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Car: 1988 760GLE, B280E, LH-jetronic 2.2, EZ115K ignition system.
I was wondering if anyone could tell me how the anti-knock system on
my 760 actually work... I mean, what does it do when one of the knock
sensors detect knocking?
I would have thought that the ECU would retard the timing for the
knocking cylinder a bit, and then gradually advance untill "correct"
timing was reached or knocking was again detected - but maybe I'm wrong?
The reason I suddenly started wondering about this peculiar issue is this:
Early this morning, on my way to work, I had to stop for gas. Beeing early, I was obviously not fully awake, and filled up with 98 octane. Never done that before, always have run the 760 on 95 octane.
After a few minutes of driving, I noticed a change in the car. The "shudder" at 1900 rpm at moderate load had vanished. Completely gone! I've been
trying to locate the source for this vibration for a long time, without
success.
Could it be that I had a knock-situation at 1900 rpm, which the anti-knock- system has compensated for, thus making the engine run rough at this
particluar rpm? Remember, the B280E has a relatively high compression ratio of 10:1...
Best regards
-Tore
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I read in either a Haynes or a Chilton's manual that the first thing that the control system does when a knock is detected is to add extra fuel - this is supposed to work faster than changing the timing.
--
3 8s & 2 7s 725,000 miles total
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With those octane numbers you must be in either europe somewhere or Australia, which is confusing because your pic is of a left hand drive car!
Anyway, I think you will find that depending on the brand of fuel, you will find that most 95 fuels are rather optimistic in their claims, in reality a lot of 95 fuels are more like a solid 91-93 depending on brand.
Once you get to the new ultimate 98 fuels though it starts looking a lot better, they generaly are a much better product, with a good solid 95-98 actual rating depending on brand (the BP Ultimate here in Oz kicks ass).
Another benifit of the better fuels is that they have a higher percentage of cleaning agents in them, and so far I have noticed better running in every car I've used the stuff in.
It could be that the extra cleaning agents have cleared up a problem, or it could just be the extra octane, but it might not be the case.
Generaly you may want to check your exhaust oxygen sensor, and/or the knock sensor itself, and make sure your air filter is clean and that there is no flow restriction in the fuel line (dirty fuel filter), all of those things could be the cause of this, the car may have been running lean before and the extra octane stoped that.
--
Veronica, my 85 760Ti
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True, I'm in Europe. Norway to be precise.
The "shudder" dissappeared within minutes after leaving the gas station, and I doubt the cleaning agents would work so fast. And, having a B280E, this car has no oxygen sensor.
I am inclined to believe that the extra octane helped me here. I might have some carbon buildup, as the car has seen nothing but slow city driving for the last couple of years...
-Tore
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"I would have thought that the ECU would retard the timing for the
knocking cylinder a bit, and then gradually advance untill "correct"
timing was reached or knocking was again detected - but maybe I'm wrong?"
The ECU (Engine Control Unit) controls the engine while the EZ-K controls the ignition. Yes, the EZ-K functions just as you have described. Timing is retarded in large increments (2.8º on the B230FT), and advances the timing in smal increments (0.35º on the B230FT) when knock is no longer detected. You have one knock sensor for each bank of cylinders.
Nice car. I'll bet it runs smoooth.
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> Nice car. I'll bet it runs smoooth.
You bet. Especially on 98 oct. :-) I wouldn't trade the V6 for any 4-banger.
-Tore
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You have the desireable V6. You would rather have the four cylinder than the early V6 and its maintenance problems.
The four cylinder B230FT engine in my wife's car is quite smooth. The one is my car is noticeably rougher. Both are equiped the same. The engine in my wife's car is better internally balanced and it shows it in running smoothness.
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Nice looking car. Are you in the US? The corner lights look Euro.
The LH system on the 4-cylinder 240s, with which I am familiar, have one knock sensor. It signals the ECU and the spark retardation is for all cylinders. Could be that the V6 has a knock sensor for each bank, but the resulting retartation would be the same. Unless, of course, your engine has a separate coil pack for each cylinder. That I don't know about.
Good Luck.
Bob
:>)
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> Nice looking car. Are you in the US? The corner lights look Euro.
Europe. Norway, actually. The corner lights (and the rest of the car) looks like Volvo's designers made it, and not how the US requirements made it look :-)
-Tore
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98 octane? Where are you located, and is that (R+M)/2 or RON or MON? (R+M)/2 is commonly referred to as AKI (Anti-Knock Index)? RON is Research Octane Number and MON is Motor Octane Number. R is usually greater than M, and thus I would suspect that 98 octane at the pump refers to the RON number? Curiosity beckons me to ask because in NYC, the highest octane I can get is... 93 AKI I believe. :)
As for the answer to your question, i would suspect that you are correct with regards to the shuddering. and i believe you are also correct as far as how the knock detection system works.
--
Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'
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> 98 octane? Where are you located?
Europe, Norway. In Europe, we use RON.
-Tore
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