Knock sensors on 4.8L Chevy engine (2001)

sensors

#1

I have a '01 Chevy Silverado pickup that will not run on regular unlead fuel. I have to put the premium (high octaine) fuel in it to keep it from sounding like it is going to send every lifter in it out thru the block. I was informed that it could be the knock sensor on this engine. Is this a likely problem? I have been doing some research on this item and have had this truck dowb ti autozone a couple of times, but it never shows a code problem. Just want to know if I am heading down the right path before I start tearing the intake off to replace these. Any suggrstions will be greatly appreciated.


#2

What does the owner’s manual recommend? If it’s premium, then stick with premium.

If it’s regular, then you’ll need to determine why it’s knocking. The knock sensor detects preignition and backs off the ignition timing, but you need to get at the source. The source of this in an engine that’s designed to take regular is often a faulty Exhaust Gas Recirculation (EGR) system. Today’s engines run hot to maximize combustion. On acceleration, the EGR system allows a bit of inert exhaust gas to displace a little inflowing air (and its constituant oxygen) to keep the cylinder temps from rising too high and causing preignition. If that’s malfunctioning, the engine will ping…and maybe even knock.

Start with the EGR system. The valve may be stuck shut. Post back.


#3

When I purchased this truck (new), I was under the informed that 87 octain was all that was required to operate this rig. I ran it on regular from the date of purchase of it till it hit 48000 miles. This is when it started with all of the noise. I took it to the chevy house and they informed me that I needed to leave it with them so that they could run some type of acid thru the engine and let it sit for the whole weekend. This was going to run me about 1800 bucks. Needless to say, I took it home and tried changing out the plugs, the oil, and the EGR valve with no luck. I finally got the tank almost empty and put super in it and it cleared right up. Tried another tank of regular in it and it started with all of the racket again. I have been running super in it ever since. I now have 160000 on this truck and it is running fine, but I am concerned that I might be doing some harm to it. I have since changed out the fuel pump (100000 miles on it) and the EGR again (112000 miles on it). Want to keep it around as long as possible.

Thank you for your post.

ledjr857


#4

I’ll second Mountainbike. You likely have an EGR system fault rather than a knock sensor problem.


#5

My guess is that they cleaned the carbon out on the suspicion that carbon buildup might be causing the preignition. They probably checked the EGR system before doing that and found it working. Carbon retains heat and buildup can cause preignition. Enough buildup could even affect the compression ratio enough to contribute to the problem.

Another possibility would be lean mixture, which will cause higher cylinder temps, but that generally carries with it other symptoms as well. If it’s running great I wouldn;t mess with it.

The bottom line is that if it’s running great and not pinging then I’d just keep it well maintained and keep running hi-test in it. It’s doing absolutely no harm. Your engine may be on the “cusp” of needing hi-test.


#6

It could also be carbon build up on the valves or cylinder head.

You could try Seafoam. It’s solved a lot of knocking chevy problems:)


#7

I really appreciate all of the posts on this item. I have replaced the EGR valve twice since I have owned this truck and expect that I will be needing to replace it again soon. The last time that this happened, I took it to AutoZone and asked them if they could read my computer and retrieve the code. The guy that did this said that it was the EGR valve and I asked him if he had heard anything about this being a problem on Chevys. I told him that this was the second one that I had to replace since the purchase of this truck and he stated that I might have a problem that went deeper than I was looking. This is why I was courious about the knock sensor. Now since I have inquired about this, I will probably be having to replace the EGR valve again, sooner than I had hoped. It seems that it goes out every 50000 miles and I have put around 60000 on this last one.

ledjr857