I need some help diagnosing this.
3.4DOHC with a misfire under load that just started recently. The misfire is not there when idling or part throttle. Just when under load.
I am not all that familiar with electronic ignitions so bear with me if you make a suggestion and I don't see where you're going with it.
My assumptions since it idles and no misfire under part throttle:
1. The plugs and wires are okay
2. There is no problem with the valve train
3. Fuel delivery is good
I have a garage I can get the car into but not enough room to drop the cradle. I also don't have a lot of free money to throw at it. I'm retired and on a fixed income. So if you want me to change out the coils/ICM/etc., expect a months wait between items depending on cost. I also don't have test equipment beyond a VOM and a power probe.
So, suggestions?

quote Originally posted by n7vrz: I need some help diagnosing this. 3.4DOHC with a misfire under load that just started recently. The misfire is not there when idling or part throttle. Just when under load. I am not all that familiar with electronic ignitions so bear with me if you make a suggestion and I don't see where you're going with it. My assumptions since it idles and no misfire under part throttle: 1. The plugs and wires are okay 2. There is no problem with the valve train 3. Fuel delivery is good I have a garage I can get the car into but not enough room to drop the cradle. I also don't have a lot of free money to throw at it. I'm retired and on a fixed income. So if you want me to change out the coils/ICM/etc., expect a months wait between items depending on cost. I also don't have test equipment beyond a VOM and a power probe. So, suggestions?

My ls motor did that once, turned out to be a bad coil.

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86 SE Convertible 3800sc 4t65e HD.

When any car I've had did it, it was wires. Id double check them, they dont have to look bad to be bad.

quote Originally posted by 2.5: When any car I've had did it, it was wires. Id double check them, they dont have to look bad to be bad.

x2

Here's a process you could try: Pull one plug wire at a time & test for the miss under load. You may be able to tell which cylinder is missing if it doesn't seem worse when that plug is disconnected. Try a different plug in that cylinder, since plugs can malfunction under load. If that doesn't fix it, try a different wire for the same reason.

I had the same problems last week with my 3.4 DOHC Fiero. Major misfire, but only under load. Turned out that the #2 spark plug wire was corroded from rain water dripping off the back window and getting into the plug wells. I replaced the wire and the car is now running better than it has all summer.

I also made a quick, temporary cover to prevent water from getting back in there. Not pretty, but it'll keep water out till I come up with a more permanent solution.