Oxygen simulators...

[Ken]

I saw this recently and wondered if I could benefit from the use of oxygen simulators in my application. Any suggestions?

O2 Sensor Simulators, pair

• 
  O2 Simulators replace the factory Oxygen sensor(s).
  
• These are sometimes necessary with bigger cams or when removing catalytic converters on OBDII cars.
  
• Simulators plug directly into existing O2 sensor harness.
  
• Sensor opening(s) in exhaust pipe must be plugged.
  
• For off-road use only.

Price: $119.95

Also, it was mentioned when I last had it on the dyno, that disabling the knock sensors is something I should do as well. What is involved there? :confused

_ken

 

[JohnZ]

Removing the 02 sensors (which send variable voltage signals to the ECU depending on sensed mixture/oxygen content) with what are undoubtedly plug-in fixed resistors (worth about 50 cents each) doesn't sound like a great idea to me. Depending on their resistance value, they'd either leave the car in "open loop" all the time, or leave it at one (fake) mixture condition all the time, defeating the flexibiilty of the ECU to maintain correct mixture and spark timing under all conditions and provide good driveability. Sounds like a classic rip-off (especially at $120.00), ignoring the fact that they're illegal and would only provide optimum mixture and ignition timing at one little isolated point in the power curve/load map.

I wouldn't disable (disconnect) the knock sensors either, unless you don't mind replacing pistons, rods, and bearings (unless you have a very carefully set up and calibrated aftermarket ignition system that performs detonation-free under all conditions). The knock sensors instantaneously retard ignition timing when they sense detonation - without them, you don't have that protection, and can start kissing parts good-bye.

 

[Ken]

John, maybe your not familiar with my engine, but it is far from stock, and the car is borderline race-only now. The knock sensors could be picking up noise from my headers or a false signal from somewhere else, and they are not allowing my ignition system to function as it should. Something is messing with my timing because my horsepower/torque numbers are definitely not what they should be. We're getting there though; the progress is just so sloooow to me sometimes.

Thanks for the feedback.

_ken

 

[Redbob]

Ken:
I doubt the EGO sensor simulators would do you any good; they're intended for OBD-II cars to let you remove a cat without setting a fault code.
The two EGO sensors upstream and downstream of the cats on OBD-II cars look for O2 readings that are in-phase, that is, that they vary more or less together.
If the upstream O2 reading goes up, the downstream reading should go up at the same time, and by a proportional amount.

If you want to see if your knock sensor is messing you up, just remove it from the block but leave it plugged into its' wire.
Without any signal from it, you shouldn't get any spark retard.
Also won't have any protection, so be careful about doing power runs this way.

Regards,
R

 

[Ken]

... the EGO sensor simulators (are) intended for OBD-II cars

Ah! Now I understand why I don't see 'em for earlier cars. Thanks.

_ken

 

[Redbob]

De nada.

One more thing about removing the knock sensor: it would have to still be electrically grounded via a jumper wire to the block, or else your ECM would set another fault code, and probably run with spark in full-retard mode.

- R

 

[69MyWay]

Redbob is right on target.

These are for OBDII systems that use up to four sensors (two pre and two post cat). The guys that hack the cats off need these to simulate the post cat temp change and keep the computer from setting a trouble code.

You only have one O2 on your car, and it is a precat style.

You need it.

There are a varity of methods for dumbing down the knock sensor. One is to ground it via wire, then mount it in a solid rubber block on the frame rail. The bad part is you will never get any spark retard, and could do damage to the motor with the high compression you are running and not know it until it is too late.

I am considering doing this to my O2 on the 90 as it picks up all kinds of back ground noise and kicks the timing back with false reasons.

 

[Ken]

Ok, waaa-aay back in the old days, before knock sensors, how did one handle detonation or pre-ignition without a device to automatically retard the spark? Obviously where there is a will there is a way, right?

_ken

 

[Redbob]

Ok, waaa-aay back in the old days, before knock sensors, how did one handle detonation or pre-ignition without a device to automatically retard the spark? Obviously where there is a will there is a way, right?

_ken

One listened for "knock" or ping, and one dialed the spark back accordingly, if necessary.

It's important to keep in mind that not all "knock" is dangerous - just the full-throttle (maximum load) knock.
At Ford, we used to call spark knock "the sound of fuel economy" since by the late '70's/early '80's our engines were leaned out and spark advanced so far that virtually all engines would ping at some time or another, usually only during part-throttle accelerations. This coincided with LBT or "lean best torque" operation.
This kind of knock will often disappear under full-throttle accleration.

Fortunately, spark knock seems to occur at a frequency around 4000 Hz, which happens to be where the average human has the greatest hearing sensitivity.

Almost as if He intended us to be able to hear spark knock, eh?

 

[Ken]

He's always looking out for us, eh?

So, it appears then that if I disable the knock sensor, I will have to set timing for the type of driving I will be doing. That is, when I want to take it to a cruise night, the timing will be at x° and when I am at the track it will be set at y°. Then it would simply be a matter of dialing it in each time, eh?

_ken

 

[Redbob]

He's always looking out for us, eh?

So, it appears then that if I disable the knock sensor, I will have to set timing for the type of driving I will be doing. That is, when I want to take it to a cruise night, the timing will be at x° and when I am at the track it will be set at y°. Then it would simply be a matter of dialing it in each time, eh?

_ken

What you have with the production ECM spark map is what GM thinks should work pretty good almost all the time, for almost all types of driving, and the knock sensor is supposed to be just a way of fine-tuning that map, and protecting against for example a tankful of bad gas.* So you could either retard your spark timing a little, or use a better grade of gas.
OTOH, "cruise night" doesn't involve racing, does it? IF you're not running WOT, you shouldn't have to worry about just a little spark knock - that is, if you find you have any at all.

The key here is, listen for knock - if you don't hear it, you prolly don't have it. And don't run excessively lean - that'll make knock more likely to occur.
Regards,
R

*The exception to this was the late '80's/early '90's Corvette L98 where the spark map was set for something like race fuel, and kept advancing until it got spark knock. If you have one of those engines, just running race fuel will get you several more horsepower - maybe as much as 15 - 20 HP more.

 

[Ken]

Well I know I don't want to run lean or I start burning pistons, eh?

 

[Redbob]

It's not running lean by himself that burns pistons, but running lean and getting spark knock.
Diesels run about as lean as you can get, but without burning pistons.

What spark knock does is this: the "explosion" disturbs the boundary layer, a thin layer of gases that is not in motion, that in effect insulate the walls of the combustion chamber - including the piston tops.

When this boundary layer is disturbed, the rate of heat transfer to the combustion chamber walls is dramatically increased, heating the walls enough to sometimes melt them.
That's what'll happen to your piston tops.


Regards,
- R