Restarting problem GDI engine(rebuilt 2011 Sonata Turbo engine)

Hello guys and I'm new to the forum and thank you again to Paul Danner

My name is George(from Toronto,Canada) and I do have a question : Last year I have rebuilt my 2011 Sonata Turbo engine – I do have non-GDI forged pistons(Wiseco 6651M865),Molnar connecting rods, but I’m experiencing a restarting problem – I can start the car at the morning(no problem),but later keep cranking and will start after 4-5 attempts(I can smell gasoline, but when I pull a spark plug is dry,just wandering if those pistons lower the cylinder pressure,they are rated 9.25:1),other funny thing – if I do disconnect my high pressure fuel pump solenoid (most of time I can restart my car) – is it possible that to be related with fuel pressure or just HPFP receiving a wrong signal -that solenoid has been controlled by ECU based on camshaft,crankshaft,fuel pressure regulator and coolant sensors,but I don't have any code(no CEL at all ,but sometimes after 4-5 attempts to start the car P0420 - it's normal - I do have aftermarket midpipe CP-E with HFC and downstream sensor finds unburned or dumped fuel).Does somebody ever has experienced a problem like that? I do really need somebody with high end scope - to live streaming the FCV(at the fuel GDI pump) - I'm curious what kind of signal ECU sends to the solenoid.Later I will post a video of what is happening during the start and restart

Thank you so much for your time,
George

wonder if the fuel pressure is bleeding off on the low pressure side of the system?? thats why it takes 4-5 times to start it. how hard is it to hook a fuel pressure gauge in

Hello there,

Thank you for your suggestion - just I forgot to mention - everything is OK with low pressure side (fuel pressure is around 70 psi - good enough for the low pressure side ),sometimes the car will restart from the first time,but most of the time it's taking more and more cranking(I'm thinking about shape of the piston dome or ECU sending a wrong signal to FCV solenoid),I think will be an another case study for Mr. Paul Danner

Thanks,
George

why didnt you put the right pistons in it?? just curious.

try scoping cam and crank sensors. thats if you have a scope

Simple answer - for more boost,the car has really nice acceleration and more then enough power and i don't like those "cheap" OEM problem pistons and connecting rods - that's the reason my previous engine has a major failure .I do have a spare cam and crankshaft sensors - I'm thinking to change both(first crankshaft and later camshaft ) -to see if will be any difference,but still i think because if lower compression ratio(ECU sending a wrong signal to GDI high pressure pump solenoid - if disconnect that solenoid I will restart my car ,but if did not connect within 2-3 seconds - no power ,even if I do plug later GDI fuel pressure pump does not work anymore - has restart the car and pray to start working )

So, just to be clear, once you start the car in the morning, all subsequent attempts will probably end up with long crank times? And, if you disconnect the high pressure pump connector, you can get it to start (albeit with low power)?

I see that you checked low side pressure, but was that during the long crank condition? Like cheryl, I'm wondering about a potential bleed down issue, or air in the system.

For what it's worth, I don't see your replacement pistons as the problem. You definitely lowered compression, but I believe that if that was the source of the problem, then you'd struggle to start the engine cold as well.

Any codes set? Besides the high pressure pump circuit code that probably gets set when you unplug the solenoid. Do you have access to scan data?

Thanks for you response ,correct at the morning i can start the car without disconnecting HPFP and if the car sitting more then 8-9 hours,no I did not get any CEL - except PO087(if I did not connect the solenoid within 2-3 seconds),i will double check low fuel side - for bleeding off during those cranking attempts

Those forged pistons(non-GDI) installed in my motor are for Genesis 2.0T(MPI motor) - www.genracer.com/wiseco-oversized-piston...oupe-2-0t-2010-2014/

Only code I'm getting after 7-8 attempts is PO420 - downstream sensor is flooded and can smell unburned fuel
Sorry ,I don't have any data

Regards,
George

I have found the problem - just quick update ,cold start for GDI engines always happens on compression stroke(not a problem - engine starts),restarting GDI could happens during intake or compression stroke,the problem intake stroke- that's the reason took 5-6 attempts to start the engine(custom tune and problem has been solved)

Regards,
George

The Pistons you took out probably looked funny compared to the ones you put in, didn't they? GDI Pistons are designed for GDI engines to direct the fuel charge under the spark plugs. GDI engines can run super lean at times, as much as 60:1. They have a very specific dome that "catches" the fuel charge and directs it up to the spark plugs to fire it. I would guess that since your pistons don't have that dome, and you changed the compression ratio, is why it required a custom tune