Question on ED17 (knock sensor)

[bikemikey]

Checking the data on my 89, I noticed that on a warm engine, closed loop, ED17 seems to be stuck on 151. ED16 (spark advance) is stuck on 0 even when I rev the engine. Isn't ED17 suppose to fluctuate somewhat. I'm thinking I have a bad ECM , I 'm going to change it out this week. Every now and then I get a code E026, but it seems to go away. I'm also thinking I have a bad knock sensor or maybe the ECM is not giving any information to ED16 . I'm getting a funky idle. Any opinions, thanks. 

[Guest Rp1967]

I remember fixing some knock sensor codes by removing the knock sensor , cleaning the threads and reinstalling.

[Barney Eaton]

I got bad idle and bad gas mileage with a knock sensor that was sending big numbers to the ECM

[2seater]

ED16 is the amount of knock retard and should remain at zero under almost all conditions. ED17 is the total knock counts and counts up steadily as knock is occurring. Sometimes it will increment upward just from starting the engine due to the noise from the starter and other things. This is normal. ED08 is the actual spark advance and should be around 20 degrees at warm idle and will generally jump up two to four degrees when dropped into gear, and yes, it should vary with rpm and may go as high as 70 degrees at very light cruise.

[bikemikey]

I need to check ED08 and see what's going on with it, I did not look at that one. I am going to change out the ECM this weekend, I'm thinking it is bad. This car will throw codes sometimes then heal itself. The way I see it, it is electronic,  26 years old and doomed to fail at some point in time. I'm also going to check the ground connection at A12 on the ECM connector. Correct me if I'm wrong, but I should get full continuity on the ohm meter ( no resistance ), am I right on that one? I still might have to change out the knock sensor, but I'll wait and see what the new ECM says. I don't like the fact that ED17 doesn't move. I'll let you know later what I find out.

Thanks everyone   

[padgett]

I expect to see a burst of knock counts on startup but not after you go into closed loop. Then they should only increment if you suddenly go from cruise to WOT  or out of a stop light as the computer takes a cycle or two to decide you need less advance.

[2seater]

I don't have a wiring diagram handy to comment on specific connections but I do know there are multiple grounds for the ECM. Yes, they should have little resistance.

 

ED17 will only increment upwards if there is actual knock occurring. You "should" be able to get it to change by sharply tapping on a solid surface on the engine brackets, like the engine lift loop at the passengers rear of they engine with the engine idling. You may actually get the engine to stumble a bit if there are enough knock counts to cause the spark retard to activate. That said, I have had one instance of a bad knock sensor, not one that gave false counts, but one that did not register when it should have as you describe. If you change it, check the torque spec as if it is excessively tight, it may be too sensitive. One other item just for my own curiosity, if you change the sensor, please let us know if there is engine oil at that port. There should not be but I have heard of a couple instances of the hidden threaded plug inside the oil passage being missing. It shouldn't matter to the sensor but more of a trivia item.

[bikemikey]

Will do. It will probably be next week, but I will get back to you. 

Mike

[bikemikey]

2seater, there was no oil on the old knock sensor, dry as a bone. I could not find a torque setting for the new sensor, so I just snugged it up. 

I also installed the new ECM and used the old PROM. The car ran fine, the idle seem to have improved a little bit, of course that was with just a few miles of testing. I'll put more miles on the car this week and see how it does. It was loads of fun installing the new ECM, when I was done I felt like a pretzel. Good thing I see a chiropractor once a month.

Mike 

[2seater]

Thanks for the info. Do the readings in diagnostics now respond as you would expect?

[bikemikey]

I haven't had a chance to look at the diagnostics, but I do know there was an improvement  when I took the car on a couple of test drives. The engine ran a lot smoother at idle and did not throw any codes so far. So I guess it was a good move to change out the 02 sensor and the ECM. I'm taking the car out Sunday , so I'll check out the diagnostics then. I'm now wondering about the PROM or memcal , whatever it's called. I suppose in time it will become an issue as well.