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Low Octane Road Trip Clogging my Cat?

Hi -

I have a stock 2004 Subaru wrx wagon with 57k miles that I purchased in January of this year.

The first few weeks with the car were superb - fun fun fun. I love the car. A few weeks after I got her, my wife and I took her on a road trip through the mnts of West Virginia. She had driven great for the first 300 miles of the trip, but after a fill up in the morning on the second day, she was knocking, shaking, and had a hard time getting up hill. No check engine lights came on, turbo seemed to be spooling properly. I started to fear that I accidentally put 87 octane when she needs 93.

As we were in hill country on a Sunday there was no place we could find to get the tank emptied, so we were forced to drive the gas out of her. I tried to baby her as much as I could, but the grade made it difficult to stay off the throttle. We filled her back up with 93 once we were down to 1/2 a tank, and disconnected the battery for an hour to reset the computer. Drove better… But not great still. Once we drove the fuel outta that tank, filled her back up with 93, and reset the computer again, she drove much, much better, but still not back to 100%.

I would guess I’ve got about a 10-15% power loss.

She was seeming to get a little better every day. Now, it feels like she’s faster some days than others. I live in NYC and only drive her on weekends. After I decided that she wasn’t getting any better on her own ( I was hoping it was something the computer would correct for), I took her to a mechanic recommended to me by a friend. Great guy, a specialist in turbo charged japanese sports cars, really honest and helpful. He drove her and confirmed the ‘softness’ - he said she was missing ‘pull’ and that I may have lost torque.

He spent the whole day checking her out and told me - oddly - that he can find NOTHING WRONG with the car. Computer diagnostics check out. There is no compression leak. Fuel filter is clean. No turbo leaks. Although he’s sure that there is less power, he couldn’t find the problem.

Didn’t charge me :slight_smile:

He did however offer a theory. He said that the only thing that he knows of that can happen when you run low octane gas is that the burn off can clog the first catalytic converter in the up pipe before the turbo. And his guess is, that’s the problem.

Does this theory hold water with you guys? I am not much of a gear head, but have a rudimentary understanding of how things in an engine work. It certainly sounds plausible - and a clogged cat would account for a horsepower loss, but I’ve never heard of that before.

Thanks in advance for the time / advice.

Drats - mobileOppsUnit.

Whatever is wrong with your car, one thing is for sure…It is NOT that one tank of regular you may or may not have purchased…The 5 octane points between regular and premium can make a barely noticeable difference in some cars but it can’t cause all the symptoms you are describing…

When you buy a used high-performance rice-rocket like this one, these type of problems are part of the deal…The first owner might have had even more fun than you…

The 5 octane points between regular and premium can make a barely noticeable difference in some cars but it can’t cause all the symptoms you are describing

The op’s car is a turbo, and those 5 octane points make a huge difference in the way the car runs. With that said I don’t think a half a tank of regular will somehow ruin a catalytic converter.

I can’t rule that it’s something else, but, I don’t agree that running 300 miles on the wrong gas in a WRX could cause something to go screwy.

With a little research, you’ll learn that the WRX is designed to run on 93 or 91… however if you put in anything less than that, the computer has something known as ‘limp mode’ which is like a safety mode. I didn’t know at the time, but since then every description I’ve read of that mode is consistent with the way the car was performing after I filled up.

The mode is suppose to be used sparingly… ie - you put in 3 gallons because whatever station your at only has 87, and you hope you can get to another before you run out of gas. My problem is, I filled up, and drove it up steep grades for 200+ miles before cutting it with higher octane fule, and I’m afraid that running in ‘limp mode’ for that long caused some sort of damage - possibly to the cat - which may have some wear anyway cuz the car’s got close to 60k.

Oh - and as far as the previous owner goes, it was my 50 year old father in law… who loved the car and babied the hell out of it - It’s 8 years old and only had 50k when I bought it from him - He was meticulous about it’s care, I have a organized binder of every service record since they day he got it in 2003…

So - my question still is, can running low octane gas in a WRX clog the cat?

No, running on low octane gas for 300 miles will not clog the catalytic converter unless the cat converter was already in bad shape. We don’t know the condition of the cat, and neither do you, but since the previous owner apparently did maintain the car properly and the car has only 57k on the odometer, a clogged cat is unlikely.

However, other types of damage are likely, such as burned valves. Once the engine is running normally (not in limp mode), you should see an improvement in performance. If you do not see an improvement, then you did probably cause damage, and it is likely to be something other than the cat converter, with damaged valves being my prime suspect.

All of that being said, I do have to question your decision to “drive the fuel out of the tank” before refilling. As soon as you realized that you had put in low octane gas, you should have stopped and put in a few gallons of premium gas (as much as you could add, without overfilling the tank), in order to give the fuel somewhat of an octane boost.

And then, if I were you, I would have continued to stop each time that the gas gauge got to the 3/4 mark, in order to add a few more gallons. If you had done this 3 or 4 times, you would have progressively raised the octane level of the gas in the tank to very close to 91 octane, and that would have been much better for the engine than driving in mountainous terrain for 300 miles with the wrong octane fuel. The gas station attendants would not have been very happy about your purchase of ~ 4 gallons each time that you stopped, but I would much rather incur some anger from gas station attendants than do damage to my engine.

What where you thinking when you decided to “drive the fuel out of the tank”?

The thing is, do we know what kind of gas the previous owner(s) put in the car before it was bought by the OP? Can they prove it if they were asked?

I didn’t realize that i put the wrong gas in right away - I drove for a bit, stopped, checked under the hood… Tried to geton the web on my phone. Drove some more… Thought maybe it was bad gas at first - I stopped at 2 other gas stations on the way to our destination and they all only had 87. Again - rural mnts of wv. I mentioned in the post, when I found a place that had 91, I was at 1/2 a tank. I filled up. (91 + 87) /2 = 89 octane. I rest the computer. Let the car rest while on the mountain. Improvement, but not back to normal. When we left, 1/2 tank later I found 93. (89+89+93+93)/4 = 91 octane. I reset the computer again. Took me 300 miles to get to 91 octane - the minimum. When i said I had to drive it out, i meant that I could get some to syphon it out for me.

Previous owner ran 93, occasionally 91 when it was all that was available. When I spoke to him about this, he did say that he did the same thing once - put in 89 and it went limp on him…

I don’t really buy into the one tank killed a converter theory or the part where the previous owner says using 89 caused the car to go limp on him.

If low octane gas was creating a problem this bad then it should have been noticeable by the clattering that was going on under the hood. The EGR and knock sensors can help to some extent but their range is limited and in a case such as this one is claimed to be I can’t see it.

There’s a lot of posssibilities but without detailed info any advice would be a wild guess.
Maybe a turbocharger impeller trying to seize up at times due to an oil feed problem?
Fuel pump getting a bit iffy?

Just being curious, as per the usual, did he happen to give you the compression numbers and if so, what are they?

Why do people keep buying these cars? 1/4 inch difference in tire circumferance and your buying a center diff, 5 octane points wrong with the gas and you are on the side of the road(this is the first time I have heard of an octane induced limp mode). And this is if your head gaskets are not leaking (OK I know all the problems don’t affect all the models but I would not get near a Subaru.)

Subaru KNEW this was going to happen, you can be sure of that… They also know that sometimes you PAY for 93 octane gasoline but you don’t get it…They don’t want want thousands of engines destroyed or damaged, owners clamoring for warranty service over something they have no control over…So they design things that will tolerate five octane points without any major problems…87 octane fuel will not “clog” a catalytic converter any more than 93 octane will…All octane does is suppress or control spark knock…If you did not detect any spark knock, then your engine was able to tolerate whatever fuel you fed it…

As for the CAT, if it’s located in front of the turbo, there is a big compromise right out of the starting blocks…The Smog Gods hold the trump cards…

So back to the basics…Do an actual compression test, not an electronic one…Look okay? Then check actual boost pressure with a gauge and see if it meets specs…

But remember…The light that burns twice as bright only burns half as long…