detonation before vtec/phoenix

[whitefun]

hi Dave, i have noticed that my ap2 will have a noise that i think is detonation. the noise occurs when i accelerate at about 3/4 throttle and in the 4000/5500 rpm range. i still use chevron 91 as it is the best available pump gas. the temps are lower outside now than in the middle of summer. does not happen every time but often enough that i am curious. no problems when in vtec as far as i can tell. not an extended period of time but for a second or so when it occurs. 9000 miles,4.77 gears,fujita f5 cai. do you think this is normal? thanks phil

[griffon]

Take it to your dealer to get documentation on the problem before your warranty runs out.

[repiv]

If you've still got warranty, you can try to get the dealer to work it out, however, with the Fujita, they may balk at covering it. This depends on how sticky your dealer is on such mods. Any other mods on the car?
I'm not sure that it's detonation since there is a knock sensor on board and you didn't indicate a CEL, so one can be fairly safe to say that it's working and doing its job. If you're making the guesstimate based on sound, it might be difficult to say for certain that it is actually detonation you are hearing. Detonation, when present, is generally more acute the more load you put the engine under. That is to say, it's easier to make it detonate the higher the gear it's in when you mash the gas or when you try to accelerate up a good incline. 1st gear should be the least evident.
Is your engine running particularly (and unusually) hot? This may contribute to other conditions that make for detonation.
Detonation can be caused by many things, some of which can be bad gas, bad plugs, poor injector function, bad fuel pressure, MAP sensor issues that don't trip a CEL. If it's bad gas, try a different source and see if the situation goes away. If you can't wait that long (full tank), add a bottle of octane boost (that also has injector cleaner components) and if you suspect water, then also a bottle of gasline antifreeze to take up the water. If the detonation was caused by these, you should see improvement within a few miles.
Check and read the plugs to see if there is an odd looking one. As for the MAP, try "freshening up" the connector by wiggling it vigorously. Possible consider cleaning the air passage under the MAP. The other end of this passage is at the inner side of the throttle body (90 degrees at 3 O'clock). Removing the intake will make this hole visible. WD-40 into the top hole and stuff a rag in front of the throttle plate to prevent the WD from getting in. Use a bit of compressed air to blow out the WD and dry the passage. Some have reported this doing wonders for their cars. It may or may not do anything for yours, but worth a thought if all else fails.
Fuel pressure check requires hardware. Leave this for the dealer if you should go that far.

[whitefun]

thanks for the quick reply! no cel,the noise is only evident under heavy load.(when i acccelerate from 1/4 to 3/4 throttle starting at a low rpm.3k to 5k is when i hear the noise).the engine temp is the same as it has always been. outside temp is a little lower .i have always purchased my fuel from the same chevron. i will try a different station in the am as i need fuel. the fuel here is awful!! i used to have many problems with my mustang .4.6 2v paxton s/c at 9 lbs boost. could you explain where the map sensor connection is so i can refresh the contacts? i will try to refresh the contacts and add new fuel in the am. if this does not work i will try the 2 fuel additives. etc. thanks phil

[repiv]

thanks for the quick reply! no cel,the noise is only evident under heavy load.(when i acccelerate from 1/4 to 3/4 throttle starting at a low rpm.3k to 5k is when i hear the noise).the engine temp is the same as it has always been. outside temp is a little lower .i have always purchased my fuel from the same chevron. i will try a different station in the am as i need fuel. the fuel here is awful!! i used to have many problems with my mustang .4.6 2v paxton s/c at 9 lbs boost. could you explain where the map sensor connection is so i can refresh the contacts? i will try to refresh the contacts and add new fuel in the am. if this does not work i will try the 2 fuel additives. etc. thanks phil

What I'm trying to get at is that doing it in 1st gear is not considered "heavy" load. Doing it in 3rd gear is heavier load and doing it in 5th or 6th is very heavy load. Does it do it more strongly the higher the gear? If it's detonation, it should. If it doesn't, it may not be.
MAP sensor sits on top of the throttle body.

[whitefun]

i am on my way out for a drive now and will monitor when i hear the noise. i recall only hearing it in the 3/4/5/ range.(6th has not been driven the same way)..i will post the results when i have tried your suggestions. thanks for the help.

[whitefun]

this is the latest. i have refreshed the map connection,added 1/2 a tank of fuel from a new source,added fuel injector cleaner. no change to this point.the 30 mile drive i took showed that the noise is only evident in gears 4,5,6. when accelerating before vtec but under heavy throttle.
perhaps i don't understand the role of the knock sensor completely. the noise is almost certainly the pinging one would hear climbing an incline in a car with the timing off or bad fuel etc... when i hear the noise it does only last for a brief moment or two. could the sensor be working properly and retarding the timing and i just have a sensitive ear or would the sensor detect detonation and fix it before i hear it?
i have a bottle of octane booster that i can try if needed. also will check the plugs for inconsistent appearance. please comment on the role of the knock sensor before i proceed. thanks phil

[repiv]

The knock sensor should normally detect detonation and the ECU correct it before the average person can hear or feel it. It is possible that the sensor may be just out of spec but not enough to throw a CEL.
It is also possible that this noise is not originating from the engine. Accelerative noises under load can also be related to the CV joints and this would appear to come from under and behind you. Do you associate this noise with any "feel"?

[whitefun]

no sir, i don't associate the noise with any tactile sensation. i would almost bet the farm that the noise is coming from the front end but i have been wrong plenty of times before. do you think i should add the octane booster and see if that eleminates (narrows down)the noise? to answer your earlier question about performance mods i have fujita f5 cai, resonator delete, magnaflow mufflers, 4.77 gears,shift beeper.
also on the way home today the car made a noise from the exhaust that i hesitate to call a back fire but more of a loud poot.. i had forgotten because it does it so infrequently but this noise has happened since i bought the car with 155 miles. usually when just starting out for the day. may or may not have anything to do with the current question but i thought i should mention it anyway. current mileage is 9100. thanks phil

[repiv]

to answer your earlier question about performance mods i have fujita f5 cai, resonator delete, magnaflow mufflers, 4.77 gears,shift beeper.
also on the way home today the car made a noise from the exhaust that i hesitate to call a back fire but more of a loud poot.. i had forgotten because it does it so infrequently but this noise has happened since i bought the car with 155 miles. usually when just starting out for the day. may or may not have anything to do with the current question but i thought i should mention it anyway. current mileage is 9100. thanks phil

Even with the stock exhaust, the S2000 has a very free flowing exhaust, with much less back pressure than most other cars. With the Magnaflows, I suspect your back pressure may be even less. I have followed an S with Magnaflows in one of the many drives I've been on and I can tell you that this type of exhaust sound is quite typical. It may or may not be related to your "detonation" situation. At this point, so long as the car other wise runs "OK", I would consider obtaining a gragh of the air/fuel throughout the rpm band. This can be done with an A/F gauge or by going to a dyno. To re-iterate, "reading" your plugs may shed some light on what's going on. You "might" be leaning out with the mods you have.

[whitefun]

i will update after i have tried your recommendations. thanks phil

[griffon]

This is sounding more like preignition rather than detonation. This can result from a "hotspot" in the cylinder/head area. Try using a "Top Tier" gasoline such as Shell or Conoco and see if the problem doesn't go away in a few tankfulls.

[whitefun]

today i added a container of octane booster(the good stuff) and drove about fifteen to twenty miles. after the first five miles i tested by going to full throttle in 6th gear from 3000 to 5500 rpm.(4 or 5 times). so far so good as i couldn't replicate the noise. i will try the same thing in the am under various conditions and see what happens.dave,if as you suspect the a/f ratio is lean due to my mods i don't mind adding booster every tank as i had to use it with the cheap 91 octane in my previous car. do you see any negative ramifications from long term use of octane booster with the s2k? i never had any issues with the blown mustang but i know the s2k is a much more advanced engine in both design and components and would appreciate your perspective. i will still pull the plugs and hope for light tan all around when i have a little more free time. thanks phil

[repiv]

If your problem is due to a lean condition, octane boost is not a permanent solution. It may only mediate a stop gap measure. Continue to monitor the situation and see if the condition is no longer evident. Check those plugs and still consider measuring the A/F. Your ultimate solution may be a stand alone ECU and a proper dyno tune.

Perhaps try your next fill up with some better fuel as Griffon suggested, maybe even a higher octane one like the Chevron 94.

[Jerry C.]

I have a 2001 with 53k on her. I am experiencing similar noises. Not all the time, but getting more frequent. Always between 4-5k rpm's. Primarily 2, 3, 4 th gear. I think 5 also, but by that time the "light" knocking is hard to detect due to speed at which I am traveling at that point. I run top tier 93 octane, have tried fuel injector cleaner, engine cleaner, and tried to "blow it out" by driving harder. I have had her since last June and I think it's a new problem, I run Mobil one and it's fresh. I read the comment about plugs but I wonder why I don't hear something at other RPM's. I do hear well but I think there is a problem. The Honda Dealer heard the noise when I took him out for a test drive. He suggested, better gas, engine treatment and if that doesn't work they have a new product and process where they open it up and "blow out the carbon", he says it's real messy. Anyway, I would appreciate any insight. By the way, I am not a "do it your selfer". It's been 20 years since I changes plugs, air filters, gas filters, or oil changes. I do not drive her hard, I have only been to 6,900 rpm's. Engine is always warm and have experienced this in a range of air temperatures.

[repiv]

I have a 2001 with 53k on her. I am experiencing similar noises. Not all the time, but getting more frequent. Always between 4-5k rpm's. Primarily 2, 3, 4 th gear. I think 5 also, but by that time the "light" knocking is hard to detect due to speed at which I am traveling at that point. I run top tier 93 octane, have tried fuel injector cleaner, engine cleaner, and tried to "blow it out" by driving harder. I have had her since last June and I think it's a new problem, I run Mobil one and it's fresh. I read the comment about plugs but I wonder why I don't hear something at other RPM's. I do hear well but I think there is a problem. The Honda Dealer heard the noise when I took him out for a test drive. He suggested, better gas, engine treatment and if that doesn't work they have a new product and process where they open it up and "blow out the carbon", he says it's real messy. Anyway, I would appreciate any insight. By the way, I am not a "do it your selfer". It's been 20 years since I changes plugs, air filters, gas filters, or oil changes. I do not drive her hard, I have only been to 6,900 rpm's. Engine is always warm and have experienced this in a range of air temperatures.

You need to state what kind of load the car is under when this happens. Under hard load, this may not be a serious problem. Under low load, it might be of some concern as it would not be a situation that would produce such a sound. Before concluding that your noise is the same as what's being talked about here, you should have a mechanically inclined person listen to it.

[Jerry C.]

I would describe it as a medium load. Not standing on it, but not just cruising. I do not believe that the noise is normal. I'm trying to get involved w/SCK locally to see someone experienced can take a "hear" at it. Thanks for the input.