Cam sensor question.??

[stangeater]

Could a bad cam sensor make my sho act like it's running on 4 cylinders? I've checked the DIS, Coil, wires, plugs, and still seems to be running on 4 cylinders??

 

[projectSHO89]

No. A bad cam sensor usually manifests as difficult to start or as severe bucking once running.

Usually it's the DIS module that causes the engine to actually run on four cylinders.

 

[stangeater]

Okay...just a thought. I'm trying to track this problem down. I'll try another DIS, who knows maybe the one I swapped on was bad also??

 

[gmorrell]

Once the engine is running and EEC has injector synchronization and DIS has ignition sync, you should be able to unplug the cam sensor with no effect in how the engine runs. An unplugged cam sensor will usually set a CEL and code in a running engine, but the engine should run fine. A bad DIS has been known to drop a coil when it gets warm.

 

[Phoenix]

Okay...just a thought. I'm trying to track this problem down. I'll try another DIS, who knows maybe the one I swapped on was bad also??

Make sure its fully grounded (you can use heat sink paste) and all 4 bolts secured (yes all 4 not only 2 or 3)

If its still doing it and you know your dis is good , then you need to check the coil , the wires and the plugs.

 

[AREA 91]

The DIS is grounded through the two lower 5.5mm bolts.

 

[gmorrell]

^^^ What he said. ^^^

Among other things, the DIS module needs a good ground to function properly, and it grounds through the two bottom screws that secure it to the intake manifold crossover tube. Additionally, for the crossover tube to get grounded, the shake brace from the crossover tube to the intake manifold back tank has to be in place. Also, there's a ground braid from the rear intake tank to the firewall, make sure this ground strap is clean and secure at both ends.

Heatsinking: DIS has three power transistors that fire the ignition coils, they're attached to the DIS back plate, which is called a heat-spreader. The heat-spreader's job is to absorb heat from the coil firing transistors and also to spread the module heat around to minimize hot spots in the other electronics in DIS, and there's a lot of brains in DIS, including a Motorola micro-controller. The heat spreader dumps excess heat into the crossover tube, and this is why we apply a layer of thermally conductive grease (heat sink grease) between the heat spreader and the crossover tube surface.

Dielectric grease is NOT heat sink grease, these two have very different properties and compounding.

Edit: It's not uncommon for an ignition coil primary winding to develop some shorted turns in the windings, this can overheat the associated DIS firing transistor in a hurry and drive that channel into over-current shutdown - now you have a 4-cylinder engine, and DIS will stay in this mode until it gets a power cycle (key off - key on). Usually, the DIS module isn't damaged by a bad coil, but it's happened. Sometimes you can just replace the coil pack and all will be well, other times both coil pack and DIS must be replaced.

 

[stangeater]

Wow, thanks for that info on the DIS!! Good stuff!
It was so weird, I was driving down the interstate, and Bam...it just started missing like a plug wire came off or something.
So far I've put another DIS on, installed new plugs, and changed the coil out with another spare I had laying around. None of this has helped the problem at all. Tomorrow I pick up a new set of plug wires that I ordered, and I'm crossing my fingers on that. If that doesn't work, i don't know where else to look?