Basic question: 1984 Corvette, 145K miles. If the knock sensor isn't hooked up or functioning correctly, would you get a check engine light?

Here's why I ask. I just finished changing my timing chain today. The old one had a LOT of slop in it. While I had the oil pan off, I noticed that the knock sensor harness didn't make very good contact with the sensor. When I plugged it back in, it seemed like it was barely hanging onto the sensor.

Anyhow, I started the car today and took it for a spin. It starts much easier and runs much better. The engine is far more responsive....I can actually feel a seat of the pants difference in power, however I am getting some low speed detonation that I didn't have before. It's not present at cruising throttle or when I nail it, just under partial throttle. I immediately suspected the knock sensor had come unhooked, but it's not throwing any codes. Shouldn't I get a check engine light if it's come undone? The light is functioning correctly.

I noticed that the knock sensor uses the same connector as the temp sensor, so I figure I will order two of them and replace them both and see if the detonation problem clears up.

I haven't checked the timing yet, because I loaned out my timing light ages ago and, of course, it never came back (never loan out tools). I don't even remember who has it, so I have to buy a new one. But I'm wondering if the previous owner had the timing set when it had the sloppy chain in it, and now that things are nice and tight again, I have too much timing.

Thoughts??

 

That's exactly what happened because it was set with the cam running retarded due to timing chain wear. Now the ignition is over advanced. Set the timing and you should be good to go.

 

Several items come to mind about your present situation. It might help your problem if you do replace the knock sensor connector. That connector is very fragile (electrically) and will often not make good connection if it is unplugged and plugged-in a few times. If the knock sensor connection is open or intermittent, then the ESC module will not "hear" anything, and the ECM will not retard the spark. Regarding codes, the earlier ESC systems did not have the capability to detect an open sensor (later systems used a 2 kOhm or 4 kOhm resistor in the knock sensor for the ESC module to detect a loaded connection), while others actually monitored normal engine vibration noise to confirm that the sensor is hooked up and working.
In light of your new timing chain, it seems a good idea to go back and check your base distributor timing.
I have a tap-off on one of the ESC module wires on my '84. When the ESC module signals the ECM that knock is occuring, this signal triggers a circuit that blinks an LED in the car, so I know when knock is occuring. I don't have to wait for it to knock terribly loud before I'm notified that knock is going on.
Good luck!

 

Thanks guys. I'm relatively certain that the knock sensor isn't making good contact. And now that I know it won't throw a code if it's unhooked or intermittent, this makes more sense. I'm betting that a new connector will rectify the problem, but I'm still going to check ignition timing as well.

Thanks again.

 

Can you show me how to wire this up on my '89??

 

how about running the car and see whether there is any knock count especially when you accelerate?

 

My '84 was throwing false knock counts. I verified that by revving the engine in neutral (no load) with premium gas and a retarded base timing setting. It still displayed knock counts. Since I didn't want false counts retarding my timing, needlessly, I pulled the wire for the knock sensor at the ESC plug. No codes on an '84, and now I am running 14* base timing on 85 octane gasoline. I have no audible knock.

RACE ON!!!

 

I had a bunch of knock counts once before. Changed fuel to 110 octane race gas and still same thing. Changed to the heaviest weight oil I could find and the knocking went way down. Removed engine and rebuilt it. Knocking went away.

 

Crawled back under the car today, knock sensor had come completely unhooked. The plastic inside the sensor has deteriorated to the point that the connector won't stay on. So, I did what any self-respecting redneck would do......I duct taped the connector back onto the sensor.

Problem solved (temporarily). No more detonation.

New sensor and connector on order. Thanks for everyone's input.

 

On some engines the KS can't be disconnected because the return signal to the ECM would be lost. My 91 severely retards the timing under light to moderate acceleration without kickdown. Does anyone know whether the KS can be "unhooked" on a 91 L98 without causing codes?

 

Have you ever asked "Why is it retarding the timing?"? Maybe the engine is shot and making a lot of knocking noises? Maybe you are using cheap and/or bad gas? How about fixing the problem isntead of trying to bypass everything and anything that hinders you without first figuring out what is broken.

 

I had a similar problem with dirty knock sensor contacts on my '92 and it threw a trouble code IMMEDIATELY upon start up on my DIC.

I think it's Code 43, I might be wrong. Been a couple of years since it happened.

 

Or maybe it's not internal to the engine. THAT is why I did the TEST before I disconnected mine. When I aggravate the situation, I can hear the engine pinging. It wasn't pinging with the timing set to 0* base, with 91 octane, in neutral, but it was retarding the timing anyway. Knock sensors will react to non-detonation noises, both internal and external to the engine. Reactions to non pertinent sources are referred to as "false counts". They are not uncommon. They can come from a partially separated motor mount, something tapping on an exhaust pipe, even roller rockers can set off the knock sensor. The TEST for a functioning knock sensor, is to rap on the block, lightly, and observe a scanner for knock counts.

"Have you ever asked "Why is it retarding the timing?"

Yes I have. I checked it out and determined nothing was seriously wrong with the engine, and proceeded accordingly.

RACE ON!!!