New guy here. My son has a 97 Grand Caravan, 3.3 L, Auto trans. that has started a random misfire but only during warmup. He has replaced both temp sensors (coolant and ambiant), cam pos. sensor (because of previous code), plugs and wires. On the scanner when this is happening, the codes are just random misfire and it doesn't set any hard codes. I'm hoping that someone here has seen this and can help me figure out what may be happening. He's checked all connections and tested primary and secondary windings on the coils and they are within specs. Any ideas are greatly appreciated.

 

Could be a sticking injector that fixes itself when it warms up.

 

I would start by checking fuel pressure and looking for vacuum leaks. The pcm is seeing multiple cyinders misfiring so you should look for something that affects all, or at least a couple of cylinders. Some other possibilities might be contaminated fuel (water or diesel), a sticking egr valve, restricted fuel rail, or a coil pack.

 

Thanks Guys. When this first started, he changed the fuel filter, checked pressure at the rail. The first codes were primary coil related and he checked the coil packs. I'll ask him about the EGR.

 

If you have had a primary coil code, there is a good chance the coil is bad. Coil failure doesn't always show up on resistance test, and even if it does it may be temperature sensitive. Check with your local parts store and see if you can return a coil, if you can, try one and see if it helps any.

 

Thanks for the answer. He tried another coil pack recently and it made no difference. Someone suggested a vacuum leak and he's looking at that today, after work.

 

try an injector flush. sometimes theres some carbon buildup in the plenum as well. youd have to remove the plenum, and get some carb cleaner and some brushes and clean out all the egr ports.

 

Yes, try a can of SeaFoam in the gas tank. Follow the directions on the can. You can get it at NAPA/CarQuest and some other places. It's good stuff. www.seafoamsales.com
Some of the later engines have had reports of the inside of the fuel rails deteriorating and causing injector plugging. I dont think your year is new enough but it might be something else to consider?