Hi all, was wondering what the symptoms of a disconnected knock sensor is on my 305TPI

 

People have said it will throw a code just because it's disconnected, but mine never did. And during normal driving, your car will run fine without it, so you prolly won't have any symptoms.

But under heavy throttle, your engine will begin to ping because the computer won't be adjusting the timing. And if you keep it pinging long and hard enough you'll begin losing power, THEN you'll get a code, and the computer will go to limp mode.

So until you reconnect the knock sensor, if your engine begins to ping, back off of immediately. But if it happens, pull over, shut down, the computer will reset, restart and away you can go again.

Edit: And I see I've responded to your first post! I definitely not an official welcoming committee, lol, but welcome.

 

Thanks for the info (and welcome) I was worried because I knocked the tip off when installing my headers (the connection had a lot of corrosion) I will replace it as soon as I can. Now to search why after my header install my car has intermittent rough idle at a stop.
Thanks again

 

Why would the computer go into limp mode? It has no idea it's losing power.

 

I don't know how it knew, so I'll guess there's apparently one other monitoring system that can tell when the engine's losing power. But I described exactly what happened to my car 9 years ago.

I'd had an ongoing pinging problem for a long time that no one could diagnose. But it never became serious enough to throw a code and make me pull over until I began long uphill mountain driving. Then after shutting it down and restarting, it was normal again as long as I didn't push it.

I found my knock sensor wire broken and hanging. I repaired the wire, and no more problem.

So from my own experience, that's what will happen.

 

You never found out what code it was?

 

Nope. Diagnostics weren't showing any codes later after having restarted it. And I never tried when the light was on and I was on the side of the road 30 miles from civilization in either direction. I just wanted to get home, lol.

 

...

 

91redTA,

I can think of two things that might be screwing up your idle based on what you've written. First, if the knock sensor wire is just "hanging" disconnected from the sensor itself, the ECM might be responding to noise on the line. The knock sensor output is relatively small in magnitude. So, the ECM has to amplify the voltage quite a bit to "see" if there's any knock. Unfortunately, it won't know the difference between electrical noise and actual sensor output. I'd connect the knock sensor wire to a good ground and see if things improve. That should eliminate any noise problems and associated spark retard, if they're present.

Second, you mention the installation of new headers. Unless you're tuning the ECM for the new exhaust system, it might take a little while to "learn" the "new" engine behavior. Also, if you have a scan tool handy, you might want to see if the car is staying in closed loop at idle. At idle, the O2 sensor can cool off enough to drop out of closed loop since there's less hot exhaust gas running through. While this was much more a problem with non-heated one wire O2 sensors, it's still possible for it to happen with heated versions. Especially if the headers have the O2 moved further away from the engine.

Good luck !

 

I have installed the Edelbrock TES headers and when monitoring my o2 sensor. It seems like it just quites working alot. I don't get any crosscounts and the voltage goto .8mV or so. Could this also be that I need to get a heated o2..??