I have a question for those of you who have more experience with this.
My question is this, is it possible to use a knock sensor to turn on a light when it senses a knock?
I would like to be able to use one to work with an HEI distributor to retard the timing without having to use an ECM. I know that some of the 80's GM vehicles had a 7 pin distributor module that used a knock sensor and an ECM to retard timing during a period of knocking. And in later years the trucks were using an EST module in conjunction with the ignition module and ECM, but in either case, the ecm only took the ac voltage from the knock sensor and converted it to a dc signal to then send back to the ignition module or the EST module in order to retard the timing until the knock stopped.
What magic occurs inside that shiny little box that makes this system work?
But if you can't do this without the ECM, can you at least use the knock sensor to illuminate a light on your dash to let you know when the engine is knocking?
I have less sensitive hearing now than I did when I was younger, and I don't always hear the detonation in the engine, so a light would let me know to back off the throttle a bit.
I know that the knock sensor puts out a miniscule ac voltage when it detects a knock. I took one and clamped it in a vise with a multimeter hooked up to it, and using a pair of hammers I hit the vise and the sensor put out just over 1.2 volts ac.
Is there any way you can take this ac voltage and use it to somehow turn on an indicator light?
It would be really nice to have a way to know when you have a detonation problem if you can't hear it yourself.
I'm sure that a lot of us would like to use something like this if we could.
So anyone know how to convert a small ac voltage into something that can drive a light bulb in the dash?
Thanks in advance, Rick
It might take some technology to make these effective.
Engine location matters, and the amplifier and knock
sensor might need some frequency tuning to match the
engine. I gave up after changing to large, low
compression engines that never knocked. More but
much cheaper fuel used, mpg suffers. Bruce Roe
So basically just too much work involved for little benefit. I understand, I'm no electronics wiz, I can handle electrical stuff with no problem, but once it goes into the shiny box and turns into magic I'm lost.
I was really hoping that it would be something a little less complicated, I guess I'll have to get a hearing aid and turn it up, lol!!
Thanks Bruce, I appreciate your input.
Rick
I don't think any of the common 80's stuff had knock sensors, they really didn't get common till the mid 90's. The 70's and 80's stuff the timing manipulation was to do with emissions and based on fairly simple inputs like speed, coolant temps, and what gear the transmission was in.
The 7 pin modules were full for full computer control. They sent what was basically a fancy tach signal to the computer and the computer sent back a command signal to tell the module what the desired timing was. Computer was able to take into account all available inputs and come up with the ideal timing. I don't recall if the 7th pin was another feedback signal back to the computer or a signal ground. These did have a limp mode where if they lost the control signal they would then use a default timing curve just based on rpm.
There were I think a few different 5 pin modules that did different things. Most of them were a very basic fixed retard or advance triggered by a simple power or ground to that pin. I think some applications it was a coolant temp sensor. This was the one some 'hot rod' people used and would wire it into their starter circuit to alter the timing during cranking for easier starts on a hopped up motor. There was also an earlier version like on the 78-79 Seville that had its own stand alone control module and that one may have been able to do more than just a fixed on or off sort of thing. There may have been a later one that was same but different used on the last carb trucks. I believe these all still used a more or less standard dizzy with weights and the vacuum advance. The module was just further altering the timing.
Early 2000's like 2005 ish I'm thinking was kinda the heyday for DIY EFI. There was a open source platform called MegaSquirt that had a huge following of just regular individuals that had their own project as well as people that formed small companies to develop and produce hardware and software. Some of these people were just enthusiasts and some were legit trained and experienced engineers in the field or related fields so there was a lot of knowledge available. That happened to be when I decided to get into it so for a few years I was daily on the forums or hands on with my own system.
The subject of knock sensors came up pretty often and I like you was really interested to see if it was something I could implement on my project. From an ECU hardware standpoint it was possible because one of the applications the hardware was developed for was as a way people could take a late model engine and make it more tuneable. Even when you had an engine that had a factory sensor it wasn't a trivial task to get it to work and on an engine that didn't have a factory sensor it was way more difficult.
Basically think of the knock sensor as a microphone that is just live all the time. Imagine those rooms of government operatives you see in the movies monitoring our conversations. 99.999743% of what is coming in is just noise and of no concern, they are listening for a keyword. The keyword in this case is the knock. Its pretty much the same as the CIA where they have to go through a bunch of training to be able to pick out that specific keyword within all that noise.
The training analogy is pretty accurate because in the lab they basically had to make the engine knock so they could see what the signal looked like then train/program the computer to pick that out of the noise. As you could imagine this was likely not a trivial process and among other things involved different types of 'microphones' placed in different areas and maybe changes to other aspects of the engine like say a rattle from a lifter that sounded similar to the knock sound. Once it worked in the lab they had to then road test it to further tune the hardware and software.
So knowing all that its really quite the project that requires a fair amount of experimenting and possibly destructive testing especially on an engine that never had one from the factory. At least on those engines you know the sensor and location and that there are not likely other things that would be making a similar noise.
I'm not even sure that knock sensors are a major part of current engine designs. Its actually a pretty poor design if you are depending on something like that to make your tune work. Same thing with O2 sensors, you don't want to have to constantly react, you would rather use them as a learning tool to be able to hopefully accurately be able to predict the proper air fuel and timing so you don't have to correct for it after it happens.
My interest in this was just to be able to keep an engine from knocking without the use of a computer if possible. I would much rather run a carburetor than fuel injection. I do understand how at least the throttle body injection works and can diagnose and repair everything short of the ECM internals.
But I'd like to stay away from shiny little boxes if at all possible.
My 81 El Camino has, or rather had a computer that was really basic, it only monitored engine speed, temperature, exhaust gases, manifold vacuum, and only controlled the mixture contol solenoid in the carburetor and the timing, and where and when the smog pump put the air, either in the exhaust manifolds or the converter, or the air cleaner. The distributor had a 7 pin module, and one of the pins was for a ground circuit if memory serves. I ran it 300K miles before converting it to the basic HEI distributor with a 4 pin module with a vacuum advance and a normal Quadrajet carb.
The 88 Suburban I'm currently converting to a carburetor was using a knock sensor, and I was thinking it would be nice if I could still make use of it. But it's not looking very likely now.
Thank TJ, great input,much appreciated.
Rick
I didn't remember that they were using a knock sensor that early but thats likely because they were never the problem so you never had to mess with em. I really liked those TBI systems. They were really simple and reliable, even today they just seem to keep working.
I think the most common issue I see with them today is the fuel line between the pump and rest of the sender in the tank rots out and kills the fuel pressure. Sucked that Chev didn't want to spend the 2 cents to put a fuel pressure test port in, at least Cadillac did so one nice thing about working on a HT4100.
I helped a guy recently with an 84 CDV that had been chasing an intermittent stumble for years. Slapped a fuel pressure gauge on and it was running about 3 psi. Spec is something like 13 psi so quite low but the dang thing overall ran and drove pretty well. We dropped the tank and the hose was just goo. No idea how it could have got any fuel to the engine at any pressure at all.
The other thing I always saw and still see with these is when people start messing with the timing and idle speeds as if it was a dumb carb. When you do that it confuses the computer and the thing just won't run right till you go through the proper procedures in the proper order and set things to the factory specs.
Everyone of these engines by the time they came to me all had a literal bucket load of parts with them. Multiple computers modules and sensors when all they needed is about 10 minutes with basic tools and a manual or a chunk of fuel line. Sometimes it takes longer than 10 minutes because you find the TPS really messed up or the plunger missing from the IAC. I remember the first time I tested one of those... that plunger may still be in orbit.
The other thing you really need is a scan tool. Ya its nice that a paperclip can flash the light but especially as this stuff is older now you need to be able to take advantage of the real time data that GM made available. When you can see what the computer is seeing you can more quickly zero in on the actual problem and not have to just guess. The other early EFI systems could not do that. A GM if you wanted to know the coolant temp you just look for that on the list and see what it says in degrees. Other systems you would have had to have a breakout board installed then look at the manual to know which pins to probe with what tool then look at the chart to see what that translates to in degrees.
I even picked up what they called a computer tester that plugs into the car in place of the computer and does basic tests on the car side of things. I had that for like 15 years before I used it but it did help track down the issues with that car which was a 90 CDV. Thing actually had a bad computer and I think what damaged it was a funky injector that that tool found.
Lol!! Yeah, I used the paperclip method for a few years before investing in a scanner, but even the best scanner didn't work nearly as well as the GM tech1 tool, and later the tech2. Wish you could have bought one of those back then.
As for when knock sensors started showing up, I think it was on some 86, or 87 models, but not all got them I guess until they proved their worth. I can't remember the exact model I had to work on at the time, but I do remember seeing it in the side of the block and wondering what the hell is this!
Rick
The consumer scan tools were not especially useful back in the day, you were much better off with a Cadillac because at least if you had the manual you could get quite a lot of information out of the climate control. LOts of people knew you could get the codes but there was actually more to the sequence if you knew how to get there where you could do some functional tests and get some live data.
I think its only really been the last 10-15 years where as long as you were working on a 10 year old car that some of the consumer or prosumer scan tools actually can do a decent job. Since I rarely own or work on anything less than 10 years old that usually works out for me. I tried lots of tools and finally found OTC. I'm guessing that they have lots market share lately but I think 80's to early 2000's they were likely 2nd only to the OEM's like the TECH1 and 2 in the case of GM.
Around 2005 there was a change in a lot of the cars (CAN) that was more or less the end of the line for many scan tool hardware platforms. CAN was different enough than past protocols that they could not just do a software update or new cable like they had been able to do in the past. So around that time frame shops and or techs had to buy the next generation tools which still would go back to 1996 so they only kept the old tools around for the few 81-95's that they saw and even in 2005 there wasn't that many coming in to the average shop.
Go to say 2015 and they hardy were ever seeing a pre 95 and were seeing tons of 2005+'s so they had to have the new tool and never used the old one so many of them end up for sale cheap. You even see TECH 2's for reasonable prices but apparently there was a period where someone made a bunch of knockoffs that don't work correctly so you have to do your research so you know what to look for.
So if you are like me and don't really work on anything newer than 2005 ish you can likely pick up something from the OTC Genisys family with the cables for under $200. Sometimes you may not get every cable you may want but they are out there. Battery will usually be dead but you can get knockoffs that work good enough pretty cheap.
I've had some scan tools that were great, but also some that were no better than the paperclip.
The best one I ever bought was at an auction, it was used and dirty, and everyone was just ignoring it thinking it's broken, so I bid on it and got it for $7 bucks. An OTC Monitor 2 that only works with the OBD1 system. I already had a Monitor 1 unit, so I was familiar with them.
The OBD2 scanners that I've bought have all been less than expected.
Rick
I have seen those OTC Monitors come up for sale but none with documents so I wasn't clear on what exactly they did or how they did it. Were they basically the OTC version of Tech1 and 2?
What I have had great success with is the OTC Genisys family which seems to cover a long time with several possibly unrelated variants. The ones I have I would guess stated with OBD2 but since at that time techs were still working with OBD1 still had excellent support for OBD1 stuff. It looks like they were updateable to the mid 2000's. Not sure if you can still update one or not I think the least updated one I have seen recently was good to like 2001. They have a bit of an odd shape to them, the top where the screen is is pretty square but the lower section with the buttons is curved in apparently so you can kinda grip it from behind with one hand?. I see these all the time for sale used often looking pretty good with tons of cables and manuals for maybe $200.
Before I found out about those I bought into the Auto Enginuity platform which is like many tools are today where its a cable you plug into a PC or phone. I have had 2 hardware revisions and several software revisions and paid a good chunk of money for the hardware plus a lot for the 'enhanced' software, like in the $1000 range and I find it to be the least intuitive most temperamental system I have ever tried to use. One issue is every time I went to use it I either had to update the tool or the PC or both which usually caused issues that they blamed on each other. Sucked. Aint none of that with the OTC, biggest issue is the original batteries have aged out and the replacements aint nothing special so you don't get a lot of run time out of em but that usually isn't a huge deal. Most of the time you just need enough battery to hold during a restart procedure.
I was mistaken on the models on the OTC scanners I've got. The first one is a Monitor 2000, which has a limited screen function, and the newer, better one is a Monitor 4000E, which has a much larger screen and a lot more functions.
I wouldn't say the newer one is as good as a Tech 1, but it's close.
They both use a cartridge that has the necessary preprogrammed information on them, the 2000 model works with cars up to 87 or 88 I believe, the 4000 model works up to 92, and maybe a few years later if you have the correct cartridge. Mine will only go up to 92 as that's the newest cartridge I got with it.
If I remember correctly, you could actually use a Tech 1 and/or a Tech 2 to activate certain systems on the vehicle you're working on. My units can't do that, they just display the particular system you're looking at, but that's still much better than a paperclip.
I don't remember the names of the OBD2 scanners I've bought, I'd have to dig them out and look, but none of them were worth the money or time I spent on them. The newest one I've got is basically just a code reader that I think I paid close to $300 bucks for, a really expensive paperclip, lol!!
Rick
With the GM OBD1 stuff was there a lot of stuff you could control with the tech1? My OTC does some stuff, its not like an OBD2. Like I don't think I have seen cylinder deactivation but I think there was things like turning fuel pump on and off and operating various solenoids like high idle and canister purge. I'm assuming the limited number of things to control was more the car than the tool. Just not enough power in the computer to offer manual controls of things.
If these units I have can activate anything I'm unaware of it. Neither one came with paperwork since I got them used.
I didn't get to use the dealerships Tech 1 or Tech 2 tools except for one time and the technician was working it for me at the time.
But from what I recall you could activate multiple systems and kill one or more cylinders with one.
I've always wanted to buy one, but new they were out of my reach, and I've never seen a used one come up for sale. I'm sure if one was available it would be bought within minutes.
I remember once I brought my friends car in to get it checked out as the engine light was on, and the Tech2 showed the misfire counts for each cylinder, so you knew which sparkplug to replace. I haven't seen that feature on any aftermarket scanner, but I keep looking.