Inlet carbon fouling

[Pugglt Auld Jock]

Here's a very interesting wee video which dramatically illustrates the "washing" action of fuel on the inlet valve when the injector is, as here, mounted in the inlet manifold. It probably makes quite a good argument for the increased efficiency of direct injection too as you can see there is obviously liquid fuel burning off the surfaces around the inlet valve seat which a direct injection system would not suffer with. On the whole I think I'd rather suffer that and keep the back of my valves clean even if I'm not getting quite such good MPG and causing slightly more pollution? To say nothing of the claimed increase in particulate emissions of DI petrol engines?

https://www.youtube.com/watch?v=UvmBLqjaZxY

 

[AndyRKett]

Quite a big problem on older cars, obviously direct injection has been around since the 90s and so plenty of cars have suffered problems from inlet fouling.

I know it’s talked about quite a lot with golf GTI owners (mk5 and later) because they are performance cars people get quite tetchy about anything that saps bhp

 

[portland_bill]

Without knowing the source of the video, I wonder its value.

That appears to be a lot of fuel entering a small cylinder, rather too much.
The burn looks a bit weak, then followed by the yellow around the inlet valve.
We have a camera inside the combustion chamber, with its own light, which seems unaffected by pressure or cumbustion temperatures. I wonder if the engine is very low compression, and the fuel certainly looks like droplets rather than a mist.

If you do a calculation from your fuel consumption in mpg, and work out the quantity of fuel for each firing stroke at an average cruise, the amount per stroke is miniscule. I've done the calculation a few times, but can't be bothered right now, but I'm thinking the head of a normal pin, not one of those big round-head jobbies, is way bigger than the amount of fuel. That vid seems to chuck it in by the bucketful, hence the amount left around a poorly seated valve?

 

[Pugglt Auld Jock]

Hmm. you raise a lot of good points there PB. The only thing that occurred to me on rewatching it was how they'd positioned the camera and the illumination. Something just didn't look right? On the other hand if you get "scientific" about it most engines run somewhere around 14:1 air fuel ratio BUT, that 14:1 is measured by weight - if I remember my college theory classes? So a helluva lot of air and a pin head of fuel!

So, on reflection, I think that engine would be so flooded it wouldn't run?

PS. Just rewatched it again and now I'm just not sure?

 

[DaveMcT]

Car Wizard was recently working on an Audi V10 with direct injection. The inlet valve ports were clogged with carbon. He used some pretty nasty chemical to clean them off.

It's not exactly an everyday car but does illustrate an issue with DI engines.

https://www.youtube.com/watch?v=8zmXyB38mRg&t=226s

 

[Pugglt Auld Jock]

I've posted a few times about my interest in finding out all I can about inlet carbon fouling on D.I. petrol engines so I was very surprised to find that my wee Ibiza engine doesn't "do" exhaust gas recirculation. I thought all I.C. engines used EGR to reduce nitrous oxide emissions etc? It'll be very interesting to see if this substantially reduces the build up of carbon in the inlets.

 

[chris3234]

I've posted a few times about my interest in finding out all I can about inlet carbon fouling on D.I. petrol engines so I was very surprised to find that my wee Ibiza engine doesn't "do" exhaust gas recirculation. I thought all I.C. engines used EGR to reduce nitrous oxide emissions etc? It'll be very interesting to see if this substantially reduces the build up of carbon in the inlets.

Egr valves are mainly on diesel's from.my experience allthrough some petrol's have them

Certainly not aware of any petrol fiat engines that's uses one

 

[jackwhoo]

Apologies for directly disagreeing with previous post but egr valves have been fitted to many petrol engines.

Earliest one I can think of off hand is 1990ish lancia dedra 2.0 turbo
Fiat croma 2.0 turbo had the same engine

Ford Mondeo 1.8 mk1s had them too

Engines that don't have them probably have sufficiently low nox emissions so the manufacturers are not forced to fit an egr system.

 

[AndyRKett]

Ford Mondeo 1.8 mk1s had them too

Indeed, my March 1993 Mondeo had one, horrible thing made of gold coloured pipes that I had to braze back together when one of the pipes broke off.

I also owned a 1995 2.0L 4wd Mondeo Ghia that had the same set up.

I also thought my 97 Saab 900 also had one, they were the last petrol cars I really did any work on. I did have the 1.4 8v Grande but did very little to the engine of that.... put the air filter in wrong ?....

 

[StevenRB45]

I've posted a few times about my interest in finding out all I can about inlet carbon fouling on D.I. petrol engines so I was very surprised to find that my wee Ibiza engine doesn't "do" exhaust gas recirculation. I thought all I.C. engines used EGR to reduce nitrous oxide emissions etc? It'll be very interesting to see if this substantially reduces the build up of carbon in the inlets.

Thing is you can design around it.

Toyota uses combined port and Di injection.

Current Mazda engines are all DI but I've not seen complaint about it occurring on them and alot of them are well into 6 figure mileages these days. Apparently with that one it is designed in such a way that the valves are held at a temperature that makes deposits unlikely to form (make of that what you will god knows what that means in reality but it seems to work).

PSA fire the injectors with the inlet valve open via the vvt to wash the back of it like the port injection would.

So although various cars...mainly German engineered have significant issues it's not inevitable.

No egr may be a strategy or it could just be clean enough burning not to have to do it.

 

[Pugglt Auld Jock]

Sorry Chris but I think Fiat are actually quite unusual in this respect. Two of the engines I know to use it are my daughter in law's Jazz: https://www.youtube.com/watch?v=-Mh6F15rZhc and my neighbour's SEAT which uses the 1.4 version of this VAG engine: https://www.youtube.com/watch?v=3abPrYOrsxo.

Here's a video which illustrates the problem and one of the better ways of dealing with it: https://www.youtube.com/watch?v=fgvNu_HVD_g

 

[Didge3]

Egr valves are mainly on diesel's from.my experience allthrough some petrol's have them

Certainly not aware of any petrol fiat engines that's uses one

My '94 Punto 1.6 had an EGR and that was an ancient engine, not sure when they started fitting EGR's to them I suspect the Punto may have been the first