I have had this car about three months, and am on ICM number 6 or 7 now. After repeated attempts, a multitude of electrical tests, ICMs are still failing like dominoes. 12V line is good. Ground line is good, 5V line is good, though a little low (Battery voltage was a little low for that test). Did the thermal paste and all that. Electrical looks good, maybe discounting alt charging voltage, more on that upon request. Cam and crank sensors are good, and the only time I get codes for them is once in a while RIGHT before the ICM actually goes. All research and testing is bringing me to either heat issues, or vibration.

All that said, I don't really have any misfires, the engine runs in it normal temp range, with the low fan coming on at what my OBDII reader says is 221. I can drive it for about a week just doing errands and such, but as a delivery driver, if I take the car to work, with all the idling and such, it dies in a day. I only work 10-12 hours a day. It doesn't last that long. I'm at a loss, and extremely frustrated, but I'm not ready to give up yet. Aside from relocating the ICM to a location off the engine, I'm unaware how to proceed. I put another brand new ICM in today, and tried spacing it away from its bracket with washers, it ran for a few minutes, and fried again. What do I do?

 

Your issue is not a common one. In 12 years of watching the V6 tech forums this is the first time I have seen this complaint. Maybe a sight with a higher volume of posts?

Since I can not speak directly to your issues I will talk about electronics in general.

There are 3 things that can cause an electronic system fail.

1.) Dirty power. Most of the time this is a ground issue or a bad alternator.

2.) A bad intermittent connection. If a connector allows the connection to “disconnect” you can get a sharp voltage spike. Think of disconnecting a light if you do it slow enough you will get sparks. Those sparks represent a voltage spike that can damage the electronics.

3.) Bad ground or a bad coil/plug wire is causing a magnetic field. This can and will cause all kinds of issues with electronics.

As a general rule you need a scope and the know how to use one to track this down. I would suggest setting up some temporary grounds, from the battery to the engine from the engine to the ICM mount. You could also wiggle all the connectors?

Do you have any of the old ICMs? You may want to reinstall one of the early ones to see if it is still bad. If it works good now you are looking at a magnetic field. I have seen electronic take up to a month to dissipate a magnetic charge. Note: They don’t always come back around.

 

Unless the engine has a bad ground to the battery, I doubt that is the case. I tested the ground wire from the ICM, which according to schematics, is the "Engine Sensor Ground", meaning if that's bad, it's likely my cam and crank sensors would be having issues. When I tested the line for continuity, I got around 0.2 ohms from about an inch from the ICM connector, all the way to one of the ground points between the engine and the chassis. As for the intermittent connection, it would only be showing up while driving the car, which basically would require I drive around with an oscilliscope hooked up to it and monitor it that way. I have jiggled everything I can reach. No voltage fluctuations. As for the old ICMs, I have two of them. The rest were all warranty swapped for the *THEN* new part. I did check them both, neither are good still. The one that was on the car when I bought it was a scrapyard part to replace a bad one, and I was advised to change it ASAP, since they are known to fail. Not long after, it died, but not completely. Instead of the board burning out, it stopped firing two of my coil packs, cyl 1-4, and cyl 5-2; the rear two of the three.

The alternator I said I would mention in my original post. So, the regulator wiring had been deleted, seemingly due to electrical issues, and I haven't been able to locate the battery light wiring, so the two wires, the regulator power, and voltage monitor, are connected directly to the battery on a toggle switch. I've read it's supposed to have a little resistance on the monitor wire, since it's supposed to be connected to the battery light, in order to achieve the correct voltage regulation. Obviously, it has a direct link to the battery. According to my battery gauge, assuming it's accurate, It's not staying at 14 volts all the time like it's in a constant state of charging. It drops to a little over 13 after a bit, which tells me that it is at least working correctly. BTW, this alt is BRAND NEW. Only been in it since a day or two after I got the car, and I put it in myself.

I appreciate the reply, I look forward to any more assistance you can offer. I will try running some new grounds and replace the unit again and see if I can find anything new happening.

 

I have ridden under the hood of cars while they where being driven to find intermittent issues. Many circuits can be viewed through the diagnostic port and a scan tool scope. Many higher end scan tools car hook inline and monitor the circuit. and also you to view the scope reading offline. The problem with voltmeters is they are next to useless to find voltage spikes. They simply do not react fast enough to show a spike. You will not even see a flicker from a spike on a voltmeter. Just because something is difficult to test or the equipment is expensive it does not mean it is not the problem. If you have electronics frying and its not magnetic fields then its most likely power spikes, they can be caused by power or ground. Vibration and heat can reduce life but the components are designed with a safety factor, meaning you would have to greatly increase heat or vibration just to cut the life in half. I am not sure I understand what you are talking about with the alternator. The alternator has two main jobs, supplying power and cleaning power. The cleaning power is most of the technology in the alternator. Before fuel injection you could buy a GM remanufactured alternator for around $49 from a GM dealer. With fuel injection the priced jumped to just under $300 and GM made them non-serviceable. GM did not want techs inside the alternator because a mistake could fry all the electronics in a car.

Every item with a winding can make a voltage spike, fans, relays, AC compressor. It is the alternators internals job to clean that power. For your car to ever be reliable you need to be 100% sure your charging system is working 100%.

 

Did you remove the toggle switch when you replaced the alternator? That could definitely cause voltage spikes.

 

I had to put the toggle switch in when I put the new alt in. The old alt that failed had no regulator wiring. So, naturally, it was running wide open. No wonder the alt failed. However, according to the schematic, the field winding power is supposed to be connected to ign+, so it turns on when the key is on, the monitor wire is supposed to be connected to the battery light, utilizing its minute resistance for what reason I'm not aware. The other two of the four wires, evidently ONLY for the 98, are a no connect. So, I'm hoping that isn't what is causing the issue, but that will be resolve as soon as I am able to pull the gauge cluster and locate the battery light wire.

 

Gorn, I added a couple of temporary grounds, as you suggested, something I usually think to try when I have power issues. I hooked an (approx) 8 ga. wire from the manifold (since the manifold should be grounded afaik), and a 14 gauge wire from that point to the ICM. No change. Incidentally, with a brand new ICM, car's still a no start. Now I may just be able to locate the problem. However, I need more information. The 5v line from ECU to ICM, the BYPASS power, does the ECU send 5v until the control line goes live, i.e., when the ICM passes timing control back to the ECU? Or does it only show 5v if the ICM is in good shape? In the past, I haven't gotten any voltage from that line unless I tested it with a brand new ICM. That doesn't mean that it wasn't some weird disconnect happening when I had it out, or before I pulled out the bad one. I usually can verify when they are actually bad, because they smell burnt.