Suspect overheating causing pinging/pre-detonation sounds
 

Hi everyone, I've been trying to diagnose this for awhile and the problem still persists. The symptoms are you get that loud rattling noise on WOT at RPM's above 5000 rpm. It only happens when the car has warmed up and has been driven for some time. If it has just warmed up to operating temperature and you redline it, there is no noise. This noise is accompanied by loss of power. It comes only after driving for awhile. I have been posting in other threads regarding this noise but have come to no solution so I am opening a new one to ask for help.

The car is 07, 85000 km mileage 6sp. It is daily driven. Regular oil changes done every 4000km. Car is redlined frequently. No CELs. The CAT is not glowing underneath the car. Coils/plugs/wires changed at 74000km (relatively new). No misfires. No leaks anywhere underneath the car. No sweet smell, or white smoke from exhaust.


Things I have done to help fix it:
- BG44K can in fuel tank DID NOT FIX PROBLEM
- Coolant flush and fill with new Mazda FL-22 coolant DID NOT FIX PROBLEM
- Jumpered fans/tested cooling fan relay 1,2,3 all are working DID NOT FIX PROBLEM

1) I have been monitoring temps with Scangauge2, on cruise, the coolant temps stay between 81C and 82C. When I hit stop/go traffic, it's between 96C and 100C! (and this is with just 1st and 2nd gear, not even going above 4000rpm). I've flushed the coolant 2 weeks ago already. I live in Canada, the ambient temperatures when this happens is only around 10 - 15C. Is this normal in stop/go traffic?

2) I verified that the driver side fan works by turning on the A/C. Both fans are working. I've also noticed while idle, my idle temps fluctuate between 93 - 97C. The fan kicks on at 97C in idle, and stops when it goes to 93C. Is this normal?

Please help. I've read potential solutions:
- fuel pump going bad (but if its bad, why would it only dump less fuel when it's hotter? It should always be dumping less fuel even when cool)
- thermostat? how to tell? The cooling fans are coming on, and the heater core is working.
- Waterpump? how to tell?
- Radiator bad? how to tell?



EDIT: http://www.youtube.com/watch?v=5naJ9Eb2R1U

This was on May 10th at Mosport. A friend was behind me video-taping it. On the straight sections coming out of the apex of the corner, you can hear my raspy exhaust note, like misfires...

So no one has any new info to contribute?

There's no way in hell I'm in the only person with this issue. :(

I did this.....look at Mesg#52 it only takes a minute to do and now cooler air is entering your engine and it can be easily reversed when it's really cold. You do use prem gas....correct.


https://www.rx8club.com/series-i-do-yourself-forum-73/diy-throttle-body-bypass-mod-36389/page3/

Premium gas only Vpower91

1) Seems normal to me. I've always run those temps. I was surprised as well. It's never been a problem for me.

2) Fan 2 is set to turn on at 100c (214fsh) ... I would say you are ok.

I have used working fuel pump, water pump and t-stat

Fuel pump overheating could result in less fuel.
- Buy Fuel pressure gauge

I think a Cobb AP would help you out here. You can monitor so much more with that unit.

It's next to impossible to diagnose problems like this via the intertubz.
No offense but are you even sure of the sound you are getting?
Really is it detonation/Pre-ignition ....
That to me is the first thing.

I'm going to be home working on my car the whole week of May 23rd ... if you haven't gotten it fixed ... come on up ... we can start swapping parts.

Any other device out there that's less than a Cobb AP that can monitor AFR, fuel pressure through the OBD-II connector?

The price is cheap is you ask me.

Plus you get the MM tuning service.

Send the logs to Jeff and see if he goes WTF dude you got something wrong ... better have a look at blah blah blah.

Plus when you are all fixed up you get the sweet MM tune.

Win Win if you ask me.

Or you can send it to the dealer and tell them you have no idea what's wrong and you are going to leave it with them. .... lol < big bucks there >

[quote=Footman;3973951 fuel pressure through the OBD-II connector?[/quote]

OH Sorry BTW can't do fuel pressure via OBD-II .... well not out of the box anyway.

BHR can set you up.

I found the code for scangauge that monitors CAT temps and AFR... I tried it out. started the car and AFR was at 14.1, slowly increasing to 14.7 idling.

What should I be looking for?

Well there is no exactly about it, this why MM has his service.

At idle anything up around there is fine. 14.1-15.1

What counts is when the engine is under high load.

Under load you don't want the AFR quite that high, they should be in the low 13's to high 12's

My understanding is that it's hard to get an NA car to knock but if you are running leaning lets say 16 -18 then you might get knock.

I do not have the experience at pushing a car to the knock limit so I'm only guessing.

Footman, I have the exact same problem. I just took my car out from winter storage, and although i couldnt get it to repeat the sound last year ( it only happened to me once) it sounds like might be back. My cat is also fried, after driving it for 30 mins, the O2 hole was redder than a stop light.

I have a spare engine, but I dont want to use my "get out of jail free" card if I dont have to.

I will gun it a few times tomorrow to see what the AFR is at high load. Are you suggesting that if my AFR is not running rich in high load/high RPM conditions, then my fuel pump is not delivering enough fuel and thus its running lean, which will generate more heat, which the engine then compensates by retarding the timings and the retarding of the timings generate that noise?

Okay, using the Scangauge and the AFR codes people have posted for the X-Gauge, I used it to watch my AFR.

On start up, it's around 14.1 - 14.7.
Once its warmed up, the idle AFR is 14.9 - 15.1

On WOT, the AFR at best is only 13.8, I never see 12 or 11.

CAT temps have never reached 1000F, stayed between 700 and 970F or so.

So these are the data. If I am not delivering sufficient fuel at WOT, can it make this noise?

Videos below and sound clips on the last one posted by others:

https://www.rx8club.com/showpost.php...5&postcount=16

https://www.rx8club.com/showpost.php...15&postcount=1

https://www.rx8club.com/showpost.php...0&postcount=21

https://www.rx8club.com/showpost.php...4&postcount=13

Dude ... it's too hard to tell much from those sound clips.

What gear did you see the 13.8 aft at and at what rpm?
A MAF reading is important as well.

If you suspect it's fuel then you either buy a fuel pressure gauge or a new fuel pump assembly or take it to a dealer.
A compression test should be in order as well.

13.8 in 2nd and 3rd gear. RPM anywhere above 5000 rpm.

MAF is good though, no idle issues, cleaned as well. I don't have a data logger so I can't get values at every point. I'll have someone sit beside me and write down numbers I see. The gauage changes values almost every second and I'm also doing the driving, so I can't be writing down numbers.

13.8 in 2nd and 3rd gear. RPM anywhere above 5000 rpm.

MAF is good though, no idle issues, cleaned as well. I don't have a data logger so I can't get values at every point. I'll have someone sit beside me and write down numbers I see. The gauage changes values almost every second and I'm also doing the driving, so I can't be writing down numbers.

Im begining to wonder if its the PCM. Its the only part no-one is touching on.
It almost sounds like the lead coils arent firing.

http://www.youtube.com/watch?v=hglAO8CEP94

this is a video of an fc with that problem, sounds very similar no?

It sounds just like that! yes!

If it isn't firing, wouldn't I get CELs for misfires?

So we are on the same page right? Almost sounds like a subaru boxter engine, lopey and gutty, like a loud burp.


I got one, but it was the first drive after a triple seafoam.

Heres the problem, it isnt really "misfiring".

My cat is shot, I need im going to get the AP midpipe so it doesnt kill my engine. When I do, i might see if i can borrow a timing light and go on some runs to see if they are/arent running.

well, I have a backup set of coils which I know are all still working. I replaced those at 74,000km. If I change the whole set, and see if the symptoms are there, then will know it's a coil issue.

But seriously, wouldn't a not firing coil cause misfires? And why are the coils not firing after an extended drive. I think we are on the wrong path here...

coils work or don't work, they don't just not work after a longer drive.

but the PCM might be the cause. Secretly its changing things all over the place, we just dont know it.

The pcm only fires the leading coils on startup, I wonder if its shorting a circut causing it to fire only the lead coils.

When things get wacky, always blame the PCM, 9/10 times its the cause

A non firing coil would produce a CEL, would it not?

Directly, no.

Indirectly, it could cause a misfire, too rich condition.... etc, but not a " your coil is fried" code

okay, how does it explain the noise happening in high rpm and now low rpm? it's firing at low rpm, but not firing at high rpm?

I just want to be sure before I start swapping parts.

That I dont know for sure.

This is what show who is the good mechnic, and who is just a parts swapper. need to find a way to test the coils while operating.