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.
dirk0
12-15-2005, 10:28 AM
Have you checked the fuel pressure?
arkieoscar
12-15-2005, 10:55 AM
Hi. Yes, he checked the pressure on the fuel rail and it was good. It only happens during warmup. I'm not sure if it's trying to go into closed loop and failing that's causing the ignition problem. He's checked all of the connectors. I don't think this uses a separate ignition module. I think that it all comes from the main computer. I used to own a shop but I've been out of the business for several years. I have forgotten alot of the details on the different systems but I'm afraid that it's the computer failing.
dirk0
12-15-2005, 11:24 AM
I had a similar problem with 2 older 3.3l engines. The first one had multiple issues. MAP sensor was acting strange and I traced other issues back to a leaking TB gasket and upper intake gasket. The second one happened this week, fuel pump is acting up. One day the psi is 40 or higher, next day it will be at 20-25psi. I’ve kept some notes on strange issues I’ve had over the years, I will see if anything stand out that may help.
gas28man
12-15-2005, 12:21 PM
I just had a thought about this. Consider the possibility that you have a vacuum leak somewhere, possibly in the lines that lead to your power brake booster, or possibly the booster itself. I had an untraceable intermittent cold-engine stall and roughness that was going on for about a month before my power brake booster failed. I replaced the booster, and guess what went away? My stalling problem. It was then that I put two and two together and recalled that I'd been hearing a slight hiss around the brake pedal when I was also having the stalling issue.
Good luck.
Rick
arkieoscar
12-15-2005, 04:16 PM
Good ideas to check. This misfire is really predictable. It starts about 4-5 minutes after startup and is gone completely when the engine reachs operating temp. This takes a little longer now that it's colder but once it's at full temp. the engine runs fine. He replaced the MAP sensor when it didn't check out on the meter. It was a little out of range. If it was an old GM system, I'd say that it was trying to go into closed loop and falling back into open loop but it doesn't set any codes and only shows the misfire codes when you scan it when it is missing.
gas28man
12-15-2005, 04:41 PM
Yeah, that was the same way mine was. It would only stall and run rough until the engine came up to operating temp. Then it was fine all day. Pay attention the next time you're driving it first thing after startup, and see if you hear a hiss when you step on the brake. That would be the big red flag that it's the booster or the vacuum line leading to it.
Rick
dirk0
12-15-2005, 09:18 PM
I looked over some of my records and I haven't found anything other than the vac leak. Hopefully it is something simple.
arkieoscar
12-16-2005, 07:40 AM
He's bringing the car over here this weekend and I'll check for vac. leaks. Now I remember why I sold the shop.
arkieoscar
12-17-2005, 11:09 AM
He's checking for vacuum leaks today. He had to work so he's not coming this weekend. He told me that he had tried a new coil pack and that made no difference.
