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Discussion Starter #1
So I have been trying for a month to fix this problem I'm having and wondering if anyone has any ideas since I took it to the dealership and they couldn't fix it or even find out what was wrong. It's not under warranty it's a 2016 Mazda 3 with 83k miles I got for a steal only 10k. So the problem only happens when I start the engine after it's been sitting around 30+ minutes. It has long crank times and sometimes I have to press start again to get it to crank. If I turn it off and back on it starts up like a champ. I know you are all thinking fuel pump issue but Mazda dealership tested it and the pressure is all good and it's keeping prime.

Things I've tried:
1. New ngk laser iridium spark plugs
2. New MAF sensor it was used but "garunteed working"
3. Dealership did intake and air service that includes throttle body and intake cleaning.
4. Replaced engine and cabin air filter.
5. Battery test are all good battery is nearly new
6. Fresh oil change and checked for leaks and keeps a good level
7. Cleaned two grounds on frame and the battery terminals

So I'm thinking since it doesn't have a physical EGR valve that the only things that could be causing it are the engine coolant temp sensor (which I just ordered today) or possible that it's the crankshaft position sensor? Seems to be worse if it is parked in the sun in the 100 degree Georgia weather. It's the craziest issue but I feel like I've tried most of the major culprits, any ideas?
 

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Discussion Starter #2
It's a 2.0 isport gas model. Drives perfect besides the starting issues and gets great gas mileage according to the cars app, but does seem a bit slow but never having driving another Mazda idk might just be normal acceleration... Probably that im just use to faster cars. Also from what I can tell it shouldn't affect it but it only came with one three button after market key when I bought it. I purchased the 4 button oem and got it programmed and use it regularly with the aftermarket one just being a backup. so the red key light starts on since they are both programmed to it
 

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I have a 2016 mazda 3 sport preferred at 60k miles, i live in Florida where i assume its hotter, i don't believe its the heat, i would recommend that you take it to a reputable mechanic to get a second opinion, its like a doctor, you always want a different opinion than the dealer. im sorry for the problems your car is giving you.
 

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Coolant temp sensor? Does the blue dash light turn off a while after the day's 1st start? That should tell it's working or not. Have the coils been checked? Fuel rail pressure up to spec? Injectors all good?

Sent from my SM-G970F using Tapatalk
 

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Somewhat surprised you haven't popped a code or two at this point, but obviously the dealership checked. My thought is directly heat related if you are not showing codes. It's obviously not any kind of vapor lock unless there is some clogging in the injectors blocking pressure. Check fuel lines to see if any have become loose and are closer to heat source? Since the car technically does not need a coolant change at this point, check the coolant 'life" anyway as some "Poindexter" may have done something with the coolant...again going back to heat being the cause and a hotter than normal engine can affect gas flow. One last thing is make sure to use a different fuel brand.
 

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I know you said dealer checked fuel pressure but i'd at least try turning the car on (not starting it), waiting 10 seconds, then starting it. If it always starts right up when you do this, then you have a good clue. My forester started having similar symptoms of long crank after sitting just today (hot day) and i know 100% it's the fuel system - by running this test repeatedly - it helps that i recently changed the pump so I suspected this was a likely culprit anyway. In my case i'm pretty sure one of the hose fittings around the pump probably needs a better seal to hold pressure while the pump is not running.
 

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Discussion Starter #7
Turning it to acc before starting a couple times sometimes helps and sometimes doesnt. The dealer had it for 48 hours and said the pressure was good and it was keeping prime so I really don't think it's the fuel pump inlet the mechanics at the dealership didn't do their job right. That was my first thought as well. The fuel pump is expensive too. I'm thinking it's something with the heat as well or the air fuel mix. I really thought the MAF would fix it. Just so weird it runs perfectly after starting. I'll check all the fuel lines and flush the coolant and put new in when I get the coolant sensor. The only other thing I can think is maybe it's that MAP sensor but I feel like that would cause more than just starting problems. I just don't want this to turn into a bigger issue and destroy my engine one day.
 

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I have had intermittent heat soak faults in CPS's that went when I poured cold water on the sensor. Might be worth a test.
 

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My first advice is stop replacing parts on a hunch. I see you're talking about the MAF and coolant temp sensors. They're good theories, but until you prove it you're just throwing parts at the car. These can be easily tested with a multimeter. Reference the service manual in the DIY subforum to get the expected resistance values.

And no the blue coolant light turning off proves nothing for the functionality of the sensor. I don't even want to discuss that one any further.

Now, I'm assuming that the cranking speed is fine but it just won't start.

Get someone to give you a hand. When it's cranking but won't start, you need to check two things: are the spark plugs firing and are the injectors firing? No spark could mean faulty crank sensor. I highly doubt this, but it's possible. The ECU may not report it if it starts to work correctly once the car starts. Simply put, it can't since it's not running itself.

The injectors are a good one to check out. The injectors are controlled by the ECU so if it isn't commanding them to open for some reason, your fuel pump may be fine but injectors not dumping fuel in. A bad relay is a possibility. I'm at work right. Now so you'll have to look up what relay powers the ECU. Swap that relay for another identical one if you can as a test. A relay is cheap.

Testing the spark with coil on plug can be fun. You're not going to use a regular indicator light since you can't get close enough to the high voltage pulse. I'd try to backprobe one of the connectors. If you can get your finger in there and touch one, you should be able to feel it snap. A mechanics stethoscope might help. Their location behind the intake manifold makes this painful, you'll have to get creative.

Another thought is disconnect your coils and then pull plugs. If injectors are working, the plugs should be wet. Problem is you'd have to perform this test when you know it isn't going to start. Might not be possible.

I'm sure it's been done, but have you tried disconnecting the battery for a while? I've found these electronics can be a little temperamental on occasion.

And yes the temperature sensor is worth a test. Could be feeding the ECU wrong data. Multimeter again, easily testable via resistance.

Good luck.
 

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Discussion Starter #12
Awesome suggestions zero gravity I really appreciate it I'll get on testing those things. The reason I went ahead and replaced the spark plugs because I was past the mfc recommended so needed them anyways and I got the MAf and temp sensor super cheap around $20 apiece. Without a CEL and such a strange and random problem it's hard to test things because I feel like most things that are going bad should cause more problems. Since the dealer couldn't fix it I'm kind of on my own here so I thank you all for the replies. If nothing that zero gravity suggested world out then I guess I'll have to try a there party mechanic. I know a good one but it's just so expensive. Maybe I'll just get a diag and do the work myself. Either way i will get to the bottom of it and when I do I'll let the forum know so that no one else has to go through a all of this.
 

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Let us know what you find. Even no CEL tells us something and helps the diagnostics. Namely, likely the ECU isn't in a state to tell you what is going on. I'm suspecting a relay but can't yet say for sure. They can be a devil to track down. Sometimes only way is to prove there is no other possibility.
 

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Be very careful about cheap engine sensors and metering. The copy components look the same as OEM but just don't work.
I always buy OEM electronic input and output devices- even if it costs a bit more.
 

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Discussion Starter #15
So I can locate the coolant temp sensor but man it's in a tough spot to get a wrench in there. Has anyone done it or seen a guide., Maybe recommend something to make it easier? I took out the multimeter and have tested a lot and it is all good so far. Hoping this will fix it as I've noticed as the weather gets colder my car hasn't had as many issues. I'm checking relays next if this doesn't solve it
 

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So I can locate the coolant temp sensor but man it's in a tough spot to get a wrench in there. Has anyone done it or seen a guide., Maybe recommend something to make it easier? I took out the multimeter and have tested a lot and it is all good so far. Hoping this will fix it as I've noticed as the weather gets colder my car hasn't had as many issues. I'm checking relays next if this doesn't solve it
Sounds like replacing without anything to back it up again, but hey it's your wallet.

I'd recommend a 1/4" ratchet and socket
 

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Discussion Starter #17
I had already ordered it. Someone has replaced it with a denso... Unless that Congress from the factory... so I got the OEM one to replace it with. Only cost $25 and is something that will eventually need to be done. I did bust out the multimeter and everything is testing good from what I can tell. I used YouTube videos because I'm not good with electronics haha. When it's cool or parked in the shade I usually don't have problems so maybe that will fix it. If not I'll going to do the cold water test on the crankshaft position sensor. If that works I'm just taking it to another shop and hope they have more luck than me and the Mazda dealership
 

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If it's taking a while to start. It's going to be timing, air, fuel, or spark. My guess after everything you've done would be a vacuum leak or temp sensor. I wouldn't think fuel pump unless it's not holding pressure or requiring prime to set.


Should ask if you've changed the coolant too. It may be that your coolant sensor is getting caught up in crap in the system and not giving the right readings.
 

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Discussion Starter #19
True I haven't thought to flush the fluid an get all new. I'm thinking exactly the same thing but the dealership assured me it was good fuel pressure and keeping prime. I thought MAF but it's good and just replaced the ECT sensor today so we will see if that does it. Maybe it is the crankshaft. I'm tired if messing with it though lol it's been a month of me testing and checking things almost every day for an hour or two. I can't wait too see what it is at this point. It's probably something stupid and simple lol. I'll put new coolant in it tomorrow
 

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My 2018 starts quickly when hot here in South Florida, but it does not have that smooth crank, crank, crank... run sound. It kinds of loafs to life after on second of crankng and after 2 seconds runs smooth. Only when hot, never when cold. Not an issue, but worth noting. Will have to keep an eye on this odd characteristic.
 
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