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spongebue 05-27-2013 02:21 PM

Very Brief MK1 Misfiring at High Altitudes
Hi guys,

I've got a 2005 Focus ZX5 (best body style of them all!). Automatic transmission, sadly, with just over 80,000 miles. The usual 2.0L engine on an '05. Today I was driving on I-70 in the Colorado mountains, making the climb from Silverthorne to the tunnel. Basically, you gain about 2000 feet in 7.5 miles with slightly varying inclines. I've only done this climb a couple times in this car, and haven't had any problems yet. This time, I was at about 11,000 feet in elevation, almost at the top before the tunnel and the decline after. Soon I felt my engine lose power. It was still on, but rather than the 60MPH at 5000 RPM I had been going, it was limited to maybe 3000RPM. Check engine light was flashing (misfire, according to the manual). Thankfully, because I was almost at the top, this only lasted about 30 seconds before she snapped back into her normal self. CEL turned off, and the car had more pep in its step.

Is this something I should really worry about? I mean, it's not exactly a drive in the city - it's pretty intense driving around there. Is there anything I can do to prevent it in the future? The car wasn't too heavily loaded (2 people in front and a small suitcase in the back, last time I had a friend with me as well and he's on the heavy side - that went fine). The biggest thing I can think about is the air conditioning. I never did turn it off that whole climb up, which I usually do, but doesn't the computer usually turn that off if it needs the power?


zetecDon 05-27-2013 03:55 PM

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sailor 05-27-2013 04:48 PM

If the warning happened to be the exclamation point (!) it would be for transmission overheat most likely, and that would reduce power then recover as soon as it cools a bit.

A/C being on & a hot day would make that more likely.

Just a guess, you can confirm which warning lighted up & folks will continue throwing out possibilities.


spongebue 05-27-2013 08:24 PM

It wasn't super hot out as I recall - just gets warm and stuffy inside when it's sunny and you've got a black interior :D

It was the yellow check engine light that went on. The same one that would tell you that there's an OBD diagnostic code waiting. But again, it was just flashing briefly, and went off on its own. The manual tells me that that signals that the engine is misfiring. Ultimately, I mostly want to be sure that there is no long-term damage to be mindful of, and if there are any tips to prevent it in the future, that would also be great.

JFrye 05-27-2013 09:09 PM

I would think it would have to do with the air temperature and density that high up. With the air going into the engine has changed, then it throws off the air fuel ratio and the computer tries to quickly adjust for it. (<- just an idea, and I may be completely wrong here) If the vehicle is used to being driven in those conditions, the computer may need to relearn for the sudden changes.

spongebue 05-27-2013 09:18 PM

Right, that's what I was thinking. To give an idea of what the car was going through, the oxygen concentration in the air goes down 1.1 percentage point (7.5% if my math is right) - 35 percent less than what you'd get at sea level. Normally I'm in Denver (5280 feet :) ). It may not be a huge amount, but it was over the course of a few minutes. Plus, I came from Steamboat Springs, CO (with a few stops in between) - lots of altitude changes on that route.

That's all based on this chart:

JFrye 05-27-2013 09:24 PM

Im not expert on this, but it makes sense to me. If Im wrong, hopefully someone else can pitch in and help get you the right answer.

mikebontoft 05-27-2013 09:42 PM

Yeah it happens a lot to vehicles making that transition in CO. Older Fords used to have the same trouble on descent. What happens is the barometric pressure sensor (doubling as the map sensor at the time) reads only at engine start-up. You'd shut it off (if it didn't die on its own) and it would fire right up and run great until the same drive is made.

I believe the sensor makes multiple samples now. I think that was their fix. So essentially when it started running like crap for you, it took another baro sample and corrected itself.

JFrye 05-27-2013 09:55 PM

Thats good information to know. Thanks for pitching it so we can help him get it figured out.

spongebue 05-27-2013 10:05 PM

Ok, cool. Heh, that reminds me of when I took my other car through the mountains for the first (and only) time. 1995 Oldsmobile Cutlass Ciera. Morning of 4th of July, a few weeks before I bought my Focus. I was on the same hill, but the opposite direction (westbound, better known as "down" in this spot). Got out of the tunnel, and spent the next few miles braking to keep my speed under control. Then my friend commented that my battery light was on. I noticed that my oil light was on as well. Oh hey! What do you know! I have no power brakes or power steering. Wonderful.

If there was a typical weekend traffic backup or ice on that highway, I'd be screwed. I was using quite a bit of force on the pedal just to maintain my speed. Popped it into neutral, tried starting up again. Nah. He didn't really feel like it. Turned off radio, climate control, etc to keep my battery conserved in case there was an alternator issue or something (remember, my battery light was one of the first things I saw). ~20 seconds later, try again. Nothing. I felt the "4 C's" needed for air traffic controllers (cool, calm, collected, and in control) but my friend (who actually went to ATC school) said it was the scariest thing he's ever been through. My speedometer acting funny with the key off didn't help. Finally, about a mile before the exit, I try for maybe the 4th time. Success.

Filled up the gas tank, and went to Burger King to get a bite to eat and catch our breaths. Friend insisted on paying for the fill-up despite my best efforts, and I think he was surprised at how much it took (probably 13.5 gallons, most I've ever seen it take was 14.5). He later asked if it was possible that there wasn't much gas in the tank, so it was tilted away from the fuel line on the steep hill. Given that it ran pretty well on the way home with a full tank (just felt underpowered due to the bigger engine needing more air, heavy car, and steep incline) I think that's most likely. Then again, if it only took its sample in the beginning, I would have expected it to cut out when I was trying to get up to the tunnel, not when I was idling down.

Thanks for your help, everyone!

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