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Y2KGUII ZD Wgn
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Discussion Starter #1 (Edited)
The ZD30DI Engine. What makes a Grenade a Grenade?

We hear the "Grenade" expression quite a bit with threads spruiking "3L Grenade" etc, hitting the spotlight, this is in no way is meant to exonerate Nissan, yes they handled it badly particularly when they knew very early on from several Sate Government fleet vehicle issues. I wonder how many (particularly Newbies) know what the classic grenade really is? Because anything outside that scope comes under the s*** happens category (and often does to many makes other than the Nissan 3L), thrown rods, seized engines from overheating are caused by many other things, they are not a "Grenade" and can happen to any vehicle given the circumstances. All the info is in this ZD30 DI subsection and any ZD30 DI Newby should read the Archives, particularly the NADS (Nissan Anti Detonation System) bits in post #1, a lot of other info is spread around so I thought I'd put some information on one page.

The classic "Grenade" is cracked pistons, but the "Grenade" does go off in varying degrees.
Piston 3 or 4 cracked, head still salvageable.
Piston 3 and 4 cracked, head still salvageable.
Piston 3 and/or 4 cracked and head cracked.
Occasionally pistons 1 and 2 can be involved in all of the above.

NOTE: When the pin does come out it usually happens rather quietly accompanied by lots of bluish white smoke from unburned diesel.

The reason for the above is very simple, prolonged exposure to high combustion temperatures (but your engine coolant temp gauge won't have changed much, if any). In trials after my rebuild with nothing more than a newly fitted EGT gauge I could duplicate what had been happening in my engine and reach temperatures in excess of 700C post turbo while my coolant temp remained in the clear zone, now the pistons used in my rebuild were far more tolerant of heat than their predecessors, but I was not going to let that situation continue.

I said the reason for "Grenading" was simple but what does get complicated is the reasons for those high temps, the over simplified reason is too much fuel for the air being pumped in. This can be from a bad MAF(over an extended period) or an over fueling chip , or as was the really bad habit of the 2000-2002 DI where the boost would drop off to ridiculously low levels (as low as 3psi in my case) at high speed and no one knew, ie, mine was an absolute classic of major proportions 3 and 4 pistons cracked and the head cracked as well, but not to the water-jacket. I had a failing MAF for quite some time which went undiagnosed by me and Nissan, by the time we found the problem I am sure partial damage had already happened and was tipped over the edge later by long trips with the boost drop syndrome, at that stage I had no gauges and this forum was in its infancy and I had not joined, so I had no idea. The early ECU's were basically just a big fuel management system, they would try to compensate for just about anything, this is one reason that when the pin does come out there is generally no warning.

OK you ask, why don't they all grenade? Well, why isn't Nissan replacing all CRD TPS pedals? simple, Nissan have more than one supplier for each item and each supplier will have nominal differences in batches of whatever they are supplying. Another reason is some vehicles may never have had the high temp exposure for long enough to do sufficient damage to self destruct, my later research has found that the ECU receives multiple signals from various sensors that open the EGR and also effects the boost level via the VNT control solenoid, dropping boost levels to ridiculous numbers at speeds over 100kph and this can last for quite a long time especially when on highways under minimal load, so a shopping trolley 3L can have no such issues.

To make the issue worse, unscrupulous operators would repair a grenade in the cheapest possible way so it could be flogged off, this was a major contributor to the repeat "Grenade", often the head was totally ignored and if the engine didn't classic "Grenade" a second time, the head would crack into a jacket with disastrous results. I'm sure there are some sleepers out there just waiting for the opportunity to screw you at the worst time.

There is another separate issue, some ceramic glow plugs have been known to lose their tips, these can be white hot and in bouncing around inside the combustion chamber they can result in holed pistons. This is why I firmly believe a glow plug timer should be a part of the NADS system although this is not considered to be part of the classic "Grenade". Having said that my ceramic glow plugs are still the original that survived a "Grenade" and they have done 245,000k, I had them out a few months ago for inspection and clean as a whistle.

All automotive manufacturers have a vehicle that doesn't always measure up, some more than others, because we own Nissan Patrols we tend to hear more about them than others.
So that is my spiel, if anyone disagrees with me, go for it.

In closing, I must point out that fitting NADS will not stop a Grenade attack if the damage has already been done, it may postpone but not totally prevent it.
 

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Rogue
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My 2000 cracked 3, 4 and the head. That was the first owner who provided me every receipt he had ever had for the car when I purchased it. The MAF wasn't replaced as part of the fix.

It continued to do about 80,000km after the rebuild still with the same MAF. No issues. One day I decided I'd change the MAF as a preventative maintenance thing. It got a bit more poke and better economy. I only had NADS fitted for less than 10,000km and I took it all off, and that was after I replaced the MAF. Have now done 140,000km since the rebuild.

So personally from my experiences and in my opinion, if the MAF was the culprit It would have blown again. 80,000km is a long time to be running with a supposedly dud MAF.
 

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Y2KGUII ZD Wgn
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Discussion Starter #3
My 2000 cracked 3, 4 and the head. That was the first owner who provided me every receipt he had ever had for the car when I purchased it. The MAF wasn't replaced as part of the fix.

It continued to do about 80,000km after the rebuild still with the same MAF. No issues. One day I decided I'd change the MAF as a preventative maintenance thing. It got a bit more poke and better economy. I only had NADS fitted for less than 10,000km and I took it all off, and that was after I replaced the MAF. Have now done 140,000km since the rebuild.

So personally from my experiences and in my opinion, if the MAF was the culprit It would have blown again. 80,000km is a long time to be running with a supposedly dud MAF.

I didn't say the MAF was the culprit, just a contributing factor under the right (or wrong) conditions. The actual MAF that was in mine when it "Grenaded" was still there up until early this year, it still works, it's in the draws as a spare. Maybe you missed my point that the rebuild pistons were far more heat tolerant than "some" of the originals.
 

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Geeyoutoo, I think you pretty well summed it up for a fairly objective explaination of the majority of failures. As you said there are a number of contributing factors so not all failures can be attributed to the same classic scenario but all of them seem to result in the same overheating of the pistons and parts of the head.

From personal experience (but luckily not my car), I have seen three blown motors as they were being dissmantled. All three had damage to similar places: the crown of pistons in a semicircular crack about 15mm in from the rim (I think it was on the rear of each piston 3 and 4), one had slumped melted section or hole in every piston and cracks in the head between the exhaust valves and glow plug hole. So the weakness to heat stress are seeming to be fairly consistent.
Two of these vehicles were totally stock standard Government fleet (around 2002) and being used for heavy towing. The other one was fairly well modified and suffered a failure when a dodgy Dgas system malfunctioned and pumped an oversupply of gas directly into the intake manifold.



Regarding the MAF.
Surely when the MAF begins to fail, it results in a drop in voltage, this provides the ECU with a lower air volume (MAFv) signal and hence the ECU is providing less fuel not more?
 

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Y2KGUII ZD Wgn
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Discussion Starter #5
Geeyoutoo, I think you pretty well summed it up for a fairly objective explaination of the majority of failures. As you said there are a number of contributing factors so not all failures can be attributed to the same classic scenario but all of them seem to result in the same overheating of the pistons and parts of the head.

From personal experience (but luckily not my car), I have seen three blown motors as they were being dissmantled. All three had damage to similar places: the crown of pistons in a semicircular crack about 15mm in from the rim (I think it was on the rear of each piston 3 and 4), one had slumped melted section or hole in every piston and cracks in the head between the exhaust valves and glow plug hole. So the weakness to heat stress are seeming to be fairly consistent.
Two of these vehicles were totally stock standard Government fleet (around 2002) and being used for heavy towing. The other one was fairly well modified and suffered a failure when a dodgy Dgas system malfunctioned and pumped an oversupply of gas directly into the intake manifold.



Regarding the MAF.
Surely when the MAF begins to fail, it results in a drop in voltage, this provides the ECU with a lower air volume (MAFv) signal and hence the ECU is providing less fuel not more?
Thanks Mate, I could have gone into more technical detail but it becomes boring and those were the basics as I had learned from my "Grenade" and others I've seen, as well as info gleaned from a friend who was a Nissan service manager years ago when mine dropped it's bundle.

Re MAF, depends on how they fail, mine failed and the symptom was not much power down low but go like the clappers up high so mine was giving a high voltage reading not a low reading, this was one of the things that got me thinking about doing a thread, I recently heard of someone getting over 5 volts from there MAF.........
 

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"This system is increasingly popular in passenger cars as well. The most important feature of a four,stroke Diesel engine with direct injection is the presence of a hollow combustion chamber in the piston head.

Its edge is particularly susceptible to cracking caused by heat fatigue [2, 3]. Cracking of piston heads ccan also occur in engines with precombustion chamber injection. The susceptibility to damage increases when the heat load of the piston is higher, which is the consequence of supercharging, air cooling, using more than two valves per cylinder and applying electronic controls.

As a result, modern truck engines can reach unit power up to 30 kW/dm3, maximum average efective pressure over 2 MPa and maximum total efficiency approaching 50%.

Heat load of the combustion chamber elements is the main factor limiting the
performance and durability of Diesel engines [4]. Taking all the elements of the combustion chamber into consideration, the most critical failure regions are the piston head and the cylinder head surface.

When the allowable temperature of the head is exceededvarious kinds ofmaterial damage
appear and excessive increase in diameter occurs, leading to seizing.

On the other hand, temperature fluctuation can cause cracking and leaking that disturbs or even makes engine operation impossible."
Source: http://www.pan-ol.lublin.pl/wydawnictwa/TMot3/Gardynski.pdf
 

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Rogue
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Nice info!!

That explains a lot. Particularly why we still see piston failures are needle and dawes valve fitting.
 

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Y2KGUII ZD Wgn
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Discussion Starter #9
Nice info!!

That explains a lot. Particularly why we still see piston failures are needle and dawes valve fitting.
As I said, NADS will not save an engine, just sometimes prolong, the damage has already been done.
 

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I bet NADS will protect a new motor (and I've put my money where my mouth is). If you have good control of EGTs the battle is mostly won.

I have no drama driving my troll like I stole it, if it lets go again...... hello duramax :cool:
 

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Y2KGUII ZD Wgn
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Discussion Starter #11
I bet NADS will protect a new motor (and I've put my money where my mouth is). If you have good control of EGTs the battle is mostly won.

I have no drama driving my troll like I stole it, if it lets go again...... hello duramax :cool:
Could not agree more, a newly (correctly) rebuilt or brand new engine will be fine. I have absolutely no concerns over mine "Grenading" again as my NADS were put in place relatively close to my rebuild.

If I have a concern it is with head cracks generated by extended glow plug "glow" prior to my fitting the glow plug timer, because we didn't really discover the bad side effects until much later.

The design of high swirl piston bowl geometry has been around for a long time and is beneficial to the DI design, so there is nothing really new there, material variation played a very big part in the "Grenade" with their inability to always accept ongoing high combustion temperatures, as said at the outset. CRD's run much hotter combustion temps without issues.
 

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If heat can be a "(...)consequence of supercharging,(...)", so this is why we need get the turbo under control, using needle and dawes valve. I think
Or not?
 

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Y2KGUII ZD Wgn
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Discussion Starter #13
If heat can be a "(...)consequence of supercharging,(...)", so this is why we need get the turbo under control, using needle and dawes valve. I think
Or not?
Yes to a certain extent but not the whole story.
Firstly a correctly setup Dawes and Needle will give a much improved linear boost curve, so there are no sudden surges and drop offs in boost (unknown drop offs being a silent killer, again the early ones were renowned for this).
Secondly we need to be careful with risks of overfuelling as this is the main source of unwanted excess combustion chamber heat.

As said this can be written up in pages and pages, my explanation was given more as a guide to understanding, there are many fallacies out there, just a few weeks ago I was told by a "Diesel Mechanic" I got talking to that the reason the DI's blew up was the fuel pump, the VP44 was failing :rolleyes:, I silently said to myself I would not recommending him to a ZD30 owner.........
 

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Thank you mate

I have a gq 92 tb42 SWB and a 07 (model made in 06) DI SWB with 41.000 km that I want to keep for a while

I blocked EGT (the air intake was cleaned) and installed glow plug timer. Ready for install SMF kit made by 4terrain, turbo timer and dual dawes valve with turbo boost and egr temp gauges.

Before to get the diesel patrol I was learning from the forum and I think that NADS are very healty for those engines. Very good information form You Gu2, Chaz and another Guys.

Out people recommends a bigger turbo and intercooler for get controlled egt temperature.

Can a K&N filter help with lower egt temperature?

What do you think
 

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Y2KGUII ZD Wgn
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Discussion Starter #15 (Edited)
Thank you mate

I have a gq 92 tb42 SWB and a 07 (model made in 06) DI SWB with 41.000 km that I want to keep for a while

I blocked EGT (the air intake was cleaned) and installed glow plug timer. Ready for install SMF kit made by 4terrain, turbo timer and dual dawes valve with turbo boost and egr temp gauges.

Before to get the diesel patrol I was learning from the forum and I think that NADS are very healty for those engines. Very good information form You Gu2, Chaz and another Guys.

Out people recommends a bigger turbo and intercooler for get controlled egt temperature.

Can a K&N filter help with lower egt temperature?

What do you think
There has been a lot of debate and threads re aftermarket air cleaners for the ZD30 DI, although there is evidence to suggest that some engines may benefit greatly from K&N I'm not sure a ZD30DI does.

The MAF is the thing that will suffer first if filtration is not spot on, I know from my experience that some AM filters see a drop off in fuel eco earlier than if I use a genuine and others show dust more quickly on the MAF, this may suggest that some aftermarket filters have finer or coarser filtration but not proven as yet to my knowledge.

Even though I've modified the hell out of mine I still retain the std filtration system (except for a safari snorkel that's been on since almost new), I'm not convinced (yet) that there are any great benefits to be gained at this point in time given doubts about the amount of air required to get any more grunt from the old girl.
 

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spot on

hi geeyoutoo,
i think you are spot on the money. a little while back i was having boost problems on my gu.
i took it to Turbo Engineering in thomas town and they pretty much told me the exact thing about the grenade effect. they believe that the engine management system is the main culprit by always trying to compensate for any arising problems.
i was boosting about 3-5 psi max. the problem Ray from Turbo Engineering explained after he put a new turbo on was quite simple.
before i bought it (from a toyota dealership) it was overboosting, so to sell it (my guess the previous owner not toyota) put a turbo with a tiny vnt screw so short that the whole turbo could not operate past 3-5 psi.
after ray put a new garret turbo (stock) on he dyno tested it and my old girl was sure enough over boosting.
Ray then installed a boost controller, blocked the E.G.R pipe and tuned it to perfection.

never had a problem since!!!!! my old girl has just clocked 302000 klms and is still performing wonderfully. even the oil stays honey gold between servicing.
 

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Y2KGUII ZD Wgn
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Discussion Starter #17
Out people recommends a bigger turbo and intercooler for get controlled egt temperature.

Can a K&N filter help with lower egt temperature?

What do you think
I can now answer your last question, NO, not that I expected it to anyway, but I fitted a K&N recently (see my build thread) just to get a feel for it, got a phone call for a family emergency and had to do a 660k round trip straight after fitting so I got a good feel for it, which I wrote up later.

As for bigger turbo, no don't, spoolup issues, but do go bigger IC if you have the opportunity.

hi geeyoutoo,
i think you are spot on the money. a little while back i was having boost problems on my gu.
i took it to Turbo Engineering in thomas town and they pretty much told me the exact thing about the grenade effect. they believe that the engine management system is the main culprit by always trying to compensate for any arising problems.
i was boosting about 3-5 psi max. the problem Ray from Turbo Engineering explained after he put a new turbo on was quite simple.
before i bought it (from a toyota dealership) it was overboosting, so to sell it (my guess the previous owner not toyota) put a turbo with a tiny vnt screw so short that the whole turbo could not operate past 3-5 psi.
after ray put a new garret turbo (stock) on he dyno tested it and my old girl was sure enough over boosting.
Ray then installed a boost controller, blocked the E.G.R pipe and tuned it to perfection.

never had a problem since!!!!! my old girl has just clocked 302000 klms and is still performing wonderfully. even the oil stays honey gold between servicing.
Thanks and good to see you are a happy ZD30 DI Camper. The benefits of the EGR block really show in the clarity of the oil long after it would normally be jet black, I slowly increased my oil change intervals after the block and have been at 10,000k intervals for some time now.
 

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Hi guys I have a few comments for you to mull over, not to try to disprove but more to get the old grey matter working.

I too had the grenade effect, but mine was very different to what you would call "the norm" I was driving home one night from work and noticed 20psi on the boost gauge and no drop off (pre dawes valve) as it normally did, then it got hot and when I pulled up at home the coolant was pressurised so the head came off the next day.

I found a cracked head and two cracked pistons, (1 and 4) with number 4 having what I would call a melt in it, this being a small spot that looks like it has had an oxy torch put to it and a weld pool formed.

Right cracked head: caused the over heating and therefor needed to be changed, no brainer and I will not even spend my time trying to think about that one but, the cracked piston i am not so sure about.

Before Christmas I pulled the head off a UD engine (Nissan truck) as it was overheating and blowing out of the expansion tank, I found 5 cracked pistons and told the boss to which he said "Thats OK all Jap engines crack pistons, you wouldn't believe how many I have seen and not changed, thats fine."

So to my cracked pistons, should I have changed them or were they perfectly OK, I am leaning towards being OK as I had no signs of smoke or even steam, no loss of power just the boost didn't drop as it normally did.

So to the "weld spot" on the piston crown, what would cause this, I would be thinking along the lines of a dirty injector nozzle and a jet of fuel hitting one spot and super heating it to the point of melt, this may be why we have melted pistons in some "grenades." So what would cause this, a build up of carbon on the nozzle, and that could be a result in the EGR heat and the oil from the blowby building up on the injectors and disfiguring the nozzle drillings so the fuel doesn't atomise but squirts a jet.

So with no argument against the ECU controlling the VNT and doing a poor job, this was something I bounced off GUToo a couple of years ago while fishing, is there a particular cause for the engine to fail or is it just when all the planets align under a certain star sign.
 

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Grenade Master
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Before Christmas I pulled the head off a UD engine (Nissan truck) as it was overheating and blowing out of the expansion tank, I found 5 cracked pistons and told the boss to which he said "Thats OK all Jap engines crack pistons, you wouldn't believe how many I have seen and not changed, thats fine."
Common rail version?

So to my cracked pistons, should I have changed them or were they perfectly OK, I am leaning towards being OK as I had no signs of smoke or even steam, no loss of power just the boost didn't drop as it normally did.
You have the engine apart now, while certainly you can get away with not changing pistons but guess what next failure is going to be. I'd actually attempting to source better pistons (material/design)

So to the "weld spot" on the piston crown, what would cause this, I would be thinking along the lines of a dirty injector nozzle and a jet of fuel hitting one spot and super heating it to the point of melt, this may be why we have melted pistons in some "grenades." So what would cause this, a build up of carbon on the nozzle, and that could be a result in the EGR heat and the oil from the blowby building up on the injectors and disfiguring the nozzle drillings so the fuel doesn't atomise but squirts a jet.
EGR doesn't increase amount of carbon necessarily I've seen engines with no EGR or CCV with phenomenal carbon build up inside combustion chamber/injector nozzles/valves over the years.
Carbon buildup on the externals of the nozzle orifices will get blown off by high injection pressure anyway(for Di 700 bars for CrD 1500-2500 bars), heck you can clean that carbon off with soft (brass) wire brush easily. Primary reasons for injector nozzles failures are poor quality fuel, wear and tear, incorrect assembly/components etc and to some degree effects of engine operation. What causes incorrect spray pattern is the failure of the nozzle needle to seal up the seat of the nozzle so the fuel drips or is not correctly atomized because nozzle leaks out under lower pressure than under which required atomization can occur. Di has dual stage injectors which are notorious for this.
So weld spot on the piston is indeed caused by failing injector nozzle dribbling/leaking fuel.

So with no argument against the ECU controlling the VNT and doing a poor job, this was something I bounced off GUToo a couple of years ago while fishing, is there a particular cause for the engine to fail or is it just when all the planets align under a certain star sign.
IMHO, it is the combination of the things unfortunately and yes the "planet alignment" will speed up the process. I also believe that the design and materials the ZD30 pistons are made of is major contributor, as they have no extra margin or ability to withstand additional stresses when fuel injection pushes in more fuel in than it should. The materials they're made from is on its last legs when it comes to current engine loads.
Put forged steel alloy pistons in, cast iron head and guess what; TD42 would be dead and buried long time ago.

So perhaps having injectors regularly checked for irregular fuel delivery/spray patterns could prevent some future failures, I don't know what that interval should be perhaps 100 thousand kays. The cost of this exercise is not what many of us would look forward to.

Cheers
 

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Rogue
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I'd imagine the 'weld spot' or melted hole is caused by hot gases flowing though and eroding a crack and increasing the temperature at that crack to beyond melting point of the piston material.
 
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