Burtonsnow157

I have a 2003 GT with light mods and just recently i discovered that i had a coolant leak under my hood so i went about changing out the intake manifold and gaskets with all genuine ford parts (PI intake was used). I did the installation correctly to a T and replaced the spark plugs, cleaned the injectors off, and even bought a new injector since one broke while changing out the o rings. So that being said, once i started the car, it ran really nice, it felt better than it used to. I did notice a very faint sucking noise under the hood at this point, but it didnt sound any different than an intake might sound, nothing really to write home about. anyhow, after an hour i took the car back out and then experienced this:

When I gave the car any moderate to heavy throttle, it sounded almost exactly like the car sounds like when traction control comes on - it was much more pronounced in higher gears going slow which was shaking the motor violently along with the transmission. It sounds as if a cylinder is missing or isn't getting any fuel. I pulled a few plugs and they looked normal. Theyre brand new motorcraft sp493 plugs. Is it possible that a coil pack went bad? I cant see there being a leak between the manifold and the heads as i even used some RTV in rougher looking parts where there was some minor corrosion. As far as i know, i did the entire install forwards and reverse exactly like its supposed to be done (its pretty straight forward).

Also, i have done a lot of searching on here and on the internet and dont really see many suggestions other than buying a coil pack and trying it in all the different spark plugs to see which one is bad. I also saw that you can disconnect coil packs one at a time to see if this makes any difference, is this correct?

one other thing - there are no CEL codes at this time after driving appx 10 miles.

oxfordgt

You have a vacuum leak. Reinstall the intake.

Burtonsnow157

My main question would be if the gaskets have tabs that line up in the head and the bolts all lined up, how could I have a leak? I torqued all the bolts down and used rtv in corroded areas of the heads. . . Could the corrosion be the weak link? Maybe the intake didn't seat properly?

oxfordgt

Something is stopping it from sealing. Shouldn't use RTV around intake ports. If you start the car before it vulcanizes is can ruin your o2 sensors.

Burtonsnow157

If I'm not mistaken, it was at the crossover only. I will Do it over and remove the rtv altogether.

Drastang

check valve cover vacuum hoses for leaks or just make sure the elbows haven't corroded away. they become old and start to feel like sponges and allow vacuum loss. aswell as EVAP hose