'08 GP Stalled while driving, then no start, no spark

[sisson_d]

I got stranded by the '08 GP today. Thankfully I had already dropped the kids off and was still a few minutes away from the highway because I was doing about 40mph when the engine just cut out. After that it would crank strong but not turn over.

Once I got the short tow home, I checked the following:
-All fuses and relays are fine
-No DTC codes
-I can hear fuel pump
-found no spark at any of the ignition modules using test light
-scan tool shows RPM data (150-200 RPM) when cranking, so crank position sensor seems good
-battery was barely 12 volts, likely from sitting with radio, blower, etc. on while waiting for the tow. Under cranking, the voltage drops to around 10.5 volts and quickly rebounds.
-no obvious problems with wiring to ECM, Ignition Control Module, crank sensor

So, I'm going to check fuel pressure. I've got a charger on the battery. But ultimately, the lack of spark at all 3 ignition modules lead me to believe the problem is the ICM (ignition control module). I have also had a few instances of a low/rough idle over the past month or so. It seemed that the car might stall at any second. I was looking toward other items, but now believe that it was a warning sign of a failing ICM.

So, any advice on how to test the ICM? It's not cheap, so I want to make sure this is the problem before I replace it. Everything I've found so far features the older designs that you find with a car that has a distributor cap, etc.

Thanks in advance for any help.
-Doug

[sisson_d]

I ended up finding this great tutorial a few minutes ago:
http://easyautodiagnostics.com/gm/3....-sensor-test-1

I have a good 12v and ground through the ICM connector.

But, I don't have a small 12v LED light handy. Does anyone know if I can assume the crank and cam sensors are getting the power and sending back data through the ICM if I'm seeing RPM data on my scan tool when cranking? It sounds like both sensors only recieve their power through the ICM. And with no DTC codes and RPM data, I'd think that means they (and their wiring) are fine.

[StumpedGMowner1]

Just posted to another thread with almost exactly the same problem. Cam sensor is bad. Crank sensor sends rpm data and fuel injection timing. Rough idle and longer starts are a clear indictor of a failing cam sensor. But as always start cheap. Could be a bad relay. Check all fuses and relays and for 12v at cam sensor before replacing it. Also they almost never set the code they are suppose to.

[sisson_d]

Originally Posted by StumpedGMowner1

Just posted to another thread with almost exactly the same problem. Cam sensor is bad. Crank sensor sends rpm data and fuel injection timing. Rough idle and longer starts are a clear indictor of a failing cam sensor. But as always start cheap. Could be a bad relay. Check all fuses and relays and for 12v at cam sensor before replacing it. Also they almost never set the code they are suppose to.

Yup, that was me. I didn't know if this GP section would be as well visited. I checked all the fuses and relays first thing when I got the car home. Thanks again for the info.

[Tech II]

If you have no spark, that has nothing to do with the fuel pump.....

You do not need a cam sensor signal for spark......

If you used a spark tester and had no spark from any of the coil terminals, it is either the ICM or the Crank sensor, or the wiring in between them......

[StumpedGMowner1]

Never said anything about fuel pump. Also if you truely believe the Cam shaft sensor has nothing to do with spark the pardon my french but your an idiot. This is directly from Pontiac repair manual. As the camshaft position sensor weakens, the signal it transmits to the vehicle’s ECM also weakens. Eventually, the signal will weaken so much the signal will switch off, and so will the engine. When it switches to the off position there is a loss of spark across all cylinders. This is due to a loss of reference to position of the camshaft for the 3x 18x signal from the crankshaft to sync ignition and fuel injection. This can happen while the vehicle is parked, or while you are driving. The latter can be a dangerous situation.

[sisson_d]

Actually, in my original post I did mention the fuel pump as one of the many things I checked, but that was before i found out that I had no spark. After that I checked the fuel pressure because I had read that if the CPS is not sending data to the ECM, then there won't be spark or fuel.

As far as the Camshaft Sensor...I'll let you guys sort that out. That's not my field of expertise. I'm gonna pick one up regardless. It's not expensive or hard to install. My engine has 110k and more and more of the original parts are starting to go south.

[Tech II]

Also if you truely believe the Cam shaft sensor has nothing to do with spark the pardon my french but your an idiot.


Name calling? Shame on you......

This is a 3800 engine......cam sensor has nothing to do with spark.......

The crank signal creates a synch signal for the ECM....so the ECM knows when the #1 cylinder is at top dead center......what it doesn't know if it is on exhaust or compression stroke......the cam signal, differentiates that......if you lose the cam signal, the ECM will make it's best guess as to when to fire the ICM at the correct time......if lost, it may fire the spark at the wrong time, causing it to run rough or stumble......It is the crank sensor and ICM and coils and ignition wires and plugs that create spark, NOT THE CAM SENSOR!

[sisson_d]

Okay, I installed the new ICM yesterday (standing outside in the freezing mist with 102 fever) and the car started right up.
I also did the cam sensor the day before, and that did nothing. But it gave me a chance to confirm the wiring for the sensor was okay. And the part it replaced had 108k miles on it. So, for $36 I wouldn't consider it a waste of time.
Thanks to all that helped!

[StumpedGMowner1]

Tech II you where correct.

[Tech II]

Thank you......