5

I'm about to betray my ignorance of cars but here goes: I am a driver from Minnesota (where the lowest octane rating is 87) vacationing in Colorado and have noticed that after I put 85 octane gasoline in my tank I have been experiencing engine knocking and difficulty going up hills. An error message (code P1383 or P1381--can't remember) read from my car's computer mentioned retarded CAM timing. Would this be related? I'm a medical student so I have very little car knowledge; but from my Google searching this seems to be related. Can anyone speak to this?

Improve this question
3
  • What make and model of vehicle is it? Engine size?
    – Moab
    Commented Aug 9, 2016 at 21:52
  • FYI you can check your owner's manual for the minimum require octane for your vehicle.
    – Bob Cross ♦
    Commented Aug 10, 2016 at 14:36
  • Thank you all so much! Apparently the problem was the timing belt and had nothing to do with my fuel.
    – Isaac Toenies
    Commented Aug 11, 2016 at 7:16

2 Answers 2

Reset to default
2

Two things:

  • Running fuel with a lower octane rating than what your engine needs will cause "knocking" (premature detonation). Colorado has fuel with a lower octane rating because higher altitude reduces the need for octane, but this isn't fool-proof.
  • Engine controllers generally deal with knocking by retarding the timing.

You fix this by either:

  • returning to 87 octane, if your tank is almost out of 85 octane
  • there are off-the-shelf "octane boosters," you may want to try some in your tank if you have a lot of that 85 octane left
Improve this answer
2

Adding to tlhIngan's answer:

You can mix fuels of different octanes (actually, it's not unusual for a gas station to have a blend valve to get the mid level octane fuel to eliminate the need for additional underground tanks). The new octane is a linear combination, you can calculate it as:

% fuel x * octane x + % fuel y * octane y

So if you've got a half tank of 85 and you fill up the rest with 89 you'll end up with:

0.5 * 85 + 0.5 * 89 = a full tank of 87.

If you've got 3/4 tank of 85 and you top it off with 93 you'll end up with:

0.75 * 85 + 0.25 * 93 = a full tank of 87.

So if you've still got a lot of 85 left in your tank just fill it up with something higher and it should correct the issue (presuming that's the issue, but it is a reasonable and likely explanation) once it runs through a bit. You don't really need additives, or to wait until your tank is empty.

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .