Knock Sensors and Wheel Hop vs. Timing

[03Steve]

99-01 Cobras come equipped with knock sensors, not sure about the 96-98 Cobras and Mach 1s.

I was out working with a car with knock sensors over the weekend. In a nutshell, with the stock knock sensor parameters...a knock sensor equipped car can pull up to 6 degrees of timing when the sensor(s) activate. There is a retard rate, which determines how quickly the timing is pulled out. In stock form, the EEC will pull out one degree of timing every 1/4 second. Wheel hop will activate knock sensors.

There is an advance rate, which determines how quickly the timing is put back in the motor when no knocking is detected. One degree will be added in per X amount of seconds. In stock form, there is a "blending ramp" for timing advance. The more RPM the motor sees, the quicker the timing will come back in.

There is one more table called advance limit. Care must be taken not to populate this table with anything greater than 0. When the knock sensors are not going off, the EEC will try to advance timing when looking at this table. In stock form, this table is populated with positive values in some RPM areas. You may be in for a nasty surprise if you add timing in another area of the tune, and forget to set the knock advance table to zeros.

 

[01 Venom]

pretty good post, thanks

 

[sur_real1]

As far as wheel hop affecting the knock sensor and timing being pulled, you can keep this from happening when you turn your traction control off right?

 

[03Steve]

No. Traction control has no effect.

In a 99 Cobra ZMR2 processor, the EEC will begin to "look" at the knock sensors at 120 degrees.

 

[lemosley01]

Steve, I assume it is the sound of wheel hop that fools the sensors into thinking it is detecting knock?

 

[Charles236]

Good information to have, just earlier today I was thinking on how driveline vibration can affect knock sensors. It appears that when the frequency of the vibration is in the range that the sensors read (actually, the knock sensors report everything that can be interpreted as spark knock, whether it is or not. The engine controller is programmed to choose what input from knock sensors to act upon)as spark knock, then timing will be reduced, lowering performance. Modern knock sensors do seem to be more finely tuned than the earlier ones, which could sometimes read high frequency vibration from an aggresive tire pattern as spark knock. Incidentaly, the Mach1 engine does have the knock sensors, they're located in the valley under the intake manifold.

 

[lemosley01]

I've heard of false positives that the knock sensors pick up from other things vibrating. Just kind of surprised that wheel hop would make the same sound.

Double hit - not only do you have no traction, but you're down on power as well.

 

[99svtvert]

Is there a way to turn off the knock sensors - I'm sure not ????.

Here's my issue, I have a built big bore using a 98 Teksid block and all forged internals, and the knock sensor holes in the valley use a different diameter bolt. The 97-98 bolt holes are larger than the 99-01 knock sensor bolt holes, so they cannot be drilled out and re-tapped.

I'd love to delete them but know I can't, but will probably have to look for some 97-98 knock sensors (how hard will those be to find ??). Although I am told they are interchangable except the bolt size. But, the connectors are different so a slice has to be done. PITA

The knock sensors were deleted in 03 due to the stonger block ?

 

[Double"O"]

i had mine set on the lowest setting

the KB really sets em off, hence why the 03/04s don't have them, the eaton did the samething

 

[99svtvert]

How do your set them "off" ??. My guess is that they have to be there; must be bolted to the block. Just checked with Ford and they are about $130 each.

 

[lemosley01]

How do your set them "off" ??. My guess is that they have to be there; must be bolted to the block. Just checked with Ford and they are about $130 each.

He means they keep detecting knock-like noises that the KB and Heatons on the 03s generate and so think that you have engine knock. The PCM gets this info and starts retarding timing, etc, because it thinks you have knock.

I believe a tuner may be able to turn them off, or maybe only a custom tune. I'm pretty sure the SCT Proracer package can.

 

[IZZY]

Good info, Steve. Its been said that the vibrations from a supercharger will also induce the knock sensors to pull timing.

 

[RoyWoods]

Steve, excellent information.

Can anyone confirm if you can turn the knock sensors off on an '01 Cobra, and if you can, what do you need to do it? Besides losing a "safey valve" are there any other consequences to turning them off?

 

[VirtualSVT]

He means they keep detecting knock-like noises that the KB and Heatons on the 03s generate and so think that you have engine knock. The PCM gets this info and starts retarding timing, etc, because it thinks you have knock.

I believe a tuner may be able to turn them off, or maybe only a custom tune. I'm pretty sure the SCT Proracer package can.

A tuner can. The guys at SCT leave them on with a N/A car cuz they put timing back in through the power band.

 

[viperbluelx]

If you've got a supercharger on your 99-01 just get a GOOD tune, turn the knock sensors off, run only good name brand 93 octane, listen for detonation.

My tuner turned the knock sensor off, but you can still log knock sensor with the Xcal2 to see what they would be doing, and the timing pulled is all over the place throughout a WOT pull, glad mine are off.

 

[Reggie]

Yes, it is possible to "turn the knock sensors off". There are a couple of ways actually. But, you have to be aware of a few things.

One way to turn them off is by a switch under scalars. It is much like the method that the rear O2 sensors are turned off.

Another is engine temperature related. There is a threshhold at which the EEC looks for to begin using the knock sensors to change timing. Setting this higher than the engine's operating temperature will disable the sensors.

The third is to populate the knock sensor advance and retard rate tables with all zeros.

When setting a knock sensor equipped car's timing tables up for best performance, a tuner must take care to populate the advance rate tables with all zeros. When the EEC sees no reading from the knock sensors in the stock tune, it will ADVANCE timing. If a tuner sets up timing to be higher than stock in other areas (borderline knock table) and neglects the advance from the knock sensor tables...it is possible to see advanced timing beyond what is being commanded in the borderline table. That is one little way to add some unforseen timing and possibly make something go pop.

-"03Steve" under Reggie's screenname-

 

[99svtvert]

Great info.

 

[sonic_4.6]

I can tell when I set mine off. It it only would happen when there was a huge shock to the drivetrain.

Oh, I noticed it alot when my motor mounts where broke... if that has anything to do with it.

 

[01 Venom]

This is a very good thread, brings to light something that is not often talked about, but has a big effect on our cars. The knock sensor has good intentions hehe, it could save your motor. But there are some performance issues for guys like us who are trying to squeeze speed out of the new edges.

Excellent thread well done