Question about combustion chamber deposits and cle

[youdontwannaknow]

Hi,
I have a '01 Acura MDX that calls for premium fuel, has a knock sensor and the ability to retard timing in case of detonation.
It has 64k miles on it right now. I am the second owner so I don't know what the first owner used for fuel and oil but I can tell you that after 10k miles under my ownership its a whole different beast now.

Recently I have been monitoring how the timing behaves on it with different octane fuels (using an obd2 scanner).
I was surprised to find that even with 92 or 93 octane fuel the timing did retard consistently under load and acceleration. Do note that I have never experienced any audible pinging even with 87 octane fuel.

I once did a compression test and the results came out at about 235psi, all 6 cylinders very close, which I feel is on the higher side. Then I did a seafoam treatment (IM vac line method) and noticed a slight drop in the compression - 210psi this time. looks like some carbon did get removed! However, I am not quite satisfied with the cleanup just because of the way the vac line is positioned in the IM I think maybe it did not clean up all cylinders pretty good.
Also I was a little cautious and conservative with the amnout of seafoam going in as this was my first time doing it so that might have been a factor too.

Long story short, I think the timing retard I am getting even with high octane fuel is because the combustion chambers still have carbon and they could use some more help.
This time I am thinking about doing the piston soak method.

Questions -

Will the piston soak remove the carbon from the walls and top end also or just the piston head ?

Typically what causes excessive carbon ? I guess rich mixtures ? Incomplete combustion (sparkplugs ?) Type of oil ? Does timing retard have anything to do with it ?

 

[ziggy]

Well, i se seafoma once a year, through my intake, on a 1995 plmyouth SOHC neon. Seafoam is VEry good when used with oil, 1 1/2 oz. per quart, for cleaning up the pistons, engine internals ect. SO is Rislone quart sized enigne treatment, and ive seen VERY good results with NAPA's MACS enigine flush. Ato rx is a safe slow way as well. However, i alwasy felt seafoam is a mild detergent at most, for hte intake. Ide try Berryman B12, 3M intake cleaner, as solvents. YOu wanna REALLY clean up those combustion chambers? Use distilled water. Yes, distilled water WILL steam balst eveything to shiny shine Just use abut 12 oz. max!!! let your intake suck it up, and watch your muffler, if its dirty enough, wiht he water, you'll see black liquid coming outa the muffler BUt, ide also recommend changing out your spark plugs, after usin seafoam or any other other combustion chamber cleaner, via the intake/throttle. becuase carb0on cna stay ro get gunked up on the spark plugs, and wont come off, unles you remove al of them, and file them carefully waiste of time, just change em out. All cars run rich at start up. Uisng an octane greater that required, is not good, jsut drains your wallet... its an attempt to baind aid the problem. Even hihger otanes, only have so much detergency. when you clean your combustion chamber out, in my opinion, you ned ot take yor time, use the whole day almost, so what your pouring it, sets an soakd for a good amount of time. Change your spark plug wires as well, when its time. Type of oil has nothgn to really do with that, its how you drive moreso ide say. Sitting in traffic, for example allows more deposits and carbont to build up, because its not good for oil like that. Higher octane burns slower. So if your car is supposed to use 87, and yuor using 93, lets say, the 93 isnt burning right, so to speak. in fact, som of the unurned fuel is running down your pistons. Not much though.
try the methods above, and do it onvce a year. Should be good to go

 

[Gary Allan]

 

[JackFish]

Lucas UCL might be worth a try.
Run it through a few tankfuls and see if it makes a difference.

The picture on the little bottle very clearly has before and after drawings showing the effects on combustion chamber and valve deposits!

 

[Mokanic]

Would you consider the possibility that the PCM is doing exactly as it should by retarding timing under acceleration? Most all ECT controlled transmissions will allow timing to advance to a preset value and then the PCM will retard timing under throttle to soften transmission shifts as determined by throttle position and air-flow through the AFM.
The MDX is not known to be a carbon beast especially those that are driven in a spirited manner.
Many manufacterers retard ignition timing to soften auto trans. shifts instead of just relying on manipulating the trans. to get softer shifts.
The reason I say this could be normal is becouse the trans. as well as other systems rely on accurate timing and any abnormal timing is going to cause some real and noticable symptoms as well as an illuminated MIL light.
I'm not saying seafoam is not helpful to limit carbon-related problems but in this case I think your MDX is doing exactly what it was designed to do. I also could be wrong having not seen the vehicle and looked at the engine data while driving it. It certainly would not be the first time I made a mistake. Good hunting and have a Merry Christmas!

 

[youdontwannaknow]

It cruises at a timing of 25-30° but soon as I step on it even lightly it rolls back the timing down to 18-19°. Are you saying this timing retard under acceleration is normal and occurs even if there is no knock detected ? I'd imagine it would be the other way around - i.e. advance the timing for power demand ? I do see a small quick spike (or dip rather) in the timing when it shifts but nothing continous.

I am almost tempted to try 100 octane(race gas? unleaded ofcourse) or dump a gallon of toluene in a few gallons of gas and see what the real no-knock timing behaviour is and use it as a reference.

 

[Mokanic]

The more you describe it,the more it sounds like a normal condition. Timimg on ECT transmissions and other systems is so critical that if it was off even slightly you would experience very noticable symptoms(bucking,trans. hunting excessive,even idle problems ALL of which will cause a MIL on condition on an OBD 2 Acura.
Late OBD2 Lexus/Toyotas will do exactly the same thing if you watch engine data on a scanner while driving down the road. They are doing this to give the customer an almost inperceptable shift under accelleration.
If you had a problem with timing,your Acura would definitly let you know with some very real drivability symptoms.

 

[youdontwannaknow]

I guess I have a mental block about this "shift under acceleration". I can understand adjusting timing while shifting but why would it run at retarded timing all along ?? (thats more like "Lexus" than "Acura" from the sound of it

, just kidding).
But seriously, the issue is really not a timing problem, I am sure of that, its just the timing retard that I think is occuring more. Everything's working fine as it should, its detecting knock and retarding timing. The issue, I think, is that its experience more knock than it should.

 

[punisher]

Quote:

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It cruises at a timing of 25-30° but soon as I step on it even lightly it rolls back the timing down to 18-19°. Are you saying this timing retard under acceleration is normal and occurs even if there is no knock detected ? I'd imagine it would be the other way around - i.e. advance the timing for power demand ? I do see a small quick spike (or dip rather) in the timing when it shifts but nothing continous.

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It is absolutely normal to see timing retard under throttle. Remember how the old vacuum advance distributors behaved? More TP voltage causes retarded timing.

Timing will dip during shifts with an automatic to momentarily reduce torque in order to smooth shifts and reduce shock loads on the clutches.

Monitor your knock sensor output, that is what you need to know the state of.

 

[youdontwannaknow]

Quote:

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Monitor your knock sensor output, that is what you need to know the state of.

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that would have been an end to all the confusion but unfortunately its an "enhanced pid" and I dont have info about it as to how to query it via obd2.