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Low RPM Detonation - PLEASE Help.

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Hey guys, would you be able to help me? I am experiencing low RPM detonation accompanied by lean AF ratios during detonation. whenever i take off from a stop in my custom supercharged toyota celica i get detonation until i have the clutch fully released and i am above 3000rpm.. (in other words the car is perfectly tuned for fully throttle acceleration, and cruising but not low RPM take offs)

Can you guys help at all? I have attached my tuning tables and all settings to this thread.

My theory is the ignition timing is dropping too quickly upon full throttle acceleration (taking off with my clutch, and putting load on the engine). The detonation will also occur if I floor it in a high gear at lower RPM and labour the engine.

Injector Specs:

Static Flow Rate @ 43.5PSI (300 KPa) = 60lb/hr / 12.0 gm/sec / 650cc/min

Coil Resistance: 12 Ohms / High Impedance / Saturated

Factory Tollerance: +/-5% (actual +/-7%)

Cone Spray Angle - single spray cone. Approximate cone angle for 90% of spray volume

10.5mm Inlet Diameter

Engine Specs: 2zzge, 1.8L, rev limit set at 8700rpm, supercharger pulley runs to 10PSI.

The setup is intercooled, however the detonation gets worse on hotter days.

Thankyou so much guys. This detonation has had my really worried about driving the car in general, and the engine itself. The car still makes full power so there is no engine damage as of yet. This car is not a daily driver. After all it makes 200fwkw and its a 1 tonne car.

Attached Files

Has this been tuned by yourself?

Personally I like to keep things simple so I usually 're-calc base' to move the inj map over to the base map, this leaves the inj map all 1's meaning that is isn't carrying out any compensations to the base map.

What AFR's are you seeing?

Have you tried logging with the map tracer and ghost activated to see what cells you're knocking in? I would do this and knock a couple of degrees off of these cells

I will try this

No it was dyno tuned by a pretty reputable place. but nothing like my car has ever been through their doors.

do any of those tables look odd to you?

I will try that tomorrow as well :) Just learning how to use my datalogit

AFR ratios are between 11 to 13 on full throttle acceleration. they go around 16-17 when detonating or engine braking

EDIT: Can I find a walkthrough on areas included in many of the settings of the FC edit software? I would love to know what it all means and how to do it

I'd suggest wiring your wideband up to the datalogit and getting a log of whats going on. From what you're saying it doesn't sound like you have a stable AFR on throttle, on engine braking you will see lean values but on cruise you shouldn't see anything leaner than 15 (14.7 is ideal)

could u give me a quick rundown on how to log AFR on datalogit?

i have the wideband logging cable wired to my cabin and screwed into the datalogit.. WHere do i go from there?

If you're prepared to begin tuning the car yourself then I'm all for you continuing down this path, after all it's why HPA came to be in the first place. One thing that I would keep in mind though - If you've dealt with a professional tuner and you're having problems with detonation as you're describing, I wouldn't be afraid to go back to the tuner and discuss your problems with them. Every tuner works differently but personally if there was an issue with a tune I had done I would put it right at no charge.

i've already taken it back and he tried to fix it. Well he didn't fix it, and the car became a bit more sluggish at low rpm.

So I took it back again and they refused to retune it, claiming that I needed to loosen the blow off valve and/or put a softer spring in the BOV.

Because my car has a centrifugal supercharger the BOV remains open in any vacuum conditions to avoid pressure buildup in the intake piping. (heat).

Does anyone from HPACADEMY have anything to add? I thought that was a feature of Gold membership.

thanks guys :)

Hey Moo11123, I'm one of the founders from HP Academy and I'm happy to try and help you :)

I've tuned plenty of centrifugal superchargers and I don't believe the BOV spring is a cause of the issue you're describing. Yes, the BOV will vent air any time you're off boost, the only issue I can potentially see would be if the BOV was too small to bypass the airflow from the SC at closed throttle - This would also be an issue at high rpm, not the low rpm where you say you are having issues.

The answer by the sounds of it is that the car needs to be tuned properly. If the fuel delivery is correct and the ignition timing is optimised then the engine won't be suffering from detonation. We teach these aspects in our courses but they are not a 5 minute fix to your problem. It's important to understand though that on a naturally aspirated engine with moderate to high compression, it's quite likely that the engine will be sensitive to detonation and this needs to be dealt with in the ignition tuning. Often you'll need to retard the timing to prevent detonation and in turn this will result in a reduction in engine torque and the 'sluggish' feeling you describe so it sounds like this may be what the tuner has attempted to do.

You don't mention what octane fuel you are running. Have you tried a higher octane?

Hi Moo11123,

Nothing is more frustrating than a freshly tuned engine that doesn't behave, and a tuner that doesn't provide the necessary help. Although your car sounds like a good starting point for learning EFI, if time is of the essence, I would suggest that you play along with your tuners ideas (even if they aren't related to the issue). The reason for this is that many people will struggle to let go of a theory, until they get to prove it right or wrong (and some will even fight for a theory after being proven wrong...). So if you replace the BOV spring, your tuner will not have an excuse for not helping you. My suggestion is of course not a good one if your tuner is lacking the knowledge to fix the problem...

Keep in mind that I'm by no means an expert on the subject, nor have I ever used the FC Datalogit. You say "detonation", but you also mention that the AFR reading goes sky high. I can't remember ever noticing a lean reading due to a knock event...? Could it be a "good old" misfire? Do you use some kind of detonation/knock detection equipment?

To answer your question/theory in your first post about ignition timing dropping too fast: If an engine suffers from knock, the ignition timing cannot drop too fast. Reducing ignition timing quickly can be used as a protection strategy, and can also be used for launch/traction control, rpm limiter ++..

Thanks for the responses guys.

I did end up putting the softer spring back in and loosened it all the way and it was still knocking.

I know it's knock because I've encountered misfire at least 5 times and this is a completely different sound and robs the engine of more power than misfire. Plus the Apexi power fc is picking it up in levels above 60 and warning me.

Guys I was under the impression the lower the ignition timing the more dangerous / prone to knock it is?

Maybe I just need to watch all the tuning courses here that I can access with my gold membership.

When I floor it at low rpm it's usually around 40-45 then drops to 18-22 then knock knock knock.

I have a daily driver so time is not of the essence.

I run 98octane currently but I am seriously considering going to E85. That is a last resort however, due to availability and the fact that I have no money for a retune.

Should I take the car for a drive, log everything and pull timing back in the cells that are detonating? How much should I pull it back as well?

Your ignition timing will be adjusting to an increase in load, chances are since your engine is N/A from the factory and is now boosted it may need to run even less ignition.

You'll be able to access all the old webinars in the archive with your gold membership, there are a lot of webinars on basic fuel tuning, understanding knock, ignition tuning and even tuning for E85.


I'd recommend our EFI Tuning Fundamentals course as this will give you a thorough understanding of the interaction of fuel and ignition along with the effects on knock. Please also make sure that you make the most of the webinar archive as there is a huge amount of information in there.

Your idea is solid of logging the car and retarding the timing but you also need to understand that a lean AFR can be a cause of knock too so you need to consider the entire tune. How much to retard the timing will depend how severe the knock is or in other words, how far over advanced the timing is right now.

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