2010 MazdaSpeed 3 will start smoothly only if revved before shutting off

mazda
mazdaspeed3

#1

My 2010 MazdaSpeed 3 (turbo charged, ~75K miles) will have difficulty starting after prolonged (>2hrs) sitting with engine off (no difference with changes in outside temperature). I would either have to crank for a very long time or crank multiple times (at least twice) before engine will turn on. No other problems (idle is smooth).

I have done simple maintenance (brand new K&N air filter, new spark plugs, new battery, MAF sensor cleaning). I took it to dealer and they have done extensive testing on fuel pump system with no luck. They recommended decarbonizing service ($150), made no difference.

Only pattern I’ve noticed is if I rev the engine before shutting off, even after sitting overnight, the engine will start right away without any problem. Modern fuel injection engine… Can’t figure it out.

I don’t know much about cars and any help would be much appreciated!


#2

Try this: Turn the key to the “on” position, then off. Then try to start it. It sounds like you aren’t getting proper fuel pressure at start-up.


#3

I agree, either improper fuel pressure or maybe a leaky injector.


#4

It worked! Without revving prior to turning off the engine. I turned to on position then off then car started right up. Does this mean my fuel pump needs to be replaced? In other words what are the possible causes of improper fuel pressure at startup? Thanks a bunch for your help!


#5

Actually to be more precise, the engine started up with a slight roughness.


#6

@Isaac Kim: The problem could be the pump, or something else could be causing the system to lose pressure overnight, such as a leaky injector. How’s your fuel economy? Is your check engine light on?


#7
Only pattern I've noticed is if I rev the engine before shutting off

About the only thing I can add is revving a turbo engine when you shut it off is really bad for the turbo.


#8

My fuel economy has not changed at about 25mpg. No check engine light.

What I don’t get is that the dealer told me an extensive testing on the fuel system was done with normal fuel pressure readings at: 1. ignition to on position with engine off, 2. residual fuel pressure after 5 min, 3. engine running at idle. I guess somehow I’m losing residual fuel pressure more than 5 minutes after ignition is put to off position.


#9

You need need to have it tested after it sits more than 2 hours. It’s either the pump or leaky injector. Find a good indy mechanic.


#10

Not an uncommon problem. The fuel rail is supposed to remain pressurized when you turn the engine off. It is sort of like a balloon with ports at each end. A good balloon, you pump it up and it stays pumped up, right? Yours is leaking somehow or the other. One end of the fuel rail is the fuel pump, which has a check valve which prevents the pressure from leaking back into the gas tank. The other end are the fuel injectors, which are not supposed to leak even a drop with the engine off. On a 2010 I’d suspect the check valve first. Usually the check valve is part of the pump assembly.


#11

Arrg! I’m so frustrated. Another $130 in diagnostics at the dealer with no diagnosis. They swear the fuel pressure holds after prolonged (~2-3hr) time with engine off. I do know that this issue is somewhat intermittent. Only reason I keep going back to dealer is I want this covered by my extended warranty since this is a certified owned car… Any advice? Do I need to just ride until this becomes a more permanent problem? I only have about 3,000 miles to go until warranty runs out…


#12

Is it hard to start (normal - no double keying) every time after sitting overnight? Has it sat overnight at the dealer for them to witness this?


#13

I doubt that too many vehicles actually hold their fuel pressure overnight. They should, however, remain full of fuel. Thus re-pressurization is rather immediate when you turn the key. Even so the pressure can certainly hold for a very long time. Perhaps it would be worth it to buy a fuel pressure gauge (though some auto parts stores have them in loaner tool programs). and do some checking yourself.

I can tell you that on my own car (which is much older and not a Mazda), the last time I checked if the car is fully up to temperature the residual fuels pressure bleeds of pretty rapidly. In hot weather it will have rough hot re-starts. But if I just check it while cold, the residual fuel pressure holds quite well. In neither case will it hold completely over night. But I don’t have any cold restart problems. Perhaps the shop has only checked it all while cold.

You did say that you tried the key on - then off - then start and it started but roughly. The next time, do the key on - off several times. Minimum of 3 or perhaps 1/2 doz to be sure. With a fuel pressure gauge on it you can actually watch what kind of pressure it gets on each turn. (From zero pressure after sitting overnight, mine doesn’t max out until the 3rd time). If a series of on-off key turns gets it to start right up smoothly, then I’d be quite confident that it is a residual fuel issue and you are ending up with a dry fuel rail. (and obviously no pressure). That’s often from a bad check valve - but obviously not bad enough to show up on routine checks.


#14

I had an old vehicle that did this and I just built the new starting protocol into my morning routine.