Detonation and EGT dropping 200 degrees C at 8500rpm?
 

I've been trying to determine what is causing (what i believe to be) detonation.

I've run both injector cleaner and octane booster through the tank on different occasions, and surprisingly the injector cleaner provides better results to remove said detonation. (But it returns on the next tank of gas without the injector cleaner or even octane booster).

Usually when I start to feel/hear the detonation I back off. I'm able to gradually apply throttle which seems to alleviate the detonation/performance loss in comparison to just mashing the throttle (which pretty much causes severe performance loss).

Anyways, so today on the highway I was just aggravated as hell over this ongoing issue (its been months and months) and just stomped the throttle. At about 8500rpm it sort of just smoothed out, so i kept it there for a good minute, monitoring the EGT which was previously at 950ish, and it began dropping quickly to around 750. (It wasn't the increased wind speed or anything because I stayed a similar speed, just different gear/rpm)

So my question being, is this a FUEL problem or an INJECTOR (or even fuel pump) problem?

Other rx8 owners around town are having zero problems with the fuel they put in.

Does the information provided above give any better insight to what it might be? considering the detonation kind of just goes away at high rpm?

Thanks for any help. (Ps. coils/plugs/wires/air filter were all replaced previously in trying to alleviate the issue)

The EGT dropping could be the ECU dumping fuel to cool the cat, as per design.
The car also runs extremely rich at those higher RPMs. More fuel = cooler (relatively speaking) exhaust gases.
I'm pretty sure that's how it works, someone correct me if i'm wrong.

Too lean can also cause EGT drop, watch for engine temp rise during EGT drop; a sure sign of lean.

PS: A/F gauges are cheaper than engines....
:ylsuper:

Its my understanding that this is what was believed early on however since then has been discovered not to be correct. <shrug> Just saying

Are you boosted or NA? If your boosted ... lower the boost.
What are you using to monitor the EGT?

What octane fuel are you running? Try higher octane.

Extensive carbon build up could cause pre-ignition .... ? Seafoam!!! Do it twice

just my two cents

seafoam

where do you live?

how long has this been happening

Are you positive what you are hearing is detonation and not coil misfire. Detonation is louder than the other and you should experience a power loss. I recently went through replacing my fuel bump with a higher output due my detonation at 7k. Checked coils several times and finally was given a new set. Detonation is now gone. Check ignitions system componets before your start dumping more money into octane booster and cleaning your injectors.

The car is stock, I've replaced the coils, plugs, wires in hopes to fix the detonation. It's been like this for quite a while (maybe 6 months or more). The highest octane we can get here is 91. I'm using scanguage/xguage to monitor the temp.

And I guess it couldn't hurt to use seafoam and see what happens.

ok as an update, i seafoamed today. overall procedure was pretty easy. almost the whole bottle of seafoam was sucked up (half per rotor). lots of smoke :)

let it sit for about an hour, then let it idle around 1000-2000 for about 10 min, shut it off, plugged in the other connector, started it back up and did the 20 revs to 6k. After that idle was pretty smooth (seemingly smoother than before). Went for a drive keeping it under 4k for about 10 minutes till i hit the highway. opened it up on the onramp then drove semi normal till i hit the next highway and just drove the piss out of it... keeping it around 9k rpm for a few min.

while it did "seem" to operate better, i still noticed the detonation and power loss (though not as bad as usual). But i'd be more inclined to say the improvement is due to the cooler air of the evening, but i guess tomorrows mid afternoon heat will be the decider.

depending on if tomorrow shows an actual improvement under worst case air temps, i may run another can of seafoam. (as who knows, maybe it was a ton of carbon in there)

I took some videos on the highway to hopefully portray the sound im hearing, i played them back and its not as easy to tell, but maybe someone with good ears can pick it up. (ill try and post them tomorrow as i cant find my usb cable)

i think im out of options if another can of seafoam doesnt clear this up. coils,plugs,wires,airfilter have all been changed... i guess next would be to change the rotors :(

What city/state you live in?

What is the noise you're hearing? Are you sure it's not your intake manifold?

When your car misfires, RX8's a known to spit oil into the intake before the throttle body, sometimes this can gunk up on the valves through the intake manifold and cause a noise.

For example, my intake manifold makes a knocking noise randomly (sounds like someone shaking a spray paint can). We discovered that the noise was coming from the Intake Manifold by using a stethoscope (sp?). Like what nurses use to hear your heart beat except for cars to identify where noises are coming from.

Throttle body cleaner will help get some of the gunk off, but not all of it. My noises are much more evident due to the loud K&N intake I have, it sounds like somethings rattling at high RPMs however it doesnt seem to be disturbing my powerband.

Anyways, just an idea, be sure your hearing the right noise....

Maybe try throttle body cleaner?

Retarding ignition will raise EGT, as advancing ignition will lower EGT - to a point anyway. Thats when the engine is otherwise in proper tune.

There may be a correlation to that with your problem, if it is indeed detonation.

Once detonation begins EGT may drop and that usually comes with a noticable loss in power; a little at first and after about 1-2 seconds power ramps down - very noticable. Not like a complete power loss, just noticable as its going to begin feeling like it has a miss.

What Octane are you using and how much percentage ethanol 10%? 91 uh .. you have cold air intake and muffler upgrade?

Just wanted to give an update here as I just replaced my midpipe with an AP one last night. (Thinking possibly of a clogged cat).

I can't say there's "much" of a difference in the problem. (It's rainy today so maybe not the best to be making comparisons), though I do still hear the same "detonation" type sound.

Things i've done/replaced
* coils
* wires
* plugs
* air filter
* catalytic converter
* seafoamed

I've been trying different gasoline as well as different octane boosters. The highest octane we can get is 91 - and there are brands of 91 that cause extreme loss of power! Octane booster doesn't really seem to help a whole lot either.

I've talked to a few local people around here that have rx8's and they have no problem at all with the gasoline causing issues.

I take videos every week or so, trying to get a good quality one that allows you to hear the sound - but during playback it's just not distinct enough on the recording.

Mmmmm well I doubt the noise you are hearing is detonation, especially if you are NA.

Drop in power at high rpm could be caused from a faulty SSV actuator or perhaps a dirty Eccentric Shaft Sensor .....

Did you try the "Throttle Body by-pass." Here is a one minute thing you can try...it helped others. I would add a can of seafoam in the gas tank when it's at half to a third left. Do this more then once the carbon is hard to remove. Do you pre-mix?

https://www.rx8club.com/rx-8-discussion-3/no-more-detonation-%2Amiac%2A-121249/

Wow ok I'll try the throttle body bypass as I always had the suspicion of ambient intake temps helped contribute to the problem.

I'm gonna be peeved, yet ecstatic if it works... I'm not a huge fan of how the new midpipe sounds, livable but well, i'd prefer to hear the engine over exhaust.

If I remember correctly coolant temps are around ~85c/185f maybe even 90's/200's?

Are the intake air temps read before or after the TB?

I don't premix.