Hi all, last week I purchased a 2004 RX-8 GT with 64,000 miles in Dallas. It is in good condition and drives very smoothly under normal situations. Gears all feel good and the engine sounds and feels smooth. I can feel the power ramp up as I approach 4K-5K RPM, but I usually shift around 3K for better economy per the users manual.

Yesterday I noticed that when I really push the accelerator down, like 1/2 way or all the way to the floor, there is a distinct knocking sound coming from the engine. Sounds like piston rods knocking under load in my old car. I was able to replicate the noise consistently. Seemed to start around 4500 RPM, but only when I was stomping on the gas pedal. Normal driving with smooth, easy (slow) acceleration doesn't produce the noise.

I have done a lot of forum surfing and I google searched the site for "engine knocking" but the threads that come up don't seem to respond to the issue. I'm somewhat afraid that this might be a death knock, but I'm really hoping it is something else as I can't afford to rebuild or replace the engine yet.

I have been using 89 octane fuel and the oil was just replaced. I have checked the oil and it is clean and clear and full. The low coolant light has started to come on, but I check the level regularly and it is not low. I think it still has the original stock bottle and sensor.

Any suggestions would be greatly appreciated.

 

I forgot to mention... Engine temp is pegged at 2 marks below center. Oil pressure stays at 3 marks above center.

Also, starting is slow. I figure new coils, wires, and plugs are in my immediate future.

 

Wondering if the sound I'm hearing is a misfire? I've been reading the posts about ignition coils and it sounds like the coils could be misbehaving...

 

89 octane is a tad low ... see if higher octane helps.

If not then look into getting a better ignition system.

 

man that 89 octane is really killing you bro, thats to low...93 and up for me. check the newbie thread, thats a ton of info on there., i used to wear a size 7 baseball cap, after reading that im a size 8 1/2 with all the info there!!

 

Thanks for the replies. I've read most of the newbie stickies. I've seen a lot of discussion about fuel octane, but it seems like some folks are all about high octane and others aren't too concerned about it. That's why I went with 89. Higher than 87...

Anyway, I filled up today with 93 and will see how it goes after work. Am planning to replace the coils, plugs, and wires next week.

So, are y'all thinking the knocking is from the fuel? Or just suggesting higher octane fuel to be helpful?

 

His gas probably isn't causing the issue, most likely it's contributing to the symptom but there is probably an underlying cause for this but low octance could be the issue. I would suggest changing the ignition system. All wires, coils, and plugs, or check first and if they're bad change.

 

Low octane gas could be your culprit.. but as stated above, it may not be the root cause.

I used to run 87 octane in the begining lol, engine started knocking after sometime. back to 93 she's been good.. Low coolant light is a very common glitch in earlier rx8.. Your coolant level sensor is most likely dying. The only cure is a new coolant bottle with a a new sensor..

 

I thought someone figured out how to remove the sensor?

 

Well, I feel kind of stoopid. I think I discovered the root cause. Could have been the fuel but I think it was the fact that I was almost out of gas when I tried mashing the accelerator. I was reading about misfires on the forum and one possible cause was low fuel causing the fuel pump to lag. I don't know for sure that I was hearing misfires, but after filling up I haven't been able to duplicate the problem. Could have been the gas, too, I suppose. I filled up with Chevron Premium.

Still gonna swap out the ignition stuff. Getting tired of cranking to get the car to start.