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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!

Reply from a Hyundai Technician

· Registered
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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!

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"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,, $$$

· Registered
17,570 Posts
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?

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

· Registered
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I don't know much about GDI engines

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??

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

· Registered
17,570 Posts
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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