the nozzle has got distorted or something, or maybe the noise I could hear was the combustion gasses escaping to atmosphere, although I couldn't see any soot past the O ring.
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Even minor distortion or damage of the injector could cause a fault and effect opening pressure. Fuel injection components are built to such fine tolerances that even the expansion caused from the heat from touching them can result in parts not fitting together.
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I picked the injectors up today, and the verdict is 5 are OK, 1 is knackered. The knackered one is the one that wasn't seated properly, and the result is the whole nozzle was blued from heat, with a very low opening pressure and poor spray pattern, even after ultrasonic cleaning. The upshot is a new one from Toyota, as they're dual stage injectors that cost about as much to rebuild and set up as a new ones.
All the injectors had a fair amount of carbon on them pointing to general overfuelling, even though the old ones I took out a year ago didn't suffer from this. So I guess it's pump off time, and get that sorted. Don't know how much it will cost, but I do know the Toyota manual has about 40 pages dedicated to rebuilding and setting up the pump.
ANyone know where I can get a used one (for rebuilding) or an already rebuilt one for swapping straight over?
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Don't know if this will be of any help but I owned a Nissan diesel pickup that had a denso mechanical fuel pump. On the top of this was a maximum fuel adjustment screw - I remember if you screwed this in (12mm locknut on a flat blade screwdriver adjuster) it ran a bit smoky (it went like the clappers though!) so we backed it off for the mot test. A half turn each way made a big difference.
On the Landcruiser I think there also is a pipe coming from the inlet manifold to a boost pressure fuel controller that you can adjust if it's overfueling when the turbo is boosting. Someone correct me if im wrong about all this.
I know your supposed to get the pump properly set up on a flow bench etc. but it's something i would try before buying a rebuilt pump.
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Did this problem ever get resolved?. I ask because i'm having the same symptons with a Y17D (Astra 1.7tdi) engine. It's been rattling under load like a paint can for well over 70,000 miles!. only now it's getting worse.... the pump has been rebuilt and timing checked with no effect. should i go for a new (expensive!) set of injectors?
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Blimey, this is an old one!
Well no, it didn't get resolved. It still makes the knocking/rattling sound under load, and so far it hasn't gone bang. I dropped the sump off again, and checked the big ends, just to be sure, and they were all ok. I also had the pump rebuilt at what I think was a reputable place, and that made no difference either. I've had various other ideas like something in the transmision or torque converter related, or maybe even a bit of extra resonance from the stainless exhaust.
So sod it, I just drive it now and see what happens.
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Sounds very similar indeed...all usual suspects checked and aligned. Been doing it for well over two years and hasn't gone bang...There is one wierd thing though, certain weather conditions and it doesn't do it, normally on days with exceptionally high barometric pressure she runs real sweet. i know there is an atmos. pressure sensor but it's not reporting itself as faulty. :-/
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