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DOHC - 2.3L Duratec / Mazda L Engines Discussions and Topics specific to the Duratec 4 cylinder engines

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Old 01-04-2016
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Starting issues

Hey everyone, I have a small issue with my '10 XLT 2.3L auto. Just about every time I go out and start the truck it starts up just fine. I let it idle for about 15-30 seconds before I hit the road. Sometimes, but its happening more frequently, the truck won't start up on the first crank. It will only happen after driving for 20-30 minutes, parking, and letting the truck sit for about 10-15 minutes.

Is this an issue for an ignition coil? All maintenance has been done recently, new plugs, wires, fuel filter, AT fluid/filter, air filter, and belt. So this isn't a neglected truck and has about 68,xxx miles.
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Old 01-04-2016
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Try turning key on, count to 3 then turn it off, turn key on again and try to start.
This double primes fuel system to build up any lost pressure.

Fuel injected engine uses an IAC(idle air control) Valve so computer can control idle.
Computer uses an ECT(engine coolant temp) sensor to tell it if engine is cold or warmed up.

A cold engine needs Richer fuel mix and higher idle to stay running, that's what the Choke plate was for on carbs, with fuel injection a Choke plate won't work, no Jets to suck extra fuel from.

So the computer runs a Choke routine based on engine temp, or doesn't run it based on engine temp.

When you turn on the key the computer starts up and checks ECT sensor temp, if engine is cold it will run a Rich fuel mix and set idle above 1,200rpm, the colder it is the higher the RPM.
As ECT sensor/engine warms up the idle will slowly drop to "target" warm engine idle, usually 650 for manual and 750 for automatic, target idle is set at factory.

So my question is when engine fails to start the first time, what is the idle RPM when it does start?
Is it "target" idle, so computer thinks engine is fully warmed up when it isn't?


Another thing you could test is if its is fuel or spark that is missing.
get some starting fluid(ether in a spray can)
Setup engine for a no start, like you described above
Before cranking starter, pull off power brake booster hose and spray some starting fluid into intake, replace hose.
Now crank starter
If it starts right up then fuel is the issue
If it doesn't then spark is.
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Old 01-05-2016
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From what I noticed the last time I had this issue, it idled fine and at "target" rpm on the second attempt of start up. Last night I drove to a friends house and we hung out for a couple of hours. When I went out to drive home, it happened again. The temps here at night are very cold, frost was built up all over. I will, however, try and recreate the issue and take your advice. Hopefully this is just a ignition coil issue, I would hate to think I would have to replace a fuel pump.
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Old 01-05-2016
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It shouldn't idle at target RPM until engine is fully warmed up, idle should be higher than target RPM if engine is colder than 190degF, i.e. temp gauge below 1/4, if "normal temp" is just below 1/2

Colder engine needs more fuel to start and to run until it warms up fully, even if just shut off 20min earlier.

"Warm air rises", the reason for that is that colder air is denser, heavier.
Air/Fuel mix for gasoline engines is 14:1, 14 parts air to 1 part fuel, this is a WEIGHT ratio
14 pounds of air to 1 pound of fuel ratio

This is why "pre-vaporizors" or 200mpg carbs were a bunch of hoey, lol, ratio is by weight not volume.

A 2.3l engine uses 2.3 Liters of air, that's a volume of air, on each full cycle, all 4 cylinder completing their 4 strokes.
4.0l engine would use 4 Liters of air.

Now 2.3 liters of cold air weighs more than 2.3 liters of warm air, cold air is heavier than warm air.
If 2.3 liters of air at 30degF weighed 1 pound, then 2.3 liters of air at 70degF might weigh .9 pounds, computer has air temp sensors and the MAF that correct for this "weight" difference.
This is why MPG will go down a bit in winter, more fuel needs to be added for the colder air, but you also get more power in the winter because more fuel can be added.

If engine temp or air temp sensors are not giving computer correct temp data then cold weather could effect starting, mix ratio could be off.
It is a longshot since computer does compare temps of the different sensors to see if they are "matching", ECT, IAT, and MAF all give computer temp reference
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Old 01-05-2016
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Sorry, I meant it idles the same on the second attempt as it does on the first. Thats what I meant to say. Thanks for your help, I really appreciate it. I'll update this post when Im able to recreate the issue. Thanks again!
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Old 01-08-2016
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So yesterday morning I drove to the nearest corner store (3 blocks or so from my home) and went inside to use the atm. I was inside for maybe 5 minutes, came back and tried to start the truck. 1st attempt, no dice. I turn the key on and off 3 times before trying the 2nd time. It did start, but I noticed it bogged down a bit. Idle was below 700 rpm before it shot up to normal idle.
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Old 01-09-2016
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are you waiting for the fuel pump to pressurize the line and injector rail

pr are you just trying to start the engine right away

the fuel pump needs a few seconds to pressurize the line and fuel rail
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Old 04-04-2016
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UPDATE: I went ahead a replaced the coil pack since I get a decent discount at the parts store I work at and I haven't had a problem since. Starts up fine now, 0 issues. Thanks for the advise guys!
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Old 04-04-2016
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Good work

Thanks for the update
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