Hello All,

I'm having an engine noise at high RPMs -> I'm leaning towards a new motor, but I'm hesitant because, from what I have read, the main sign of a blown rotary motor is hard starts when its hot, and mine starts every time.

First off, the car is a 2005 Rx8, 6-port/6 speed. Mileage on the odometer is little over 120,000miles. It does have the sticker for the oil related engine failure recall, not sure though if my car is a flash only or engine replaced deal (previous owner dealt with it). Has less than 5,000 miles on ignition system parts, I rebuilt the transmission installed with new clutch maybe 10,000 miles back. Only mods are the centerforce clutch and polyurethane engine mounts. Cooling system was overhauled maybe 20k miles ago. I keep up with 3000-4000 miles between oil changes, and I do regularly check the engine oil level. Has a new MAF sensor, new Cat, and new front O2 sensor. Engine noise started just before tranny rebuild, and has gotten worse since.

(Side note, I recently replaced the starter with the upgraded one. What happened is I flooded it, and the deflood procedure killed the old starter. While I waited for the starter to come in I still drove it. With the weak starter it would still start, barely... But I would think if its starting on a dying starter the compression has got to be good)

So heres the problem in detail. There are no noticeable problems after start up, while the engine is cool. There doesn't seem to be any problems either on short drives (less than about 20 minutes). The car seems to be running at full power.

Once I drive for more than say 30 minutes, if I launch the car, you know let the RPMs get up to 8500-9000 before shifting, it starts making some really bad noises. Noises start around 6000 and get louder with RPM. Noise is LOAD related, not RPM, as I can pull over and ref the engine with no noises. I've tried to record it, but its just hard to do and my phone's mircophone doesn't seem to pick it up. With the summer, it seems to start making noise at lower rpms (maybe 4500-5000) under load.

Noise as I best could describe it, I kind of sounds like a metal pin rapidly hitting metal, kind of like a bunch of small misfires in rapid succession. Noise goes away simply by taking my foot off the gas. When I heard this noise, there does seem to be some power loss.

Its kind of hard for me to pin point where its coming from, as it sounds like the front some times, but I think its near the rear of the engine on the passenger side, almost like right there where the exhaust manifold and transmission are.

I know its not the transmission or clutch as it was making the noise before hand. Exhaust I have checked for leaks/cracks, and even replaced the gaskets for the hell of it, but found no issues or resolve. Did verify all the valves move as they should, and tried running sea foam through the engine (prior to replacing ignition system).

I'm kind of leaning towards worn out bearings in the engine but part of me would think the engine would be done already if that were the case. Its been this way for several months, took it out of service for a few months while I tingered with it but found nothing really.

Compression, as far as I can test it my self with a regular compression tester (I know, not very accurate), appears to be fine, both rotors are equally compressing on all three sides.

Further more, I have trouble at Idle. Again no problem when cool or short drives. Say after launching it, or a long drive at high way speeds, when I return to idle the idle is rough. Idle speed jumps around, tries to stall out, then comes up to 1200 or so then tries to get back to 800. The whole time the engine is back firing more than usual. I know rotarys backfire normally a little bit, but this is like "pop pop pop" instead of just the occasional pop.

Any thoughts?

 

Ouch, no one venture to even throw out a guess? Hmm... How about the fuel system, anyone ever have an injector get stuck? How does the car react? If I get some time I will run the computer on it and see if I can get some PID data graphed. I'm thinking either A) its an exhaust leak before the front O2 or B) a injector getting stuck open...

Andrew

 

My best guess would be a condition called MIC (marbles in a can). I have attempted to search this site and found no reference to it. However you can search it and it will give you details especially over on the RX8 club. I would post you some links, but I am not sure how that would go over with the moderators here. My understanding that the SSV is worn and begins to make that noise and will need to be replaced. Kind of a PIA to get to, however since you have performed all the maintenance you mentioned above, should be a piece of cake for you, if in fact that turns out to be your problem.

 

Sounds more like a fuel pressure problem ,pressure drops off as pump gets hot and caused detonation [or pinging ] witch feels like engine is missing

 

Ah, ok... Shop Manual requires special in-line fuel pressure tester... Is there any other way? I wouldn't doubt it has the original fuel pump in it, which I've heard tend to die after 100k miles.

 

Not all pumps die so early have seen many still ok at past 150k

 

Kasper,

I had not even seen your post lol... I actually had the SSV out at one point to clean it when it got stuck. I don't remember there being any play in it, and it does open/close with a vacuum hand pump on it. Theoretically if the SSV valve was coated in carbon, then the APV would be too... I did however verify the APV does move by removing the motor and turning it by hand. Turns easily, now that I remember, the car did throw a code at one point for the APV being stuck which prompted me to remove the APV motor in the first place. Never had that code come back... I could once I get my other vehicle on the road again, take the intake off and see what the APV looks like, perhaps its not opening all way? Under heat perhaps it's expanding just enough to get caught up? Not sure why the car wouldn't throw a code though...

Sound is only audible under a heavy load and mid-to-high rpms. It does seem to be worse when its hot out, but does make noise regardless. Long drives cause issues at idle where the car wants to stall...

Fuel trims if I remember right at on the high side some where around +10% to +14% which is a little high. Haven't had time to put the computer on it with school and work, but when I can I should be able to graph the O2s and see what the fuel is doing...

Thanks,
Andrew

 

I would check your fuel pressure and fuel regulator first to be sure they are good

 

WJMRTY,

I was under the impression these things don't have a fuel pressure regulator, and pressure was controlled by the fuel pump, am I wrong?

Do you know where to purchase the inline pressure tester?

Andrew

 

Hi Alt3r3go,

I found your thread with knocking engine sound at high rpm, low power at loads, stalling idle. I have exactly the same with my Rx8 2004. Could you pease let me know about the solution for you problem. Thank you. Saby