Damn detonation
 

Guess I'm gonna finally get a wideband to keep an eye on this. It was dyno tuned by a local Miata shop and ran fine, even during the hot Houston summers.

Lately it's been cooler and now it's detonating under boost. Car seems more powerful, but I'm not going to be boosting till I get the wideband hooked up and see what's going on.

Could be spark related too. On my MS it retards timing when IAT's go up, and advances timing when IATs go down. So you could be knocking from too much timing as well. Post more info on your setup. This threads useless without specs, details, etc.

I could post my maps but the Xede goes by it's own numbers, meaning it makes no sense in real world numbers. But that is a good suggestion, I'll try pulling some timing and see how that works before I get my WB.

I'm very new to the Miata turbo world, and I hope I recognize detonation if/when I hear it. I've heard different descriptions, so I'm trying to be aware of any unusual sounds under boost.

it sounds like small marbles being shaken in a small coffee can under your hood. Detonation is the devil and will kill your motor.



OP,
I'd pull back the base timing and see if that helps. I dont know shit about the Xede, so I could be off base. Have you pulled a plug yet to see if it's leaning?
Did it seem like a tendency to ping more as the ambient temps gradually decreased, or did it just do it.

Detonation sounds like a ton of small pebbles kicking up and hitting a car's wheel well but the sound comes from the engine compartment.

Thanks for the descriptions. They're similar to what Stephanie at BEGi told me. I'm hearing lots of new sounds now (I just picked up the car from BEGi yesterday), so I'm learning the good ones and hopefully (not) the bad ones.

It's not a daily driver so it rarely gets driven. I drove it last Sunday when it "cooled" down into the 80's, that's when I noticed detonation under boost. Prior to that I've driven it in the 90+'s and it was ok.

Last night was in the high 60's and I still got detonation. I haven't thought about looking at the plugs. I won't be suprised if it's all sooty considering the car "seems" to run rich. Poor gas mileage and distinct rich exhaust smells. But I will check that also.

The plugs might give you an indiation of the degree of detonation and if you see any damage at all you'll need to replace them. Otherwise you risk sending parts of the plug rattling around the combustion chamber and afterwards the turbine, and that can be very expensive.

Running rich is not a cause of detonation. If you are indeed running rich, and have detonation, timing's most likely the cause.

If you are detonating at the same psi level in cooler weather, I doubt it is the Xede maps. I would be more suspicious that you have a bad tank of gas, low coolant levels, coolant leak, etc... Heat is what generates knock. You might just use up this tank of gas and see if the next tank does the same thing.

To give you a heads up though, I am planning a trip to Houston in Nov. I can take a look at the car and do some tuning if needed.
Stephanie

Checked the plugs and they look normal. Fresh tank of 93 octane yesterday after it was nearly empty. Also, the car was overheating yesterday, but I found out my cooling fan relay was bad so I replaced that this morning. It was working just fine tonight and not overheating, yet still detonating.

Idle vacuum is normal and I haven't noticed anything else indicating a vacuum leak.

Hooked up the LM1 tonight and had my buddy drive. At idle AFR's are near 10. At cruise it's about right. Under boost it'll range from 10 to low 12's until about 5200 RPM where it starts pinging and AFR will jump to unacceptable levels. Not exactly sure what because once I hear detonation my driver is lifting off the throttle so it'll display 20's.

Before lifting it's definately past 12.5.

I also had my laptop/Xede software hooked up and realized it's over my head to have somebody drive while I'm listening for detonation, watching the WB02 and which cells are active that need tweaking. I tried adding more fuel to what appeared to be the cells that start pinging but everything just happens so fast it's overwhelming and I didn't get anything productive done. Probably not something I anticipate getting good at.

I didn't even bother with timing.

Stephanie, I've decided to take a drive to ya'll. I'll try to give you a call tomorrow. I'm glad I played around with it a little but I'd rather let the pros mess with it.

I always say it sounds like metalic popcorn cooking

Buck

LOL. I like this description.

When was the last time the fuel filter was changed? My car suddenly started detonating and no amount of tuning would get rid of it. A new filter solved all my problems.
Stephanie

I went ahead and replaced the fuel filter, it had about 26K miles and 4 yrs on it. Unfortunately that didn't fix the problem.

While down there I noticed an exhaust leak but it's after the cat and 02 sensors so I doubt that'll affect anything.

Spark plugs were are the recommended plugs for boosted applications and they went in a little over 1K miles ago. Would bad spark plug wires do this?

Another tank of fresh 93 octane and it's still pinging a little.

So with nothing else changed, it started pinging. Changed the fuel filter with no help.

Maybe the original (I assume) fuel pump is getting tired.

detonation:
https://www.miataturbo.net/forum/t24991/

I'm in Beaumont if anyone wants to borrow my ears.

Eh no thanks. I'm trying not to damage the motor.

I was going to volunteer my detonation headphones, but since you're a ---- you can die of gonorrhea in a Turkish prison. You're the kind of closet queer that gets curb-stomped. Watch you're fucking back man, now you've pissed off a commando who fought missions too dirty and depraved to be acknowledged by the military. Aside from my feaux personality on the internet, I don't exist. No social security #, a funeral a few years ago, and more government issued feaux ID's than you've seen in your life.

Well, Hustler is definitely back... :giggle:

Installed the Walbro 190lph-hp pump tonight and took it out for a spin. I didn't replace the carpet/insulation over the rear deck so the pump's really loud but I didn't notice any detonation. Hopefully get things all sorted out during the Houston dyno meet tomorrow.

Damn, I shoulda chimed in sooner. Yeah, stock 99' fuel systems are a JOKE. I'd plan on upgrading it to a return system in the future. POPSTOY on miata.net had to put a 255HP in his 99' to hold fuel pressure to redline at 170whp. 190HP wouldn't do it. Pretty shitty fuel system. I changed my pump twice trying to "fix" my loosing fuel pressure. Still looses pressure at high load and the amount of fluxuation varies, which makes tuning the top end of my fuel maps impossible. Got a Mallory 30-100PSI 1:1 fuel pressure regulator I'm going to use to convert to a return style setup this summer. For now, I tune uber rich so when the system sucks I don't go too lean. And I'm still N/A...

That was worth reading 3 times...at least!