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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Pretty soon after I installed my SuperRam about a week ago, my datalogs started showing increasingly-high knock counts: on 7/29, my datalog showed about 1.4 knock counts per minute, but my last log today shows 18.3 counts per minute!
The weird thing is that these knocks occur at low RPM--they are very heavily weighted along the 1250 RPM line--and almost exclusively within the first 5-10 minutes of the engine running (more if the engine was cold to start, less if it was warm). I'm only running about 25 degrees of timing in the worst-affected places, whereas other areas of my tune with as much as 40 degrees of advance show no knock counts.
I initially chalked this up to piston slap from my forged pistons, but when I realized that the knock rate was rapidly getting worse I began to get concerned. Another observation that pointed against piston slap is that I still see knocks when I start out with a hot engine (200 °F startup coolant temp).
My VE tables are fairly-well dialed in (within about +/- 4% of 128 BLMs in the affected area) and I've tried pulling as much as 10 degrees of timing with no effect.
In the early stages of the engine running, when knock counts are still rapidly rising, lightly revving in neutral gives a few knock counts as the RPMs fall back down. Another thing I thought was interesting is that the graph of knock count shows gradual increase punctuated by large bursts of knock count-- one instance in my last log showed 42 counts in 10 seconds. Other than that, I don't really see any patterns in the data.
I can't say I know what detonation sounds like, but I don't notice any "marbles in a coffee can" noises or really anything abnormal.
Super Ram? Man you got pretty awesome package now enough to make the rest of us jealous!
Wecome to TGO . Some really knowlegable folks here and the moderators are all good people. They run this forum right IMHO.
Back to your problem with high knock counts that 1250 range is pretty tough to hurt the motor as there isn't enough air and fuel mix to do much damage. If timing is pulled to 25 degrees it may still be to high at 1250 RPM. Not going to hurt to try reducing timing all the way to base/idle timing. Remember whenever you increase the VE of engine the less timing/advance you need. That Super Ram may have something to do with this.
If reduced advance doesn't stop the knock then I can recommend trying a richer mix - kinda shooting from the hip here but you should see what it does. Again the Super Ram my be affecting how the fuel is getting washed into the cylinder runner at that RPM.
It's a blast for sure! Far from optimized but it still pulls pretty good.
Thanks! I may post mostly on Corvette Forum but I've found a wealth of information here for sure, especially in regards to tuning.
I pulled some more timing, and I'm still seeing the problem. On my last run, I still saw 13 knock counts in cells where timing was 10-15 degrees and 43 knock counts from 15-20. I've dropped timing once more so the max in the range I'm seeing knocking is 10° advance, so we'll see where that gets me.
The weird thing is, I saw this problem (of a smaller magnitude) before installing the SuperRam. Same deal--knock counts in a straight line across 1250 RPM--just with about a fifth the total knock counts.
Is there a way to make the mix richer just in those cells, or do I have to use the scalar to adjust the target AFR across the board?
Thanks for all your help (here and on the Corvette Forum).
Remember the knock sensor is just a microphone. It can pickup noises that are not actually knock. It's not a perfect system. Checking the knock sensor waveform with a scope against a known knock event might be prudent.
Just an added thought it could be just one misbehaving piston. Not trying to talk you into a lot of work but a separate data scan for each cylinder with the plug wire pulled might show a violator. But that maybe a whole lot more work than you want right now. Easy for me to suggest but not so easy for you to test. So I just want to throw this out there as you may have a better form of the idea.
Thanks for the suggestion. That does sound like a lot of work, but at this point I'm ready to try pretty much anything. Just a couple of thoughts, could it be that my plugs are too hot or that the valves aren't adjusted right on that one cylinder?
Actually, if it were one specific cylinder, would pulling all the plugs to look for speckling work? I'd think if it were limited to one cylinder that I've had hundreds of knock events on the plug would look pretty bad by now.
I just ran another datalog with the spark table maxed at 10°, and I still got 12 knocks in cells with 5-10° advance. Same deal, clustered around the 1250 RPM line. Interestingly though, I had knocks in the range of 15-30°, when the spark table in those cells clearly commands only 10° advance. What's going on here?
I only had 21 total knock counts though, so it seems to be an improvement. I can't say for sure that isn't attributed to starting with a dead cold engine, though.
EDIT:
My real hangup here is that the knock counts are purely RPM-dependent. I have cells just 300 RPM away from where I'm seeing knocks that have 25° more timing, and they're not knocking. Granted I know a whole lot less about engines than you do, but to me that seems like a rotating part is hitting a resonance and causing false knock right around there, is that possible? Come to think of it, I failed to rebalance my flywheel for my new engine. I don't have any noticeable engine vibration even at high RPM, so I shrugged it off, but could it be causing this?
EDIT 2:
Went on another datalogging run (same tune, but I dropped closed TPS spark advance from 16° to 10° in a couple cells) and kept having knock. Interestingly, it looks like my adjustment to the closed TPS advance shifted the knocks higher up in the kPa range--whereas they were focused around 40 kPa before, now they are located more around 80 kPa. So it appears that timing does have an effect on this, which would seem to eliminate it being a false knock. However, about a third of the cells with knock counts showed just 6-7° of spark advance! These were all about 20% throttle at 1300 RPM, for a pressure of ~70 kPa.
I'll pull the plugs, and if I don't see anything abnormal I'll go back to a more driveable timing map and drive with one wire off at a time to see if I can track down a bad cylinder.
I'd like to take my car somewhere tomorrow, and I don't have much to do today except fix this problem, so any suggestions anyone could give me would be greatly appreciated.
Last edited by C4ProjectCar; 08-04-2017 at 04:34 PM.
Is there a way to make the mix richer just in those cells, or do I have to use the scalar to adjust the target AFR across the board?.
Sorry but he last time I did a tune the software had a table for A/F ratio and I could change as many blocks at a time as I wanted. Had timing (of course) and VE tables to.
You should post what your using for tuning software and someone else might chime in with the right help.
I'm using TunerPro RT. As far as I know, not having an AFR table would be a limitation of the ECM code mask, not the tuning software.
Just got my D/S plugs out, and they look fine to me. One thing I noticed is that they're a very cold plug--Delco 41-602--which is as cold as Delco's scale goes.
Edit:
Got the P/S plugs out, they look fine to my untrained eye too. Although do the plugs overall look a bit dark for just 1400 miles? Passenger side plugs on the right
Last edited by C4ProjectCar; 08-04-2017 at 06:51 PM.
Since the plugs were the wrong heat range, I decided to change to the plugs suggested by AFR (Autolite 3923). That actually seems to have helped; my last datalog (where I was using my full-timing tune) showed just 13 knock counts in the same period as the rest. That may have just been due to the cold engine, though.
It seems the majority of the knock counts occur shortly after I drop to cruise after a period of hard acceleration.
Edit:
Scratch all of that. It's still getting a ton of knock counts (including when it isn't even in gear and I just hold the throttle at 1250) and a lot of them are just in cruise.
And the car just started hunting at idle real bad, and both my headlight motors just started acting up (I've replaced both of their gears and bushings recently). Can this car just give me a break?!
Last edited by C4ProjectCar; 08-05-2017 at 12:48 AM.
Since the plugs were the wrong heat range, I decided to change to the plugs suggested by AFR (Autolite 3923). That actually seems to have helped;
Edit:
Scratch all of that. It's still getting a ton of knock counts (including when it isn't even in gear and I just hold the throttle at 1250) and a lot of them are just in cruise.
And the car just started hunting at idle real bad, and both my headlight motors just started acting up (I've replaced both of their gears and bushings recently). Can this car just give me a break?!
I'm interested to see what some enrichment does here. Sorry can't tell you how to do it though.
Yea, corvette headlights have been a problem ever since they made them hide back in 1963. Hey don't forget the car is 25 years old! You want mediocrity then buy a new Prius every 5 years.
Well sometimes I have to fix something at least twice to get it right.
Yea I don't have anything solid to suggest for knock counts in that one range. I think I'm reading that you can have knock counts but it may not be enough to pull timing. Can you watch real time with your software to see if timing advance is being subtracted when the ECM reports those knock counts??
Kinda suspicious of a lean mixture too. Also that odd ball injector maybe at fault and pulling the plug wire on that cylinder is where I would start to test.
Thought I had noisy lifters. Having no frame of reference because I went from inoperable injectors straight to D3's. Turns out the Bosch injectors are crazy loud and since the injectors are fired all at the same time it sounds like one big noisy lifter.
Thought I had noisy lifters. Having no frame of reference because I went from inoperable injectors straight to D3's. Turns out the Bosch injectors are crazy loud and since the injectors are fired all at the same time it sounds like one big noisy lifter.
Good to hear about the injectors - I may not have a bad lifter after all!
I think I'm getting somewhere with the knock counts! I was driving with my windows down, holding the car at 1250 RPM, and I noticed a squeaking sound. So I came home, popped the hood, and tried to reproduce it. Sure enough, right at 1250 RPM something is squeaking. I tried to get a video of it, but it seems to be intermittent: I got one squeak on my video, and then it stopped.
Best way to find noises like those is to take one of those stethoscopes with the metal rod and try and find where the noise is loudest at. Def seems like it could be accessory related.
I've tried with the vacuum line to the ear trick (can't really use the stethoscope since holding it to a spinning pulley doesn't work great).
The issue is that the squeak only is loud enough to stand out intermittently and at that particular RPM, and it's hard to poke my head around the engine while I'm feathering the throttle and monitoring RPM on my phone.
I tried spinning the pulleys by hand with the engine off, but none of them were hard to turn. The air pump and water pump both had a little resistance, but I think that was just from turning the pump itself rather than from bad bearings.
I've tried with the vacuum line to the ear trick (can't really use the stethoscope since holding it to a spinning pulley doesn't work great).
The issue is that the squeak only is loud enough to stand out intermittently and at that particular RPM, and it's hard to poke my head around the engine while I'm feathering the throttle and monitoring RPM on my phone.
I tried spinning the pulleys by hand with the engine off, but none of them were hard to turn. The air pump and water pump both had a little resistance, but I think that was just from turning the pump itself rather than from bad bearings.
You'd put the stethoscope on the most adjacent stationary object. E.g. If it was a pulley, you'd put it on a bracket closest to it or closest to the suspected bearing
The bad bearing or whatever it is seems to be getting worse--knock counts are rising even at idle. I couldn't reproduce the squeak, but if knock counts are rising then there has to be something making a noise I can find.
I disconnected the EST wire to preclude the possibility that spark knock was occurring (it's pretty much impossible for a stoichiometric mixture to knock at 6° with 8.5:1 dynamic compression, right?), and as I watched the knock counts tick upward, I put a mechanic's stethoscope on any possible source of noise. I tried the AIR pump, the alternator, the AC compressor, the belt tensioner, the power steering pump, and the water pump.
Now I don't really have a frame of reference here, but they all sounded pretty normal to me. The water pump seemed a tad squeaky through the stethoscope, but I think it'd take a pretty obvious noise to set off the knock sensor.
I've verified that my knock sensor works by rapping on the block with a wrench as I watched knock counts, but is it possible my knock sensor is just a bit too sensitive? I replaced it when I replaced the engine, and I was sure to use a torque wrench to tighten in (14 lb-ft, I think?).
For now I'm moving on with the rest of my tuning by bumping the min knock RPM up to 1400, but I would like to sort this out so I can tune the spark tables in that region.
I've only got a week before I go back across the country for college, so I'd greatly appreciate anyone's insight on this.
EDIT:
Well that's no good. Ran it for a short while with the belt off, and I was still getting knock counts. So either I am seeing actual detonation, my knock sensor is bad, or something in the rotating assembly or valvetrain is causing the noise.
Noisy roller rockers, maybe? I adjusted them to 5/8-3/4 turn valve lash, and I'm reading they can need up to a full turn to get rid of false knock?
Last edited by C4ProjectCar; 08-16-2017 at 09:26 PM.
I wonder if the cam is moving or dragging? But knock sensors and the Cal Pack are selected to identify detonation/knock and filter out unrelated signal. Sorry but something like that is just to difficult to identify over the internet.
08-03-2017, 09:53 PM
