Coked up inlet manifold (effect on diesel fuel consumption?)

[ted frater]

I picked up a spare cyl head for my Vitara 1997 5 door diesel . Thats with the Mazda 2ltr,mr turbo intercooled motor.
This head had done some 121,000 miles and the inlet ports, manifold , and post egr valve section of inlet was severely coked up with oily exhaust gas carbon. About 1/8 in thick in places.
My motor has done only 83,000 miles and as far as I can tell, has never been apart.
One of the things I did some 3 months ago was take off the intercooler and have a look see inside. all oily, so i washed it out with petrol several times. Lots of oily residue from that.
After I got my vitara some 9 months ago, on adviceof a friend I blamked off the EGR valve in my programme of engine efficiency improvement. As anside that has certainly made a noticeable difference in fuel efficiency.
so i expect my inlet ports etc to be somewhat fouled up but by no means as bad as the sparechead Ive here.
Now, the question is,
When off boost from the turbo, how much efficiency am i likely to lose with
a dirty fouled up inlet system?
Ive always thought that its important to keep the inlet system clean and smooth
to get the best cyl filling possible, especially on a diesel, where one is always looking for the max amount of clean cold air getting into the cylinders?
Any thoughts or advice welcome.
Ted
In Dorset
UK

[COcyclist]

Originally Posted by ted frater

on adviceof a friend I blamked off the EGR valve in my programme of engine efficiency improvement. As anside that has certainly made a noticeable difference in fuel efficiency.

When off boost from the turbo, how much efficiency am i likely to lose with
a dirty fouled up inlet system?
Ive always thought that its important to keep the inlet system clean and smooth
to get the best cyl filling possible, especially on a diesel, where one is always looking for the max amount of clean cold air getting into the cylinders?
Any thoughts or advice welcome.
Ted
In Dorset
UK

We only get the VAG passenger diesels here in the states but from what I have read, the clogging is most noticeable when you are trying to flow a lot of air or make a lot of power. You may not be losing much efficiency at light or part throttle driving.

Do you have any data about your mileage gains without EGR? On the VW blocking off the EGR confuses the computer and many report decreased mileage.

[Backtobasics]

2 questions:
Where does the EGR return into the intake manifold?
Where the the crank case evacuation system (vent tube, etc) return to the system? I would not expect a PCV on diesel due to lack of vacuum.

These would probably have to return into the suction side of the turbo (I would think).

My concern is the crank case evac and egr dumping sooty air back into the intake or pre turbo, allowing the soot and blowby to blow all over the intake before being re-introduced to the cylinders.

The only way I see to keep it clean would be periodic spray with carb cleaner / intake tract cleaner. Perhaps you could reposition the crank case vent system to introduce into the air box, before the air filter, where the filter could trap the soot before it heads into the intake manifold?

[UFO]

That's EGR for you. I cleaned my manifold once two years ago, I'm going to check it again this spring. If it's plugged up again, EGR=byebye.

[ted frater]

Hi Cocyclist,
Figures? for improvement? I dont hink I can seperate this factor from all the other things Ive done.however the difference I think it has made is the difference between letting the engine have cold dense clean air as opposed to hot low oxygen air.
Like running on a cold day to a hot day.
On my suzuki diesel, the egr is ECU controlled tho there isnt a lambda sensor anywhere.
IF you put a blanking plate between the valve and the inlet manifold the ECU is not confused its doing what its supposed to but theres no exhaust gases to pollute the incoming air.
As for economy running around with lots of stop starts im getting about 42mpg, driving carefully.Apart from the above the other benefit is that the oil keeps so much cleaner between changes.
Hi Back to basics,
TheEGR return is into the manifold downstream from the throttle position sensor but before the manifold branches into 4 pipes of the cast ali manifold.
The crank case breather feeds into the inlet pipe just upstream of the turbo.
Yes, it would make sense to route it the upstream side of the air cleaner, but thats a dry element type. Id have to fit an oil bath type off a 2ltr peugeot diesel I scrapped recently. will look at that in the daylight. Its 11.30 pm here just now.
OR I could do what used to be done 50 yrs ago, that just vent to atmosphere!!
As an aside, I was looking at some old photos i took of a car I ran in 1955.
we found a 6 ltr 4 cyl Renault landaulette from 1908. I restored it to road worthy condition, and took it to The Veteran run in Novembet that year. That was from london to Brighton and was fine. We set out from There to go the 120 miles back to Poole dorset, it was A fantastic trip.as we were running on the original acetylene lamps fed frrom a central generator on the running board The very white light was as good as a modern filamant bulb but a lot whiter, no dip of course.Side lights and tail light were oil.
Its no longer with us but its now 103 yrs old!!.
Ted
in Dorset
UK