F22a1 Engine Detonation

[Kev1990]

Hello I just realized after getting my exhaust sealed and queit when im really pushing the car sometimes at 2.8k rpms I get detonation especially at 3.5k rpms and so on so now that I have realized this im not being hard on it but the only way I can explain it is like a metal ring rattling or something never had to deal with detonation before thank you in advanced to anyone who helps.

[Fleetw00d]

Is your ignition timing correct? Typically, the further advanced the timing, the more prone it is to detonate. Do you have any idea how clean or dirty your combustion chambers are? Built up carbon can remain hot (kind of like embers from a fire) and cause pre-ignition. In excess, it can even tend to increase the compression ratio which will increase the tendency to detonate. Using a fuel system cleaner (Techron, Sea Foam, etc.) may help clean things up.

What kind of fuel do you use (brand name and grade)? Running something like Shell premium may also help clean things up (they claim) and the higher octane should reduce the pinging.

[wildBill83]

Are you sure you have detonation? Knocking or pinging are the typical noise descriptions for detonation. What it sounds like is there is some mechanical resonance. Is there actually any noticable loss in performance?

[johnl]

Is the engine at normal operating temperature? If it's running hot then this will increase the likelihood of detonation.

Do you have the correct spark plugs? Are they in good condition? Do the plugs look like the AFR is lean? (i.e. the plugs would look quite white on the porcelain and maybe show signs of over heating on the electrodes). A lean AFR will burn hot and increase the likelihood of detonation. Lean AFR could be caused by dirty or damaged injectors, a blocked fuel filter, low fuel pressure.

As mentioned already, overly advanced ignition timing can cause detonation. The ECU should be able to adjust the running ignition timing to spec (whatever that may be at any moment according to rpm, throttle opening etc.) so long as the 'base' ignition timing is at least close to correct. If the base timing is too advanced though, the ECU may not be able to retard the timing enough to prevent detonation.

Pre-ignition doesn't (in my understanding) make an audible noise as detonation does (these are often confused terms, but they mean quite different things). An engine can suffer mild detonation for a fairly long time without serious consequence, but eventually it will cause damage (depending on how bad the detonation may be). Pre-ignition is far more dangerous and can cause very severe damage very quickly (possibly in seconds rather than minutes...). If you can hear 'pinging' then my bet is that it isn't pre-ignition, but I can't guarantee that pre-ignition isn't occurring.

Bad fuel can cause detonation. This can either be because the inherent octane rating is too low (these engines don't require a particularly high octane, unless the compression ratio has been increased or the engine has been supercharged), or, some of the more volatile component chemicals of the fuel could have evaporated enough to cause the octane to be less than when it left the refinery. Fuel bought in out of the way outlets that have a low sales turnover could suffer from this because the fuel may have been sitting in the storage tank for a long time...

[Kev1990]

Well it almost sounds like crinkling tin foil or something but I looked it up and saw a video on a honda couple years newer then mine and it is definitely detonation I am actually running Chevron techron synthetic conentrated fuel injector cleaner in the current tank I actually have a new fuel filter full tank of gas from where I normally fill up the tank. The engine is very queit and smooth no loss of power that I feel but the distributor I have turnt back towards the firewall a bit isnt that advanced? Spark plugs, fuel filter, air filter and a recent valve adjustment done but im sure there is a possability that it has been doing it for a while just couldnt hear it over the loud exhaust leak I had. It seems like detonation to me but I cant be sure. On any of your cb7s the correct ignition timing setting is normally the distributor set somewhat in the middle isnt it? I know I cant just go by looks and to get a timing gun but I will check out the ignition timing. Yes the engine is at normal operating tempature.

[johnl]

The engine is very queit and smooth no loss of power that I feel but the distributor I have turnt back towards the firewall a bit isnt that advanced?

Looking at the distributor from the rear of the engine (i.e. from the right hand side of the car), rotating it anti clockwise advances the base ignition timing and clockwise retards it. You really do need to adjust the base timing properly with a timing light (with the ECU in 'diagnostic mode').

However, in the short term you can mark the current distributor rotation (a scribed mark on the distributor and a corresponding mark on the engine), then rotate the distributor clockwise a few millimetres to see if the pinging lessens or disappears (i.e. retard the timing). The scribed mark is just to make it easy to restore the original timing if needed, and to keep track of what has been done. If it still 'pings' then retard it some more. Keep retarding until it stops pinging, but if you can't get rid of the ping by retarding the timing then it's not being caused by overly advanced ignition timing, so reset to where you started and look elsewhere (overly retarded timing is bad too as it can burn exhaust valves).

Note that even if the ignition timing is retarded to the point at which detonation ceases to occur, this isn't necessarily the point at which the most power will be produced (or fuel economy maximised). In the old days most of the time it was, but this was only due to less than great combustion chamber design (such engines are 'detonation limited', most modern engines aren't). Modern 'pent-roof' combustion chambers can maximise power and economy at less advanced ignition timing than the 'detonation point', so tuning the ignition timing 'to detonation' (or just short of it) probably won't be optimum (even if it usually is with older engine designs).

This is because igniting the fuel too early will cause an excessive pressure rise in the cylinder that takes power for the rising piston to overcome (i.e. wastes power), even if detonation doesn't occur. It isn't dangerous, just not efficient. What's really happening here is that modern engines are just more resistant to detonation, so it's easier to advance the ignition timing too far and pass the point at which maximum power is achieved and still not induce detonation. Older combustion chamber designs would very likely make more power if the timing could be further advanced, it's just that detonation gets in the way...

On any of your cb7s the correct ignition timing setting is normally the distributor set somewhat in the middle isnt it?

Yes, nearish the middle of the distributor adjustable rotation. With correct base timing the exact rotation of the distributor will vary a bit from engine to engine, some engines will be dead centre, some will be a bit 'advanced' and others a bit 'retarded' (relative to rotational position of the distributor not the timing). This is only because of manufacturing tolerances.

[Kev1990]

So I adjusted the ignition timing once still heard it not nearly as bad though adjusted it a second time and the sound is gone for good so far but can't say for sure the distributor is where it should be its right in the middle just about with a tiny bit towards the advanced side I'm not sure if its worth messing with it or not by bringing it a little bit back more advanced to see what happens the car had a bit of power when I adjusted it the first time then it seemed like not so much after the second. Idk though might try advancing it again very little.

[johnl]

So I adjusted the ignition timing once still heard it not nearly as bad though adjusted it a second time and the sound is gone for good so far but can't say for sure the distributor is where it should be its right in the middle just about with a tiny bit towards the advanced side I'm not sure if its worth messing with it or not by bringing it a little bit back more advanced to see what happens the car had a bit of power when I adjusted it the first time then it seemed like not so much after the second. Idk though might try advancing it again very little.

This '.' is a full stop. If you use it at the ends of sentences then your post will be much easier to read. This (e.g.) 'A' is a capital letter, if you use them at the start of sentences then your post will be easier still to read. This ',' is a comma, it helps too. Your post would look something like this;

So I adjusted the ignition timing once. Still heard it not nearly as bad though. Adjusted it a second time and the sound is gone for good so far. But can't say for sure the distributor is where it should be. Its right in the middle just about with a tiny bit towards the advanced side. I'm not sure if its worth messing with it or not by bringing it a little bit back more advanced to see what happens. The car had a bit of power when I adjusted it the first time, then it seemed like not so much after the second. Idk though might try advancing it again very little.

Sorry for whinging about this, but attempting to read unpunctuated posts gives me a headache, and increases the likelihood of your meaning being misinterpreted.

Anyway, it seems that overly advanced ignition was the culprit. You should still set the base timing with a timing light, but in the meantime the engine won't now be slowly damaging itself if the pinging has gone.

As I said, having the timing adjusted so that it is only just advanced / retarded enough to stop detonation is unlikely to be where the engine will produce the best power and economy (but it won't be far off). This will probably occur with the timing a little less advanced than that, so advancing the timing from where it is now may not be the best thing to do. Short of setting the timing on a dynamometer, the factory setting is likely to be the best place to set it, but the difference probably won't be much.

[Kev1990]

Trust me John I understand. My last typed update was literally sitting at a stop sign waiting for a shit load of passing traffic because last Friday I got my actual and final DL probably shouldnt even have my DL but I dont text and drive lol I've done about 800 miles since last Friday running everywhere in my cb7 F.T.W . Thank you for your help though John. BTW I don't like improperly written posts myself although I've been known to throw a improper post together.