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Hard to start when engine is warm. Cold start missfire.
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JZenith
Novice
Apr 18, 2023, 9:17 PM
Post #1 of 10
(935 views)
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Hard to start when engine is warm. Cold start missfire.
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I have a kia cerato/k3 1.6turbo and the problem is this.
Cold start have some missfire, but smoothen out after a few cough.
When the engine is warm, if you shut off and start again within 2 minutes, it starts perfectly smooth and fine.
But then you shut off the engine and start after it sits for 5 mins or so, it will start choking, difficult to start. sounds like out of fuel, black smokes in the exhaust.
Things i have done;
new crank & cam sensors
new o2 sensors
new MAF sensors
new set of plugs and coilpack
serviced throttle body
cleaned valve carbon
replaced new fuel injector
replaced low fuel pump and high fuel pressure pump
smoke test, no leaks
radiator leak test, no leak
cylinder scope, all looks great.
compression test, is good
checked ECU board and program, all good.
none does the job. car still behave the same.
been to 6 workshops and 3 of them asked me to overhaul the engine.
the car runs perfectly fine once started. the issue was only hard start. im not sure whether i should pay that much of money to solve that small issue.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Apr 19, 2023, 12:31 AM
Post #2 of 10
(929 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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1st, this isn't sold to the US as far as I know still basics for checks and my questions, thoughts below.
What model year and miles/km on this?
The parts tossing is wrecking diagnosis for it also try to quit that or the multiple shops are just not getting it yet. The end all isn't usually an overhaul if in seconds it's fine.
The smoking, coughing with first start ups seems over fueled or possibly under fueled till it's just a bit warmer.
Sensors should adjust that just one perhaps not this list you have going on.
Good luck hit back with what year/miles it has at least we have a better chance to zoom in on it but you'll need a better shop/tech probably if not equipped yourself,
Tom
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Sidom
Veteran
/ Moderator
Apr 19, 2023, 12:42 AM
Post #3 of 10
(921 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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This sounds exactly like a car with a skewed coolant temp sensor. If it's reading too cool by 10 or 20°, when you go for a warm start it adds too much fuel and floods the engine out. The symptoms are exactly as described, Hard starting and black smoke out the back.
You can check the data after the car sits all night. Look at the coolant temp sensor reading, it should be the same as the ambient temperature
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JZenith
Novice
Apr 19, 2023, 6:09 PM
Post #4 of 10
(893 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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1st, this isn't sold to the US as far as I know still basics for checks and my questions, thoughts below.
What model year and miles/km on this?
The parts tossing is wrecking diagnosis for it also try to quit that or the multiple shops are just not getting it yet. The end all isn't usually an overhaul if in seconds it's fine.
The smoking, coughing with first start ups seems over fueled or possibly under fueled till it's just a bit warmer.
Sensors should adjust that just one perhaps not this list you have going on.
Good luck hit back with what year/miles it has at least we have a better chance to zoom in on it but you'll need a better shop/tech probably if not equipped yourself,
Tom
Im from Malaysia, its CBU unit from korea.
100k km, roughly 62k miles ODO year 2015.
my guess is the timing, but workshop checked the ignition all is great.
fuel system checked with scan tool monitoring purgevalve, high pressure pump solenoid, fuel injector, fuel rail pressure, throttle body angle and MAF, all looks great.
i've been to Kia service centre to expert / performance workshop that deals with aluminum engine, with the same answer.
Tear down the engine and get a high precision machine to measure the head and block as aluminum engine weakness is heat and deformation. As every other thing have been checked thoroughly by few workshops, only left was the engine body itself.
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JZenith
Novice
Apr 19, 2023, 6:11 PM
Post #5 of 10
(892 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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forgot to mention the coolant temp sensor was swapped with another car for testing, still the same.
ECU reading for coolant temp also normal.
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 19, 2023, 6:18 PM
Post #6 of 10
(889 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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This shouldn't be that hard for a knowledgeable tech to troubleshoot.
The first thing I would do is monitor the fuel pressure watching how it reacts when the key is first turned on and after the key is shut off. They would need to see if it is hitting full pressure immediately and whether it hold the same rest pressure when shut off. That can tell you a lot.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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JZenith
Novice
Apr 19, 2023, 7:27 PM
Post #7 of 10
(884 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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did that too.
the fuel rail pressure drop overtime.
but is the ECU that send signals to drop, and confirmed with an identical car, it is programmed that way.
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 19, 2023, 7:30 PM
Post #8 of 10
(881 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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No, it is not programmed that way. How fast does it drop and how much?
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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JZenith
Novice
Apr 19, 2023, 7:57 PM
Post #9 of 10
(876 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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it drops from 500psi to 0 in about an hour.
the expected fuel pressure drops accordingly with the actual fuel pressure.
we checked with an identical car and it is programmed that way.
i too wasn't believing this but it is. and the identical car starts right off even when it has 0 psi in it.
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Hammer Time
Ultimate Carjunky
/ Moderator
Apr 19, 2023, 8:01 PM
Post #10 of 10
(874 views)
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Re: Hard to start when engine is warm. Cold start missfire.
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Fuel systems are simply not programmed to release fuel pressure. The computer doesn't even have power supply to do that after the key is shut off.
OK, you have your opinion and no interest in our advice so I'm going to close this question now.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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