Is you Knock sensor taking performance down for the count?

[LGAFF]

Interesting to note that after running 12.4s @ 117.5mph and then adding a lightweight flywheel I saw a decrease in performance. I had been running 12.6s at 114.5-115 range.....I then noticed my knock sensor was unplugged, problem solved right? wrong! after plugging it in I saw no change, then last year I purchased a Tech 1.....my car was pulling 10 degrees of timing,constantly and in fact on hard acceleration I was pulling even more.....

So I went down to my local parts store and purchased a ZR-1 specific replacement...Pete had warned me to check it by OHMing the sensor and that a ZR-1 sensor should OHM at 3.0-4.0....wrong resistence; this sensor from O"Reillys tested at 99.

Then I tested the one on the spare motor, bad too..no reading

Now keep in mind my 92 has 23K miles on it....and even with the timing retard it seems very seat of the pants fast.....so how many of you weekend warriors at the strip are losing .2-.5 from timing retard.

Time to pull the Fluke meter out and check yours....oh, by the way GM discontinued the Z knock sensor....they are still availble from some vintage parts places, Jerrys, and I imagine Kurts too.

Thanks to Pete for the heads up!

[mike100]

I have not observed much pulled timing on my tech1 data. maybe a degree or two and a small ping when it is hot, but mostly it is showing the full amount of timing when I have done the recording under accel at the data rate the scanner is capable of.

The biggest question is why does it pull timing when you disconnect the sensor? Does it have to have a grounded signal to run properly?

I can't recall, does it list a timing retard number? I do know that the total timing shown is 6 degrees less because the raw value does not include the 6 degrees of lead cast into the sensor mount/crank notch.

I will check it next time I change the oil out of curiosity.

[LGAFF]

I do know that are cars with known false knock issues that use a resistor to create a false signal that the sensor is present to thus avoiding "False Knock" and avoiding timing pull from the sensor disconnect.

[LGAFF]

Early 85=89 TPI uses a 3.9K knock sensor, wonder if that would work for us?

[Pete]

If you unplug the sensor the ECM thinks the sensor is bad basicly there's no singal/voltage going to the ECM and will retard timing so you don't blow up/hurt motor.

Pete

[Paul Workman]

Tuning the knock sensor...

This may open the door to using currently available knock sensors... What say you Tuner Pro gurus?

C-link (http://www.chevytalk.org/fusionbb/showtopic.php?tid/249317/)

P.

[XfireZ51]

Paul,

We'd need to determine if the EST module in the ZR is specific to the motor(which I suspect due to the completely different motor architecture)
or it works w another KS. Perhaps Marc H. or Jerry could shed some light on that. The knock strategy in the stock calibration is pretty aggressive and clearly designed for better safe than sorry. Knock parameters deal w amount of retard,
Duration and decay rates. These can be reduced typically. If you've data logged a dyno tuning session, you'll see that the LT-5 isn't prone to knock at the top end. Knock shows up right around torque peak, between 4-5500 rpm. In my last tuning session I had 34d for top end advance w no knock. However, power was down. So no sense in keeping it there.
Proper installation of the KS is important(ie overtightening) to avoid false knock.

[XfireZ51]

"Now keep in mind my 92 has 23K miles on it....and even with the timing retard it seems very seat of the pants fast.....so how many of you weekend warriors at the strip are losing .2-.5 from timing retard."

That's why I datalog my runs.

[LGAFF]

Well the knock sensor in my 90 motor was bad too, the one from 966......maybe that explains the drop in performance on the dyno.

So knock sensor in my 92 dead at 23K miles, in my 90 and 143K and the spare motor at 40K

[gbmidyear66]

I'm confused... I had understood (incorrectly?) that the LT5 does a self test of the knock sensor / circuitry at start up. If the seonsor is inoperative - presumably it will indicate a DTC?

[LGAFF]

never saw one on the 92 when it was off..

[VetteMed]

I'm confused... I had understood (incorrectly?) that the LT5 does a self test of the knock sensor / circuitry at start up. If the seonsor is inoperative - presumably it will indicate a DTC?

Yes, this should trigger a code 43.

[scottfab]

I'm confused... I had understood (incorrectly?) that the LT5 does a self test of the knock sensor / circuitry at start up. If the seonsor is inoperative - presumably it will indicate a DTC?

This is almost true but not quite. Yes the ECM will do a test of the ESC module once after start but these two conditions must also be present:
1. Eng temp above 194deg F.
2. at or near WOT (high load)

So, based on this circuit description it is entirely possible to not get a code 43 when the sensor is unplugged.

[gbmidyear66]

This is almost true but not quite. Yes the ECM will do a test of the ESC module once after start but these two conditions must also be present:
1. Eng temp above 194deg F.
2. at or near WOT (high load)

So, based on this circuit description it is entirely possible to not get a code 43 when the sensor is unplugged.

Thanks for clarifying the fine print Scott

So..... if you drive like a granny (I can assume LGAFF does not qualify on this count), OR you've changed your thermostat and/or fan cut-in - you won't get a DTC?

I dunno - I have early activation of my fans and I still see temps > 200. Sounds like I need to disconnect the sensor and see what happens.

[scottfab]

Thanks for clarifying the fine print Scott

So..... if you drive like a granny (I can assume LGAFF does not qualify on this count), OR you've changed your thermostat and/or fan cut-in - you won't get a DTC?

I dunno - I have early activation of my fans and I still see temps > 200. Sounds like I need to disconnect the sensor and see what happens.

I also have early "fan on" but don't see temps north of 200 on short drives so in my case I'd not see a 43 (if sensor or ESC were defective) on every drive.
I can tell you that yesterday I hit WOT at above 200 several times on the way back from Home Depot because I chose to go to the one that is a few miles farther away than the one nearest me. I did this ostensibly to test to see if I'd get a 43 but also as an excuse to feel the WOT and to save some $ by shopping in a "no sales tax" US state :dancing

[Vettetech1]

Bring up this thread again. Got a 92 zr1 here has a code 43. Suspecting a knock sensor issue. OHMed the sensor and it is at 3.891k. Customers car not sure of full repair history on it. Know all primary and Secondary injectors have been replaced over the past 3 years, and the fuel regulator was replaced last year. Just don't seem to have the power it should. Any suggestions would be helpful as i don't see to many of these.

[LGAFF]

Is your ASR light or other lights coming on? I had a crack in the board of my chip for the knock sensor

[Pete]

Did you or somebody replace knock sensor?
You might have a 1990 knock sensor.

I will check and get back to you later.

Pete

[XfireZ51]

Have a read on this thread for some additional explanation. It's not a matter of knock, it's a matter of the knock sensor circuitry being operational. You don't get a MALF code if knock is occurring.

http://www.thirdgen.org/techboard/diy-prom/651662-code-43-esc.html

[Vettetech1]

Is your ASR light or other lights coming on? I had a crack in the board of my chip for the knock sensor

I did see the service ASR light come on yesterday, but it isnt on now. The service ride control light will go on and off while driving but it did that last year also. This all started as a feeling of a miss in power mode when you get on it. I checked the injectors and had 2 secondary injectors at 8 ohms the rest were 12.6. I replaced the 2 bad ones and suggested we replace the other 2 secondaries that were OE. So over the past 3 years all 16 injectors have been replaced. The car was running like it should fast and strong, it then sat for 2 weeks till the owner came, when he picked up the car he said it was running rough and thought maybe it just needed to be driven. Now it acts like its missing on hard accel in both power and non power modes. Like injectors are messed up again. I put my solus pro on it and found a 43. hit up google and found you guys. cleared the code and havent seen it back on yet but haven drove it either. Can feel the miss or stumble just goosing it in the bay.

[XfireZ51]

The Service ASR light will come on when in ALDL mode. So if you connected your scan tool, you'll see the light. The Service Ride Control will light if you've started the car 3 times without moving it.
Does the vacuum pump come on when you turn ignition "ON"? It's in the front passenger side by the coolant overflow "bottle". It should only run for a few seconds. If it continues, there's a vacuum leak and will affect secondary operation. With your scan tool I would check all sensor values with ignition "ON" making sure they are within range, like TPS, MAP etc. Check hoses like the PCV connections and the MAP sensor.
Have you pulled plugs and how did they look?
I know this sounds basic, but from our perspective here, it helps to understand the baseline condition of the car before speculating on what's going on.

[Tyler Townsley]

Check to see of both pumps are working. Many times falling on its nose on hard accel is cause by the secondary pump being bad. OE pumps do not like sitting for long periods of time and also do not like running with the tank lower than 1/4 tank.

Tyler

[Vettetech1]

See that's what I was wondering I know this car sits. When he came to pick it up it was sitting on reserve with one bar left. Per my boss I just pulled the plenum to recheck the injector ohms 12.4 to 12.8 across the board. Is there anything else I should check while under this damn plenum. Also what is the failure rates of coils and the module on the underside of the plenum.

[Pete]

Knock sensor is the correct unit and ohms correct.

You need to look at common issues on this forum.

Just a couple that come to mind with the issue you are having is wires and injectors.

Injectors can ohm good and still be bad check for leaky injector before you go changing fuel pumps.

Pete

[Vettetech1]

Knock sensor is the correct unit and ohms correct.

You need to look at common issues on this forum.

Just a couple that come to mind with the issue you are having is wires and injectors.

Injectors can ohm good and still be bad check for leaky injector before you go changing fuel pumps.

Pete

Thanks Pete that was my biggest concern was the knock sensor ohms. I got the upper off and don't see any fuel dripping from the injectors. Seems to hold fuel pressure on the gauge and run in spec. Car ran great after injector replacement but now has a miss, almost like a cracked plug. Seems to idle nice. Pulling plugs now to see if i can see a odd one but so far they look pretty good. Back to the drawing board.

[Tyler Townsley]

See that's what I was wondering I know this car sits. When he came to pick it up it was sitting on reserve with one bar left. Per my boss I just pulled the plenum to recheck the injector ohms 12.4 to 12.8 across the board. Is there anything else I should check while under this damn plenum. Also what is the failure rates of coils and the module on the underside of the plenum.

If the tank was that low it may have picked up some not so good gas. Try some injector cleaner and a run through a tankfull of gas. To check a plug miss I pull the plugs and put the boot on, lay them on the plenum and crank the car, all plugs should show the same spark color/intensity.

To check for fuel flow look at the plugs when you have them out to make sure they are all the same color. Check by switching the plug to a good cyl and see if the plug 'cleans up' and the other has change color. If its black leaking inj if its too brown lean condition/bad plug.

Tyler

[Pete]

Just a thought.
Please don't tell me you used Bosch spark plugs or some other expensive fancy name plugs.
If so take them out and replace with a resistor plug.

I like to diagnose from cheap to expensive.

Pete

[Vettetech1]

Just a thought.
Please don't tell me you used Bosch spark plugs or some other expensive fancy name plugs.
If so take them out and replace with a resistor plug.

I like to diagnose from cheap to expensive.

Pete

I hate Bosch, Champion, Denso, and NGK. I know some people live by those plugs but i have never had luck with them. This thing has only got 23000 on it, never beaten original tires (which blow by the way they are so damn hard and slick). It still has the OEM Delcos in it which are as clean looking as the day it left the factory. Think I found the problem, just waiting on plenum gaskets so i can put it back together. Think it is my fault, I didnt realize when i pulled the upper to do injectors i had some coolant get down in the #8 spark plug well. I think is was causing a high moister issue and i think the spark was jumping through the boot. So I dried it out checked plug gaps. (customer doesn't want to replace them yet) and we have a good set of take off LT5 wires im gonna snag a #8 wire. (Maybe pray to the car gods) I'll let you all know how it turns out in a few days.