Knock sensor

[mikeH1995]

I have a 1995 k1500 with the 5.7tbi and 4l60e. The knock sensor code has been on for a while now. I put a new knock sensor with plug, coolant temp sensor, distributor, cap, rotor, plugs, wires, and map sensor. When coming to a stop at normal operating temp the down shift causes the rpm to drop just below 500 and it feels like it's going to die, it has not died yet. Once it's above 1,500 rpm it runs great just sluggish on the low end.

 

[Schurkey]

Verify fuel pressure.

Connect a scan tool, look at the data stream.

Follow the GM Service Manual diagnostic process to find the source of the knock sensor code.

 

[mikeH1995]

Verify fuel pressure.

Connect a scan tool, look at the data stream.

Follow the GM Service Manual diagnostic process to find the source of the knock sensor code.

How do I verify fuel psi? I'm going to look for someone that has a scan tool for obd1. Is the GM service Manuel online? I have a repair manual, that tells you nothing.

 

[thinger2]

I have a 1995 k1500 with the 5.7tbi and 4l60e. The knock sensor code has been on for a while now. I put a new knock sensor with plug, coolant temp sensor, distributor, cap, rotor, plugs, wires, and map sensor. When coming to a stop at normal operating temp the down shift causes the rpm to drop just below 500 and it feels like it's going to die, it has not died yet. Once it's above 1,500 rpm it runs great just sluggish on the low end.

Keep in mind that the factory tach does not read from zero to 1000 rpm.
It reads from 500 to 1000 rpm.
Look at the segments on your tach.
The low end is a smaller segment than the rest of them.
It fooled me at first and has fooled a lot of people.
So you are not idling below 500, you are idling below 1000.
It wont read below 500 because 500 is zero for a factory tach.
When you replaced the knock sensor, did you pull the starter to do it or did you fish the wire through.
That wire is pretty fragile and it often gets pinched by the starter install or gets stripped on the heat sheild burrs and shorts to ground if you pull it through.
When you pulled the old knock sensor did it pee coolant out of the hole?
It should have.
If it didnt that drain is plugged full of crud.
Poke it and stand back and let it pee.
When you installed the new knock did you coat it with any kind of thread locker or anti sieze and then install into a drain that was not peeing coolant?
It is a single wire sensor so the body of it grounds to the block.
And a continuity test will tell you if it is grounded.
A good multi meter will really help you.
It doesnt need to be a Fluke.
It only needs to do continuity "tone"
and have removable and interchangeable leads.
The problem with adding random parts is that instead of one thing being out of parameters and needing to be reset,
Now you have 5 or ten things out of parameters and they all need to work together.
Imagine that you were conducting an orchastra and heard a sour note from a player.
Would you loose your mind and kick the whole brass section to the curb and replace them with random high school band students and expect them to come toghether and play a perfect rendition of whatever you think they should sound like?
Every time you randomly replace a part on a TBI system without any kind of diagnosis it just makes more problems.
You end up in a situation where everything is out of parameters and now you are digging around looking for 40 year old gm logic flow charts.
In my experince?
Only fix one system at a time.
Set the timing.
Run it till its hot
Pull the plugs and take a look.
That is the baseline.
Compression test, leak down test all of that.
I think that we are all trying to speak the same language,
But I also think we have a wall between modern understanding of these sytstems and the older pre internet pre cell phone knowledge.
Sometimes I feel like that rotten old dried up de-hydrated fart in the cave who is all jumped up big balls because he gets to tell Indiana Jones whiich tea cup he can have.
**** off I picked the GM TBI you rotten old smelly turd.
Take a shower and get a life.

 

[df2x4]

Is the GM service Manuel online?

Yup, the '95 GM service manuals are available for download here:

https://www.gmt400.com/threads/88-98-service-manuals.43575/

 

[mikeH1995]

Keep in mind that the factory tach does not read from zero to 1000 rpm.
It reads from 500 to 1000 rpm.
Look at the segments on your tach.
The low end is a smaller segment than the rest of them.
It fooled me at first and has fooled a lot of people.
So you are not idling below 500, you are idling below 1000.
It wont read below 500 because 500 is zero for a factory tach.
When you replaced the knock sensor, did you pull the starter to do it or did you fish the wire through.
That wire is pretty fragile and it often gets pinched by the starter install or gets stripped on the heat sheild burrs and shorts to ground if you pull it through.
When you pulled the old knock sensor did it pee coolant out of the hole?
It should have.
If it didnt that drain is plugged full of crud.
Poke it and stand back and let it pee.
When you installed the new knock did you coat it with any kind of thread locker or anti sieze and then install into a drain that was not peeing coolant?
It is a single wire sensor so the body of it grounds to the block.
And a continuity test will tell you if it is grounded.
A good multi meter will really help you.
It doesnt need to be a Fluke.
It only needs to do continuity "tone"
and have removable and interchangeable leads.
The problem with adding random parts is that instead of one thing being out of parameters and needing to be reset,
Now you have 5 or ten things out of parameters and they all need to work together.
Imagine that you were conducting an orchastra and heard a sour note from a player.
Would you loose your mind and kick the whole brass section to the curb and replace them with random high school band students and expect them to come toghether and play a perfect rendition of whatever you think they should sound like?
Every time you randomly replace a part on a TBI system without any kind of diagnosis it just makes more problems.
You end up in a situation where everything is out of parameters and now you are digging around looking for 40 year old gm logic flow charts.
In my experince?
Only fix one system at a time.
Set the timing.
Run it till its hot
Pull the plugs and take a look.
That is the baseline.
Compression test, leak down test all of that.
I think that we are all trying to speak the same language,
But I also think we have a wall between modern understanding of these sytstems and the older pre internet pre cell phone knowledge.
Sometimes I feel like that rotten old dried up de-hydrated fart in the cave who is all jumped up big balls because he gets to tell Indiana Jones whiich tea cup he can have.
**** off I picked the GM TBI you rotten old smelly turd.
Take a shower and get a life.

I did not remove the starter. Fluid did pee out when I replaced the knock sensor. The sensor is grounded correctly. Timing is set and the new plugs still look new after about 50 miles. Normally at idle in gear the tach reads 650, when coming to a stop it drops to 450 for a second then picks back up. I'm going to check the wire from the sensor to the computer tomorrow. Compression test was normal. What is a leak down test?

 

[thinger2]

Basically a compression test tells you if that cylinder is compressing.
A leak down test tells you if that cylinder is holding preesure and for how long it holds that pressure.
Also can tell you if that loss is through the valves or the head gasket or the rings.
But I dont think that is your problem.
What you describe is an idle stumble or idle drop that recovers.
Almost certainly a TBI system issue.
I would start with fuel pressure test and fuel filter.
And keep in mind that every time you randomly replace a part on a TBI system without diagnosis you are not only acting outside of the ancient GM diagnostic flow chart.
You are also introducing unkown variables into that process
This is a big problem because you have no idea if the new part is good.
And they quite often are junk.
So you need diagnose that part and then do it again for the new part.
OBD 1 doesnt tell you much.
It codes when something in that system is out of parameters
When you bolt on a bunch of parts.
Everything in that system is out of parameters.
And that leaves you with a pretty complicated and ancient flowchart based relearn process.
ITYN.
"Ityen"
If, Then, Yes,No.
Way way back in the paper tape reader punch card days we were known as "Ityenidiots"
The OG geeks.