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Discussion Starter #1
I had just taken the car for a (very) leisurely 1 hour drive with the family when all of a sudden it started to miss badly. I limped it home about 10 minutes on the highway with the engine intermittently running normally or barely running at all. No warning lights at all on the dash - no knocking or loud banging. A few times I saw a puff of smoke out the exhaust when transitioning between running/missing. When I pulled/lurched in the driveway, there was smoke coming from under the hood - I took a brief glance and it looked like some kind of oil from somewhere was dripping on the exhaust under the engine bay. It's possible the cats were really hot from unburned fuel going through them but I don't know where the oil was coming from. Level on the dipstick seemed fine. It seemed like there may have also been a clunking noise from the passenger rear of the car as I was coming up the driveway as well. I really didn't have time to look at it closely and frankly I was too pissed off to deal with it.

I just had new struts/mounts, a rack and pinion, and a 3.27 diff installed but haven't touched anything engine-related. The car doesn't get driven much and usually just short trips. The battery was replaced after a bunch of weird miss problems last year but nothing like this.

Any thoughts on where to start figuring this out?
 

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Discussion Starter #2
Seems like half of the motor isn't firing and it's dumping fuel straight out the exhaust. It's at a shop now but they haven't sorted it out yet. Open to thoughts... I told them to check the ground bolt under the battery - any other common electrical glitches that may be worth checking?
 

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Know the odd coils/injectors and even coils/injectors have separate fuses in the engine compartment fuse block. Believe at least the ignition coils have different grounds as well. Both might be worth a gander.
 

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Discussion Starter #4
Thanks - I checked the fuse box and nothing was obviously burned out there. I spoke to the shop again and they confirmed that the coils were getting power but not sending spark to the plugs on the right side of the engine. The shop owner's son is a GM tech - they're going to leave it for him to look at after hours to avoid wasting a bunch of time (and my $) on it.
 

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The same fuse that powers up the coils, also powers up the fuel injectors on that same side. If the shop was using an alternate ground source (when verifying power to the coils), the normal ground that the coils require to complete the circuit could be faulty. All 4 coils on the passenger side, receive power anytime the ignition is turned on (as well as the injectors). All 4 coils on that side have their ground return wires spliced together into a single wire that is routed to the front of the passenger side cylinder head. I think you should check that grounding stud location carefully. If all 4 coils read continuity from pin A to that grounding location, or read 12 volts going from pins D to A , that would tell you that the primary side of the coils circuitry is OK. The triggering circuit to fire off the secondary side of each of those 4 coils, comes from the ECM an the retrurn ground from the coils secondary side, go back to the ECM which is grounded internally.
 

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Discussion Starter #6
Awesome info, thanks so much. With the help of the GM tech, the shop pretty quickly tracked down a broken ground wire inside the harness somewhere - probably the same one you're referring to. They patched it and everything was good to go (although I still haven't picked it up). They also had to fix the exhaust since the cat on that bank had heated up so much from the unburned fuel going through it that it started to leak at one of the flanges.

I'm pretty relieved they were able to find it so quickly. I had a similar weird ground issue on my last rig and it took a lot of time and money to track it down.

Thanks again for the help everyone!
 
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