LT-1 no fire
Intermediate
Joined: Sep 2006
Posts: 38
Likes: 1
The best connector to use for the test is labeled "Ignition System Test Connector" in the schematic below.
It is about 15 inches or so up the harness from the opti and usually has the pin letter labels (A B C D) on it for easy reference. Note the schematic is for an F body but a corvette is similar. I could not find the exact corvette (Y body) schematic.
You need to probe into the back side of that connector with your volt meter.
It is about 15 inches or so up the harness from the opti and usually has the pin letter labels (A B C D) on it for easy reference. Note the schematic is for an F body but a corvette is similar. I could not find the exact corvette (Y body) schematic.
You need to probe into the back side of that connector with your volt meter.
Last edited by bjm206; Jan 25, 2012 at 08:23 PM.
Thread Starter
Intermediate
Joined: Sep 2006
Posts: 28
Likes: 0
From: Texas
Well, I'm a little frustrated now. I went through all the trouble of changing the opti, just to find out it isn't my problem. Same issue I was having before. Anyone else have any suggestions???
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Did you verify you have reference voltage to Opti? Also, ignition feed? On pins D and C respectively?
Same issue right, no signal from Opti? No spark?
Just high or just low or both?
How do you know this, scan tool or voltmeter?
Is wiring from ECM to Opti ohm check ok?
Same issue right, no signal from Opti? No spark?
Just high or just low or both?
How do you know this, scan tool or voltmeter?
Is wiring from ECM to Opti ohm check ok?
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
Gee there is a shocker. You just paid the LT1 tax. Double check the harness going to the opti. I had a brand new one corrode up and the connectors lost tension. Measured OK with a meter but made no contact when plugged in.
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Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
This is a REALLY good point. Individual pin tension needs to be correct. It is VERY possible that poor pin fit to the corresponding pins can and will cause problems. They do loosen up over time due to age/heat/cold/vibration. Pin fit is important. They do make/sell various tools to do this. Not expensive at all. In a pinch the very tiny eyeglass screw drivers may work.
Burning Brakes
Joined: Apr 2006
Posts: 1,218
Likes: 7
From: Burleson Texas
Sounds like your trouble isnt in a component.
UNLESS....
are you just changing the cap and rotor, or are you replacing the ENTIRE opti? I know it may sound like a dumb question, just have to ask.
If you trouble shoot the opti a bit deeper, then maybe you will find something a little more concrete.
In that trouble shooting guide, it pretty much said if the opti has power and isnt sending out a pulse, its bad. Yet, there is more to it.
I have been through this myself about a year ago, and I racked my brain trying to convince myself it wasnt the opti. I am an electronics tech, and at the time I was in the navy with access to some fancy tools. I took a few home to help me. (dont worry, I returned them
)
This is what I would do in your shoes...
1) Verify Ground on ALL ignition related components.
2) Verify all fuses related to the situation are good.
3) Verify Correct voltage at battery and all components invovled.
these are the first three steps I take in almost any situation. Since you say this happened on a rough road, makes me think something has wiggled loose. I would go as far as checking the connections on the rear of the ECM, unlikely, but hey, its easy to check.
Next is where I would take it a step further.
4) test for spark on #1 (which youve done).
A.) if no spark go to 5.
B.) if spark is present, the icm and coil are working. Trouble lies in timing, high voltage side of opti for other cylinders or else where.
5) Test for spark on coil to opti ignition high voltage wire. First test on the side that connects to the opti. Then test on the coil itself. This is done to ensure the wire itself is good.
A.) if no spark go to 6.
B.) if spark is present, go to X
6) Disconnect the ICM connector. Verify +10v DC or more from PIN A to ground and PIN D to ground on the ICM connector. This tests the coil, and wiring all the way back to the ignition fuse. (key on engine off)
A.) If no voltage, check fuse and wiring.
B.) if correct voltage is present the secondary wiring of the coil could still be bad, but we'll assume its good. Continue to step 7
7) Verify Pulse signal at PIN B of ICM. This is done with a voltmeter or o-scope. It should be a pulse (AC Voltage) that varies between 1-4v. On a scope, it will look like a square wave, Each pulse corresponds to a cylinder firing. (your cranking the engine to get the pulse)
A.) if no pulse, go to 8
B.) if pulse is present, ICM is faulted. Replace, and return to step 4.
8) Verify pulse signal at ECM connector to ICM. PIN B5 (dont have the book infront of me, might want to check that pin location).
a.) if no pulse, go to 9
B.) if pulse is present, the wire or connecton to ICM is faulty. Check continuity, check short to ground. Replace wire, connector, or repair.
9) The signal to the ECM for the ignition comes from the opti. This is where a scope would be handy. Test at both the opti, and the extension cable!!
9.1) Pin A on the opti is Low resolution signal. It will be different for each pulse, but only four variations. So you will see 5 pulses get progessively longer after each other, then reset after 5 pulses. Crank the engine and watch the scope. here is a pic, the low resolution signal comes from the big long slots on the wheel. (the 5th pulse is like a marker for the pcm to know when the cycle restarts, it wont correspond to a cylinder or mechanical event) It will cycle through twice per rotation of the crank.
A) if no signal, optical sensors in the opti are bad. replace opti.
B) if there is signal continue to step 9.2.
9.2) PIN B on the opti is the high resolution, it is the 360 small slots in the optispark trigger wheel. it will pulse 720 times per crankshaft revolution. Use the scope and look for this signal. It may be hard to dial in, but a signal is what you are looking for regardless of how perfect you can get it. You might want to use a scope with the capture feature.
A) if no signal present, the optical sensors arent reading. Replace optispark.
B) if there is signal, go to step 9.3
9.3) PIN C should be 12v (not sure, dont remember). check to ground.
A) if no voltage, check wiring and PCM
B) If voltage is present, go to step 9.4
9.4) Ground. Check continuity on wire.
A) if no ground continuity, inspect wire and PCM
B) if ground is good, Opti is faulty.
After all of this, you have tested the opti, coil, the ICM, the ECM input and output, Voltage on all components and you are left with only one thing that could be wrong...
Cap and Rotor. (btw this is what my problem was, the rotor wasnt secured properly and it came off. I found out AFTER buying the opti.)
Here is some more info:
http://ridingwithposssi.tripod.com/optispark.html
http://www.diyautotune.com/tech_arti...t1_lt4_l99.htm
UNLESS....
are you just changing the cap and rotor, or are you replacing the ENTIRE opti? I know it may sound like a dumb question, just have to ask.
If you trouble shoot the opti a bit deeper, then maybe you will find something a little more concrete.
In that trouble shooting guide, it pretty much said if the opti has power and isnt sending out a pulse, its bad. Yet, there is more to it.
I have been through this myself about a year ago, and I racked my brain trying to convince myself it wasnt the opti. I am an electronics tech, and at the time I was in the navy with access to some fancy tools. I took a few home to help me. (dont worry, I returned them
)This is what I would do in your shoes...
1) Verify Ground on ALL ignition related components.
2) Verify all fuses related to the situation are good.
3) Verify Correct voltage at battery and all components invovled.
these are the first three steps I take in almost any situation. Since you say this happened on a rough road, makes me think something has wiggled loose. I would go as far as checking the connections on the rear of the ECM, unlikely, but hey, its easy to check.
Next is where I would take it a step further.
4) test for spark on #1 (which youve done).
A.) if no spark go to 5.
B.) if spark is present, the icm and coil are working. Trouble lies in timing, high voltage side of opti for other cylinders or else where.
5) Test for spark on coil to opti ignition high voltage wire. First test on the side that connects to the opti. Then test on the coil itself. This is done to ensure the wire itself is good.
A.) if no spark go to 6.
B.) if spark is present, go to X
6) Disconnect the ICM connector. Verify +10v DC or more from PIN A to ground and PIN D to ground on the ICM connector. This tests the coil, and wiring all the way back to the ignition fuse. (key on engine off)
A.) If no voltage, check fuse and wiring.
B.) if correct voltage is present the secondary wiring of the coil could still be bad, but we'll assume its good. Continue to step 7
7) Verify Pulse signal at PIN B of ICM. This is done with a voltmeter or o-scope. It should be a pulse (AC Voltage) that varies between 1-4v. On a scope, it will look like a square wave, Each pulse corresponds to a cylinder firing. (your cranking the engine to get the pulse)
A.) if no pulse, go to 8
B.) if pulse is present, ICM is faulted. Replace, and return to step 4.
8) Verify pulse signal at ECM connector to ICM. PIN B5 (dont have the book infront of me, might want to check that pin location).
a.) if no pulse, go to 9
B.) if pulse is present, the wire or connecton to ICM is faulty. Check continuity, check short to ground. Replace wire, connector, or repair.
9) The signal to the ECM for the ignition comes from the opti. This is where a scope would be handy. Test at both the opti, and the extension cable!!
9.1) Pin A on the opti is Low resolution signal. It will be different for each pulse, but only four variations. So you will see 5 pulses get progessively longer after each other, then reset after 5 pulses. Crank the engine and watch the scope. here is a pic, the low resolution signal comes from the big long slots on the wheel. (the 5th pulse is like a marker for the pcm to know when the cycle restarts, it wont correspond to a cylinder or mechanical event) It will cycle through twice per rotation of the crank.
A) if no signal, optical sensors in the opti are bad. replace opti.
B) if there is signal continue to step 9.2.
9.2) PIN B on the opti is the high resolution, it is the 360 small slots in the optispark trigger wheel. it will pulse 720 times per crankshaft revolution. Use the scope and look for this signal. It may be hard to dial in, but a signal is what you are looking for regardless of how perfect you can get it. You might want to use a scope with the capture feature.
A) if no signal present, the optical sensors arent reading. Replace optispark.
B) if there is signal, go to step 9.3
9.3) PIN C should be 12v (not sure, dont remember). check to ground.
A) if no voltage, check wiring and PCM
B) If voltage is present, go to step 9.4
9.4) Ground. Check continuity on wire.
A) if no ground continuity, inspect wire and PCM
B) if ground is good, Opti is faulty.
After all of this, you have tested the opti, coil, the ICM, the ECM input and output, Voltage on all components and you are left with only one thing that could be wrong...
Cap and Rotor. (btw this is what my problem was, the rotor wasnt secured properly and it came off. I found out AFTER buying the opti.)
Here is some more info:
http://ridingwithposssi.tripod.com/optispark.html
http://www.diyautotune.com/tech_arti...t1_lt4_l99.htm
Thread Starter
Intermediate
Joined: Sep 2006
Posts: 28
Likes: 0
From: Texas
I'm sorry for the delay guys. I let myself get a little too frustrated and put the cover on the car. I haven't messed with it in a couple months. I'm going to double check some things that were mentioned on the last couple of posts. I will report back. Thanks again.
Thread Starter
Intermediate
Joined: Sep 2006
Posts: 28
Likes: 0
From: Texas
A little update. We did some more troubleshooting today. Turns out that I'm not getting anything out of the coil. So we traced it down to being the icm. So I went down and bought a $90 module. Well, no go. So the opti, coil and icm have all been changed. Still won't get fire. In the morning I will start tracing more wires.
Any possibility the cps could cause no spark as well as no code? I would think it would still get spark from the coil, just not out of the opti.....
Any possibility the cps could cause no spark as well as no code? I would think it would still get spark from the coil, just not out of the opti.....
