Have a very strange misfiring issue.

[Blake S]

I have a 99 eclipse non turbo that i had as a project car and i did a motor swap. The 420a is whats in it. When I start the car cold it will run like a top for about 2-5 mins and then it will cycle into this very strange kind of half misfire. I have checked compression, injectors, replaced the coil pack and plug wires. The plugs are new too. They are platinums. The original computor that was in it would not report engine data. When i bought the car there was an extra comp in the trunk so i installed that and the car runs no different. Have not run the second comp on a scanner yet. But like i mentioned, it still runs exactly the same with the other comp. I also recently ran a timing light on it and cylinders 1 and 2 run constant but 3 and 4 almost run at a gallop that the best way i can describe it. it almost seems like im getting late spark because its like those cylinders will hit but not at full power because there is fuel coming out the exhust. So i swapped the crank sensor with the one on the old motor because i knew that sensor was working properly...nothin. Still runs the same. At a total loss of ideas here. Any useful tips to try would be greatly appreciated.

 

[TSI_1G_90]

Sounds like timing, but I'd do a proper boost leak test before I messed with timing just to be sure. Complete and correct instructions are all over this site.

 

[Sebba]

No check engine light?

My ex girlfriends 420a did that after the o2 sensor failed.

 

[Blake S]

well i have a o2 obd light because i chopped off the cat. so do i need to do that bypass or whaterver its called to trick the sensor

but it was also doing that before i dropped the cat converter so idk. ill still swap em out i guess. oh and im kind of a novice mechanic so im not quite following what you mean by boost leak, its not turboed. thanks for the input from both of you!

also one more thing. if the timing was off wouldnt all cylinders be off timing?