Dangers of Blocking EGR
Submitted: Monday, Feb 19, 2007 at 08:21
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Snowy 3.0iTD
If you own a pre 2005 Nissan 3.0L Patrol and you have blocked off the EGR you need to read this. After hearing so much about this I decided to trial it for a few months on my 2003 3.0L. It all worked fine with the exception that at 110km/h on light throttle such as cruising along flat sections of hwy, where I do lots of kilometers, the turbo boost would drop to less than 5psi, where it use to sit around 8-12 psi. Initially I didn't think much of this until I read on other forums that when this happened their Exhaust Gas Temperatures (EGT's) were going
well over 500C. So I borrowed a pyrometer and hooked it in just after the turbo but before the catalytic converter. On a trip from
Whyalla to
Adelaide (380km's) and back over the weekend, sure enough everytime the car settled in to 110kmh the boost dropped to less than 5psi and the EGT's started steadily climbing at one point reaching 540C. Reading other online forums some people had possible solutions, but they were talking about 'back-yard' solutions to try and fool the computer, which sounded like a recipie for disaster to me. So I have reinstated the EGR, figurring that sacrificing a small efficiency gain is better than destroying my engine. Will submit another post with fuel consumption figures in another couple of weeks.
Cheers
Snowy
Reply By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 09:18
Monday, Feb 19, 2007 at 09:18
Yes this is the risk of blocking the EGR. The soluton is to not fool the computer, but to fool the boost controller which is a simple vacuum operated actuator on the "wastegate" (variable vane type).
This is a practice widely used on normal waste gated turbos by the rice burner brigade, and simply requires a manual boost adjuster readily available and costing $50. The adjuster is plumbed into the vacuum hose gong to the actuator. The adjuster has a spring and ball seal that once pressure (vacuum) reaches a certain amount (adjustable) then it leaks a small fraction of air into the vacuum hose, thus changing the actuator position and raising boost.
Low boost at cruise was always a problem on my Patrol, without the EGR blocking. I believe high EGT is the cause of the engine failures on vehicles that have not blocked the EGR system, due to low boost at highway cruise when fueliing is high. This is particulary when towing. It seems in my opinion, an engine manaegment issue that aids the Patrol meet emmission specs and therefore can't be engineeered out causes the problems. Of course Nissan can't fiddle with emissions laws, so the fix is to make the engine tolerate higher EGT by adding more oil, ceramic piston tops etc etc.
Now while Nissan my not want to fiddle with emissions control, there are owners who happily would. Increasing boost to more reasonable levels at highway cruise seems a logical place to start lowering EGT. This is easily done with a manual boost adjuster, a very common mod on just about every rice burner you see cruising our streets full of
young people.
AnswerID:
222620
Follow Up By: 3.0turbob - Monday, Feb 19, 2007 at 09:32
Monday, Feb 19, 2007 at 09:32
David,
Would the manual boost control still work with the turbo being a variable vane ?If so, how?
Rob
FollowupID:
483452
Follow Up By: Snowy 3.0iTD - Monday, Feb 19, 2007 at 09:34
Monday, Feb 19, 2007 at 09:34
David
I only had the problem of low boost and hight EGT's when the EGR was blocked. As far as I am aware the Garrett turbo on the ZD30 does not have a wastegate, but a series of vanes positioned radially around the exhaust side fan, controlling the flow of gasses on to the exhaust side fan. The ZD30 turbo essentially has two boost positions (high & low) you can definitely notice this change on the boost gauge and boost normally ranges on
mine from 8-20psi of boost. I do wonder what effect it would have on computer/engine if suddenly the boost was controlled to a single value? I would be interested to know if anyone has fitted one of these to a ZD30, what it drives like, and if there are any potential long-term effects. Can you get a boost-controller with in-cab adjustment?
Cheers Snowy
FollowupID:
483454
Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 10:09
Monday, Feb 19, 2007 at 10:09
3.0turbo
Yes it would, The VVT uses a variable nozzle control actuator to adjust a series of vanes prior to the turbine that allow gas to bypass the turbine.
Snowy- This is essentially an internal wastegate, since it allows the gas to bypass the turbine. It really only has two states, it is not continuously variable. It has a bypass state and a normal (high boost state, so in result, it is essentally the same as a wastegate.
I am not recommending controlling the boost to a single value. What I am suggesting is that you connect a manual controller into the system and you don't use it when driving around at lower speeds thus the VVT works normally. Once you are on the highway and the boost drops, you simply turn the adjuster and restore boost to a higher values perhaps 6psi.
David
FollowupID:
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Follow Up By: Snowy 3.0iTD - Monday, Feb 19, 2007 at 10:57
Monday, Feb 19, 2007 at 10:57
Having just spoken to a couple of different turbo mobs, the biggest problem is that boost controllers are designed to work on a pressure line, while the ZD30's boost control operates via a vacuum line I think.
FollowupID:
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 11:07
Monday, Feb 19, 2007 at 11:07
That doesn't present a problem. For vacuum applications most controllers simply require the valve to be plumbed backwards so to speak. There are quite a few systems using vacuum
FollowupID:
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 11:29
Monday, Feb 19, 2007 at 11:29
Oh and yes you can get one with in cab adjustment, that would be necessary for the setup I am talking about
FollowupID:
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Follow Up By: Snowy 3.0iTD - Monday, Feb 19, 2007 at 12:07
Monday, Feb 19, 2007 at 12:07
David
Is the high boost position of the turbo activated by high vacuum or no vacuum? If it is the low vacuum case then that would mean that when the turbo kicks in to the low boost case this is caused by a high vacuum, so a a boost controller would allow you to reduce the vacuum and bring the boost up. If it is the other way around then the boost controller could only reduce the boost pressure as it can not generate more negative pressure, so then you would have to adjust
the nut on the actuator arm for the vanes and use the boost controller to reduce the boost, which I think you would need to very careful with as I am bit reluctant to start adjusting the actual turbo itself.
Snowy
FollowupID:
483494
Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 12:13
Monday, Feb 19, 2007 at 12:13
It is activated by high vacuum, so the boost controller bleeds air in. You have very fine adjustment. One guy I know experimented with a bit of beverage tubing running into the cab, and a small adjustable drip feeder from a sprinkler system. It worked
well as a
test.
FollowupID:
483496
Follow Up By: Member - Geordie C (WA) - Monday, Feb 19, 2007 at 23:18
Monday, Feb 19, 2007 at 23:18
Yes I have done the same with a
T junction and thin rubber vac hose to a cheap brass needle valve as a bleed off. It works
well for pressure or Vac systems. However, you are in full control and need to watch a boost gauge so don't open the valve all the way or it can go over boost. Not as fancy as the expensive rice-burner options with pre-set spring valves, toggle switches and fancy looking red alloy fins but it works if you use it carefully.
FollowupID:
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Reply By: wilko65 - Monday, Feb 19, 2007 at 11:54
Monday, Feb 19, 2007 at 11:54
I am not sure that I understand the relationship between the blocked EGR and the variation in boost pressure? One of the EGR's jobs is to direct exhaust gas back into the cylinder to aid in the cooling of the combustion process. It does this due to the fact that the exhaust gas has a lower oxygen content than the intake air and thus does not burn as
well and in fact will partially extinguish the combustion process. So if the engine management system still thinks the EGR is working and therefore delivering the same amount of fuel for a given engine load, I would expect to see a rise in EGT if the EGR is blocked. The boost pressure is affected how ? Under full throttle the EGR is blocked by the ECU supposedly. Maybe there is another reason the boost drops off? I would be interested on peoples theories for this?
I have a 2003 3.0ltr manual with around 120,000klm. I have had the car from new. My EGT runs at anything around 300 to 450 at around 100 - 110klm/h on most roads. I have seen it as high as 600 on a long steep
hill at 110klm/h and full throttle, but I wouldn't hold it there. I do not have my egr blocked, nor do I have a Dtronic etc or any other mods to the engine.
AnswerID:
222643
Follow Up By: Snowy 3.0iTD - Monday, Feb 19, 2007 at 12:13
Monday, Feb 19, 2007 at 12:13
wilko
Plumbing exhaust gas back in to the cylinder will lower peak combustion temp which occurs for a fraction of a second, but the overall gas temp has to go up, instead of all your intake gas being at 20C or there abouts some of it is at 200C or higher.
It is just a theory but I suspect that as the EGR opens the computer has to wind back the boost slightly so that exhaust manifold pressure is higher than the intake manifold pressure, when the EGR isn't blocked the gasses flow allowing the two manifold pressures to be close to equal (just enough difference to ensure flow) but the computer does not sense a blocked EGR, you have no EGR flow, so high exhaust manifold pressure and low intake manifold pressure. Just a theory.
Snowy
FollowupID:
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Follow Up By: 3.0turbob - Monday, Feb 19, 2007 at 12:29
Monday, Feb 19, 2007 at 12:29
But isn't the turbo (variable vanes) controlled by vacuum taken off the manifold, and not the computer. (sorry, I'm just trying to get a bit more of an understanding, I'm very reluctant to mess around with standard factory settings)
Rob
FollowupID:
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 12:53
Monday, Feb 19, 2007 at 12:53
IT is controlled by a special type of relay you can see it near the airbox, this is controlled by a similar signal to that used for the injectors. Definitely controlled by the computer.
FollowupID:
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 12:55
Monday, Feb 19, 2007 at 12:55
BtW Iam not recommending this...I couldn't a afford to do that. :-)
Just telling what I've learned.
So don't fiddle with anything if you aren't comfortable
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Reply By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 12:20
Monday, Feb 19, 2007 at 12:20
Yes the boost is dropped by the actuator. It seems to drop boost at certain revs. You can predict the exact point it will drop boost as you are driving along. I know some people have reported a drop in boost at highway cruise due to the EGR blocked, but I've not noticed this.
Mine always was low at highway cruise, due to the action of the VVT at about 2100-2200 rpm. As I say I see this as an engine management issue. Low boost would be required when the EGR is wide open (at highway cruise) otherwise the gases may never flow into the intake at high pressure. But with the EGR blocked this is not an issue.
So you can see Nissan's dilema. if they make the car run higher boost at highway cruise (in order to lower EGT) they will have to disable the EGR, which means the car won't meet emmission specs. So the answer is build engines that can tolerate more heat, and fix the old ones when they blow up.
AnswerID:
222649
Follow Up By: diesel dave - Monday, Feb 19, 2007 at 18:16
Monday, Feb 19, 2007 at 18:16
Hi David
I'm new to learning about the patrol engine's but slowly getting there. does everything explained above apply to the 2.8 ltr as
well ? i know where and how to block the EGR off but everything I've been reading is about the 3.0 ltr. any information would be very grateful.
Thanks
Dave
FollowupID:
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Monday, Feb 19, 2007 at 19:04
Monday, Feb 19, 2007 at 19:04
No the Patrols problems as far as I am concerned stem from two areas, and none of these apply to the 2.8.
The first is the variable vane turbo dropping boost at highway cruise, resulting in high EGT (exhaust gas temperature). The related issue is the EGR (exhaust gas recirculation) which is blocked by some because it fills the induction with soot and potentially could block the intercooler. Some believe it contributes heat to the combustion, but I doubt that it makes much difference.
In my opinion the melted (not cracked) pistons are due to high EGT (exhaust gas temperature).
The other issue and most likely cause in my opinion of pistons cracking is overboost. I have experienced this myself- not the pistons cracking, but the overboost at low speed thankfully. Sometimes when the MAF (mass airflow sensor) goes kaput, it does not throw up a code but simply disables the boost controller. This turbo at max boost seems capable of delivering 32 psi.
Mine pushed 21 psi at quite low revs with the MAF failed. The related issue is that some believe a faulty EGR valve that is open at low boost results in exhaust gas contaminating the MAF which causes it to fail.
Therefore there are some including me that beleive that the best course of action is to block the EGR system, lower the maximum boost setting (by adjusting the stop limit of the actuator) and fitting boost guage and pyrometer (EGT monitoring) and fitting some sort of manual in cab boost controller to increase boost and thus lower EGT at highway cruise. Oh and carry a spare MAF.
Cheers
David
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Follow Up By: Muzzgit [WA] - Monday, Feb 19, 2007 at 23:59
Monday, Feb 19, 2007 at 23:59
I have had the EGR blocked for about 12 months now. The only discernable difference is it seems to spool up a bit quicker from low revs. I don't have boost guage, EGT, or anything else.
David, I am having difficulty figuring out how exhaust gas could fowl the MAFS. The MAFS is up near the airfilter.
But yes I agree "and carry a spare MAF."
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Tuesday, Feb 20, 2007 at 08:17
Tuesday, Feb 20, 2007 at 08:17
"some believe a faulty EGR valve that is open at low boost results in exhaust gas contaminating the MAF" personally I have the same difficulty.
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Reply By: PhilZD30Patrol - Monday, Feb 19, 2007 at 22:09
Monday, Feb 19, 2007 at 22:09
Hi
Isn't the EGR there to minimise noxious exhaust emissions that stuff up the enviroment?
If the answer is yes, why would anyone want to deliberately stuff up the enviroment by doing engine modifications for very little gain and possibly contribute to a very bad future for your and my grand kids?
Phil
AnswerID:
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Follow Up By: Member - Geordie C (WA) - Monday, Feb 19, 2007 at 23:47
Monday, Feb 19, 2007 at 23:47
Yes,
the egr is there to meet emission requirements to lower NOx (Nitrogen oxides NO2 and NO3 collectively NOx) emissions (which are very reactive gases and along with ozone are bad for producing photochemical smog). This reduction in NOx is achieved by reducing the oxygen level in the intake air by adding some burnt exhaust gas.
However, the egr by adding burnt exhaust gas also reduces the efficiency of diesel combustion and produces more soot in the form of micro aerosol particles (nasty to our lungs). Then they add a catalytic converter and sometimes particle filter. Really they should look at far better combustion processes such as adding injection of supplementary LPG or Natural gas to diesel motors to improve combustion, more power and economy with less soot and NOx.
G
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Tuesday, Feb 20, 2007 at 08:22
Tuesday, Feb 20, 2007 at 08:22
I guess saving yourself $12000 every 50,000 to 100.000 kilometres is justification enough. Photochemical smog has been reduced bucket loads, and Australia hardly suffers as many who have travelled to Mexico City or Tokyo will attest. The CO2 is the real problem. Best way to stop CO2 is don;t rive cars I guess. So the EGR is in my mind a small factor versus $12000.
However for Nissan it must be is a real problem. How do you engineer your way out of that? The only way is to build more heat tolerant engines.
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Follow Up By: Snowy 3.0iTD - Tuesday, Feb 20, 2007 at 08:23
Tuesday, Feb 20, 2007 at 08:23
The other simple part is that when you have unburned hydrocarbons in the case of EGR you also get Carbon Monoxide (CO), a tasteless, odourless, colourless toxic gas, I guess the legislative bodies who set emission laws figure this is better than NOx emissions, and wasting fuel?
Cheers
Snowy
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Follow Up By: David from David and Justine Olsen's 4WD Tag-Along - Tuesday, Feb 20, 2007 at 08:28
Tuesday, Feb 20, 2007 at 08:28
Yes it is interesting. Also bear in mind the greatest pressures on manufacturers to meet emmissions specs coincided with fuel shortages.
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