I want to temporarily disable knock control on my '91 Chevy Suburban.

Without burning a PROM, is there a way to feed a fake signal to the ECM so it won't set a knock sensor code?

I understand if I unplug the sensor a code will be set, as there is a load resistor inside the sensor to detect an open or a shorted knock signal.

I could defeat that test with a toggle switch and grounded resistor, but are there other conditions for which the ECM checks?

For example, I have read the ECM advances timing at some point to induce knock, then look for a knock pulse, or that it looks just looks for activity on the knock signal input.

Can anyone tell me how it really works and how I can fool it?

 

Deleted

 

I want to temporarily disable knock control on my '91 Chevy Suburban.
Is it a 305 TBI?

Without burning a PROM, is there a way to feed a fake signal to the ECM so it won't set a knock sensor code?
Using a resistor jumper

I understand if I unplug the sensor a code will be set, as there is a load resistor inside the sensor to detect an open or a shorted knock signal.
Yes and timing will be retarded = lost of engine power

I could defeat that test with a toggle switch and grounded resistor, but are there other conditions for which the ECM checks?
Yes, read your next point

For example, I have read the ECM advances timing at some point to induce knock, then look for a knock pulse, or that it looks just looks for activity on the knock signal input.
Yes when ecm meets certain threshold for engine coolant, load and maybe speed.

Can anyone tell me how it really works and how I can fool it?
I believe you need a chip burn to turn off ESC test but someone might chime in with a better solution.

 

Thanks for your help. It's a 454 CID 3/4 ton R2500. California version.
Engine coolant temperature can be fooled so that might be an easy way, if indeed that is one of the factors.

 

Well, in fact I know nothing about big block 454 TBI. Might want to search other sites for Suburban as well.

EDITED: Your ecm should be 16147060 or 16127470 with a $85 mask. If you're ever interested in finding out your knock parameters.
http://www.gearhead-efi.com/Fuel-Inj...Information-85

 

Source code with comments on operation would be nice.

Not looking to pirate code, just looking for a way to disable it externally.

 

Your ecm should be 16147060 or 16127470 with a $85 mask. If you're ever interested in finding out your knock parameters.
http://www.gearhead-efi.com/Fuel-Inj...Information-85

 

If I may,
Problem is, you might fool the ecm for your knock sensor, but you will also fool it for a bunch of other things. Expect problems.
Thanks

 

Moved, not DIY_PROM related.

RBob.

 

Thanks for the links. The forum requires me to sign up to read the files.

I tried to sign up over there but the forum won't send a link to confirm my email. I tried it from my desktop and my phone. I requested a password reset and it asks a random question, the answer to which can only be "LS1". On my desktop it says I gave the wrong answer, but it works on my phone. But it never sends a password reset email.

I'll have a friend try to register then send me the files.

 

From: BMAY
;------------------------------
; ERR 43 PARAM'S
; KNOCK DET ERROR
;------------------------------
L85B3 FCB 20 ; TIME FOR VOTAGE OK TEST
L85B4 FCB 230 ; UPPER VDC THRESH, 4.6 VDC
L85B5 FCB 20 ; LOWER VDC THRESH, 0.4 VDC
L85B6 FDB 0010 ; 10 SEC PRIOR TO ERR 43 TEST
; (RESTART TME VAL)
;
L85B8 FCB 60 ; 60 SEC ENG RUN TIME PRIOR TEST
;
L85B9 FCB 23 ; 4 DEG SA REPLACES SKP RETARD VAL IF ERR 43
; (256/45) * SPK RESTARD VAL
;
L85BA FCB 10 ; 10 SEC TEST PERIOD FOR VOLTAGE, ERR 43
;
L85BB FCB 170 ; 87.5 Deg c COOL MIN FOR ERR 43 TEST
L85BC FCB 192 ; 104 Deg c COOL MAX FOR ERR 43 TEST
;
L85BD FCB 179 ; 69.9% TPS PWR ENR BYPASS ASSUM PWR ENR CONDITION
; IF TPS GT 99.6%
;
L85BE FCB 128 ; 3200 RPM UPPER LMT FOR ERR 43 TEST
L85BF FCB 195 ; 81 Kpa LOWER LMT FOR ERR 43 TEST
;
L85C0 FCB 46 ; 16.2 Deg SPK PWR ENR ADDED TO CAUSE KNOCK
; DEG SA * (256/90)
;
L85C1 FCB 91 ; 31.9 deg SPK PWR ENR ADDED TO CAUSE KNOCK IN
; 2nd MODE PWR ENR, (DEG SA * (256/90))
;
L85C2: FCB 2 ; 2 KNOCKS, KNOCK LMT MIN (12.5 Msec Period's)


From: BAMW
;---------------------------------------------
; ERR 43 PARAM'S
; KNOCK DET ERROR
;---------------------------------------------
L85B3 FCB 160 ; TIME FOR VOTAGE OK TEST
L85B4 FCB 230 ; UPPER VDC THRESH, 4.6 VDC
L85B5 FCB 20 ; LOWER VDC THRESH, 0.4 VDC
L85B6 FDB 0010 ; 10 SEC PRIOR TO ERR 43 TEST
; (RESTART TME VAL)
;
L85B8 FCB 60 ; 60 SEC ENG RUN TIME PRIOR TEST
;
L85B9 FCB 23 ; 4 DEG SA REPLACES SKP RETARD VAL IF ERR 43
; (256/45) * SPK RESTARD VAL
;
L85BA FCB 3 ; 3 sec TEST PERIOD FOR VOLTAGE
;
L85BB FCB 170 ; 87.5 Deg c COOL MIN FOR ERR 43 TEST
L85BC FCB 192 ; 104 Deg c COOL MAX FOR ERR 43 TEST
;
L85BD FCB 255 ; 99.6% TPS PWR ENR BYPASS ASSUM PWR ENR CONDITION
; IF TPS GT 99.6%
;
L85BE FCB 128 ; 3200 RPM UPPER LMT FOR ERR 43 TEST
L85BF FCB 195 ; 81 Kpa LOWER LMT FOR ERR 43 TEST
;
L85C0 FCB 34 ; 13.3 Deg SPK PWR ENR ADDED TO CAUSE KNOCK
; DEG SA * (256/90)
;
L85C1 FCB 68 ; 23.9 deg SPK PWR ENR ADDED TO CAUSE KNOCK IN
; 2nd MODE PWR ENR, (DEG SA * (256/90))
;
L85C2: FCB 2 ; 2 KNOCKS, KNOCK LMT MIN (12.5 Msec Period's)
;---------------------------------------------

 

IMO, your best bet is get a kit for chip burning and TunerPro software. I don't think there is anyway around it for what your are trying to achieve.

You need to change this for the maximum DegC allowable (151DegC I believe), so knock retard gets disabled:
L802C FCB 100 ; 35c, MIN COOL FOR KNOCK RETARD
; (Cal val = (DEG +40) * (256/192))

And also turn b4 to 0, so knock test won't occur.
L8577 FCB $3C ; 0011 1100, ERR FLG WD 4
;
; b7 = 1 = ERR 39, TCC STUCK OFF
; b6 = 1 = ERR 41, 1x CAM SENSOR FAIL
; b5 = 1 = ERR 42, SPK MONITOR
; b4 = 1 = ERR 43, KNOCK SENSOR
;
; b3 = 1 = ERR 44, o2 LOW
; b2 = 1 = ERR 45, o2 HI
; b1 = 1 = ERR 46, NOT USED
; b0 = 1 = ERR 47, NOT USED

Cheers!

 

Thanks very much! I appreciate your help. I'll post results when or if I have any.

 

You’re welcome