Reading KR with a genisys

I hooked mine up tonight and never got any KR at all. Even at hard acceleration. Does that scanner read it right? I hope so cause that would be a great thing!

Don't know what the Genesis is capable of reading.
Can't you tell by the screen readings.?

Ya it said it was reading it. It even had another reading that was saying when the sensor was reading and not reading so I fig it was working. We have a smart cable for it that will read pretty much any car. Only thing that I thought was wierd but I have some issues with this car is where it said crank/cam error it said 1.

Well, with all that said, I guess you have no KR.
Congrat's.

wiht your mods and a properly maintained motor you shouldnt have much KR. if you do have some it will be at the top of 2nd gear WOT like 70+mph.
scan up there and see if you have any. if you still have 0* or close to it then maybe consider dropping a pulley size.

does the scanner read anything else? i'm not familiar with that model.

The Genesis is a commercial grade scanner used in a lot of garages.
I've just never used one, only read some literature on them.

Connect the scanner and tap on the engine block with a hammer. You should see some KR if the sensors are reporting correctly.

Make sure you scan the exact same situations you intend to drive with the smaller SC pulley. If you plan to run a 1/4 mile at over 90 mph, WOT, you need to do that with the stock pulley, scanner attached and logging the data for analysis. Just driving the car and hitting the throttle hard does not guarantee you have zero KR.

In my 95 I'm getting a reading of over 111 knocks with ZERO KR on my Snap-on Scantool. I'm getting no audible pinging or knocking. The odd thing about this problem is that it magically starts when the scantool indicates the engine coolant temp is at 163*F. The performance symptom is lean misfiring and exhaust backfire with reduced power. Could this be from an internally shorted knock sensor? The PCM is storing no codes.

ironclyde wrote:

In my 95 I'm getting a reading of over 111 knocks with ZERO KR on my Snap-on Scantool. I'm getting no audible pinging or knocking. The odd thing about this problem is that it magically starts when the scantool indicates the engine coolant temp is at 163*F. The performance symptom is lean misfiring and exhaust backfire with reduced power. Could this be from an internally shorted knock sensor? The PCM is storing no codes.

I believe the computer doesn't start reading KR until the engine temperature reaches around 160. If you are getting misfires and have other symptoms, I would focus on fixing those first.

I can appreciate that. However, I get none of the bad symptoms, until the temp gets to the magic 163. Then all of a sudden, it's like the engines universe wants to spin backwards. Anyway, I've replaced every known sensor, except the knock sensor. So, I'm wondering if the knock sensor is grounding when it gets hot. So, to me, it would make sense that the knock sensor is loosing all impedance when the knocks read high when hot. I'm mystified why the PCM doesn't retard the timing accordingly.

98riv is correct. The PCM's knock-sensor turn-on value is 158ºF exactly. So you know the knock sensors are working correctly, because they're reporting data to the PCM just above that temp.

What we don't know is what "over 111 knocks" means. Knock is not an on/off thing. The knock sensors are actually mics that pick up sounds. Maybe the "111" value is considered background noise, and "1000 knocks" is the threshold for active KR. If you were knocking significantly, you could hear it under boost below 158º coolant temp (I don't recommend WOT on a cool engine, but it would be audible).

Probably what's going on - the knock isn't that severe, so the PCM isn't taking action once warm because it knows the levels are acceptable. If a knock sensor is in fact faulty, it's only one, because obviously the PCM is getting some input at the correct temp.

With regard to the "111 knocks" I'm not exactly certain what it means either. However, the PCM is not registering KR as the knock increases; it starts at 0 then works it way up to 111 or higher after the engine goes over 160 deg., per the scantool. My guess is that the 111 refers to a ratio of pings or knocks per rpm. It's a Snapon scantool from the 90's. It's the only thing I can find in the area that reads my pcm. I have access to a Genisys but, the damned thing takes so long to set up, I gave up in using it.

So, I'm going to pull the knock sensor and test the impedance. It's supposed to be roughly 4000 ohms. I'm also going to put a stethoscope on the engine to see if there is some noise I can't hear. Hell, maybe my exhaust is too loud or something...

Quote :

However, the PCM is not registering KR as the knock increases; it starts at 0 then works it way up to 111 or higher after the engine goes over 160 deg., per the scantool.

What's most likely happening is your KR sensors are reporting the 111 knocks below 160º, but your PCM chooses to ignore it, then once above that number, the knocks are visible to your scan tool.

I saw the same thing when I ran a 160º t-stat one year. In the fall I would watch coolant temp drop to 158º and then no KR. Once above 160º it would report the knock to my scanner. Looking at the PCM's program, you can actually see that 158 is the knock sensor activation value. Mine is now set to -40ºF.

If your knock sensors are bad, this would be the first I've heard of one failing.

I have seen a knock sensor fail before - it was physically damaged. That could also possible explain the issues - maybe it's shorted internally, could have been hit by road debris or something, or the wire is rubbed through and grounding outside the sensor. It's not an issue until the PCM starts to listen for knock at 160...

I'd lean towards a wire with insulation damage before the sensor itself though...

I'm inclined to believe both of you guys on this. I'll be checking it all out and letting you know if I find anything out. As far as I know the knock sensor is original. Eventually, everything breaks down. But I didn't want to change it arbitrarily. I'd like to know what the actual cause is. Guessing can be real expensive. Even when guesses are somewhat educated and deductive...

I worked on several problem areas today trying to figure out what the heck is going on with my false knock readings. The first thing I did was to move the knock sensor from the back side of the engine to the front side between the A/C compressor and the starter motor. That managed to reduce the knock to less than 1/4 of the previous 111 I was getting before. As far as I can tell the knock count is the total number of detonation episodes the PCM is recording within a given period of operation.

My reason for moving the KS to the front of the block, is that I'm guessing that there is less static noise at the front of the engine near the center of the block, which might falsely register as pre-ignition noise. The factory location is near the front of the block very close to the timing chain and the accessory drive. Other false knocks might come from exhaust ticks, transmission noise or exhaust resonation that would be trapped within the echo chamber between the block and the firewall.

So, prior to the relocation of the KS, my "knock count" was 111 in 7 minutes. Today, after I relocated the knock sensor, it dropped to 24 within the same period of time.

I've also been spending some time cleaning the various grounds around the engine bay. Each time I clean the connection and get a better ground some things improve. Yet other symptoms pop up. For example, after I was gloating about the reduced knock count I decided to clean the ground contact for the O2 sensor, Evap purge solenoid, and SC bypass solenoid (If I recall they share the same ground post located underneath the coolant reservoir. After that was all nice and conductive again, the temp gauge and shift indicator stopped working. Oddly, the transmission mode switch grounds through the switch into the body of the trans. I haven't looked to see where the temp gauge grounds but it's probably in the sensor.

Anyway, I remember reading about trying to relearn the PCM by disconnecting the battery for a little while and then reconnecting the after 30 minutes. So, that's what I did... And Bingo! The temp gauge and the shift indicator worked like magic. However, for some reason the overheat light stays on and the A/C doesn't blow cold air.

This is getting trippy, but my guess is that this car is suffering from a number of grounds. So, the electrons like water are seeking the path of least resistance. That would mean that where the grounds have been made good again the current flow is higher and therefore diverting energy away from the higher resistance grounds that I haven't found yet.

The best part is that it is running a lot better. Though, I can tell I have a long way to go.

Thanks for your time and forbearance, through a very trying time in my Riveria experience.

Unfortunately, this is more "old car with lots of electronics" experience not limited to Rivieras...

Sounds like you are disturbing brittle wires! Keep trying though, you are on the right path somehow.

Cleaning the grounds is making everything better. I haven't encountered any brittle wires. Just lots of corrosion on the terminal lugs.

Moving that knock sensor to the front of the engine made eliminated most of the knock the sensor was picking up. My exhaust is really loud so I'm sure that some of the knock was echo chambered between the exhaust and the block. Another thing I believe was adding to the clutter was timing chain and accessory noise.

At this time, the EGR is still opening on acceleration. The scantool is registering the request as "Desired EGR," which I think is bass-ackward. My understanding of EGR theory is that the EGR is supposed to be commanded closed under acceleration and idle. It does close it at idle at least, now.

I would be very concerned about moving that knock sensor to the front without knowing the PCM's trigger point for "real" knock. Until you register at least a tiny bit of KR and compare the knock count, you can't know what the threshold is. That is a frightening prospect that the GM engineers made sure to eliminate when they calculated the noise from accessories and valvetrain. Even though you are 'sure' the exhaust is influencing your knock sensor, there's no actual evidence this is happening.

A couple things come to mind right now: 1) serious 3800 modders don't move their knock sensors around, nor make assumptions about knock counts. KR is what matters, and folks who know these engines don't mess with our only line of defense against cracking pistons. If KR is believed to be false, that can be addressed. Other than some cases of transmission parts causing false KR, this isn't a problem. I can't remember, what are your actual KR values?

2) the other thing: why is it so often assumed that automotive engineers are either stupid or part of some conspiracy to screw the customer? Sure there are areas we can improve on these cars, but the reason isn't because of lack of smarts at GM, it's because at the time these cars were made, priorities were different, and decisions were made at higher levels that resulted in some undesirable outcomes. We don't see knock issues with other Series I (or Series II) SC 3800s, so why should your case be any different?

Hey Aaron, I appreciate your candor.

I should give a little more history about this project.
I bought this Rivi from a guy in Phoenix with blown head gaskets. It actually overheated because he broke the serpentine belt and continued driving it, until the engine started knocking. I asked him if he had any other trouble with the car before he blew his engine and he said 'no.'

Anyway, I had a perfectly good running SC motor from a 95 Park Avenue that one of my daughters totaled the first day she had it. So, I dropped the PA motor into the Rivi and thought that it would be a no brainer.

At first, things went real well and I had a blast beating a lot of the local rice and other unsuspecting foreign matter. Then, all of a sudden, I could hear lots of detonation coming from under the hood when moderately accelerating. Later you could hear detonation under almost any condition after the engine was warmed up. Within a couple of weeks of taking it easy, while troubleshooting the ping, it developed a rod knock.

So I pulled the pan and checked the situation out. I found the #6 bearing was hammered paper thin and the crank was damaged. When I tore it all down, I if found the pistons, combustion chambers and the spark plugs had signs of detonation. At that point I decided to rebuild the engine.

So, since the rebuild I haven't been getting any KR registered but there is a knock count. However, the Scanner does show less spark advance when the ping is audible. That was even before moving KS to the front of the engine. I tested the FP and the regulator. They were marginal, so those have been replaced. I'm also running a 160 degree t-stat. Oddly, the EGR and the IAC are opening when I accelerate. If I'm correct they are supposed to closed when accelerating.

Another development has been the low speed misfiring under light acceleration after the engine is warmed up. My guess is that the PCM is registering the whiplash of the timing chain and the transmission noise as knock when there actually is very little.

Nonetheless, it's not the engineers that are the problem at most car manufacturers. Generally it's the bean counters and the Federal regulators that prevent us from having better performing cars. In the case of the knock sensor location, it would make sense to have it located where a lot of noise is generated to prevent any problems from occurring under warranty. Add-ons like EGRs are intended to make some one in a federal bureau feel good that they have contributed something to save the Earth.

So why is my case any different? Hell if I know. Maybe I'm a little paranoid about ruining another engine. False knocks registering with the PCM, wild EGR and IAC operation have me a little concerned. So, after moving the KS, I'm getting a much lower knock count from location that is nearer the center of the engine and closer to the heads than the original. All that without the trans, timing chain, accessory and exhaust noise.

I think maybe, I have a bad PCM. I've tried about everything else with no improvement in the lean misfire. When I disconnect the EGR, things do get better, but the PCM doesn't store any codes. Anyway, I'll keep trying.

Warning warning warning! Some of the computers don't start to actively reduce knock until the temp is above 160. Running a 160 tstat might be part of your problems.

I know you are in a '95. I'm not sure what years they did this, but I know most of the Series II engines don't listen to the knock sensor until it's over 160.

I would go to at least a 180 thermostat until you know for sure. The detonation could be what took out the bearing. If you have audible ping, that's an issue.

Good catch, deekster. There's so much going on in that sig, I didn't notice he has the 160 t-stat. Nights get pretty chilly out there this time of year (below 65ºF ambient is bad news with 160). Definitely should swap to 180 for 'winter' months.

I added the 160 to reduce the pinging. Like I said the damn thing runs perfectly until it gets over 160. Then the lean misfires start. The scantool is telling me that the IAC and EGR are going to 99% when accelerating. It's as if they are opening at the same rate as the TPS. Aren't the IAC and EGR supposed to close or at least restrict their relative flows when the throttle is opened to accelerate?
I can even power-brake and still get the same readings. In fact the IAC and EGR will go to 99% when the TPS is at 10%.

Stock Spark Control Coolant Disable (ignore knock if coolant below this temperature) is 70*C ~ 158*F. I'm not even sure the Knock Sensors are turned on, or reporting, below that point.

Have you installed a PROM, or have anything else wired in to change the "tune"? Are we even sure the scan tool is reporting the proper values? That doesn't make sense about the EGR and IAC duty cycles....

Wait a second... The KR at 160 was discussed on page 1.

I was just thinking too - what sensor are you reading, and how do we know it's what we need to see? I'm very unfamiliar with the scanner and what you want to be scanning on an OBD-I car anyway.