Bongo Fury

I'm in the process of removing my head, and have found the that the inside of the inlet manifold (and big hose joining it) are caked in soft oily sludge. There is also oil in the big pipe coming out of the turbo.

I guess this is due to turbo blowing out oil, collecting in the intercooler and travelling on to inlet manifold.

I plan to clean out the inlet manifold and intercooler, and all pipes between turbo to intercooler and inlet manifold, but I assume it will build up again.

Do these symptoms mean I've got a faulty turbo? Is there an easy fix for this problem? Should the manifold and pipes be spotless or is some oil normal?

I'm working on a very low budget so a replacement turbo is not an option at the moment.

Thanks.........Rob

Your sludge is undoubtedly a result of the EGR system (exhaust gas recycling). It is there to meet Japanese emissions controls and not required in this country. If stripping the head etc down then you can disable it permanently by blanking off the inlet and exhaust manifolds and removing the EGR system entirely. Alternatively just block off the vacuum pipe and leave the rest in place.

Sorry, I didn't fully answer your question. Expect some oil in the pipes and turbo. It's the sludge you don't want. Eliminating the EGR should stop it coming back and in theory should give slightly improved performance and consumption.

Thanks for a very useful reply Ian, but where would I find the vacuum pipe to which you refer?

Now you are asking. I think I got the hint from a thread on this forum then isolated it as a process of elimination. If you can bare with me, I'll have a look tonight and take a picture for you.

Hope you can make this out. If you lift the engine cover on the driver's side, at the very top left of the opening you should see the round EGR diaphragm thingy with a tube sticking out and a pipe connected to it. Remove the pipe and bung it up with a tight fitting bolt, ball bearing or similar. I also tied mine out of the way with a cable tie to stop the bolt shaking out.[/img]

Now that seems far simpler than blocking off the pipe with a bearing ball or similar - nice one Veg

PS - I presume the valve stays permanently shut??

If like my old Townace (and no reason to doubt it isn't), the valve is activated by vacuum. So with the engine off I'm assuming the valve closes and can't open again with the vac pipe removed. I would have preferred to have disabled it properly by blocking off both manifolds and removing all the gubbins but couldn't easily get to the rear of the engine so took the easy way out. If and when I have to work on the engine or turbo area, I'll sort it then.

Clean? - you haven't seen the other side

This is getting to be a very interesting thread.

Does anyone have any opinions on the long term effects of doing this ?.

Thanks again Ian, excellent pic. I've actually got all the gubbins in the back at the moment because I'm taking the head off so I might take the decision to blank the inlet and exhaust manifolds and leave the egr off entirely.

Just to confirm your diagnosis, I looked more closely at the curved metal junction bit which bolts onto the inlet manifold. Into this runs a big hose from the intercooler which was a little oily but not terribly so, and the metal pipe of the egr. At the point where this egr pipe joins the junction piece, this is where all the sludge starts and absolutely cakes the entire inner surface of the inlet manifold. So, excellent diagnosis I think.

You're right 2sticks....this is an interesting thread! As something of an environmentalist, I was initially concerned about disabling a supposedly positive environmental device which has the effect of reducing the amount of crap being ejected into the atmosphere........but I quickly justified the action thus: If I obtain extra mpg by doing this, this will offset some if not all of the egr benefit. Also The amount of sludge this device is sending back into my engine is incredible; it must be causing additional wear and generally problems. So by disabling the egr, I'm potentially saving another engine from being manufactured to replace mine, and therefore saving a huge amount of energy (required to process aluminium etc). So the net effect is.....I'm doing the planet a huge favour!

I'm close to getting my cylinder head off, so will report what the inside is like soon.....and....when I get it all back together....I'll post report on performance/economy effects. At the moment my van is a good but not great performer running at an unsatisfactory 24 mpg average.

Thanks again Ian.

Oh my! Just checked all the earlier posts about egr blanking.....loads of conflicting opinions...now I'm not so sure!

Earlier posts suggest that the egr actually allows the engine to run cooler, so given my overheating issues I'm not sure I want to disable it now....but I don't want all that sludge in my engine!

Below is an extract from Wikipedia

http://en.wikipedia.org/wiki/Exhaust_ga ... el_Engines

written by Robert Bosch, an authority on diesel engines.

EGR in Diesel Engines
In modern diesel engines, the EGR gas is cooled through a heat exchanger to allow the introduction of a greater mass of recirculated gas. Unlike SI engines, diesels are not limited by the need for a contiguous flamefront; furthermore, since diesels always operate with excess air, they benefit from EGR rates as high as 50% (at idle, where there is otherwise a very large amount of excess air).

Since diesel engines are unthrottled, EGR does not lower throttling losses in the way that it does for SI engines (see above). However, exhaust gas (largely carbon dioxide and water vapor) has a higher specific heat than air, and so it still serves to lower peak combustion temperatures; the diesel engine's efficiency is still improved by reduced heat rejection and dissociation.

Implementation of EGR
Recirculation is usually achieved by piping a route from the exhaust manifold to the inlet manifold, which is called external EGR. A control valve (EGR Valve) within the circuit regulates and times the gas flow. Some engine designs perform EGR by trapping exhaust gas within the cylinder by not fully expelling it during the exhaust stroke, which is called internal EGR. A form of internal EGR is used in the rotary Atkinson cycle engine. EGR in the R.A.C.E. can be utilised with spark-ignition or Diesel enhancing the thermodynamic efficiency of this cycle.

EGR can also be used by using a variable geometry turbocharger (VGT) which uses variable inlet guide vanes to build sufficient back pressure in the exhaust manifold. For EGR to flow, a pressure difference is required across the intake and exhaust manifold and this is created by the VGT.
Other methods that have been experimented with are using a throttle in a turbocharged diesel engine to decrease the intake pressure to flow EGR.
Early EGR systems were unsophisticated affairs utilizing manifold vacuum as the only input to an on/off EGR valve; reduced performance and/or drivability were common side-effects. However, modern systems utilizing electronic engine control computers, multiple control inputs, and servo-driven EGR valves typically improve performance/efficiency with no impact on drivability. In the past, a meaningful fraction of car owners disconnected their EGR systems. Some still do either because they believe EGR reduces power output, causes a build-up in the intake manifold in diesel engines, or because they feel the environmental intentions of EGR are misguided. Disconnecting an EGR system is usually as simple as unplugging an electrically-operated valve or inserting a ball bearing into the vacuum line in a vacuum-operated EGR valve. In all cases, the EGR system will need to be operating normally in order to pass emissions tests.

The paragraph above applies to the majority of imported Japanese MPVs with 10+ year old diesel engines and automatic gearboxes eg. Bongos, Lucidas, Granvias, Delicas etc. The ?unsophisticated? EGR systems are meant to reduce NOX (various oxides of nitrogen) emissions. They can be produced during "over-run" when ordinary air, which is about 20% oxygen and 80% nitrogen, without fuel enters the combustion chambers while they are still very hot. The oxygen in the air combines with the nitrogen in the air instead of with hydrogen and carbon in fuel. The EGR system works by diverting some of the exhaust gas through a metal pipe, around the back of the valve cover into the inlet manifold. A flap valve where that pipe goes into the inlet manifold is opened by a vacuum servo which is controlled by an electric signal applied to a solenoid-operated vacuum valve. Much of the diverted gas is soot and mixed with diesel and oil forms a sticky sludge.

General opinion is that in a 10-year old car it does more harm than good - causing a lot of carbon soot to build up in the inlet manifold and in the EGR system itself, possibly even preventing the flap valve closing - therefore allowing some exhaust gas to recirculate in "normal" driving.
I?m not sure where the idea that removing the EGR will increase heat output. The engine burns either fuel/air or fuel/air/recirc air. The same thing really. Engines are designed before the addition of EGR.

I disabled the EGR on my Townace some two years before trading it in for the Bongo. The inlet manifold had an appreciable build up of sludge baked onto it and had blocked about 15% of the bore of the turbo pipe. I had no ill effects after removing the EGR and noticed a slight improvement in acceleration and fuel consumption as a result. Don?t just take my word for it. I can quote many many owners who noted improvements after disabling the EGR system. Check some of the bulletin boards for yourself.

I was pleased to see your post above as it confirms this condition applies to Bongos as well.

An excellent contribution Ian, my instincts tend to lead me to trust your judgement implicitly.

As I read it:

if you have a fairly new engine it would be better to leave things as Mazda intended.

Older engines may benefit from disabling the EGR system if you have problems with sludge.

I would take it as a given that you will have sludge. If not so arduous a task it would be worth taking it off just to see.

To give a balanced view though, I would anticipate a number of contributers reading this thread being reticent about tampering and leaving well alone. I have to confess I had similar views before removing the turbo pipe on my Townace and seeing all the sludge that had formed. It really was a kick up the backside to do something about it.

Yes, excellent info Ian. I'm back on the disablement side now! However, I think I'll take the vacuum pipe approach rather then leave off the whole system just in case!

I'm going to take some pics of my manifold and try to post them later so forum users can see the extent of the sludge problem.

Rob