Will the knock sensor always pick up rod knock?

High PSI · Jun 7, 2013

8-years ago I blew up the bottom end of the factory 7-bolt in my 2g. Lack of time and motivation caused the car to sit until two months ago when, home (stateside) from Australia (new home) on a break, I decided to bring it back to life.

I bought a "fully built, mint condition" 2.3L SBR 6-bolt off someone local a few years back, and just finished the swap yesterday. The engine started right up (whoop!), but has a horrid knocking noise. My dad (pretty experienced engine builder) doesn't think it's rod knock, but I'm paranoid as all hell.

Just idling the engine (which is all over the place ATM - still some work to do) didn't reveal anything on the output of the knock sensor. When my 7-bolt went I had it configured so that it would flash the CEL when I detected knock. I wasn't logging with Link when I blew it up, but the CEL flashed more and more frequently for about 5-10 min until the engine just shut down.

How sensitive is the knock sensor? Assuming it's properly installed and functioning, is it possible to have rod knock and not have it detected by the knock sensor?

Thanks guys. I'll post a video of the car idling later as well so you can hear the sound I'm describing.

90laserdsm · Jun 7, 2013

The knock sensor doesnt pick up rod knock. The knock sensor picks up when the air/fuel mixture is off from the ignition timing.

High PSI · Jun 7, 2013

90laserdsm said:
The knock sensor doesnt pick up rod knock. The knock sensor picks up when the air/fuel mixture is off from the ignition timing.

False. It is designed to pick up detonation, but it may also pick up rod knock or other phantom knocks like a rattling heat shield, exhaust, something rattling around the block, etc.

My question is, is it possible for the knock sensor NOT
to detect (mis-diagnose) something as significant as rod knock.

90laserdsm · Jun 7, 2013

well ive had rod knock and it didnt pick it up. but you shouldnt need a sensor to tell if it has rod knock

lowboost13 · Jun 8, 2013

A knock sensor could pick up rod knock but u shouldnt need it to becauae as soon as you get it... You know.

LarryJoe · Jun 8, 2013

My motor just spun a bearing a couple days ago. No signal from my knock sensor though. Weird though because it always picked up the lifters when driving from a cold start.

risknjtsi · Jun 8, 2013

you did mention that you bought that motor a few years back. maybe you should drop the oil pan and see if you have anything going on in there.

crash89 · Jun 8, 2013

I had an engine go on me last spring. I was doing some pulls and upping the boost on a new set up. I kept seeing knock earlier and earlier in the rpm. We tried pulling a lot of timing and messing with fuel to try to correct it but it kept coming. Then we started to hear it.

So, in some instances I believe the knock sensor could and does pick up rod knock.

High PSI · Jun 8, 2013

lowboost13 said:
A knock sensor could pick up rod knock but u shouldnt need it to becauae as soon as you get it... You know.

I don't, though. I'm honestly not experienced enough to hear the sound and be able to pick up exactly where it's coming from or what the issue is (lifters, piston slap, rod knock, etc.). I'm looking for some way to diagnose it without pulling the engine all apart because, frankly, I'm out of time.

risknjtsi said:
you did mention that you bought that motor a few years back. maybe you should drop the oil pan and see if you have anything going on in there.

Agreed this is the best solution, but I'm flat out of time on this car. In 6-days I'm moving back to Australia for the foreseeable future and don't have time to start pulling it back apart again. I have to get this car down to my storage place 50-miles south. If the engine is shot, I don't have time to rebuilt it and no reason to keep a car that I can't just come home and drive, so it's basically either drive it and hope the knock goes away, or drive it until it grenades and then figure out what to do from there (possibly part it....

).

crash89 said:
I had an engine go on me last spring. I was doing some pulls and upping the boost on a new set up. I kept seeing knock earlier and earlier in the rpm. We tried pulling a lot of timing and messing with fuel to try to correct it but it kept coming. Then we started to hear it.

So, in some instances I believe the knock sensor could and does pick up rod knock.

It did in my last 7-bolt as well, but my question is does it ALWAYS pick up rod knock. From the responses I've gotten, it looks like the answer is no, not ALWAYS. So basically my lack of any knock readings just means no detonation.

handsome_black · Jun 8, 2013

A flashing CEL means possible damage to your cat's, so maybe it was not rod nock that messed up your engine. Unless your set up only flashed for when the knock sensor detected knock.

They are fairly sensitive though, and the correct torque when installing them is critical, to much and its over sensitive, to little and it might not pick up anything.

High PSI · Jun 8, 2013

handsome_black said:
A flashing CEL means possible damage to your cat's, so maybe it was not rod nock that messed up your engine. Unless your set up only flashed for when the knock sensor detected knock.

They are fairly sensitive though, and the correct torque when installing them is critical, to much and its over sensitive, to little and it might not pick up anything.

I have DSM link and configure it so that it would flash a CEL when I had over (I believe) 3 degrees of knock retard. When I blew the 7-bolt
I did a long 3rd gear pull. The CEL never flashed while pulling at WOT. However, after the pull I heard an audible knock (not detonation) coming from the engine. The CEL flashed once every 30-seconds or so for the first couple minutes as I attempted to limp the car home on the highway. Eventually the knock got louder and louder, and the CEL flashed more and more frequently until it was a disco light and the engine just shut down.

That's 8-years ago on the old 7-bolt. If the "new" ("5k mile") 6-bolt suffers the same fate I'm going to loose my mind. Fingers crossed I'm being paranoid and it's just lifters or something. I suppose there would be a slim chance that the engine I bought had an extremely early stage of rod knock off the bat (that the previous owner messed it up and immediately shut it down).

Mischif · Jun 8, 2013

The knock sensor is basically just a microphone attached to the block. Then the ecu is progrommed to listen for specific frequency(sound). Since the sound of detonation has a unique tone to it. Although its programmed with for a lack of a better way of saying it, not that great of precision. So it will also register other things as detonation, such as slight vibrations on the block as well as the beginning stages of rod knock. However once rod knock becomes obvious the knock sensor will no longer register it.

At first rod knock can sound exactly like lifter tap and can be extremely difficult to differentiate the two. But once it gets bad enough you WILL know when it is actual rod knock.

Petergeralis · Jun 8, 2013

One way to identify problem cylinder is while engine is idling pull one ignition wire off at a time to listen for change in the sound of the noise. If you hear change then you know what cylinder. Then you can check if it's rod or a quick double knock like wrist pin or piston rock.

YZFR1 · Jun 8, 2013

High PSI said:
I have DSM link and configure it so that it would flash a CEL when I had over (I believe) 3 degrees of knock retard. When I blew the 7-bolt
I did a long 3rd gear pull. The CEL never flashed while pulling at WOT. However, after the pull I heard an audible knock (not detonation) coming from the engine. The CEL flashed once every 30-seconds or so for the first couple minutes as I attempted to limp the car home on the highway. Eventually the knock got louder and louder, and the CEL flashed more and more frequently until it was a disco light and the engine just shut down.

That's 8-years ago on the old 7-bolt. If the "new" ("5k mile") 6-bolt suffers the same fate I'm going to loose my mind. Fingers crossed I'm being paranoid and it's just lifters or something. I suppose there would be a slim chance that the engine I bought had an extremely early stage of rod knock off the bat (that the previous owner messed it up and immediately shut it down).

If you are indoubt about your engine internals, one good way to know what's going on inside without taking anything apart is to cut open your oil filter.

Jeff99GS · Jun 8, 2013

Like YZFR1 said, Sometimes simply draining the oil and inspecting it can give you some answers.

I would drain the oil into a CLEAN pan and then pour it though a funnel with a coffee filter or a piece of a white t-shirt at the end. When all the oil has drained through the filter remove the filter and check for Gold (brass colored) flakes. That would be a tell tail sign of bearing failure.

Also check your Harmonic dampener (crank Pully)...when those fail they make a KNOCKING sound that is very similar sounding to a rod knock. They separate into 2 pieces and wobble. The wobble makes it tap the timing cover and create a KNOCK KNOCK KNOCKING sound.

risknjtsi · Jun 8, 2013

you can try the old start the car and pull out the plug wires to see if the knock goes away if it does you know you have a bad motor

bigbird94 · Jun 8, 2013

It could be a collapsed lifter. Pull the valve cover and look for loose rockers, in addition to draining the oil as others have said.

High PSI · Jun 9, 2013

Thanks for all the suggestions guys :thumb:

I addressed my coolant leak and started the car up yesterday. Below are a few vids. Note that the car is currently idling at 1,500rpm-1,700rpm:

[ame=http://youtu.be/6EHkUejwCBM]6 Bolt Tapping at Startup 1 - YouTube[/ame]

[ame=http://youtu.be/42hTEJlx4rs]6 Bolt Tapping at Startup 2 - YouTube[/ame]

[ame=http://youtu.be/MkUmEhiPyV0]6 Bolt Tapping at Startup 3 - YouTube[/ame]

I pulled the plugs and it had no effect on the knocking/ticking noise. It's pretty quiet up top, so I don't think it's the lifters. I'm hoping (fingers crossed) it's just the timing belt cover hitting something, or one of the idler pulleys making noise as it seems to be loudest at that side of the engine. It almost sounds like it's coming from the balance shaft area, but this engine should have the balance shaft removed (and I timed it for the hell of it anyway).

Did a compression test as well - #1 = 175, #2 = 175, #3 = 175, #4 = 160

Pulling the timing cover off this afternoon...

DSMnoobsause · Jun 9, 2013

Drain the oil into a super clean pan and look for metal shavings/chunks. Post a pic of what you find.

Jeff99GS · Jun 9, 2013

Doesn't sound like a Rod knock to me. Have you checked that crank pulley yet? In that last video the Pulley looks bad to me. See that split between the 2 halves? that's Rubber between there. The rubber splits and causes the pulley to separate.

Take a flat head screwdriver or a prybar and stick it behind that pulley and see if you can gently pry it outward. If the pulley MOVES at all then it is bad. I had one go bad and it sounded exactly like that.

High PSI · Jun 9, 2013

DSMnoobsause said:
Drain the oil into a super clean pan and look for metal shavings/chunks. Post a pic of what you find.

I can drain the oil later, though not sure what that will show if that will be a good indicator of anything since the engine has only been idled for ~10-minutes with the oil that's in the engine now.

Jeff99GS said:
Doesn't sound like a Rod knock to me. Have you checked that crank pulley yet? In that last video the Pulley looks bad to me. See that split between the 2 halves? that's Rubber between there. The rubber splits and causes the pulley to separate.

Take a flat head screwdriver or a prybar and stick it behind that pulley and see if you can gently pry it outward. If the pulley MOVES at all then it is bad. I had one go bad and it sounded exactly like that.

Here's a video of the crank pulley:

6 Bolt Crank Pulley - YouTube

It does move a bit, and it is pretty beat up, but could that possibly be the cause of the noise? It's more of a "tapping" or "knocking" noise, and I just don't see how the split rubber on the pulley could contribute.

I ran the engine (briefly - water pump is disconnected) without the lower timing belt cover on and without any accessories on the crank pulley, and I don't believe the sound changed at all..though it was hard to tell because the engine was idling considerably higher.

I guess I'll order a new crank pulley, tensioner pulley, and idler pulley...

Jeff99GS · Jun 9, 2013

It's hard to tell from the video if your pulley is bad or not, but trust me it makes a WHOLE lot of noise when they go bad. Sounds JUST like a rod knock. I know it seems like a pulley could not cause the noise, but it does.

Do a search for harmonic dampener or crank pulley separating. There is a ton of threads about it. Even some videos of the noise somewhere.

It looks pretty old to me, Any autoparts store should have a replacement for that pulley (harmonic dampener) I think I only paid 50 bucks for a new one.

Here is a video of a bad crank pulley knocking I found on youtube. read his comments, he thought he had a rod knock

You must be logged in to view this image or video.

bcjjones · Jun 9, 2013

I was going to suggest the harmonic dampner also, as it doesn't sound like rod knock to me. I can't remember now but when mine went bad I believe I removed the accessory belts and it quieted the noise down. That's how I diagnosed mine.

YZFR1 · Jun 9, 2013

Just thought i would mention that draining oil by itself is not going to be a give away sign of a bearing failure. I've had a premature thrust bearing wear on my first piston engine build. After draining all the oil i didn't see anything in the super clean oil pan. It was not after i cut the filter open that all the silver colored treasure started pouring out, all just from one premature bearing wear.

DSMnoobsause · Jun 10, 2013

YZFR1 said:
Just thought i would mention that draining oil by itself is not going to be a give away sign of a bearing failure. I've had a premature thrust bearing wear on my first piston engine build. After draining all the oil i didn't see anything in the super clean oil pan. It was not after i cut the filter open that all the silver colored treasure started pouring out, all just from one premature bearing wear.

99% of the time it works. Sorry your experience wasn't as easy. I do this for a living and have never seen 0% sign of failure in the oil when it was a rod,main or thrust.

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Will the knock sensor always pick up rod knock?

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