Knock sensor?

[ScoobyDoo82]

Well I've had this problem since I bought my GP...

 

After a while of driving (usually only city driving, has never happened on the freeway), the Check Engine light will come on and the car will start bogging down when you go to take off. It idles just fine, just bogs when you take off. Over the course of the drive the CEL will stay on for long periods of time and then shut off and the car will drive fine after that... then it'll come back on, off, on, etc etc. The CEL code is 43 (Knock sensor error)... what I was wondering is does this sound more like the knock sensor going bad, or a wiring problem?

[RobertISaar]

intermittent knock sensor codes can be trigged by anything from a bad ground, alternator noise, lifter tick, excessive engine movement, flaky connections, etc, etc....

 

basically, lots of stuff, is there any other constant condition other than during city driving?

[RobertISaar]

i decided to dig a bit deeper to get the exact conditions for you:

 

for a 89 and 90 (and oddly enough 92 and 93) 3.1:

 

the knock sensor circuit goes above 3.5 or below 1.5 volts for ~1/2 second, DTC 43 sets.

coolant temp above 90*C, MAT over 0*C, engine speed between 3400 and 4400 RPM, the ECM adds extra advance momentarily, if no knock, DTC 43 sets.

 

for a 91 3.1:

 

knock sensor indicates knock for 3.67 out of a 3.9 second period of time: sets DTC 43.

knock sensor voltage above 3.75 or below 1.25 volts for ~5 seconds, sets DTC 43.

 

 

 

it's also mentioned that if the EST enable line doesn't recieve it's 5 volts during the "extra advance" test, that can cause a fail as well.

 

 

 

want the "walkthrough" for checking out what is going crazy?

[ScoobyDoo82]

Other than slow/city driving theres no other conditions. It never comes on at a precise time, but ONLY when its warm and when im driving in slow moving/stop & go traffic. For what its worth, code 23 (MAT reading -30*F for more than 10 seconds) is also present. I've tried brake torquing it, and simply hitting potholes and thats never triggered it either.

[RobertISaar]

fix MAT sensor issue before attempting to figure out code 43 issue, they MAY be related.

[ScoobyDoo82]

Hokay so, I cleared the codes and the MAT sensor code went away and doesnt seem to be coming back but the knock sensor error remains. I made a break through though in the form of a ton of vacuum lines disconnected... all the ones leading to the TB were unplugged, and that black thing that mounts to the rear of the intake plenum was disconnected. So I connected everything with instant results obviously, it runs a lot better and when the CEL comes on for the knock sensor it doesnt bog down as bad anymore. Does that give you a better idea?

[RobertISaar]

LOLOL, i'm amazed it idled.

 

and that "black thing" sounds a lot like the MAP sensor... does it have a 3 wire, green plastic connector?

[Jonpro03]

How did your car run?!

 

 

Magic of OBD1?

[RobertISaar]

Magic of OBD1?

 

magic? no

 

assumed MAP value based on TPS, IAC, A/C status, P/N status and engine speed? yes.

[Jonpro03]

Magic

[RobertISaar]

well, magic is a PITA to decipher too.

[ScoobyDoo82]

Its been running like royal dog poop lately, but I was surprised it was still running too.

 

And no its not the MAP sensor, its some black box with a vacuum hose and another hose running to it, and it has a red/blue connector.

[RobertISaar]

that would be the carbon cannister purge solenoid then.

 

got a multimeter?

[ScoobyDoo82]

I do.

[RobertISaar]

pull the A plug on your ECM (should be colored black), pin A11 is your knock sensor, should be a dark blue wire, connect the positive probe to that wire via the mating side of the harness plug, connect the negative probe to a known good ground, see what resistance you come up with. ideally, you should see around 3900 Ohms. if it's significantly higher or lower, than that will be an issue.

[ScoobyDoo82]

At first I had NO idea what you were saying but once I took a minute and read slow I get it now... should I disconnect the battery when I do this?

[RobertISaar]

there are no grounds or constant positives on the A plug, so no, you don't need to.

[ScoobyDoo82]

Can I just probe the knock sensor pin and ground it out to the battery?

[RobertISaar]

could, but the knock sensor isn't fun to get at on a LH0. i'd try the ECM connector first, see if it gives any clues.

[ScoobyDoo82]

I knew I worded that wrong... I meant can I probe the ECM pin, and ground it on the battery.

[RobertISaar]

ah, in that case, yes. any good ground will work(upper intake usually works for me).

[ScoobyDoo82]

Alright thanks, I'll do that tomorrow and let you know what I find out.

[5speedz34]

Just my .02 cents: Every W-body that I've owned that has thrown the knock sensor code, replacing the knock sensor took care of the issue.

[ScoobyDoo82]

Im thinking thats gotta be it... the conditions that it throws a code doesnt make sense to be a wiring problem. If it was a wiring problem I'd think bumps, brake torquing would cause it, or it would be on all the time and its not. I'm still gonna test it though just in case.

[gp1991]

i have this EXACT same problem on my 91, ever since i got it i have noticed it.