2003 Sonata 2.7 running rough after head rebuild
 

I just rebuilt the heads after a timing belt failure and it runs rough and spits and pops when running. Thinking it was a firing probem, I have checked a coupe of manuals and said the spark plug connections on the ignition coil should be 1,4,2,5,3,6, but looking at the coil on the engine it is marked 4,1,2,5,6,3. I did not disturb the coil upon removal. Could it be a crank or cam shaft issueor something else?

Totally confused.
Jim J.

If you pulled the heads, then did you carefully make sure all the sprockets lined up when you put the timing belt back on? You had to check not only the cams, but make sure it was in sync with the crankshaft pulley.

If you're sure about that, then suspect an intake leak someplace.

If you are unsure about the firing order, then switch the wires around and try that. I'd follow the manual. Are you sure you know which cylinder is #1?

I wouldn't suspect a sensor problem until I checked everything else because I assume they weren't a problem before you removed the heads. Did you use YOUR cam sensor, or did you put another one in the head?

Thanks for the reply.
The timing marks are lined up.

It will be hard to check for leaks as the motor won't stay at idle.

The manual I followed came from the hyundai service website. Wierd thing is I did not disturb the wires on the ignition coil. #1 cyl is on the right bank (firewall side).

I used the original sensor.

The motor can run if I keep reving it up and I can't hold it at a steady rpm. From the left bank I can hear a back fire sound. Sounds like it is coming from the #2 cylinder. I disconnected that cyl and it calmed down a little but still would'nt stay running.
Still in confusion
Jim J.

When you pulled out the cam sensor, are you sure you got the little rubber gasket out? Then did you get the gasket in correctly? The sensor position is critical to proper operation of the EFI system.

To check for leaks, get an old Windex bottle filled with water, and spray all around the intake manifold. If you have a leak there, the water should get sucked into the hole, and it should smooth out for a few seconds enough for you to pinpoint the location.

Here's a gif with the firing order I found.

I checked the hmaservice site, and found the diagram as confusing as could be. It does jive with the diagram I posted, though.

The timing belt is design to run in only one direction, usually marked with an arrow showing direction of travel. Make sure you have not installed it backwards. The slight difference in the shape of the belt cogs can throw off timing enough to cause the symptoms you describe.

I swapped the wires and no change. It seems to be (the backfire) coming from the left bank around the #2 cyl. I'm hesitatant to keep the motor running at high RPM's for fear of it totally blowing up. I'm going to try to cancel out the spark plug wires and see if that does anything. If that doesn't work... to the shop it goes. Thanks for your input. If you can think of any other possible checks... let me know.

I checked the arrows and the belt in the right direction.

LOOK AGAIN, THE CORRECT ORDER IS: 1,4,5,2,6,3... wires on the coils

The true firing order is 1,2,3,4,5,6

Look at the diagram I posted, the hmaservice.com diagram is terrible and misleading.

Resolution to problem
 

Put this in your memory banks. I found the cause. Seems the electrical connectors on the throttle body that control the airflow were backwards. Swapped them out and the motor runs great.
Thank you for your input!

celebrating with a few beers!

Jim J.