Background: The engine is a stock Mazda reman unit installed at Pettit. The engine ran 100% flawless from the first start up and currently has bout 11,000 miles on it. Now, it seems that out of nowhere the engine is detonating very hard... at 7-8psi... sometimes on the primary turbo before the transition and if not before, then immediately (100 RPMs) after transition. I only held the throttle once while accelerating WOT in 3rd gear and after the transition it detonated mildly 3 times but once it got past 52-5400 RPMs, everything calmed down and pulled hard detonation free till I let off at 7400rpm. It seems that it won't detonate unless its 100% WOT. Even at 50% throttle with the stock twins, it will sit at the set 7-8psi and have no issues.

It is not lacking fuel. At the first sign of this problem I promptly installed a new fuel filter... which didn't help. I also had a new Cosmo pump laying around that I installed hoping that it was just a weak fuel pump... but no... and the car otherwise runs wonderful.

I changed my plugs (stock) and new wires were installed when the engine was installed. No, the wires are not crossed. I already checked. The coil harness was replaced when the engine was installed.

Like I said, the car is running 7-8psi. I took the pill out of the actuator line bringing the boost down from 10psi hoping that low boost would stop the detonation... but no.

I cleaned off the CAS and the ring hoping that was causing some sort of interference... but no.

I then thought it might be something bad with the ECU. Pettit ECU out, stock ECU in… but no.

So there has to be something else that is causing interference somewhere. With that being said is there anything you can think of that I didn't mention? The coil harness was replaced when the engine was installed and like I mentioned, the car runs great otherwise.

I have talked to Cam at Pettit a few times hoping that we can figure it out together over the phone before I make another trip down there for the same problem (already went once last week) but we can't seem to get it sorted out and he doesn't seem like he wanted to spend a whole day trying to figure this thing out at the shop.

I am by no means new to FD's but this really is driving me nuts. Cam told me to post it up here and see what some of the extremely experianced guys think about it.... so any thoughts, comments or concerns, please let me know.

TIA!

--Andrew

 

What are your exhaust AFRs? Your car may be tuned too lean.

Are your injectors large enough? Are they clean?

 

you've done all this troubleshooting, and you think you're detonating, how do you even know for sure its detonation?
i wouldnt be messing around, get a wideband on that thing, on a dyno or borrow from a friend, take a mortgage out on the house and buy one, SOMETHING.

 

I had the car on a dynojet before this little problem. A/F's were 11.5 pre transition. Post transition 11.0 and from there its all down hill to 7500 rpm @ 10.2. Its a nice safe tune.

I know its detonating. Like I said, I am not new to this stuff.

Injectors were cleaned and flowed prior to the engine install.

I know it needs to be on the dyno to check A/F and timing but I was hoping that somebody might have some insight on something that I may have missed. Last thing I want right now is to throw some load to the engine on the dyno and have it eat a seal.

 

wow i detonated once and popped a seal.. i'm amazed u can continually be pinging like that with no adverse affect...


are your coils ok?

have u checked/re-set the timing?

 

i would put it on a dynojet again with AFR's since the problem has started. i think if it came out of nowhere then it has nothing to do with your timing/ignition.

 

See, thats what I thought too hence why I started with replacing the fuel pump and filter since those are realitivly common problems but since that didn't rectify the issue at hand, I have to look elsewhere.

Oh trust me. I know I am riding on stolen time at this point since it has pinged quite a few times. I am actually very VERY surprised that the engine is still in one piece. A few of my other motors never even came close to matching the strength of this one. Thats why I am scared to dyno it. It might only handle one more ping before she lets go. That would suck the big ***.

Thanks for your help so far but keep it comming. Hopefully somebody will look at this while they are bored at work today and chime in as well!

Thanks again!

--Andrew

 

Perhaps one of your injectors is starting to stick and go lean.

I would wideband it again and be absolutely sure there is enough fuel flowing through the engine.

Dave

 

So it consistently detonates but yet you still have compression? Damn, the only two times I heard the detonation sound my motor went bye bye :\

 

I had a very similar experience just a few months ago. Engine started making a buzzing sound at full boost in certain parts of the rev range. At first i thought it was bad gas, ran it out and refilled. Didn't really help. So i lowered the boost from 14 to 12psi (stock twins). Didn't help. Put it on a dyno, AFRs were good (high 11's), but it was knocking and losing power around 5500 rpm, but then would pick it back up and run fine to redline. The car also started backfiring excessively on any deceleration so i figured it wouldn't hurt to get some preventative maintenance done. (The engine was rebuilt by PFS and had about 12k miles on it.) I replaced the primary plugs with the same heat range as the secondaries (they were the stock type plugs and i felt that since i was pushing a bit over 100hp over stock it would be wise to go a heat range colder). That did help a bit as the ones in there were copper instead of platinum and showed some visible wear, but didn't totally cure the problem. The guy at the dyno guessed by the way it was behaving that it might have ignition breakup. I took it to a shop (P1 Automotive in Charlotte) and had them replace the spark plug wires, coils, and sent the injectors out to be blueprinted. Turns out one of the primaries (which were the 850cc stock secondaries moved to the primary position) was leaking pretty badly, causing my excessive backfire. (While i was at it i also had them enlarge the 1200cc secondaries to 1300cc.) Having the injectors cleaned made a world of difference. When the guy reinstalled the injectors it ran pig rich, even though nothing had been changed in the tune. After retuning, the primaries went from running at 85% peak duty cycle to 65%, and there was no pinging at all. Now i dont know if it was from the coils or injectors, but after that i had no more problems.

The other thing i thought it might have been was a bad intake seal somewhere. That can also cause similar symptoms...but less likely.

Hope that helps!

 

plug wires! could also be the cas's or wiring harness too (if it didnt get replaced).

they do ping with bad plug wires though

 

all of my TII motors took about 4 or 5 good pings before cracking the corner off one of the rear apex seals...

 

I have a spare set of coils and harness from my blue car laying around here too. I will slap them on and get new plug wires. I just double checked and I was mistaken. The coil harness was not replaced. Goddamn it. I bet thats what it is. Lemme go check this **** out and I will let you guys know.

Thanks!

 

Good luck, I am curious to find out what the problem is. You must be experiencing some extremely mild detonation for your motor to still have good compression. Whenever I have detonated, I have DETONATED lol.

 

That's what I'm saying, you guys sure it's detonation and not just breakup?

 

ok you prob are not detonating but getting a little spark knock. could be that you have a bit of carbon build up on the rotor face. under boost it gets hot, and while it will not cause a premature ignition (detonation) but it may cause some uneven burning in the chamber (ping/ light knock). could explain how it has not grenaded the engine yet. this is assuming it is not break up as said above /\

you said you have checked all the usual suspects, so try doing the water flush de-carbon method. run some water through the vac line on the uim while holding the rpms up. do a search for a more through walk through

 

Unless there is some serious premature carbon build up there is no way thats it. Engine has only 11k miles.

I changed the plugs again. All kinds of bad **** is going on. Didn't have time to pull the old coils and harness but I will give it a shot in the morning.