Knock sensor bypassed, why is knock retard still present?

big dave · 07-18-2002, 09:58 PM

In trying to repair the knock retard problem I've been having, I decided to try a 3900 ohm resister in place of the knock sensor. It is my understanding that the resister should effectively take the knock sensor out of the equation and I shouldn't see any knock. Not so. According to the scanmaster, I'm still getting pretty much the same amount of knock as before.(9 degrees and medium throttle in high gear, 3 degrees at WOT, and maximum of 9 degrees in neutral while revving. What else am I missing that can cause timing retard?

kmook · 07-18-2002, 10:28 PM

Id like to know also since with my new setup its pulling 9* just at idle, hohum, the joyes of driving a tug boat.

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Ken Mook - 97' SS #2544
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Injuneer · 07-19-2002, 08:53 AM

First pull the wire off the knock sensor (or the resistor, in your case) and see if that wire is providing 4-6V referenced to ground - use the engine block. That verifies the wiring and the PCM. If you have 4-6V, anything between 3,300-4,500ohms should simulate the KS in a 93-95 engine. Wired of course from the single sensor harness wire to ground. If you are using a 96/97 PCM, I believe it is looking for something more like 100Kohms.

Fred

[This message has been edited by Injuneer 94FormM6 (edited July 19, 2002).]

rskrause · 07-19-2002, 09:24 AM

It seems easier to me to disable it by reprogramming (provided you have the capability). I gave up on the knock sensor, having spent many hours trying to cure false knock. So I have just zeroed it out in software.

Rich Krause

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

big dave · 07-19-2002, 09:30 AM

Fred, when I'm checking this voltage, is it necessary to have the key in the "on" position or will the voltage be constant regardless? Thanks.

SILVERZZ28 · 07-19-2002, 09:35 AM

Key must be on. Double check your resistor and make sure your wire is not bare anywhere .(grounding out)

big dave · 07-19-2002, 12:38 PM

I cut the wire 4" from the computer and spliced in the wire with the resister from there. I grounded it out on the frame. Are there any other sensors that can instruct the computer to pull timing? I did try another computer but that did nothing to help cure the problem. In fact, I actually got more knock retard with that one I assume because it was a stock computer.

SILVERZZ28 · 07-19-2002, 03:53 PM

just to clarify, You did not put it inline did you. You have the resistor tied to the computer end wire and the othe side of the resistor is just going to a ground? Not sure if anything else will retard the timing. I did not think there was.

Quote:

<font face="Verdana, Arial" size="2">Originally posted by big dave:
I cut the wire 4" from the computer and spliced in the wire with the resister from there. I grounded it out on the frame. Are there any other sensors that can instruct the computer to pull timing? I did try another computer but that did nothing to help cure the problem. In fact, I actually got more knock retard with that one I assume because it was a stock computer.</font>

big dave · 07-19-2002, 06:35 PM

That's correct, the wire coming from the computer was connected to the wire with the resister then run directly to a ground. The knock sensor was not being used.

396jon · 07-20-2002, 01:27 AM

I thought that the wire goes to the knock sensor then th eresistor then ground.....the resistor goes between the sensor and gound?

I ve been meaning to do it....but been to busy....

I ve had the same problem.....been trying to get the time to get edit....

RCF925 · 07-20-2002, 12:34 PM

I second RSKrause, I gave up on the Knock sensor and used Tunercat to zero spark retard tables, No more miss

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94 Z28,M6,355ci,8.9 CR Vortech S-Trim w/Aftercooler,Tunercat Prog.,DIY desensitized KM, Forged Internals,Port.&Pol. Heads w/3 angle grind,Bal.&Blue.,Crane 215/224-532/532-112LSA cam, 1.6 RR & Fireball HI-6R Ignition ,36# SVO Inj.,Magnecor Plug wires,Edelbrock Shorty Headers with Flowmaster,High Flow Cat,BBK 58mm TB ,K&N CAI,Luk Clutch,Eibach Pro-Kit w/Panhard Rod ,Global West SFC's,RK Sports 5-way adj. shocks & LCA's, Slotted Rotors, Auburn Posi w/Motive 3.73, Niche J-series 18" rims 10.5 rear,9.5 front,Autometer F/P & A/F & Boost Gauges ETC.

big dave · 07-20-2002, 06:36 PM

Fred, I checked the voltage and got 4.7 volts. What else can I check and is that voltage sufficient?

Injuneer · 07-20-2002, 08:58 PM

4.7V is fine. It almost seems like the PCM isn't seeing the sensor (or the resistor) at all. I don't run a KS, and I run the engine off a MoTeC, but I still use the stock PCM for idle air and the speedometer, so I still have my ScanMaster hooked up. At idle it will show 9-deg retard... it will vary in low single digits when the car is driven, and if I hit the throttle hard it will jump as high as 15-deg. But that is how it reacts with the harness connector hanging loose.

I'm sort of out of ideas on this one. If you hook the single PCM wire to one side of the resistor, and hook the other side of the resistor to ground, check the voltage drop across the resistor, to see if the connections are good.

Fred

big dave · 07-21-2002, 10:12 AM

Thanks alot for the info/help on this one. I've been battling this for a couple months now and it definitely has an affect on the performance at the track and on the street. I was wondering if I could have a grounding problem somewhere. I can see where the plastic tubing that houses the wires for the o2 and knock sensors has made contact with the headers and am wondering if one of those wires may have been burnt. It is impossible to get down to those wires without dropping the header. The black wire with the white stripe is what I'm particularly concerned about and am trying to find out if that is a ground wire. If so I would like to snip that wire closer to the computer and run that to a more convenient ground if possible to see if that has any effect on the retard.

Tofus 93Z28 · 07-21-2002, 04:51 PM

my friend has a 97ss and is having very similiar problems.. on the scanmaster he is reading 5-12 degrees of knock just off of idle along with various degress of knock through the rpm band..Ok, we have measured resistance on the KS... could not get a steady reading but typically hung around .800-.900k..spiked a couple times to 1-3k. we had 4.98 reference voltage...
we also started it up and tapped on the knock sensor, block and exhaust with a hammer, knock reads 0.. then with no tapping and a very light throttle, knock jumps to 5-12 degrees..... any ideas.....

he also has noticed glowing blue plugs at night..the plugs in it are autolites 106, msd wires and msd 6al unit on the vehicle... modifications to car- 1 3/4" slp headers, and ATI pulley.

FWIW, he reset the computer,(disconnected battery for 4 hours) knock went away for 25 or so miles then back to the bull.

This seems to be a problem thats affecting alot of 97 cars...

Anyone find a cure.....?????????????