I bought my 04 rx8 about 2 years ago with low compression. I did a full engine rebuild and i can’t get it running right for the life of me. Besides engine rebuild I did new plugs, plug wires, coil packs, ssv, crank sensor, maf sensor, o2 sensor, ssv solenoids, fuel pump, Starter, and battery. I started to gain some ground on it after a year and it would run pretty good and cold start good but would not start again for like 10 minutes after running for a while, anyone know why? It would also sometime hesitate in the high rpms, anyone know why? Then when I was out driving it just straight died and wouldn’t start, wasn’t even trying. Since then I put in a new fuel pump and crank sensor and no luck. Any help would be very appreciated!

 

Those sound like symptoms of low compression. When you say you rebuilt it, what exactly was changed? Were the retained parts verified to be in spec?

Do you know what caused the first engine to die? Was the cat ever inspected?

 

I had the housings and plates checked and resurfaced and all new seals and internals besides the rotors themselves. The motor before I had it overheated and lost compression.

 

And it doesn’t have the cat anymore, has the two res test pipe

 

Did you compression test it after install? Especially important to do once the rebuilt engine is fully installed and running.

 

Yes, I don’t remember the exact numbers and it was with a piston compression tester. But how could low compression just make it randomly shut off when it was running fine?

 

As the engine heats up the metal expands causing lower compression hot than cold. this is why you need to test with a rotary specific tester on a warm engine to get true numbers. Engine not starting or cutting out while warm is a compression related issue generally.

 

Hmm. What rpm were you at when it died?
It's possible it threw a seal, but that's rare. You can pull the spark plugs and check for metal fragments.

 

It would start pretty good cold just not warm and now it won’t start at all. It was probably at like 4k rpms

 

It shut off and back on a couple times 5 minutes before, but then it did it again and it stayed off like how it is now

 

Interesting. I guess lets start eliminating problems. To start it needs fuel, spark, compression and the correct amount of air.

Can you confirm you have spark on all 4 with a spark tester?
While you have the plugs out, I'd check them for fuel, oil and metal fragments.
Can you confirm you have fuel pressure? This might be the fuel pump dying.
Do you get fuel smell from the exhaust while cranking?