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Discussion Starter · #1 ·
Hi, I am from Denmark, I have a Sonata from 2003 with a V6 2.7 litre 4speed-AT, and for a while a go, I put some bad and dirty gasoline in the tank. I changed the fuelfilter after that, and put some tank/injectors cleaner in the tank to clean her up.
Now when I want to start the car, (Attention, ONLY when it have been min. 2 hours of waiting since last time it was runing), it cranks about 5-7 seconds and THEN it starts. If I shot her of and try again exactly after, it starts up just fine.
When I drive it, it runs just perfect. Nothing wrong at all.
Of course now she have only clean gasoline in the tank.

I have tried to change the coolant tempature sensor for the ECU, spark plugs and crankshaft sensor but no luck!
What could it be?
 

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what makes you think you had 'bad and dirty' gas? unless its something like throwing gas in that was sitting in a jerry can for a couple years in the corner of the garage, that doesn't happen so often. i would never rule it out, but bad gas is always one of the last things i would guess at being the problem.

if there was justified reason to believe gas was bad, yes fuel filter and injector cleaner are good ideas....one of the only times i would ever recommend putting anything but gasoline in the tank!

now secondly, i want to say stop replacing parts at random! i don't understand why people have the urge to do this. what logical reason was there to replace the coolant temp sensor or crank sensor?? if you want to replace parts just because you can, you'll be spending a lot of money, time and not solving the problem.

not having anything for ECU scan, there's a couple options i can think of off the top of my head. (BTW a 'professional' tester will show nothing over what a cheap one will if all you need is the codes. don't be afraid to get yourself one). this could be a relay starting to fail for either the ECU or fuel pump. may be commanded on and relay does not respond. 2 hours may be the minimum time for this to happen. swap those relays with another one not critical for starting, say the horn.

i'd also check for small fuel leaks. get the car running and warm, then stop and immediately start checking. follow your nose.

another diagnostic test: a spark indicator light. $2-3 test tool, you put this against a plug wire and it flashes when the high voltage pulse is sent to the plug. try this with someone cranking for that 5-7 seconds. play with it before hand to make sure its working and you're using it right. if you're not getting anything during this hard start, that means coils are not firing. not bad coils, but would confirm ECU is not getting power.

really want more info on that 'bad' gas! i did run into one years ago where a douche friend somehow put diesel into his tank. that thing never started right after that.
 

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Extra crank time might be needed to build fuel pressure.

What did sock on bottom of sending unit look like during filter change ?

Some cars have a code that sets for fuel pressure, I would test what fuel pressure is during the extended start time.
 

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Extra crank time might be needed to build fuel pressure.

What did sock on bottom of sending unit look like during filter change ?

Some cars have a code that sets for fuel pressure, I would test what fuel pressure is during the extended start time.
that's what i was getting at with the leak. good addition! a fuel pressure test might be a good idea, also while starting up. fluids will pressurize very quickly as they don't compress so well, but a small leak or blockage could hold that up for a few seconds.
 

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Discussion Starter · #6 ·
Hi again. Thanks for the very good replies. When I say bad gas, I MEAN BAD gas! (From other cars, suck it up, and filtered it, and then in my tank. (They are mine, YES. AND I know it was a bad idea, but just ignore that :))
The problem occured right after the trip I had when I put the bad gas in the tank. So it is obvios that it is something with the fuelpump or something like that.

The fuel pressure test sounds like a good idea, how do I do that?
 

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that's all it is. you just need to use a T-fitting to plumb it into your fuel system somewhere. usually the line where it hits the fuel rail is ideal. don't need anything particularly special for fittings, just use whatever is appropriate and clamps. compare results to the specs on www.hmaservice.com.

i'd advise using your nose first. easier and cheaper test. checking the intake filter screen on the pump in the tank is also a good idea.
 

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Discussion Starter · #8 ·
"checking the intake filter screen on the pump in the tank is also a good idea."
Can you explane how I get in to that without removing the hole tank?
 

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unfortunately the documentation is very vague....the sonata is not a car that i have done much with either. all hma says is to 'open the trunk door' to get at the pump and lines.

really that is all it says! so i would guess you have some sort of access door in the trunk? would be under the carpet in there possibly behind the spare tire?
 

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Hi, I am from Denmark, I have a Sonata from 2003 with a V6 2.7 litre 4speed-AT, and for a while a go, I put some bad and dirty gasoline in the tank. I changed the fuelfilter after that, and put some tank/injectors cleaner in the tank to clean her up.
Now when I want to start the car, (Attention, ONLY when it have been min. 2 hours of waiting since last time it was runing), it cranks about 5-7 seconds and THEN it starts. If I shot her of and try again exactly after, it starts up just fine.
When I drive it, it runs just perfect. Nothing wrong at all.
Of course now she have only clean gasoline in the tank.

I have tried to change the coolant tempature sensor for the ECU, spark plugs and crankshaft sensor but no luck!
What could it be?
Sounds like a fuel pressure regulator. Do a search, as SBR711 has a post on how to test for this.
 

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The fuel pump has a check valve that helps keeping the fuel lines pressurized after you shut off the engine.
If some dirt got in there, now the valve doesn't close properly and pressurized gasoline will slowly drain back into the unpressurized tank, while pump is not running (engine shut-off).
That's why initially takes so much time to build-up pressure, but right after that it doesn't. Takes a while for the fuel filter and lines to fill up back to pressure.

When you start the engine, just PAUSE a little more on the 'contact' position, instead of going right to 'start'. Some 4-6 seconds should be enough. In this way the pump works and builds up the pressure and you don't wear your battery, starter for nothing...

Final solution would be replacing the pump inside the tank - it's just not worth trying to clean an old pump that might fail anyway shortly and pump is sealed anyway. Replace the pump pick up screen too, some manufacturers won't even warranty the pump if screen filter is not replaced.

Examples of internal check valve:

 
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