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Recently my 2007 Mazda6 (2.3L I4) has been taking longer and longer to start in temperatures colder than about 5 F (-15 C). The car usually sits overnight for about 12 hours after I get home from work; it typically starts better when I’m leaving work in the afternoon. Today I had the key turned for about 4 seconds, then gave it a short rest and after another 2 seconds of starting it fired up. Normally it kicks up almost instantly.

The starter turns over quickly but the engine doesn’t catch, so I don’t think it’s a battery or starter issue. When it finally does catch, the engine lugs at very low RPM for several seconds and sometimes dies on me at this point. It starts up more easily after this though. Often I’ll give it a little gas right as it starts, then it lugs for a shorter period of time before spiking up to about 2.5k.

I have also had it start with no trouble but then lug at very low RPM until I rev it a bit. After this, it drives just fine and I have no reduced power while driving normally.

Other info:

  • Vehicle has about 106k miles
  • I replaced original plugs with NGK Iridiums about 10k miles ago when I bought the car
  • Coil packs and wires are original
  • Just replaced battery about a month ago with a Duralast Gold (590 CCAs)
  • I know nothing about the state of the fuel system, but haven’t had any issues so far
  • Turning the key to "on" and waiting for the fuel pump to shut off before starting doesn't seem to make any difference

Seems like a fuel pressure problem. Issues with coil packs doesn't seem likely. Any other thoughts? What tests should I do to figure out what to do next? (I can't test fuel pressure myself, would have to take it somewhere)


UPDATE

This morning it was right around freezing (slightly below freezing overnight); much warmer than it has been recently.

I still had a little trouble starting this morning, about 6 seconds of cranking then gave it a couple seconds rest and it started almost immediately on the second try.

I drove about 10 minutes to an appointment. The engine reached normal operating temp but I didn't go any faster than about 40 mph.

After about 45 minutes I came back out to my car and it wouldn't start at all - or rather, it would crank and quickly start to turn over but then immediately die. After 4 or 5 tries of this I started to worry I'd need a tow, but with a combination of holding the key on start and feathering the gas pedal, it finally choked and sputtered and then revved up to idle like nothing had happened. It ran fine all the way to work.

I'm becoming less convinced this is directly related to outside temperature. What should I test next?


FINAL UPDATE

It turns out that it was a fuel pressure problem, as originally suspected. See my answer posted below.

  • It's probably just cold - can you put it into a garage overnight - a friend or neighbour perhaps and see if it starts better. – Solar Mike Jan 16 '17 at 8:29
  • I agree - but it started fine last winter and it was fine in similar temps earlier this year until a couple weeks ago, so I'm wondering if it's an indicator of something starting to fail. I don't have a garage available to me; I'll just have to wait for some slightly warmer weather. – Dan A. Jan 16 '17 at 15:37
  • Either a blanket or tarpaulin to help keep some of the wind off, or put a SMALL (300 - 400W) electric heater under the bonnet (a safe position...) on a timer for a few hours before you need to start... – Solar Mike Jan 16 '17 at 20:40
  • It was a slightly warmer day today and I've had the most trouble yet... see updated post. I'm becoming less convinced this is directly related to outside temperature. – Dan A. Jan 18 '17 at 18:16
  • I think you need to check fuel filer and fuel supply - when was it last changed? – Solar Mike Jan 18 '17 at 20:23
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I am assuming no check engine light? Strange to have this mix of issues and not throwing diag codes - you'd get a misfire code for instance if you had a weak coil pack. Based on this intermittent issue I'm thinking it's possible you have bad gas ... I'd try topping up with premium. Fuel filter is in the gas tank and really more of a grit filter; I'd highly doubt that's it.

Edit: also I'm assuming you've checked the oil level and it's topped off? I have basically the same engine in 3 cars I maintain (Mazda5, Mazda3, Ford Focus) and it's solid and reliable. Main known issue is passenger side motor mounts failing. All well over 100k mi. And they all started without issue besides a slow crank when it was 0F degrees for a week in Chicago recently.

  • It hasn't been that long since my last oil change, but it actually was a little low (low enough to start keeping a closer eye on it). I topped it up but it didn't seem to make a difference. I did fill up from 1/4 tank with premium yesterday, I'll let you know if it's any better over the next couple of days. – Dan A. Jan 20 '17 at 18:06
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    This was totally it. After filling with premium I have had zero problems starting. On the one hand, I'm relieved that it was an easy fix. On the other... I'm disappointed it wasn't something more interesting... – Dan A. Jan 22 '17 at 23:10
  • Didn't really follow up in a timely manner... but about 3 days after posting this comment (around Jan 25) the problem came back. Unfortunately this wasn't it, but I did eventually find the culprit. See the answer I just posted. – Dan A. Mar 29 '17 at 3:49
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It sounds to me like you have a sticky injector or four. Once it warms a bit (which happens very quickly on the injectors) it will respond properly and start spraying when asked. Difficult to test at home. Try running some SeaFoam through the tank. And if you are really super cool run it through the intke manifold as well.

  • I actually have a can of SeaFoam lying around at home that I bought a while back but never used. Even though it's running fine now, I might use it anyway just because. There aren't a lot of instructions on the can, although I've seen a lot of different ways to use it on YouTube. Got any tips or a link to a method you agree with? – Dan A. Jan 22 '17 at 23:12
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    The easiest way to deal with the fuel injectors is to use in in your gas tank. Run you tank down to less than a quarter tank. Dump in the full can of SeaFoam and fill up the tank. Then drive. Running through the intake is a bit more complicated and very dependent on the exact model of car. I would join a mazda6 forum and get advice from the experts on your specific car. – enderw88 Jan 24 '17 at 1:51
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These are symptoms of a failing fuel pump.

After Neil's answer, I filled with premium and the problem seemed to go away for a few days. Soon after it was back with a vengeance and about a week after asking this question, the vehicle wouldn't start at all. It would crank but no amount of fiddling would get it to start.

The telltale sign for me was that I could no longer hear the fuel pump hum for a couple seconds after turning the key.

I had the vehicle towed to my house. I picked up a new fuel pump from the local O'Reilly to the tune of around $250 and replaced the old one. It started instantly and I have had zero problems in the two months since.

Moral of the story: Just because you can hear the fuel pump running when you turn the ignition, doesn't mean that the fuel pump is working well.

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