GDI engines suffer dirty intake valves?

[rmay635703]

Originally Posted by niky

That's assuming buyers are smart enough to refill the water tanks. GM ditched water injection because they weren't.

Unlike urea, where you can have a big enough tank to last till the next oil change, you'll need to refill a water tank often... Unless you have a big reservoir, several times per fuel tank. And it needs to be distilled to keep from clogging nozzles... which will add to cost.

(I love water injection, mind you...)

I agree with the poster above, limp mode would be a very good motivator to add water and "other" water applications have overcome the nozzle clogging issues (mineral deposites) with plain tap water using a combination of being injected through a synthetic and pressure.

Also there is the fact that a proper design could be "cleaned" easily but I digress.

[RobertISaar]

Originally Posted by niky

Big incentive to pay attention.

still wouldn't stop it.....

i still see people kill their brand new cars by never once having the oil changed, even if the dealership they bought it from never charges them AND reminds them to do so.

some people..... just don't care.

[Howlermonkey]

Originally Posted by Old Mechanic

Yep, the first EFI Z cars (1975-76 federal) did not have EGR valves. The intake manifolds were super clean. When they added EGR everything inside the manifold downstream of the egr entrance was covered with a tar like residue, except the intake valve stems where the injectors sprayed fuel.

regards
Mech

As a z-car specialist going back to my time at "z-shop of Miami" in the 80s, I agree with your assessment on non-egr engines being clean of the egr fouling but those non-egr engines still fell victim to fuel deposits on the back of the intake valves which would grow until they eventually looked remarkably like what you would find on an egr equipped engine.

The mechanism is explained below.

In my experience, all of the injected nissan "L" engines (L28e and L24e) suffered intake valve coking and I made a good portion of my living removing deposits that looked as if someone had impaled a Hershey's kiss on the valve stem and slid it down to the back of the valve.

That's a lot of accumulation and, once it get's a foothold, even the pcv oil mist will start sticking regardless of the detergent fuel being sprayed directly onto it.

On this engine family, my theory is that the initial fuel deposits are very "rugged" and stick with much enthusiasm to the point of not being removed by the thermal shock of cold fuel on a hot valve and also being immune from the fuel detergent.

Once adhered, the fuel deposits insulate the area where the fuel is sprayed and the accumulation accelerates.

Once this happens, the pcv oil mist adheres to the fuel deposits since the high temperature that would normally embrittle it and cause it to chip off in chunks is no longer there.

You end up with a large, black mass on the stem that threatens to fully choke off flow.

Once begun, the above mentioned insulating allows both fuel and PVC mist to accelerate it's rate of accumulation.

Yes, it is much more gnarley with the addition of egr skank to the mix but non-egr versions of this engine family are not immune if the proper conditions are met.

Driving these engines insanely hard seems to be the best "medicine" and the reason we saw rarely saw this on turbo engines is because the type of driver who is motivated to buy the turbo version of the ZX would be more likely to drive them "insanely hard".

This statement is only directed at this engine family though similar things can happen if the same conditions for causation are met.

Also know that fuel composition is constantly evolving which will vary the nature of deposits or lack thereof throughout the timeline.

The newer gdi engines have their own set of issues and causation though much is caused by pcv oil misting and valve timing schemes to encourage egr without needing a dedicated egr system.

I feel a better designed pcv system in gdi engines that can prevent any oil in mist or liquid form from reaching the intake tract while still passing the other products of blow-by through the engine will work best at reducing or eliminating the deposits we are currently seeing.

Contrary to popular belief, egr can enhance efficiency at low load cruising because the lower combustion temperatures allow for more spark advance before the onset of pre-ignition.

[Simonas]

Did anyone mention anything about water freezing? I don't think the farther north countries would appreciate water injection...

[niky]

You can set the system to wait till the engine is warm... And heat the tank with the coolant.

[Simonas]

Yes, that could work. But what about the water expansion when frozen? If the reservoir were tapered then the ice could slide up the sides as the water freezes and expands. The pump could be mounted on top with a rubber hose going to the inside of the tank, so the pump wouldn't get frozen.

[niky]

You inject water for simplicity's sake. If you want to make more power with injection, then you add methanol to the water (which is how drag racers use it). Methanol acts as antifreeze.

[RobertISaar]

a 50/50 mix of water/methanol has a freezing point of around -40*F, IIRC.

[serialk11r]

I recall reading an article somewhere where someone was saying that PCV is likely the reason for gunk because external EGR isn't very common these days.

In that case I wonder if Porsche owners see this issue to a lesser degree, because their cars all have dry sump lubrication which in theory should not be allowing as much oil to go through the intake since the sump is a huge catch can. I know for typical cars if you drive them hard the intake will get dirty with PCV crud; I had my brother rev my car's engine while I tried to diagnose a rattle once and I noticed that at 5000rpm and up as soon as he let off the gas a puff of smoke would come out the exhaust, which has got to be oil. If I were buying a new car with wet sump I'd probably have a catch can ready to go on knowing this.

[Simonas]

Yes, methanol would work, but it is illegal (meaning it is classified as dangerous and you have to have a permit) in some Eastern European countries because drunks like to "have a drink". Of course, I don't see why it should be the government's job to keep them from having themselves killed by their own stupidity. But still, it is sad and is a pain for many people who can't have access to methanol.