3A90 Intake valves stuck open, carbonized, full of gunk and car won't start

[BRagland]

No rudeness percieved. I would be very happy if it were just bad gas, but that local company using half a dozen 3A90 Mirage has had each one repaired during the first year with the same trouble, and some have come back again. They drive short distances in town, and fill up locally.
I drive long distances only, and fill up at good brand stations wherever I need gas. Usually far from my home and rarely at the same place. Both cases same problem, only thing in common is the type of engine...

I will just have to wait and hope there will be no re-occurence.

In that case I reckon it has to be other of the two I mentioned: the PCV valve and/or a gasket problem.

Since your engine does not have EGR, the only other source of contamination that high up on the valves is PCV or gasket.

Of course, there is one other alternative: Someone hates that local company and has been dumping sugar is Mirage's they think belongs to them, maybe they mistook yours as belonging to that company. I doubt it though

I don't see natural accumulation of carbon happening this fast in such a small and efficient engine. The intake valves would be clean because of fuel spray. Worst case would be just the exhaust valves. Even back in the 40s and earlier, to have valves loose compression this early with those smokey bumbling engines was a rare rare sight. Doesn't make sense that today we'd see a problem that's virtually unheard of until you have put hundreds of thousands of kilometers on the engine. You're engine is just too young today, and even back in the ugly days, to have carbon build problems that bad. There would be other signs too: Smoke out the tail-pipe, degraded performance, rise in fuel consumption for the engine to output such amounts carbon in such a short amount of time.

[Tinker1980]

I've heard of this problem on the direct injection engines.

Could an oil leak cause this?

Maybe these cars are not so great after all.

I've got 30,000 miles on mine with zero trouble. That's Miles, not KM.

[Cobrajet]

I've got 30,000 miles on mine with zero trouble. That's Miles, not KM.

Me too.

[deleted user]

Drain every drop of what fuel is left. Have a sample tested for quality, based on the belief that the fuel was your issue. The repair shop statement seems to confirm that there are a lot of fuel quality issues in your area. In 30 years I have seen the same issue ONCE in over 60,000 hours on the job.

I think blaming it on anything without concrete data about the condition of the rest of the fuel is a waste of time and I posted this position when I wrote that the recommended cleaning procedure would only correct the SYMPTOMS and not correct the base issue, within the first five posts of this thread.

Imagine the fuel being bad enough even diluted with what was left when you refilled to actually reduce your mpg by 5%.

No amount of oil (none lost anyway) will cause this problem in an engine without egr. It would make a huge, impossible to ignore cloud of blue smoke as would any overfill of the crankcase (not done).

I'll put it this way, with the exception of terrible quality fuel introduced into the system, a system that has operated flawlessly for 20k kilometers:

How would YOU make it do what it did.

The ONLY answer I have is pour something like sugar or molasses into the fuel tank, or some very old, very smelly very rotten (or contaminated intentionally) gas into the system.

The deposit requires a source of material to create the deposit. PO stated he had control over that possibility after the refill so it had to happen at the point of the refill.

Looks like a duck, walks like a duck, quacks like a duck. It ain't no dang elephant.

regards
mech

[Daox]

I'm going to have to agree with Old Mech. The only thing passing by those valves is air and fuel. So, it has to be one of those two. Even DI engines don't have problems THIS early on. That would make me look at the fuel... If its that common of an issue, I'd call up the Mitsu dealer and have a word with them about it. If nothing else, it makes them more aware and puts more emphasis on fixing it.

[gone.a]

OP perhaps you want to add you issue to the http://mirageforum.com/forum/showthr...-so-far/page18 thread so the community can keep track of such thing?

[foama]

I'm going to have to agree with Old Mech. The only thing passing by those valves is air and fuel. So, it has to be one of those two. Even DI engines don't have problems THIS early on. That would make me look at the fuel... If its that common of an issue, I'd call up the Mitsu dealer and have a word with them about it. If nothing else, it makes them more aware and puts more emphasis on fixing it.

I have done similar runs with a totally different car with no problems. It received fuel from the same sources as the Mirage.

If the problem arose from one filling, wouldn't the car have smoked or ran different?

Question:
Could it come from too much overlap or non-optimal cam timing?

[deleted user]

To cause what you have described so far.

A single trip with a refuel, then several hundred kilometers to home.
Overnight cool down then attempted to restart cold and no go due to intake valves not closing properly (no compression).
In a car with very low mileage, almost brand new, with no other symptoms except 5% reduction in mileage on the return trip.

Instead of focusing on my hypothesis being incorrect, propose an alternative hypothesis. 30 year in the trenches working on cars here.

It doesn't mean I have to be right but it would be nice to know what caused the problem and how to prevent it in the future.

What's left in the tank is your only evidence.

regards
mech

[cyclopathic]

I have done similar runs with a totally different car with no problems. It received fuel from the same sources as the Mirage.

If the problem arose from one filling, wouldn't the car have smoked or ran different?

Question:
Could it come from too much overlap or non-optimal cam timing?

It still comes down to bad gas, oil or sugar. Otherwise even if intake valves are hot there will be nothing to form.

Could it be someone dumped sugar into gas station tank? Are there any other car brands having similar issues?

Edit: here is an article on how deposits form. http://airtexmobile.airtexproducts.c...n-engines.aspx

The only thing I can think of is too high octane rating and not enough detergent in gas. Engine was probably designed to work with 87 fuel, so higher octane may still be burning when intakes're opening up

[TheTransporter]

I have noticed in the winter my mirage runs VERY rich. If i stall my car shortly after start up it will flood and ill have to wait to start it again.

Another thing. REDLINE YOUR CAR. i do it on a semi regular basis. That gunk buildup could be because you ONLY use it for short trips with little rpm variation.

Give it some rpm! I usually do 1,2, and 3 to redline merging onto a highway to clear out the engine. Only when warm mind you!