'93 5.7L Knock sensor

[slythee]

What would the truck run like if the knock sensor was bad?

[2000CAYukon]

Originally Posted by slythee

What would the truck run like if the knock sensor was bad?

If the knock sensor is reporting engine knock when there really is none, then the ECM would retard the timing. This will lead to poor performance and may also lead to reduced gas mileage.

If the knock sensor fails to report engine knock when there really is engine knock, then the engine could experience pinging. If the pinging is bad enough, it could result in engine damage.

//2000CAYukon

[heavyredchevy]

How can you tll if its bad... Would the check engine light come on... or is that only if it senses knocking

[2000CAYukon]

Originally Posted by heavyredchevy

How can you tll if its bad... Would the check engine light come on... or is that only if it senses knocking

Very good question and I should have included it in my other post.

If there is no knock detect under full throttle it can set a code. Also if there is constant knock, it can also set a code.

Unfortunately, it can't detect if the sensor is reporting more knock than actual but it is not on constantly (which will set a code).

A scan tool can be used to retrieve the knock count and that can help determine if it is bad.

On my 90 K1500, it is not uncommon for me to see knock counts around 50 to 100 for my 30 minute commute home.

Of course, the engine is original (except for timing chain and intake) and 122K miles.

//2000CAYukon

[heavyredchevy]

So could this be the problem when I get a really random decrease in power at all differnt speeds, and times. Some days I feel it more, other days I dont really feel it.

[2000CAYukon]

Originally Posted by heavyredchevy

So could this be the problem when I get a really random decrease in power at all differnt speeds, and times. Some days I feel it more, other days I dont really feel it.

You should monitor knock count with a scan tool. I bought a cable and use a program call WinALDL (free download, do a google search on it). It is pretty basic but it will show knock count. Otherwise, find someone with a scan tool to look at knock count.

If you still have the original air cleaner assembly, check the valve for the heat riser above the exhaust manifold. When the engine is warm, the valve closes so only cold air goes into the TBI. Mine was bad and I wired it closed.

Do you know what the fuel pressure is when this happens? You need a special adapter (unfortunately) for TBI. Should be 9 to 13 PSI.

Ignition wise, the pickup coil and magnet on the shaft tell the ignition module when the rotor points at a plug. If the upper shaft bushing is worn or the pickup coil is bad (corrosion), it can give a wrong signal to ECM and that can affect performance. The ignition coil can also cause performance issues when they go bad. When mine went out a year or so ago, it felt like it was loosing power in the upper rpm range.

Is the timing chain original?

Good luck!

//2000CAYukon

[heavyredchevy]

Originally Posted by 2000CAYukon

You should monitor knock count with a scan tool. I bought a cable and use a program call WinALDL (free download, do a google search on it). It is pretty basic but it will show knock count. Otherwise, find someone with a scan tool to look at knock count.

If you still have the original air cleaner assembly, check the valve for the heat riser above the exhaust manifold. When the engine is warm, the valve closes so only cold air goes into the TBI. Mine was bad and I wired it closed.

Do you know what the fuel pressure is when this happens? You need a special adapter (unfortunately) for TBI. Should be 9 to 13 PSI.

Ignition wise, the pickup coil and magnet on the shaft tell the ignition module when the rotor points at a plug. If the upper shaft bushing is worn or the pickup coil is bad (corrosion), it can give a wrong signal to ECM and that can affect performance. The ignition coil can also cause performance issues when they go bad. When mine went out a year or so ago, it felt like it was loosing power in the upper rpm range.

Is the timing chain original?

Good luck!

//2000CAYukon

I have checked everything that you said but the pickup coil. if anything was wrong i should have noticed it during the tune up.

[heavyredchevy]

Can you give me more info on this WinALDL. Where did you get the cable from? Will it work with OBD 1?

[2000CAYukon]

Originally Posted by heavyredchevy

Can you give me more info on this WinALDL. Where did you get the cable from? Will it work with OBD 1?

WinALDL only works with older 160 baud ECMs but that includes the ECMs that run the TBI trucks and cars. Therefore, this will not work on all OBD-I ECMs, just the slower ones.

Here is the link to WinALDL http://winaldl.joby.se/

I bought my cable from http://www.akmcables.com/ but the WinALDL website shows you how to build your own.

How is the idle quality?

//2000CAYukon

[heavyredchevy]

Somedays its fine other days it has a surge or a lil miss. I just moved to Laramie Wyoming for school, its a much higher elevation than Wisconsin, and I have been noticing it more. I think its because of the elevation, the thin air is making it run rich. But it had some slight idle problems before hand.

[2000CAYukon]

Originally Posted by heavyredchevy

Somedays its fine other days it has a surge or a lil miss. I just moved to Laramie Wyoming for school, its a much higher elevation than Wisconsin, and I have been noticing it more. I think its because of the elevation, the thin air is making it run rich. But it had some slight idle problems before hand.

My low end miss ended up being a bad connection at the ignition module inside the dist cap. Both vents were pretty clogged and corrosion built up on the connection. I cleaned the connection and vents, put dielectric grease on the pins and low end miss was gone. I still have some idle issues (hunts a little up and down) but otherwise the miss is gone. The miss was also causing it to run a little rich (BLM was 109).

The pickup coil feeds the ignition module an AC signal that is converted to a digitial signal that the ECM uses to fire the injectors. So if this is off, it will cause issues.

Can't hurt to pull the ignition module to take a look. Also check for any play in the dist bushing.

//2000CAYukon

[heavyredchevy]

It has been a while since I checked those things, and wouldnt hurt. Im glad you told me about that program. Im going to get a cable for it when i get the rebate for from my phone.

Thanks

[budlat]

I note you have a K&N filter. Though K&N denies it, the oil that's used on the filter gradually causes deposits on the elements of the Mass Airflow Sensor, which affect its signal. Results in improper fuel feed by ECM. It's easy to clean. I do mine every six months or so. Use aerosol electric contact cleaner and perhaps a Q-tip if its really dirty.

[horse482]

An easy way to test to see if the knock sensor is working is, with you or a buddy hold a timing light on the timing mark while the other lightly taps on the block buy the knock sensor with a hammer. The knock sensor is located on the right side of the block down by the starter. If the timing mark moves when you tap on the block then the sensor is working, but if it doesn't then you have a bad knock sensor.