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Okay, so it’s been a while since I updated my progress. We got a new battery, and I reset the VATS system so that I have no more security issues. Now I’m simply dealing with a crank-no start-no spark. Checked for spark at the coil, wasn’t getting any. My dad picked up a new coil because I figured that the ignition module and coil came as one assembly. I now know that they don’t.
So I’m asking to see if my mind is in the right place. With key off, the power supply to the coil is switched to ground. Key on, not cranking the power supply wire turns to 1.5v. That 1.5v is the distributed to the control module, but I’m still not getting spark at the coil. Even with the replacement coil on there.
What steps do I need to take to complete the diagnosis?
_______________________________________________________________(Original Post Below)I’m currently working on my dad’s 1995 Cadillac Fleetwood Brougham. The original problem was that the car died on the side of the road. When I got to work on it, I saw no spark and assumed that I was having optispark issues. Fast-forward to now, I’ve put a new optispark on it but I am still getting a no start condition with no spark. So how does the VATS play into this? The dreaded pass key fault was intermittently occurring before the car died the first time. It has progressively gotten worse until I couldn’t even reliably try to start the engine without getting shut down by the VATS. So now I’ve moved on to addressing the VATS problem before I continue to the no-start.
I ordered one of the VATS bypass resistor kits just to have it available in the process. I started by measuring the resistance of both available keys and got a reading of 1.127 kOhms. That is obviously right on line with one of the 15 possible resistance values, 1.130 kOhms. I figured that either way I would be okay bypassing the lock cylinder with the appropriate resistor. So I proceeded to do that. Unplugged the connector and cut the orange coupling of the two white wires just before it goes into the lock cylinder. I then tied the resistor into the two white wires on the connector side. I double-checked the resistance value of the wire through the connector and I got the desired 1.130 kOhms on the nose. Next I plugged this back into the appropriate connector and tried the key. I still got the pass key fault.
So then I was thinking that perhaps the circuit was shorted out or something. I checked with the power probe and had a good ground and was getting 5v, which is the correct amount of control signal from the ECM.
I’ve looked at the wiring diagrams that I can find and it looks like the next logical step is to look at the VATS decoder module. But I wanted to check here to see what everyone thinks about this. I’m not exactly sure how to confirm that the decoder module is bad and I also wanted to check and see if there was anything I missed in the diagnosis thus far.
Thanks in advance.
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this might help you
http://www.superchevy.com/how-to/ghtp-1109-optispark-problem-solving-and-fix/I’ll start by saying that testing coil resistance is useless. Coils fail under load. They can pass a resistance check and still be bad as the current used for testing is not sufficient to fully load the coils.
With that in mind, in your situation I check for a signal going to the coil first. Similar to what I show in this video. Regardless of how the coil is controlled, they all work the same way.
In order for a coil to fire, it needs a good power supply and a switched ground. If you don’t have spark, look for those ingredients. If you don’t have one or both, trace it back to the source and you’ve likely found your problem.
More info here.
http://www.ericthecarguy.com/faq/solving-automotive-no-start-problems
As you pointed out you may also be dealing with a security system issue. For this you may need to use a GM scan tool unfortunately. Security systems are proprietary and often off the shelf scanners will not have the capability to communicate. Come to think of it, your vehicle isn’t even OBDII so I suppose that doesn’t matter anyway.
If you don’t have factory information already, you might see if you can seek out some service manuals to help you troubleshoot.
Please keep us updated on your progress.
Thanks for the info Eric. I should probably clarify that I’m entirely focused on fixing the VATS issue right now and will address the other issues once I get it straightened out.
A quick update on where I am.
The car needs a new battery, as I can’t even get the current one to hold a charge long enough to try turning the car over more than once.
My dad was unconvinced of that fact and wanted to try trickle charging the battery again before buying one. It’s his money, and I understand, so we tried again today after he put it on the charger some time this weekend, and had the same result. I’m hoping that I was just getting some weird problems due to low battery voltage and with a fresh battery we won’t have any VATS issues.
I’ll keep posting as I progress through it.
Okay, so it’s been a while since I updated my progress. We got a new battery, and I reset the VATS system so that I have no more security issues. Now I’m simply dealing with a crank-no start-no spark. Checked for spark at the coil, wasn’t getting any. My dad picked up a new coil because I figured that the ignition module and coil came as one assembly. I now know that they don’t.
So I’m asking to see if my mind is in the right place. With key off, the power supply to the coil is switched to ground. Key on, not cranking the power supply wire turns to 1.5v. That 1.5v is the distributed to the control module, but I’m still not getting spark at the coil. Even with the replacement coil on there.
What steps do I need to take to complete the diagnosis?
Thanks in advance.
Okay, so I think I’m beginning to understand this optispark system finally. I’m trying to determine whether I’m going about this correctly from a diagnostic perspective or if I’m misunderstanding how this is supposed to work. I’m attaching a couple pics to hopefully explain what I’m talking about. The first is the wiring diagram for distributor/ignition system. The second is my hand drawn diagram reflecting my questions and assumptions.
Now the questions, working from the bottom of the hand drawn diagram up.
1) I’m supposed to see a square wave pulse on the low resolution signal coming from the optispark, correct?
2) The white wire running from B5 on the PCM to port B on the ICM should be pulsing on and off ground when the engine is cranking, correct?
3) I could simply apply ground to port B on the ICM and should then be able to read ground on port D of the same?
4) If power is applied to the coil, and thus to the ICM, when it is not switched to ground, should I read power on port D?
Hopefully my questions don’t make me look too foolish. Just trying to understand the way this system is supposed to work so I can tell what’s going on with this thing. Thanks for any help.
I tested the ICM off of the car today, and it tested good. Looking over the wiring diagram caused me to wonder if I’m receiving the low res signal from the distributor. It doesn’t look like I’m getting one, but I couldn’t access everything very well so I went ahead and pulled the optispark. Now I’m looking to rig up a way to test for the signals with the optispark off of the car.
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