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1994 camaro z28 convertible lt1 90k original miles
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Discussion Starter · #22 ·
no i had that done in a shop about 6 years ago, keep in mind it has been not working correctly for the last 3 years. Back then i was new to the lt1 engine so when i ran it through a car wash and dried the car, after it would turn over but not start and i had to have it towed to the chevy garage.
 

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no i had that done in a shop about 6 years ago, keep in mind it has been not working correctly for the last 3 years. Back then i was new to the lt1 engine so when i ran it through a car wash and dried the car, after it would turn over but not start and i had to have it towed to the chevy garage.
Are you 100% sure we're looking at the low res pulse? Here are two pictures of the wheel, look at the high res (outer) and low res (inner) slots in the wheel. The outer pattern would give a square wave. The inner would be much different.



Scroll down a bit on each page. The signal should change when the pickup is over the slot. Look close, the inner is 4 narrow and 4 different size slots.

Al in Tucson
 

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Discussion Starter · #24 ·
no I have no clue which pulse I am looking at I just know which wire I'm hooking the scope up to. I know how the opti works as far as the discs with different size holes and that the sensor gets one signal from the slots and the other from the holes that are sized different for the other signal. I know nothing about the scope I was under the assumption that if I hooked it up to that wire it would get the signal that I wanted to look at. I have tried to look for videos or even write ups that explain what I need to look for with this engine when using a scope but so far I haven't found anything that is specific enough to help. I'm guessing that the opti got condensation in it so has enough corrosion that it is disturbing the signal enough to make it run poorly but still run, but that's why I wanted to look at the signals with the scope so I could say with more certainty what is going wrong. If it is the opti I am just going to save up and get the 24x conversion so I don't have to worry about all the issues especially with the un vented version, but its a lot of money to spend if my current problem is not in the opti. since it is still in the car I was hoping I would find more videos and things with people using them on the lt1 so I could learn more about what I need to look for and if there is a different place I am supposed to hook the scope up other than the pin b wire at the ICM because that is where everything I have found so far says to connect the scope to, but since I haven't seen anybody use one on an lt1 engine, except one video but they were in too much light so I couldn't see the screen on the scope they had or where it was connected, I don't know what to look for from the test other than clean square waves, the test I did had squarish waves but they were very distorted at times with extra lines and things like that but they did get closer together and everything when I increased the rpm but I couldn't get pics of that since I was short on hands all the pics are during idle.
 

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1994 camaro z28 convertible lt1 90k original miles
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Discussion Starter · #25 ·
Well I finally found on this site where someone was explaining where to hook the oscilloscope up to the car and its not where I was hooking it from what I understand. I was hooking it up at the pin b wire on the icm side of the engine and I need to hook it up directly to the wires that come out of the opti and go to the pcm on the other side of the engine with the wires that sit on the intake manifold. One wire carries the low res signal to the pcm and another on the same harness carries the high resolution signal. The wire I was testing comes from the pcm after it has already looked at those signals and tells the icm when to fire the coil through the opti to the spark plug wires. So I will do this tomorrow and go from there.
 

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Well I finally found on this site where someone was explaining where to hook the oscilloscope up to the car and its not where I was hooking it from what I understand. I was hooking it up at the pin b wire on the icm side of the engine and I need to hook it up directly to the wires that come out of the opti and go to the pcm on the other side of the engine with the wires that sit on the intake manifold. One wire carries the low res signal to the pcm and another on the same harness carries the high resolution signal. The wire I was testing comes from the pcm after it has already looked at those signals and tells the icm when to fire the coil through the opti to the spark plug wires. So I will do this tomorrow and go from there.
The thing they call the ICM is a version of a regular HEI module. My 95 has a MSD 6AL, I home made a driver to replace the ICM. At least your wave forms make sense now.

Al in Tucson
 

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Discussion Starter · #27 ·
Definitely, after I do the test I will post some of the pictures of the screen on the scope and at least this time I will be able to say with certainty that its either a hi or low res pulse.
 

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Discussion Starter · #28 ·
I am having trouble getting this test to work properly, the first time I tried last night I got a reading but by the time I got out of the car to look at the screen then pull out my phone to take some pics it killed the car. I also accidentally had it set to 1 volt or something so all that the screen would show was lines rather than a wave that was readable but it was set to 500ms so that part was correct then today when I tried again every time I had the scope hooked up the car wouldn't start, it was set to 10 volts this time. It would start right up when I disconnected the scope every time and I tried it about 5 times. Is there a reason it would either kill the car or make it so the car just wouldn't start when the scope was hooked up, it was connected to the low res signal wire and I am pretty confidant I had a good ground because I ran a 6 gauge wire bolted to the grounding block on the passenger fender area. The wires for the probes aren't that long so this allowed me to get the scope closer to where I needed it and still have a good ground.
 

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There is ABSOLUTELY no reason for the scope to kill the car, UNLESS you have a problem with the wire going from the pulse to the scope. Something like its insulation is burnt and it's grounding.

Or if something in the scope died. Put your meter on Ohms and check the scope. Meter leads to scope leads. It should read very high Ohms and the scope's zero line should jump up indicating a voltage. You can also set the scope on 5 Volts per division and read the battery voltage, it should be very close to what your meter reads.

About Ohms, a direct short should read zero Ohms. That's touching the leads together. Nothing is impeding the flow of electricity. If you measure your resistance, one lead pinched in the fingers of each hand, you'll see high resistance. Your body is "resisting" the flow of electricity.

You had the scope set to one Volt a division, that's what it should be set at. 500 MS is 1/2 second per division. That seems to me to be a good starting point. You can adjust that when you get it working. I would expect to be at around 50 MS.

One thing you don't want to do is connect the scope to the ANY spark coil leads. That's a no-no. If you want to see what's going on at the coil's primary leads, ask me and I'll tell you how.

You're doing well. Just having teething problems.

Al in Tucson
 

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Discussion Starter · #30 ·
The only things I have tested with the scope so far is an AA battery and the 2 places on the car but they are both low volt wires, I think both wires are at 5 volts dc maximum. That scope doesn't seem to measure ohms, the only options are ac, dc, and ground. The scope will still measure positive volts from an AA battery so I'm assuming that it isn't shorted out but I am no expert when it comes to oscilloscopes to say the least.
 

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Discussion Starter · #31 ·
The odd thing is that it starts up right away and runs every time but when the scope was hooked up to the wire it wouldn't even fire while it was cranking and I repeated it about 5 times I also re connected the positive wire to the car every time because I was thinking I wasn't making good connection or something and that was messing with the signal to the pcm causing it not to start.
 

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Discussion Starter · #32 ·
Except when I did the test last night but then the car started and the screen was still flatline, it started reading 20 seconds after the car started and read it for about 15 seconds before the car killed, then the screen was flatlined again but the car started right up after that when the scope was disconnected but wouldn't start again with it connected. Thats also why I waited to test it again today and why I was thinking it was a bad connection with the scope and the wire on the car that was causing the problem but that was just a guess.
 

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The only things I have tested with the scope so far is an AA battery and the 2 places on the car but they are both low volt wires, I think both wires are at 5 volts dc maximum. That scope doesn't seem to measure ohms, the only options are ac, dc, and ground. The scope will still measure positive volts from an AA battery so I'm assuming that it isn't shorted out but I am no expert when it comes to oscilloscopes to say the least.
You measure Ohms with a meter. I assumed you had one.

Al in Tucson
 

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Discussion Starter · #36 ·
The meter I have is an "astroAi' brand 6000 count amazon buy, I think it was like 40 or 50 bucks so nothing special and from what is on the shoebox page I did that test right but its more of a test to see if the opti is pulsing but I think its a better test for a car that is a no start just to see if the opti is sending the signal through the pcm to the coil but wont diagnose any problems just a working or not kind of thing, but at the time I wasn't sure if the meter should have varied more in voltage while turning the car over but now I know a normal meter cant read fast enough to diagnose those things. I thought i was supposed to use the scope at the same spot as that but from what i understand the only way to look at the signals both low and high is between the opti and pcm with a scope not after the pcm has looked at the signals and sends the info to the icm and coil. I just got another break from things here so i havnt used the meter to check out how things are working with the scope but i will get that checked tonight. Thanks for the help im still learning the electronic side of these cars so its been a slow process.
 

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I understand...

Your meter is fine. No problem there. Most of the time it's not how good the meter is, it's how well you understand its capabilities, and how well you understand what it's telling you.

Looking at the pulses from the ECM to the ICM is no problem for the meter or the scope. From the ICM to the coil, could be a problem. Don't chance it.

Diving into electronics without some basic training is not easy. You're dealing with lots of new stuff. Has to be a bit frustrating.

Al i Tucson
 

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Discussion Starter · #38 ·
when I test the scope for ohms with the multimeter it reads a steady 9.4 ohms and there is no reaction on the screen of the scope when I make connection for the test. When I test ohms on myself the meter reads between 5600 and 6000 so that seems like its reading fine, but is just a little over 9 ohms when testing the scope sound like to low of a number?
 

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when I test the scope for ohms with the multimeter it reads a steady 9.4 ohms and there is no reaction on the screen of the scope when I make connection for the test. When I test ohms on myself the meter reads between 5600 and 6000 so that seems like its reading fine, but is just a little over 9 ohms when testing the scope sound like to low of a number?
Scope died. Explains your "no start" problem. Did it come with a schematic?

Al in Tucson
 

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Discussion Starter · #40 ·
It came with assembly instructions even though it came assembled so I can get a decent idea of what things are from that but its not a schematic as much as colored pictures showing where to solder certain parts to the board and places to verify voltage before its fully assembled.
 
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