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Discussion Starter · #1 · (Edited)
I need some help as I have exhausted all my mechanical knowledge on this 2013 Sonata GLS with 4-cyl GDI motor and only 69k miles...

Symptoms:
Car turns over strong and motor "starts" almost right away, but RPM's fluctuate between 300-600 rpm (fights to stay alive, maybe 2 cylinders?) and eventually stalls. BUT, sometimes it starts and idles fine at 1500 rpm after attempting to restart the car 10-15 times. Once running, it will drive and perform perfect all day (no knocking, no hesitation, no rpm fluctuation, etc.) Turn off the car, it becomes a roll of the dice whether it starts or not. No check engine light illuminated besides in AUX position, and no codes appear when connected to scanner.

Things I've checked:
-I can hear the fuel pump turn on (and no issues while driving suggest its working properly)
-Cleaned throttle body (made no difference)
-Pulled spark plugs and they look good.
-Disconnected and reconnected every plug connector I could reach
-Battery and connections solid, reads 12 volts on meter.
-Car has no MAF sensor so that cant be it.
-High pressure fuel pump has fuel (how can I check that it isn't faulty?)

What else should I look for before throwing money at expensive parts? What makes this strange is this just began happening, but once it starts it runs perfectly. Here's a few things I've thought about: Fuel pump- but wouldn't that show signs while driving too? Crankshaft position sensor- the RPMs raise when turning over and car never stalls while driving. Timing belt- cranks normal, not rapid.. and wouldn't it run crappy once started? Purge valve- usually to blame after fueling, but this does it randomly after car is turned off at any time. Fuel filter- again, wouldn't I notice hesitation while driving? Dirty valves- I know GDI motors are notorious for carbon buildup, but would that prevent a car from starting? Then why run prefect when started? I'm so lost..

I'm a decent DIY mechanic so throw any knowledge you have at me, I'll be able to troubleshoot it at least!

Thanks!
 

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I need some help as I have exhausted all my mechanical knowledge on this car with GDI motor...
Just another gasoline 4 cylinder,, no voodoo really


Things I've checked:
-I can hear the fuel pump turn on (and no issues while driving suggest its working properly)
-Cleaned throttle body (made no difference)
-Pulled spark plugs and they look good.
-Disconnected and reconnected every plug connector I could reach
-Battery and connections solid, reads 12 volts on meter.
-Car has no MAF sensor so that cant be it.

What else should I look for before throwing money at expensive parts?
Scan for DTC , best for HYundai dealer to do complete FAULT CODE SEARCH of all onboard modules and print


What makes this strange is this just began happening, but once it starts it runs perfectly. I first thought fuel pump, but wouldn't that show signs while driving too?
Has a primary low pressure pump that feeds the high pressure GDI pump.. fuel pressure test the primary pump ??

Crankshaft position sensor- but RPMs raise when turning over
Nope, starts and runs, so PCM knows crank is in motion and where


Timing belt- but it wouldn't run perfect once started, right?
THETA has a chain...

Purge valve- usually to blame after fueling, but this does it randomly after car is turned off at any time.
Expect to see a 0441 DTC if purge at fault

I'm so lost..

I'm a decent DIY mechanic so throw any knowledge you have at me, I'll be able to troubleshoot it at least!

Thanks!
Reply from a Hyundai Technician
 

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Discussion Starter · #3 ·
sbr711,

Thanks for the thorough response. I'll try taking it to the dealer and have them do a full diagnostic scan and see if they find anything hidden. I can hear the low pressure fuel pump in the tank turning on. Is there an easy way to check fuel pressure leading up to the high pressure pump? Timing chain- good to know! ;)
 

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I need some help as I have exhausted all my mechanical knowledge on this 2013 Sonata GLS with 4-cyl GDI motor and only 69k miles...

Symptoms:
Car turns over strong and motor "starts" almost right away, but RPM's fluctuate between 300-600 rpm (fights to stay alive, maybe 2 cylinders?) and eventually stalls. BUT, sometimes it starts and idles fine at 1500 rpm after attempting to restart the car 10-15 times. Once running, it will drive and perform perfect all day (no knocking, no hesitation, no rpm fluctuation, etc.) Turn off the car, it becomes a roll of the dice whether it starts or not. No check engine light illuminated besides in AUX position, and no codes appear when connected to scanner.

Things I've checked:
-I can hear the fuel pump turn on (and no issues while driving suggest its working properly)
-Cleaned throttle body (made no difference)
-Pulled spark plugs and they look good.
-Disconnected and reconnected every plug connector I could reach
-Battery and connections solid, reads 12 volts on meter.
-Car has no MAF sensor so that cant be it.
-High pressure fuel pump has fuel (how can I check that it isn't faulty?)

What else should I look for before throwing money at expensive parts? What makes this strange is this just began happening, but once it starts it runs perfectly. Here's a few things I've thought about: Fuel pump- but wouldn't that show signs while driving too? Crankshaft position sensor- the RPMs raise when turning over and car never stalls while driving. Timing belt- cranks normal, not rapid.. and wouldn't it run crappy once started? Purge valve- usually to blame after fueling, but this does it randomly after car is turned off at any time. Fuel filter- again, wouldn't I notice hesitation while driving? Dirty valves- I know GDI motors are notorious for carbon buildup, but would that prevent a car from starting? Then why run prefect when started? I'm so lost..

I'm a decent DIY mechanic so throw any knowledge you have at me, I'll be able to troubleshoot it at least!

Thanks!


All modern vehicles has even the computer for a brain and fuel system for a heart. Forget the brain functions as those toss codes . Any of your sensors dying toss codes. What’s left , the old standby...FUEL FILTER , FUEL PUMPS.
First thing I do with any issues after a car has 50 k is toss on a new fuel filter. Why, Just because! Remember while most of the old school maintenance items run great right to 100 k the gas you use is scrungier than its ever been. Your cars are far more sensitive to fuel issues than ever as well. With that in mind it’s the usual suspect. It’s been that way since the 90’s.
When a regular rail injection system starts to die it? usually begins by starting very hard. That’s because though it runs on 45- 55 psi it needs 60ish to light off. What a DI needs I can’t say and I can’t even tell you how to check mine. One thing for sure , with a dual pump system it’s got twice as many pumps to fail, that’s a given.
Here’s another thought. Have you cleaned that power valve using the aerosol spray can with the tiny straw yet? Being it’s a 13 you, ??*♂ like me ( can sitting on shelf 9 months now) might want to do that first. Still along with that $8 from Wallymart I’d put a new filter on before seeing a Stealership. Good luck!


Sent from my iPad using Tapatalk
 

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All modern vehicles has even the computer for a brain and fuel system for a heart. Forget the brain functions as those toss codes . Any of your sensors dying toss codes. What’s left , the old standby...FUEL FILTER , FUEL PUMPS.
First thing I do with any issues after a car has 50 k is toss on a new fuel filter. Why, Just because! Remember while most of the old school maintenance items run great right to 100 k the gas you use is scrungier than its ever been. Your cars are far more sensitive to fuel issues than ever as well. With that in mind it’s the usual suspect. It’s been that way since the 90’s.
When a regular rail injection system starts to die it? usually begins by starting very hard. That’s because though it runs on 45- 55 psi it needs 60ish to light off. What a DI needs I can’t say and I can’t even tell you how to check mine. One thing for sure , with a dual pump system it’s got twice as many pumps to fail, that’s a given.
Here’s another thought. Have you cleaned that power valve using the aerosol spray can with the tiny straw yet? Being it’s a 13 you, ??*♂ like me ( can sitting on shelf 9 months now) might want to do that first. Still along with that $8 from Wallymart I’d put a new filter on before seeing a Stealership. Good luck!


Sent from my iPad using Tapatalk

"That Power Valve"...... help me understand that one..

GDI use Primary pump at 65-75 to feed High pressure pump.... Easy fuel pressure test coming into GDI pump..

High pressure pump increase fuel pressure from 550 - 1500 PSI depending on need and PCM duty cycle valve on GDI pump.. Need data stream to watch fuel desired and actual values

Is this thing up to date for programs ?

We didnt fill it with E-85 did we ??

Fuel filter, naaa.... going to buy pump module,, $$$
 

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sbr711,

Thanks for the thorough response. I'll try taking it to the dealer and have them do a full diagnostic scan and see if they find anything hidden. I can hear the low pressure fuel pump in the tank turning on. Is there an easy way to check fuel pressure leading up to the high pressure pump? Timing chain- good to know! ;)
He is the best we got!!
 

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Discussion Starter · #7 ·
I'm planning to borrow a fuel pressure tester later this afternoon. Does the Sonata have a schrader valve or something I can connect the gauge to? Otherwise, what is the best method for testing the fuel pressure between the primary pump and high pressure pump on this car?

Thanks!
 

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I'm planning to borrow a fuel pressure tester later this afternoon. Does the Sonata have a schrader valve or something I can connect the gauge to? Otherwise, what is the best method for testing the fuel pressure between the primary pump and high pressure pump on this car?

Thanks!
Inline with fuel line to nipple on GDI pressure pump inlet.. will need adapter of some sorts to get in
 

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I don't know much about GDI engines
Heard talk about intake valve getting dirty with carbon build up

On other cars, the coolant temp sensor can feed bad information to ECU
So ECU doesn't know what amount of fuel is correct when cold
It can be trying to run at normal operating temps when cold???

Idle air control valve, or idle speed control??
What about a vacuum leak???
Cold there is a leak?? Then after warms up, thing expand to fill gap????
Does a GDI engine even have anything like these??
 

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I don't know much about GDI engines
Ok

Heard talk about intake valve getting dirty with carbon build up
Ehh,, we not had to deal with any concerns,, dry intake, not like it going to "sponge" fuel from air tract and cause drive concerns

On other cars, the coolant temp sensor can feed bad information to ECU
Can have bum temp sensor on anything out there



Idle air control valve,
No, ETC, motor driven throttle, PCM control plate angle for idle,, also PCM hold throttle for cruise

or idle speed control??
See above

What about a vacuum leak???
Not been concern with YF in most respects

Cold there is a leak??
Ehh

Then after warms up, thing expand to fill gap????
Intake manifold is hard-thick plastic with o-ring at 4 port





Does a GDI engine even have anything like these??
Fuel pressure test of primary pump and residual pressure inspect
 

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I had the similar problem before, starter motor worked great but hard to start the car, idle speed not stable, no code, engine died at stop sign. Turned out to be bad ECU connection, to be specific, ground wires on the engine, they worked as negative ECU terminals. Cleaned them and no problem anymore
 

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Something that pop up in past,,, seen it more so with Turbo,, verify volyage at battery while cranking.....

Seen a few that grind like nobody business,, but the available voltage drop down in 10V range,, we dont habe enough voltage to turn on PCM...

We take and touch jump box clamp to battery while grinding, and it'll light up and run,, then alternator take over electric making duty
 

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Discussion Starter · #14 ·
UPDATE: Fixed the problem! Turned out to be the primary fuel pump having low fuel pressure, so I replaced the fuel pump and now the car starts perfectly. Thank you to everyone who helped me troubleshoot.
 
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