bad missfire???

[chevelle_ss_69]

I have the 3.8 sc, i just recently put the msd coil packs in it, about two weeks or so after i started to notice a really bad miss when i was on the expressway. Doin like 60-70 just cruising then when i would go to accelerate normally not flooring it or anything it would feel like the engine was gonna fall out of the car. If i let or the gas and then hit it again it would accelerate just fine but not until. The car idles just fine not even noticable really. Does anyone know what this maybe be, i put in a new fuel filter to see if maybe it wasn't getting enough fuel but it still does it. Thanks for any help.

[Mickey#1]

What year & how many miles are on it?

If the check engine light is on then stop by your local autoparts store & get the codes read. You might also want to swing by a muffler shop & have them check the catalytic convertor.

[chevelle_ss_69]

its a 99 with about 160,000 no codes right now though

[BNaylor]

Out of curiosity what brand ignition wires and spark plugs? My experiences with the MSD coils is they can be finicky depending on the brand OE or aftermarket wires. They must have low resistance. Other possibility since you did not have the problem before the coils were replaced is defective coils.

[chevelle_ss_69]

i have delco wires and delco irridium plugs so should i put something else in there

[BNaylor]

The MSD coils should work fine with the Delco Premium Silicone 7mm wires assuming that is what they are. No known issues with the Delco Iriidium plugs but I'd inspect each one to be sure. Check the resistance of the wires. On Delco about 500 ohms per foot. Plus you could check coil resistance.

[chevelle_ss_69]

alright ill do that at work tonight and see what i come up with, i was thinking about the plugs but it got to me when it didn't idle rough or seem to miss at all except when i would put it under a load at 60 to 70. everything is pretty new tune up wise. the plugs only have about 10,000 along with the wires so....its got me

[HotZ28]

In addition to all the fine advice given above, be sure that all the plug & coil wire terminals are "snapped" in place. You must here it click when installing the boot! Use a liberal coating of dielectric grease in all the boots before installing. One loose terminal can cause havoc when using MSD coils. In addition, be sure that you do not have a cracked insulator on one of the plugs!

[BNaylor]

I'm leaning towards defective coils. Very common issue with the MSD Blasters in the 3800 community. If he still has the OE GM coils I would re-install them and then see what it does.

Really no need to run aftermarket coils since the OE have been proven to be the best around. I installed MSD Blasters on my GTP for the looks only but I used the MSD 8.5mm wires. 50 ohms resistance per foot.

In the meantime with a DMM:

Ignition coil primary resistance = 0.5 to 0.9 Ohms
Ignition coil secondary resistance = 5K to 10K Ohms