Detonation (knock)

G-Papi · Nov 5, 2006

I made it happen. After hearing of it, and being skeptical, I finally made it happen in the CX-7. My skepticism was probably fostered by my knowledge that the vehicle has a knock detector that would sense preignition, and cut power.

The chain of events is this:

1. 10 miles of expressway driving at speeds of 60 - 75 mph, and about 1/2 mile of driving after the exit.

2. Ten minutes in the pharmacy.

3. Returned to vehicle and left parking lot. At the first straight stretch, I floored it in third gear. There was a serious and loud spark knock (rattle) and a heavy cloud of grey (not blue) smoke from the exhaust pipes. (at about 4000 rpm) I immediately backed off the gas. The knock ceased (along with the smoke).

4. Easing back on the gas in 4th gear produced smooth acceleration with no knock or smoke. Heavy acceleration after that point was unable to reproduce the knock.

5. Back to the dealer I will go.

arlsmazdaspeed · Nov 5, 2006

change your plugs!!!

G-Papi · Nov 5, 2006

New car at 6k mi????

Brian MP5T · Nov 5, 2006

bad gas??

91 Octaine MINIMUM.

G-Papi · Nov 5, 2006

93 octane Shell

xavier · Nov 5, 2006

G-Papi said:
93 octane Shell

That was my exact situation. I was in third and I didnt even floor it. I was 1/2 throttle in third and got to about 4,000 rpms and then it started knocking. 92 octane for me all the time. I think there is a problem with the tuning and I dont think something as small as colder plugs is going to solve the problem.

Brian MP5T · Nov 5, 2006

Wow, I was totally not expecting you both to say High Test..

I also agree that the plugs are not going to solve this..

The tune is a Mazda thing so I would ask the dealer.. If many people ask the dealer, perhaps mazda will modify the map (Flash) like the MSP was in late 2003..

xavier · Nov 5, 2006

Brian MP5T said:
Wow, I was totally not expecting you both to say High Test..

I also agree that the plugs are not going to solve this..

The tune is a Mazda thing so I would ask the dealer.. If many people ask the dealer, perhaps mazda will modify the map (Flash) like the MSP was in late 2003..

Thats where Im starting but I have already gotten "unable to duplicate the problem". Hopefully, the flash Mazda is working on for the 6th gear 60 mph hesitation and stuttering will solve the problem. Hopefully but doubtfully.

G-Papi · Nov 6, 2006

It's more likely a turbo cooling than a tuning issue. I had one other car spark knock like that. It was an older Ford that was overheating badly.

My first response (after backing out of the gas) was to check the gauges. Temperature was where it always is - about midway.

Anyway, if I get the "can not duplicate" response, then at least I'll have the episode documented, in case it blows the hell out of one of the pistons next time.

xavier · Nov 6, 2006

G-Papi said:
It's more likely a turbo cooling than a tuning issue. I had one other car spark knock like that. It was an older Ford that was overheating badly.

My first response (after backing out of the gas) was to check the gauges. Temperature was where it always is - about midway.

Anyway, if I get the "can not duplicate" response, then at least I'll have the episode documented, in case it blows the hell out of one of the pistons next time.

I understand that it is a cooling issue but thats what tuning if for. Tuning, if done correctly, minimizes the chance of detonation by monitoring variables such as timing and temp and controlling those variables if possible to keep the liklihood of detonation to a minimum. I understand that it is impossible to eliminate the chances of knock but all it takes is one instance of knock to blow a motor (if its severe enough). Not saying your motor will blow on the first instance but it could.

1Sleepy93 · Nov 6, 2006

It's the damn top mount IC that causes the problem. Heat soak it and it's no longer cooling air but heating it. The grayish cloud was unburned fuel most likely.

xavier · Nov 6, 2006

Well I got a call from the dealership that has my CX7 and they said the CEL was partially due to a loose air intake boot. Now I did remove the intake baffle but I was careful to make sure the intake was reinstalled correctly. Maybe I should have tightened the intake clamps down a bit more. Anyhow that could account for my detonation as if air was entering the intake past the maf, it would cause a lean condition which would make knock more likely. I'll assume this was user error this time. PEBSWADS error! (Problem Exists Between Steering Wheel And Driver's Seat). Anyhow, I got the PCM flash, a sensor for the auto climate control, and the oil change. They are also washing her and vaccuuming her out. Woohoo. I pick her up at 4 today

G-Papi · Nov 7, 2006

I think that the loose coupling may have accounted for your CEL. The knock appears to be another issue, I believe. I had a long talk with my service advisor yesterday, and we agreed that it's probably an intercooler issue that is a "product design" matter. It presents itself as an excellent case for a turbo timer that I wish Mazda had installed as standard equipment.

As it turns out, it seems that Mazda knows something - but isn't being specific in its statement. The Owners Manual has a vaguely worded (to me) statement buried on page 4-12.

After driving at freeway speeds or up a long hill, idle the engine at least 30 seconds to cool the turbo before turning off the engine. Avoid simply shutting the engine off abruptly after a long or hard drive. Damage to the turbocharger may result.

It seems to me that that kind of information should have been more prominently displayed.

Anyways, I'm scheduled to go in tomorrow morning and go out with a technician to see if we can reproduce the condition.

Man, this sucks.

xavier · Nov 7, 2006

I hope all goes well. I picked up my CX7 yesterday and I havent been able to reproduce the knock...yet (knock on wood-no pun intended)

G-Papi · Nov 8, 2006

Verdict

Could not duplicate the problem. But at least it's documented if I have problems later on. No flashes due. No codes showing. According to my ECU, everything's hunkey dorey.

Rick's CX-7 · Nov 9, 2006

G-Papi said:
I think that the loose coupling may have accounted for your CEL. The knock appears to be another issue, I believe. I had a long talk with my service advisor yesterday, and we agreed that it's probably an intercooler issue that is a "product design" matter. It presents itself as an excellent case for a turbo timer that I wish Mazda had installed as standard equipment.

As it turns out, it seems that Mazda knows something - but isn't being specific in its statement. The Owners Manual has a vaguely worded (to me) statement buried on page 4-12.

It seems to me that that kind of information should have been more prominently displayed.

Anyways, I'm scheduled to go in tomorrow morning and go out with a technician to see if we can reproduce the condition.

Man, this sucks.

Mazda is not referring to detonation on page 4-12, but instead, they are referring to oil coking. The oil gets so hot inside the turbo, that it can actually turn solid and block oil lines, therefore killing the turbo. That's why some serious turbo guys have turbo timers; so their car's engine stay running after they turn the key off and exit the vehicle.

I do think the mounting of the intercooler is less than desireable. You have to think like Mazda does though....packaging, simplicity and cost.

Anyway, I wanted to say hello to everyone here. I've been a very loyal GM owner for the last 14 years and it has cost me dearly. Just got rid of my 02 Camaro Z28 for a new CX-7. I had a rare coolant leak into the engine of my Camaro and the Chevy guys refused to even aknowledge it. So I traded it! I must say the CX-7, although nowhere near my 12 sec Camaro, is very fun to drive. I really like it and fit and finish is light-years from my old car.

I do miss my Z28 though!

Again, nice to be here among my fellow ricers.

JUST KIDDING GUYS!!!!!

G-Papi · Nov 9, 2006

Welcome Rick.

G-Papi · Nov 9, 2006

There's something going on, and it all has to do with heat. The oil issue is understood, but something caused that spark knock for me, and I'm down to that in my process of elimination.

Rick's CX-7 · Nov 9, 2006

Thanks, G!

I wanted to ask you all; do you feel your CX-7 fall on its face in the upper RPMs? Does your CX-7 keep on pulling hard in the higher power band. Mine seems a bit weak up top, which is a bit rare for a turbo car and even more strange for a DOHC engine. Peak power is at "only" 5k RPMs, which supports my feelings. Don't you guys see that a bit odd? Why isn't this engine making peak power a bit higher up?

Shoot, my 16V V8 kept on making power after 6k RPMs. Very weird to me!

Rick's CX-7 · Nov 9, 2006

Well, as you suggested, the issued my very well be the IC. That and possibly agressive tuning.
If you look at it, the IC sits on top, which is where the heat is going to go. Add to that, the plastic casing around it and now the IC is inside a pressure cooker. Mazda does channel air to it, as long as you move. Once you stop, the IC is going to get hotter and hotter.

My advice is to not hammer it after prolonged idling, heavy city traffic and short periods of shut down.
I guess you speed freaks are going to have to wait until a front mounted IC comes out.

Detonation (knock)

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