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I'm in Ruidoso, New Mexico this week at an elevation of 7,000 feet & we fueled up this morning with regular fuel at a Shell station. Regular fuel here is 86 octane.
However, after we drove off, the engine began to knock. It tapered off gradually throughout the day, but it still occurs on occasion. How do I fix this situation? Fuel up with a few gallons of premium? And maybe just fuel up with premium from now on?
I never had this problem in El Paso with 85 octane fuel!
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
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What is the year and make of the vehicle? Is this latest fuel 10% ethanol, and did you get that in El Paso?
Elevation should make no difference in newer fuel injected vehicles as the air/fuel mixture is controlled by the computer and accounts for the differences in air at elevation, but ethanol
will affect performance, and more at high elevation.
Jeez, Soviet, do you know how to get lost! The issue is with the oxgenates in the mountain gas formulation. The knocking, unless severe, isn't going to hurt the engine. Next fill up a dose of premium would likely help it along. You also need to know when you come out of the mountains the engine will run like crap with low power until you get the mountain formulation out of it. While a little unconventional, I usually put a quart of acetone in the tank when coming down. It cleans the varnish out of the fuel system and keeps the engine running right for that tank. But beware that acetone is also a plasticizer meaning it will slowly dissolve any plastics in the fuel system. But on the road it shouldn't be an issue.
Good stuff, guys! Thanks so much! I was really very surprised that our 2008 Honda Odyssey was knocking, since I thought the ECU would take care of it. Oh, well.
Good stuff, guys! Thanks so much! I was really very surprised that our 2008 Honda Odyssey was knocking, since I thought the ECU would take care of it. Oh, well.
Thanks for the help! We were worried for a bit.
With the knock sensor on this engine, the ECU should adjust the ignition timing as needed within 1-2 cylinders knocking.
Under no driving circumstance should you ever hear an audible engine knock if the car is running properly.
I'm surprised that if you heard engine knocking sounds, that the "check engine" light didn't come on in response to setting a hard code in the computer.
Fueling with higher octane fuel will help, but there's an engine management system failure here if you can hear and audible knock.
With the knock sensor on this engine, the ECU should adjust the ignition timing as needed within 1-2 cylinders knocking.
Under no driving circumstance should you ever hear an audible engine knock if the car is running properly.
I'm surprised that if you heard engine knocking sounds, that the "check engine" light didn't come on in response to setting a hard code in the computer.
Fueling with higher octane fuel will help, but there's an engine management system failure here if you can hear and audible knock.
Well, it was knocking for a while quite regularly and then it GREATLY tapered off to the point where it knocked only twice an hour or so. We shall fuel up with premium this morning on our way to the slopes.
87 is the minimum for the Odyssey. Light knock can actually be normal at low engine speeds, but should go away quickly and of course, the computer should adjust. Heavy knocking is always bad. With the 86 and at a bit of an altitude, I would expect some knocking. The computer cant eliminate all of it because eventually you will have no power left to move the car. It just tries its best to keep it from happening. But, if its severe enough, it should throw a code and CEL.
If its good now, you should be good to go. It could have just been a sub par tank of gas too.
I have to agree with sunsprit. There should be no knock on modern engine. Knock sensor should report to ECU and ECU should adjust whatever it needs to adjust, and it should be done instantly basically.
Btw, high altitudes are much lower in oxygen content due to lower barometric pressure. ECU will try to compensate by lowering petrol level in mixture, believing it's running rich.
Hey, Tovarisch, why don't you go to any parts store and read error codes, just in case, with a scanner? Free anyway. No, not all codes show CEL.
87 is the minimum for the Odyssey. Light knock can actually be normal at low engine speeds, but should go away quickly and of course, the computer should adjust. Heavy knocking is always bad. With the 86 and at a bit of an altitude, I would expect some knocking.
You apparently have no experience with higher density altitude automotive operations.
The normal pump octane for "regular unleaded" fuel across the Rocky Mountain region is 85 octane, and every car rated for "regular unleaded" will do just fine on it with a properly functioning knock sensor and ECU.
It is not "normal" to expect audible knocking from these engines at 7,000' elevation, and the computer doesn't "learn" this as a baseline of operations for the OBD2 until a fair number of start cycles have been completed, definitely a lot more than a typical tank of fuel's travel. The engine management in this car is highly dependent upon the knock sensor to signal the ECU to retard the standard ignition curve under load.
Even if the OP had obtained a less than 86 octane load of fuel, the car should still have run normally, with about a 15% less than normal power delivery at maximum load. For the most part, in normal driving, the engine is not tasked with delivering 100% of it's ability and should well be able to drive the car around. The most degradation that a typical driver will notice is the lesser performance off the line and accelerating to speed, at cruise the car will be able to maintain the normal speeds.
Please note that I'm based at over 6,000' elevation here in Wyoming and routinely drive to much higher elevations on a daily basis .... and that I'm in the automotive consulting biz, calling upon every automotive repair shop in my territory with technical support. This ain't guesswork, it's real world daily knowledge and experience; I deal with driveability issues on a daily basis as an industry pro. As well, I'm a pilot using a C182 to travel the region, and am very familiar with density altitude affect upon engine performance; something that many pilots from out of the region don't have to deal with very frequently so tend to ignore it in their operations ... until it comes to bite them at a critical time.
Last edited by sunsprit; 12-24-2012 at 03:15 PM..
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