Pinging during WOT

[psyctrance]

Hi All,

 

Looking for some help again since my most recent fix didn't fix the problem.

 

Bike: '97 1100RT with 91K

 

Symptoms: Pinging at WOT during all RPM and load ranges.

(During all other throttle openings the bike runs perfect, and transitions smoothly)

 

Initial thoughts: Fuel delivery or back pressure (air flow) problem

 

Based on the symptoms I figured that fuel deliver or air flow had to be the issue since if I slowly increased the throttle then the pinging would only manifest itself at high rpm near red line. So, this last weekend I changed the fuel filter as I did not know when it was last done. I also replace the pump pre-filter at the same time. Due to the weather I wasn't able to ride it imediately, but I did notice that it started easier and idled more smoothly when cold. Now that we finally have a dry day I rode to work and discovered that the problem has not gone away. Anyone have any ideas?

 

Other possible things in my mind are as follows:

*Remaining fuel system components: pump, regulator, injectors.

*Carbon build up in the cylinders: might try misiting some water into the intake while it's running (steam clean so to speak)

*Clogged CAT or exhaust: would cause increased back pressure and generally only be noticible at high throttle openings.

*burn exhaust valves: hope this isn't the case.

 

Other info: The bike has newer plugs, and received a valve adjustment and TB synce about 8k ago. After which the bike ran great until about 3k ago.

 

I look forward to hearing your input, and thank you for your time.

 

Cheers,

David

[Firefight911]

Perhaps you have already ruled this one out, or not. The pinging you are hearing sounds as if detonation, or pre-ignition, is occurring.

 

This is typically caused by running a low octane fuel. Lower octane fuels run cooler and burn (ignite) quicker than a higher octane counter part. The higher octane fuel will burn slower and hotter, allowing for a proper burn timing relative to piston location.

 

Side note: The slower, hotter burn is what gives higher octane fuels "more power." This is due to the increased pressure generated from the combustion of the fuel/air mix.

 

The other obvious issue is that of timing. Unfamiliar with your bike and the ability to alter/check timing so I can't help here.

 

Just as in automotive applications where knock sensors are present, the timing is retarded (not a learning disability!!) in the presence of knock (detonation).

 

This puts the ignition closer to top dead center and therefore, alters the timing of when the fuel/air mixture burns and expands to create the pressure that causes the piston to go down on the power stroke.

 

I would focus on these two areas. Go simple first. Get the tank completely run down and fill with high quality, high octane fuel and repeat your ping scenario.

 

Another techy familiar with your bike can shed light on your options for timing control/adjustment.

 

Good Luck!!

[psyctrance]

Thanks for the response, I guess I should have included the type of gas I use. In CA all we get is 91 octane, typically Chevron, and that's all I've ever used. Prior to the filter change I used Redline's injector cleaner/ octane booster. This had no positive effect. I don't think the issue is the quality of the gas.

[peterbulgar]

Could be several things, but at 91K miles my guess would be carbon buildup on the heads and pistons. A compression test that shows abnormally high compression would indicate carbon buildup, although a normal reading would not rule it out. (At 91K miles your rings and valves may not be sealing that well, which would compensate for reduced combustion chamber volume due to carbon buildup.) An experienced tech should be able to peer into the combustion chamber with a small mirror and a strong light and evaluate what he sees. Give Cal BMW a call and ask if someone can check for carbon without removing the head.

 

Finally, winter gas in CA contains a higher level of oxygenates than the summer formulation - this may be contributing to the pinging.

 

FWIF my '04 with 24K miles pings occasionally if I whack open the throttle at 4K RPM in 6th. NTF at my recent 24K service, which was performed by a dealer.

peter '73 R75/5, '04 R1150RA

[Guest]

It's probably carbon build-up. I would inject water into each throttle body while the bike is runing and engine hot. Should should clean you up for a while.

 

This procedure is easy to do. Pull the vacumm hose off the throttle body vacumm port. Take a 2' piece of hose and connect it to the nipple. Put the other end of the hose in a pint of water and have at it. Repeat on the other side.

[psyctrance]

Thanks! I thought that might be the case. Unfortunately the weather is supposed to be crap this weekend so I can do the work but won't be able to test until we get a clear day again. Will keep you posted.

 

Cheers,

David

[Reddog99]

Definitely carbon build-up. My '97 started it slowly at about 70k and slowly got worse. You'll hear a lot of remedies (water, gas additives, run-the-piss-out-of-it, etc, etc.), but the only SURE cure is to pull the heads and scrape the carbon off.

 

Pat

[beemerman2k]

A BMW mechanic told me my 2000 RT with 88K has carbon buildup and gave me some gasoline additive to pour in my tank. Cleared the problem instantly. I'll get the name of the additive and post it here.

[DEF]

Hi All,

 

Looking for some help again since my most recent fix didn't fix the problem.

 

Bike: '97 1100RT with 91K

 

Symptoms: Pinging at WOT during all RPM and load ranges.

(During all other throttle openings the bike runs perfect, and transitions smoothly)

 

Initial thoughts: Fuel delivery or back pressure (air flow) problem

 

Based on the symptoms I figured that fuel deliver or air flow had to be the issue since if I slowly increased the throttle then the pinging would only manifest itself at high rpm near red line. So, this last weekend I changed the fuel filter as I did not know when it was last done. I also replace the pump pre-filter at the same time. Due to the weather I wasn't able to ride it imediately, but I did notice that it started easier and idled more smoothly when cold. Now that we finally have a dry day I rode to work and discovered that the problem has not gone away. Anyone have any ideas?

 

Other possible things in my mind are as follows:

*Remaining fuel system components: pump, regulator, injectors.

*Carbon build up in the cylinders: might try misiting some water into the intake while it's running (steam clean so to speak)

*Clogged CAT or exhaust: would cause increased back pressure and generally only be noticible at high throttle openings.

*burn exhaust valves: hope this isn't the case.

 

Other info: The bike has newer plugs, and received a valve adjustment and TB synce about 8k ago. After which the bike ran great until about 3k ago.

 

I look forward to hearing your input, and thank you for your time.

 

Cheers,

David

 

Your suggestion of “water injection” while sound for older technologies and fuels, likely will not help much with today’s unleaded fuels. In days past, water (should be mixed with a bit of alcohol) aspirated into the engine would partially lodge in the somewhat porous lead deposits and break them loose due to the temperature shock and the water flashing into steam at combustion.

 

Today’s deposits are likely the result of oiling of the upper cylinder. However, this may not require teardown and the old fashioned scraping of the combustion chambers (used to do this on my 60s vintage Brit bikes….called for in the manual).

 

There are aftermarket preparations that will dislodge carbon deposits by mixing with fuel. Others require administering them through the intake track or spark plug port. And the good ones do work.

 

Also, your detonation may be the result of somewhat advanced timing. Did the servicing folks change ignition timing?

 

Did they change your oil? If so, did they change brands or grades?

 

You indicate this came on rather quickly. Has the engine song changed at all (other than the detonation rattle)?

 

As for valves, do a compression check. Also a compression leak down test will confirm ring to cylinder wall condition.

 

Also, check fuel pressure…the fuel system pressure is somewhat critical.

 

My ’01 GS detonates somewhat as I approach and transition through 4200 RPM in 3rd and higher gears. I notice it particularly when the summer heat comes on here in Houston. But, the detonation disappears after about 50 miles of riding at constant load, high gear at highway speeds. I attribute this to my commuting and the doggy RPMs I ride at during the week as well as sea level barometric pressure (more air, higher BMEP). It is deposits, likely on exhaust valves which are hot spots that cause my detonation.

 

Oh yes, I also use Autolite plugs (single ground electrode style). I also run one heat range cooler plug in summer months. And by the way, check those spark plugs. They will tell you what is going on in the combustion chambers, especially if there is some upper cylinder oiling occurring.

 

Finally, check you oil consumption, has the bike begun using any oil? If so, it could be rings or valve guides…lots of advice….no real solutions…….sorry.

[DEF]

A BMW mechanic told me my 2000 RT with 88K has carbon buildup and gave me some gasoline additive to pour in my tank. Cleared the problem instantly. I'll get the name of the additive and post it here.

 

 

Notice your avatar says dual plugs..no surge.

 

I say, single plug..no surge......my '01 boxer is smooooooooooth and never surges...of course, yours doesn't either.

 

I agree regarding the fuel additive...I believe the carbon chasers use an amine compound to rid the combustion chambers of carbon...and they DO work (the good ones, that is).

[EricJRW]

What's WOT?

 

Tried a few searches, can't figure it out.

 

Thanks and sorry for the interuption.

[Les is more]

Wide open throttle

[EricJRW]

Thanks... I figured something to do with acceleration, but wasn't quite sure what.

[RFW]

This is typically caused by running a low octane fuel. Lower octane fuels run cooler and burn (ignite) quicker than a higher octane counter part. The higher octane fuel will burn slower and hotter, allowing for a proper burn timing relative to piston location.

With respect, this is rubbish. I think you misunderstand the basic causes of detonation in an internal combustion engine.

 

The speed of burning, has nothing to do with a fuel's tendency to transition from normal progressive burning mode, to detonation mode. Further, higher octane fuels do not "burn cooler" than lower octane fuels.

 

Just as a stick of dynamite can burn quietly and quite safely if you light it with a match, yet under other circunstances (exposure to shock) it detonates, gasoline in an engine does the same thing and under the right circumstances can suddenly switch from a smooth burn to detonation.

 

A higher octane fuel is harder to provoke to transition from normal linear burning mode, to detonation mode where the flame front speed suddenly increases by several orders of magnitude (and the entire cylinder contents ignire at nearly the same instant).

 

Ability to resist detonation is related to chemical properties of the fuel itself, not how "cool" it burns, or how "slowly" it burns, when in the normal burning mode.

 

Higher octane fuels do tend to have a slightly slower flame front burning speed, but this difference is insignificant, and certainly is not the reason for their higher octane rating; it is a side effect of it.

 

Bob.

[Firefight911]

Bob,

 

The speed of burning has everything to do with a fuel's tendency to transition from normal progressive burning to detonation mode. I think that I could probably have used a better word or a deeper explanation. Or, I may have combined two separate actions. One being ignition of the fuel/air charge and the other being the burning of the fuel/air charge after igntion.

 

By speed, I refer to how quick it ignites and how long the flame front exists after ignition.

 

Higher octane fuels have a lower volatility. This means, simply put, they are more stable and can withstand more variables to the ideal. They can withstand higher heat, higher compression, and contaminated combustion chambers (carbon build up that can cause "hot spots" prior to igniting. These "hot spots" can act as a spark plug igniting the fuel/air mix out of time or in the wrong place/wrong direction within the combustion chamber. The "hot spot" is cooler than the spark plug but hotter than the combustion threshold of the fuel/air charge.

 

This higher octane also slows the speed of the flame front spread that is created after ignition. This slower burn would be related directly to "speed." Or would "quickness" be better suited here?

 

As this discussion relates to cooler burn or hotter burn I offer this, again simple, explanation.

 

You agree that higher octane fuels have a slower (related to speed) flame spread. This in turn causes higher heat being generated in the combustion chamber. This in turn causes a higher expansion of the gases in said combustion chamber. (Just envision a hot air balloon - more heat, more pressure. More pressure, more potential for work (power)) Or, try passing your hand through a flame, first quickly. Now repeat, only go slower. You felt more heat when you passed throught the flame slower.

 

Is this insignificant, as you say. Taken by itself, yes. But, cumulatively over time it adds up. This taken with timing to initiate the burn along with RPM and design of the engine mechanicals (valves, combustion chamber design, overlap, intake design, etc.) all come together to make a model of power potential.

 

If you will note, I stated lower octane fuels burn (ignite) quicker than a higher octane counterpart. If you control the burn/ignition "speed" you can eliminate the poetential for detonation. All other things being correct (mechanical timing, etc.)

 

Detonation is, potetnially, more than just a sudden increase in flame spread. It is also caused by the imporper source point of the flame front.

 

That "ping" you hear. That is the concussive sound waves of the flame front bouncing against the cylinder walls/piston due to detonation. Over time, this will kill an engine.

 

Sorry if I was unclear.

[RFW]

Regarding your "interesting" ideas on detonation, and how it is influenced by higher or octane fuels, I think you need to take a crash course in thermodynamics. Your comments have little to do with "science", although to be fair, it is difficult for a layman to understand since this is not only a complex subject that people have written entire PhD theses on, it seems counter to everyday common sense as well. As a result, you have managed to violate several basic thermodynamic principles as well as some basic chemical ones too.

 

You stated that a higher ocatne fuel is less "volatile", and burns "slower" which somehow accounts for lower tendency to detonate. First of all, you apparently misunderstand the definition of "volatility". Volatility is simply a measure of the rate at which a liquid evaporates. Nothing more. It has nothing at all to do with combustion. To illustrate, Freon is HIGHLY volatile, yet completely incombustible.

 

As a simple example that flies in the face of your reasoning, ordinary benzene (a ring structure of 6 carbon and 6 hydrogen atoms) is far more volatile than gasoline, and yet has an octane rating well above 110. In addition, the speed of the flame front during normal burning of benzene, is significantly faster than in gasoline. Yet is resists detonation so well, that it was once considered as an additive to gasoline in place of Tetraethyl Lead (until the EPA got its knickers in a knot, since the stuff is mildly carcenogenic!).

 

I'm sorry but your layman's explanation of this complex subject is full of fundamental misconceptions.

 

Bob.

[Joe Frickin' Friday]

The speed of burning has everything to do with a fuel's tendency to transition from normal progressive burning to detonation mode.

 

The overall rapidity with which the contents of a combustion chamber are transformed from reactants to products is indeed an important factor in avoiding detonation. If one wishes to avoid detonation, the reactants should be burned rapidly so that the reaction is complete before it can transition to detonation; this is a big reason why San Jose BMW’s dual-spark mod helps quell knock in an engine. The laminar burning velocity (LBV) of the fuel is only one factor in that overall rapidity (others include turbulence, mixture ratio/homogeneity, pressure and temperature); if high-octane fuels did indeed have a lower LBV (and if LBV were a factor in their knock resistance), that would run counter to this understanding. Note also that high-octane gasoline nowadays is frequently produced by adding alcohol, which would raise octane # while also raising LBV.

 

As it turns out, there is no particular correlation between LBV and octane number:

In this plot (from Heywood’s “Internal Combustion Engine Fundamentals”), iso-octane (octane # = 100, by definition) is seen to have a lower LBV than “gasoline”, but methanol (octane # also pretty close to 100) has a far higher LBV than either gasoline or iso-octane.

 

 

Higher octane fuels have a lower volatility. This means, simply put, they are more stable and can withstand more variables to the ideal.

 

In discussing fuels/chemistry, volatility describes how readily the fuel evaporates; it’s not a good description of the fuel’s resistance to autoignition. As an example, diesel fuel is not very volatile – it evaporates much less readily than gasoline – but you would not want to a gasoline engine on it because it would resist autoignition poorly.

 

They can withstand higher heat, higher compression, and contaminated combustion chambers (carbon build up that can cause "hot spots" prior to igniting. These "hot spots" can act as a spark plug igniting the fuel/air mix out of time or in the wrong place/wrong direction within the combustion chamber. The "hot spot" is cooler than the spark plug but hotter than the combustion threshold of the fuel/air charge.

 

Surface/hot-spot ignition can result in knock, but knock can happen without hot-spot ignition. Knock/Detonation is more than just surface ignition; it is the spontaneous, extremely rapid reaction of a large portion of mixture ahead of the advancing flame front, resulting in (or augmenting) the production of supersonic shock waves that reverberate throughout the cylinder. Knock/detonation can also happen in the absence of hot spots, through a combination of high temperatures, high compression ratios and excessive spark advance.

 

This higher octane also slows the speed of the flame front spread that is created after ignition. This slower burn would be related directly to "speed." Or would "quickness" be better suited here?

 

Again, octane number and LBV do not correlate; see above.

 

You agree that higher octane fuels have a slower (related to speed) flame spread. This in turn causes higher heat being generated in the combustion chamber. This in turn causes a higher expansion of the gases in said combustion chamber. (Just envision a hot air balloon - more heat, more pressure. More pressure, more potential for work (power)) Or, try passing your hand through a flame, first quickly. Now repeat, only go slower. You felt more heat when you passed throught the flame slower.

 

Even if high octane correlated with higher reaction rate, it does not follow that the amount of energy released is any different. As it happens, iso-octane and ~92-octane# gasoline have very nearly the same heating value. And if I compare ~92-octane gasoline with methanol (octane # = ~100), I find that gasoline has over twice the heating value of methanol.

 

High-octane fuels resist detonation through a couple of mechanisms. One is a higher autoignition temperature, which is kind of self evident: you can get the fuel hotter (either by more advanced spark, higher compression ratio, or higher operating/ambient temps) before it detonates. The other one is a thing called ignition delay: after exceeding the autoignition temperature, the mixture persists for a short-but-significant period of time before the reaction really gets under way. Check out these plots from Heywood:

 

 

These are pressure traces taken from a rapid-compression machine. Each tick mark on the horizontal axis represents 1 millisecond. So the machine takes mass of fuel-air mixture, and in the first two milliseconds compresses it to high pressure and temperature, and holds it there. The two plots are supposed to demonstrate the details of early autoignition chemistry at differing pressures/temperatures, but note that after compression in both cases there is a period of 4-5 milliseconds before the mixture finally releases the vast majority of its energy.

 

So in addition to lowering temperatures and/or compression ratio, and eliminating hot spots (carbon deposits), the rapid-compression machine points to another way of getting around knock: finish normal, deflagrative combustion as quickly as possible, either by higher turbulence (better port design or higher RPM), or by smaller combustion chambers (like an inline 4 instead of a boxer), or by a multi-spark design (give San Jose BMW a call).

 

To the OP:

As noted, it sounds like your knock came on pretty suddenly. What happened 3K miles ago, and what have you noticed as being different since then?

 

-warmer weather?

-higher/lower fuel consumption?

-higher oil consumption? (oil will form deposits which can cause surface ignition, but the oil itself is also low-octane; get enough of it into the combustion chamber, and it’ll exacerbate knock even before deposits have truly built up.)

-higher oil temperature? What’s the RID saying lately?

 

My engine started pinging a bit around 35K miles. At 40K, I installed GS tubes, and it started knocking BAD (at least by my ear). After several different fuel additives didn’t help I took the heads off and scraped things out. It was great for about 10-15K miles, then it came back. I took one head/cylinder off, and measured everything: piston, ring gaps, bore, etc. All were within spec, compression was fine, I wasn’t consuming a ton of oil, and most important of all – there was no evidence of detonation-related damage. With no damage, I decided the knock didn’t much matter. I put it back together, and despite lots of WOT operation, the engine is still healthy at 110K miles. In fact, it’s not as bad as it was when I first put the GS tubes in, as the knock/hi-temps help to clear out those deposits.

 

If you can establish that your engine is healthy despite the knock, get some ear plugs and just ride it. Beat it like a rented mule. Assuming your engine is healthy, if you regularly engage in WOT operation, the knock should diminish over time, even if it doesn’t go away completely.

[psyctrance]

Hi Everyone,

 

Thanks for all of the input. I've discovered that it is very difficult to get water vapor into the engine via the air box, and didn't feel like taking off the tupperware to get to the thottle bodies this weekend. I might give this a try again this weekend since the weather is supposed to be nicer.

 

I'd love to know what gasoline additive you'd suggest to resolve this problem as I'd like to avoide pulling the heads.

 

The plugs check out, and there is no indication I have a problem with compressions which would warrant a check or leak down test. I could go out and purchase a guage, but don't really see the point. If the problem was compression related I would notice a significant decrease in power throughout the power band, which I haven't. Nor have I noticed increased oil consumption or smoke from the exhaust. I do my own maintenance so timing hasn't been changed, and the bike ran fine when I bought it with 80k on the clock last year. This seems to have been a gradual problem that began after a high altitude (7-9k ft) trip mid last year in the Sierras. During the trip I did notice a higher than normal oil consumption but not since. I was also using BMW's dino oil at the time, and have since switched to a Belray semi-synthetic.

 

At this point everything points to a carbon buildup, just need to know the best method to deal with it.

 

Best Regards,

David

[Joe Frickin' Friday]

I'd love to know what gasoline additive you'd suggest to resolve this problem as I'd like to avoide pulling the heads.

 

A lot of folks swear by Techron, but it didn't touch my problem. I used BG Products' "44K". Made a difference, although for me it was temporary. Give it a shot.

[Firefight911]

And I stand before you, humble.

 

Thank you for the lessons! No, this is not a sarcastic comment but a genuine exposing of the soft under belly.

 

I shall learn more from this! And, have a chat with them that edumekated me way back when!!

 

Tanks!

[Joe Frickin' Friday]

Thank you for the lessons! No, this is not a sarcastic comment but a genuine exposing of the soft under belly.

 

I shall learn more from this! And, have a chat with them that edumekated me way back when!!

 

Glad you found it useful. I'm occasionally lacking in practical knowledge, but when it comes to theory, I'm grossly over-educated (plus I do engine research for a living), and I have reference books in my possession that I can browse through (and occasionally copy/scan/post). RFW's right: engines and hydrocarbon combustion are ridiculously complex topics, eminently suitable for Ph.D. theses. I went to school with a guy whose thesis was all about laser-induced fluorescence of the CH- radical that exists very briefly in a hydrocarbon flame front. The idea is that if you blast the combustion chamber with a particular wavelength of laser light, the CH- radical will fluoresce for a very short time and give you a snapshot of the location of the flame, allowing you to observe the details of flame front structure. He wasn't even studying flames in an engine, his whole thing was just developing this technique for someone else to apply to engine research. Anyway, if you're going to study such an esoteric aspect of combustion, you gotta know all of the surrounding issues. And he does; he understands hydrocarbon combustion to a ludicrous level of detail (short, short summary: there are a bazillion intermediate reactions that take you from fuel-air mixture to CO2+H2O). I still occasionally ask him questions about combustion, and I typically walk away with my head spinning.

[greer]

Beemerman--Did you ever get the name of the additive? Thanks!

 

Sarah

[RFW]

And I stand before you, humble.

No need for that! One of the most important objects of this forum is learning! All of us have at diffeent times found that ideas we thought were correct, needed some tweaking!

 

Bob.

[Firefight911]

Alright then!! I stand before you, tweaked!!

[Pilgrim]

Mitch mentioned - ". . . In this plot (from Heywood’s “Internal Combustion Engine Fundamentals”),. . ."

 

If you are at all interested in what your engine may be doing, I recommend that you place this book on the back of your toilet for casual perusal while clearing the mind.

 

I am innumerate. Anything beyond balancing a checkbook is very nearly more than I can handle.

 

But during a bad spell with a Harley engine I was building, when detonation was just eating my lunch and very nearly consuming pistons, too, this book helped me find out stuff I needed to know. It also pointed out stuff I wish I hadn't discovered, like that I had built detonation into the engine the way I shaped the combustion chamber and ports with a die grinder.

 

My copy is 25 years old, and no doubt a great deal more has been discovered since then. However, the fundamentals are unaltered, mostly.

 

You may want a newer one,but go find one somewhere.

Pilgrim

[beemerman2k]

Wow, deep discussion.

 

OK, I'm finally getting back with the name of that fuel additive a BMW mechanic turned me on to. Worked like a charm on my bike. I added one dosage 2 tanks ago and I still have not encountered pinging again.

 

Anyhow, it's called, "Red Line" brand "Complete Fuel System Cleaner". Hope this helps!

 

Now I'll go back and read this thread in its entirity.

[psyctrance]

I have some of the Red Line stuff. Looks like the weather is going to be nice so I'll be able to give it a try and take a long ride at the same time. If it doesn't work I'll try the Chevron stuff. I hope this sorts it out since I'm planning a coast to coast run and back this June.

 

Thanks again everyone!

[EffBee]

Beemerman--Did you ever get the name of the additive? Thanks!

 

Sarah

 

Try MotorVac. We use it at the dealership. Works wonders. Follow the directions precisely.

[smiller]

My engine started pinging a bit around 35K miles. At 40K, I installed GS tubes, and it started knocking BAD (at least by my ear). After several different fuel additives didn’t help I took the heads off and scraped things out. It was great for about 10-15K miles, then it came back. I took one head/cylinder off, and measured everything: piston, ring gaps, bore, etc. All were within spec, compression was fine, I wasn’t consuming a ton of oil, and most important of all – there was no evidence of detonation-related damage. With no damage, I decided the knock didn’t much matter. I put it back together, and despite lots of WOT operation, the engine is still healthy at 110K miles. In fact, it’s not as bad as it was when I first put the GS tubes in, as the knock/hi-temps help to clear out those deposits.

 

If you can establish that your engine is healthy despite the knock, get some ear plugs and just ride it. Beat it like a rented mule. Assuming your engine is healthy, if you regularly engage in WOT operation, the knock should diminish over time, even if it doesn’t go away completely.

Also note, as per Mitch's experience and general fact, that some pinging in an engine is not necessarily harmful. If it sounds like the cylinders are full of marbles whenever you open the throttle then the problem should definitely be addressed, but light/occasional pinging is not necessarily anything to worry about.

[Fireant]

You may also want to try a product called 'Sea Foam' (purchased at Auto Zone). I've used it successfully in both automotive and motorcycle applications. Had a significant problem with oil in the intake (through PCV) in a 3.8L V-6 (2000 Mustang) which resulted in SEVERE pinging/detonation at light to moderate throttle. Followed directions on the can (unusual for me): added proportioned quantity through a vacuum line to the intake tract with engine running: the resulting carbon exiting the tailpipe was impressive. Added balance of container to the fuel tank. 3.8L now runs BETTER than new, even with 90K miles.

[DEF]

Hi Everyone,

 

Thanks for all of the input. I've discovered that it is very difficult to get water vapor into the engine via the air box, and didn't feel like taking off the tupperware to get to the thottle bodies this weekend. I might give this a try again this weekend since the weather is supposed to be nicer.

 

I'd love to know what gasoline additive you'd suggest to resolve this problem as I'd like to avoide pulling the heads.

 

The plugs check out, and there is no indication I have a problem with compressions which would warrant a check or leak down test. I could go out and purchase a guage, but don't really see the point. If the problem was compression related I would notice a significant decrease in power throughout the power band, which I haven't. Nor have I noticed increased oil consumption or smoke from the exhaust. I do my own maintenance so timing hasn't been changed, and the bike ran fine when I bought it with 80k on the clock last year. This seems to have been a gradual problem that began after a high altitude (7-9k ft) trip mid last year in the Sierras. During the trip I did notice a higher than normal oil consumption but not since. I was also using BMW's dino oil at the time, and have since switched to a Belray semi-synthetic.

 

At this point everything points to a carbon buildup, just need to know the best method to deal with it.

 

Best Regards,

David

 

Carbon buildup comes a result of the stuff that gets into the combustion chamber and is ignited. If compression is low, the stuff doesn’t combust completely enough and you get carbon deposits on everything, hence the need for a compression check.

 

If the compressions checks out, valves may be the culprit, hence a leak down test. Oil is usually the stuff that leaves the most deposits. Carbon can be removed almost completely with combustion chamber cleaners. Techron will help but is not aggressive enough. While I cannot recommend a brand name, there are treatments available that are formulated specifically for removal of carbon deposits. A BMW boxer with 90K miles should not be full of carbon. You need to look for the source of the carbon if, in fact, it is carbon that is causing your problem. One more suggestion, you might try to borrow a small scope-camera and peek inside the combustion chambers and view them first hand. If carbon is excessive, you’ll see it.

 

Products that are used for combustion chamber decarboning are available from Mopar and Master Blaster. I have not used them but the good ones do work.

 

Finally, you might want to change oil brands just to confirm your problem is not oil related.

[Reddog99]

A BMW boxer with 90K miles should not be full of carbon. You need to look for the source of the carbon if, in fact, it is carbon that is causing your problem....

If you believe a 90k boxer shouldn't have too much carbon, then you haven't owned too many BMW boxers.

 

Pat

[psyctrance]

Hi Everyone,

 

The Redline stuff seemed to help, along with the long ride. It only pings lightly now in top gear at WOT, aka high load. I think the root cause of the problem is my short daily trips to work. Any amount of oil that gets into the cylinders doesn't get a chance to fully burn away. That combined with the crap weather and lack of recent long trips seems to have built up. I'll do another treatment this week, and see if it completely resolves the issue.

 

Another related question is when a valve job should be considered? This may turn into my project bike as I'm thinking of getting another cheap bike for commuting and shorter trips, such as the Kawasaki Z750S. (One can never have too many motorcycles ) Also thinking of doing the dual plug conversion and larger intake vales offered through San Jose BMW. Anyone had experience with these, or offer a cost estimate on just the valve job?

 

Thanks again!