I have a 2000 S10 Blazer with 126,000 miles (bought it with 57,000). This vehicle has a spark knock (more like a chatter). I hear it under mild to moderate accelleration. We have had this vehicle for 5+ years and the entire time it has had this noise, so I figure that it is something else or it would have eroded a hole in a piston by now. I have put 93 octane in it..no fix, replaced the EGR valve..no fix. I have had the timing reset twice and the mechanics said they cannot find any problems. We not to long ago replace the fuel injection system (I call it "the spider"), distributor cap, spark plugs, wires. It runs great, holds 40+ lbs of oil pressure at operating temp and gets 20+ MPG. I have no idea what this could be and nothing I have done has solved this problem. I would appreciate any help. Thanks.

 

Spark knock can be caused by carbon buildup in the combustion chambers creating hot spots. Try an upper engine cleaner to clean the cylinders/valves and see what happens.

 

thanks.

 

I have a 2000 Blazer with 128,000 miles. Since we have had the vehicle (57,000 miles when we bought it), it had always had a noise that we assumed was a spark knock, sounds like chattering. I will give you a list of the stuff I have did to get this thing to quit.

93 Octane-Didn't help
New EGR+PCV-Didn't help
Seafoam (fuel system/upper engine)-Didn't help
Petron plus oil treatment (I really didn't do this for spark knock, but I think its supposed to help)-Didn't help

Okay a little history on the engine. About 2 years ago the fuel system "spider" was replaced. It runs very well (aside from that freaking noise), doesn't smoke, runs smooth and at the correct temp, gets good fuel mileage (20+), and has good power. Now it does have one lifter that chatters every now and then, could that be what Im hearing...? Also, I heard some were that the balance shaft could make a noise that sounds like detonation. I don't know, its kind of frustrating. Im thinking that it is not detonating because we have driven it for over 70,000 miles with this noise and I figured that if it was I would have blown a hole in a piston by now. If anybody has had this problem let me know. Any info is greatly appreciated.

 

We have a 1997 Blazer 4x4 with 116,000 miles at 89,000 ours started the same thing. It is a piston slap or possible lifter rattling in the bore. Ours runs great gets 20+ miles/gal, 40 PSI oil pressure. I have tried Seafoam thinking it was a spark knock as you. It has been tuned up & serviced regularly since we have owned it. The bottom line is drive it until it blows up, or have the engine rebuilt, or replaced. Personally we are driving ours until it dies then replace the truck. We are looking for another Jeep Cherokee with a 4.0. Our Grand Cherokee is a 5.9 Limited so mileage is 14-18 MPG. We like to have a 20+MPG SUV around. I'm a retired mechanic & it has driven me crazy also. But after conferring with a few mechanics I know we have come to the above opinion. Why it doesn't come apart is the real question or when. I hope I own it in a way when it does so I'll know for sure, if it ever does. Man 70,000 miles & still going tells me I might get close to 200,000 miles or more out of ours. By then it will be out of my fleet for a lower mileage truck. I will run a vehicle up too about 250,000 miles then they have to go. We drive too many miles in places where we can be 100s of miles from help.

 

Thanks, I don't know why I didn't think of that before, given the history of piston slap in GM engines, DUH. But, isn't piston slap a little louder than a spark knock (not trying be a smart tail, Im just asking because I don't know). Anyway, that would make sense or it could be that lifter, because I have a lifter that taps every now and then. Would a compression test tell you if you had piston slap? But, yeah, I have driven it for over 70,000 miles just the way it is and it really hasn't given me any problems (aside from the faulty fuel injection spider). My brakes have given me more problems than the drive train (knock on wood). Anyway, I pretty much have given up on trying to make it run quiet. I have come to the decision to just run it til it blows up too.

 

I also have a lifter rattle every so often on ours. I have always thought it was a little loud for a piston slap myself but when I had other mechanics I know listen to it they seem to think that is what it is. To me it sounds more like a lifter that is in a lifter bore that is wore & letting a lifter rattle around. One thing with ours is under load (driving) the noise only happens above 3000 RPMs. Just sitting about 1500 RPMs it will rattle. We had a 1988 T-Bird with a 302 in it & it had a piston slap but it only made noise when cold.
I run synthetic oil in our Blazer hoping it will add life to the engine by allowing oil into places dino oil doesn't get into easy. But you gave me a lot of hope that our Blazer may give us another 40,000+ miles. I like our Blazer, we drive the heck out of it. I try to keep the RPMs down below 3000. It has traveled a lot of off road. We go hundreds of miles on back roads. So it gets used a lot & hard at times.
My deal with this Blazer is when I bought it used I paid more than I wanted because I thought it was a low miles truck 87,000. Which it was with a good carfax but what I found out after was the dealership had to put a used engine in it before I bought it. I had a lot of issues which they fixed, but this Blazer & us didn't get off to a very good start. But since it has been pretty much trouble free. But it owes me free miles, because of what I paid for it. I gave $5000 cash out the door last spring.
A compression check won't tell you anything except compression. If your getting good mileage & it isn't missing I'm sure the compression is passable.
Lets see how long these two engines will run. Heck we might both get 200,000+ miles out of them. The used engine that they stuck in ours had about the same mileage as the truck had when we bought it.
PM me if it goes south & I'll do the same.

 

I hope the engine in mine lasts for a long time, because as of a week ago the trans went out and that is gonna cost me a pretty penny. You said you have a 4X4 Blazer right (you name suggests that too), that would mean that it would have a 3.42 rear gear, right. Does yours have the G80 limited slip ? I have the 3.08 rear gear and Im thinking about a gear change in the future. What kind of fuel mileage does yours get around town?

 

Our Blazer has 3:73 gears with a G80, We get an average of about 18 MPG. The worst we ever got was 14.7 the best 23.7. On the road cruising at 65-70 we get around 18-21.
Remember if your changing gears on a 4x4 you have to change both front & rear. The cost is pretty high. You can buy a lot of gas for a gear change. If you do it yourself & buy used gears anywhere from $400 to $800. If you have it done my guess is about $2000 to $3000.
To make sure you never have to do a tranny again buy a B&M SuperCooler from Jegs or Summit. I see Amazon.com has them for the same price also. I believe the one I bought for ours was a 5"x11"x3/4" it was $50. I installed it myself. They fit real neat on the right side in front of the condenser. I bracketed ours away from the condenser about a 1/2" I had to drill one hole large enough to feed cooler hoses through. It toke about an hour to install. I swear by these coolers. I burned the tranny fluid so bad towing a 5000# trailer that the fluid was blowing out the vent. Well I had the system flushed with new filter drove it a few thousand miles & had it flushed again all the fluid then added the B&M cooler. I have driven it 17,000 more miles & towed that same trailer once & the fluid is as clean as it was after the second flush. We do a lot of hard off-roading with it. In fact we are headed out this morning for a run that will take us about 140 miles of nothing but dirt roads & trails.