1990 C4 Corvette Base Model Knock Sensor

I kept getting the 'Service Engine Soon' light and did the paperclip code read procedure. I got H43 (Knock Sensor)

I replaced the knock sensor, located just in front of the starter on the passenger side on the block. I noticed three things when I removed the old one.

1) The tip of the knock sensor, that part that is inside of the block, was rusty, with a little dried crud on it,
2) No water came out of the hole, and that hole is a water jacket, so, hmmmmmm.
3) After replacing the knock sensor with a new one, I still get the 'Service Engine Soon' light.

Problem: When I attempted to remove the the new knock sensor, the head just spun, that copper/bronze part with the hex head on it. It spun without turning the body, that part screwed into the block.

I put some vice strips on the knock sensor body to loosen the body (that part that screws into the threaded hole. The body broke off, leaving the threaded part of the knock sensor inside of the block. I wanted to see if I can clean the water jacket to allow water to flow.

Question: How do I get that threaded nipple out of the block? Also I did a search and learned that the 1990 C4 should have two knock sensors. I have only one.

Any way, lets get this threaded end out of the block.

 

Might throw some rust penetrator on it and let it sit for a while.

https://oards.com/best-penetrating-o...-rusted-bolts/

Then get some vice grips or a bolt extractor and try to start turning it.

 

Where did you do your 'research'? I believe your '90 should just have one.

 

Thanks for the recommendation. Vice Grips? I was using vice grips which caused the knock sensor to break off at the stem. I have since drilled a hole down the center and will trying to drill it out just before the threads, then using a tap, clean the threads to install the new knock sensor. I tried an easy out, but I was unable to get a good grip on the stud.

 

I did my research in the most typical way. I googled it. While under the car, I saw only one, on the passenger side, just above the starter.

Here is the answer that I got from my google search::::::::

"A 1990 C4 Corvette, equipped with either the L98 or LT5 V8 engine, has two knock sensors."

 

As far as I know, the 7727 ECM only has a provision for one sensor.

 

Okay, C4 guys. I need more knock sensor help.

I got the broken knock sensor out, and installed another new one.

First, my first knock sensor did not yield coolant coming out of the knock sensor hole. With all of the drilling, the clinking, the clanking, and other vibration, coolant did come out of the knock sensor hole. As a matter of fact, I put a drain pan down, and after unscrewing the sensor nipple, water came flowing out of the knock sensor hole.

I noticed a lot of rust like debris come out in my bucket. I flushed the radiator/engine and got clear, clean water out of the knock sensor hole. I installed the new knock sensor, and it did not solve my Service Engine Soon light, H43.

I did the paper clip procedure to get the codes.

I got two codes:

H31
H43

H43 is knock sensor. I did resistance on the knock sensor. I got 0999.

I cleared the codes, started the engine, and the Service Engine Soon light came on after about 10 - 15 seconds.

For the people in the know, what can I do to fix this issue? My knock sensor wire was oily and frayed in a couple of places. I spliced new wire in and re-installed the connector, cleared the code again, and started the engine. Engine ran perfectly. However, the Service Engine Soon light came on again.

I disconnected the green connector on the ECM on the driver side under the hood. This connector has two dark blue wires. The knock sensor's wire looks dark blue. How do I test the knock sensor circuit to ensure that there is a connection between the knock sensor and the ECM? Let's do this next. Test the knock sensor circuit. Someone chime in, please. Thanks

 

Yellow connector at the ECM. Cavity 11. Dk Blue. But that's not how you check it.

Turn key to RUN. Disconnect knock sensor. Measure voltage on dk blue wire at sensor to ground. Should be appx 4.5-5 Volts. If = NO, the wire is open. But I don't think this is your problem.

"999" is not correct. You want 3300 to 4500.

From the FSM Code 43: [If voltage at sensor is OK] check resistance of knock sensor between sensor terminal and engine block. Should be between 3300 & 4500. Is it?
YES: Check harness and sensor connector.If Ok: Remove ECM and be sure Mem-Cal is properly seated. If Ok: Replace Mem-Cal.
NO: Faulty knock sensor. (Note: I had a sensor that measured ok between its terminal and the shell, but high ohms to the block. I removed it, cleaned the threads on the sensor and block, and that resolved the 43.)

If you measure 999 Ohms, you were given the wrong, or a faulty, knock sensor.

 

IHBD,

Thanks for your response. Your response gives me a valuable option to try. Also, thanks for telling me about testing the knock sensor. I will do this on Sunday, turn the key to the ON position, then test the voltage between the knock sensor wire to the engine block. I will be looking for voltage, 4.5 to 5 volts. I will report back that reading.

Now, regarding the resistance of knock sensor between terminal and block, checking while knock sensor in installed in the block. I will be looking for 3300 and 4500. Again, I will report back my reading.

Now, your instruction was to check the resistance between the sensor terminal and the engine block. If it is within the range, 3300 and 4500, you stated that I should check the harness and sensor connector. What am I looking for to determine if it is okay? I stated above, that the wire at the sensor was frayed, and I removed that damaged wire and installed good wire.

Now, please tell me what I should be looking for to affirm that the knock sensor wire and knock sensor connector are not damaged. If I replaced bad wire, I presume that the wire and connector are not damaged. If there is something in particular, or a test done to affirm that the wire and sensor connector are good, please state this test.

Removing the ECM and checking the Mem-CAl. I presume that I need to remove the ECM cover, identify the Mem-Cai, and affirm that it is properly seated. I will do this on Sunday.

Now, when you say, replace the Mem-Cai, do you mean get another one and install in the current one's slot? Please clarify.

Note: When I removed the broken knock sensor nipple from the freeze plug hole, I did clean the threads in the hole, after the fluid stopped flowing. The new knock sensor had the material on the threads, and I did not remove it. I also did not tighten the knock sensor too tightly this time. I will presume that the threads made constant contact with the threads in the freeze plug hole.

Two things in conclusion

1) How do I test the knock sensor wire from the ECM (Yellow connector, Cavity 11) Dark blue wire, to the connector at the knock sensor at the block to test the wire is good?
2) Test the knock sensor resistance (ohm reading) from terminal to block, and reading should be between 3300 and 4500

I will report back with my readings to affirm the results. Thanks again

 

Both questions were answered in post # 8

You have a bad or incorrect knock sensor. Take your VOM with you to the parts store when you go to purchase another one. Measure it right at the counter. It has to be 3300 to 4500 Ohms..

 

Acknowledged. I will get another knock sensor, and using my ohm meter, test the resistance between the knock sensor terminal and the threaded nipple (that part that screws into the block.

 

I went out this morning and tested according to your instructions. I got 4.8 volts when testing the knock sensor, key to the ON position, connector terminal to the block.

I tested the knock sensor, terminal to block, and again, I got a reading of 9.99. So, I made the presumption that the new knock sensor was bad. I went to O'Reilly and got one from a different location. I had my meter on me and tested it at the store. 3.898 was my reading. So, I bought it and installed it.

I tested the knock sensor again after installing it. Reading was 3.898. I assembled everything and started the engine. No Service Engine Soon light. So, I will check this one off as repaired.

I want to thank you again for your patience and input. I can now pass this knowledge on to the next person who needs to learn it.

 

Cool! Good info here.
Sad the "new" sensor was defective. More and more these crap parts are becoming a regular issue, frustrating everyone from the DIY'ers to the repair shops. Eric O from Main Street Auto (on YT) has been on a rant about this more and more.....

 

South Main Auto. Dude's a wiz with electrical related problems.