misfire.....

[Biohzd]

98 Chev 350.....

Missing (not lost). Replaced rotor, cap, wires, plugs. Still missing. Scan indicates random misfire. Distributor substituted and is ok, coil replaced and is/was ok, wires removed and test ok, poor spark on cylinders 5 and 8.

 

[DEERE3594]

Thats a vortec right? I dont have any experience with them but my 89 TBI runs, funny, if you will with 87 octane. Try running 93 threw it, that's all I run in my gasser and the wife's cars.

 

[Biohzd]

Ya, vortec. Been running high octane in it since almost new 'cause it didn't seem to like the low.....

 

[RYDNHI4X4]

If I am not mistaken those Vortec's have there own coil pack for each cylinder right above the valve cover. I had one whole side go out long time ago in my old 2000.

 

[83GMCK2500]

Not until the newer generation of small blocks did they get coil-over-plug ignition. There is one coil powering the distributor on the Vortec 350s.

Did you use AC Delco Platinum plugs? In my experience if you don't on that engine you're asking for hick-ups. They are gapped from the factory at the requisite .060" or whatever it is. I can't explain it but if you're using OEM ignition components (coil, cap/rotor) those engines really love the Delco Platinums. I never tried the Iridium, couldn't justify the extra $$$. I also have no experience with aftermarket ignition components like an MSD ignition box or aftermarket coils, just bone stock engines.

 

[btfarm]

I'd first do some swapping around of the plugs then the coil packs to see if the problem moves with the swap. You're sure the wires are ok?

 

[Biohzd]

Multiple answers to folks:

Yes, single coil. Yes to ac delco platinum plugs. Gapped by hand to .06.

Very Very weak spark out of these two plug wires, color is redish not blue and won't jump a gap w/o bridging with a screwdriver, switching plugs won't make that go away. Wires check out on ohm meter and have been swapped around to verify that is just the two cylinders. Should drop in another cap just to make sure that there is not a cap problem though.....

 

[83GMCK2500]

Have you inspected the underside of the cap for any corrosion or blemishes on those contacts?

 

[Biohzd]

Ya, have checked both old and new caps. Appear to be 'normal.'

 

[buddy]

Ahhh, the 350, thats my kind of territory, even though mine is an LT1. Do you have a separate Ignition module from your distributor, maybe by the Ignition coil? Mine is separate because I have the Opti-Spark distributor by my water pump, but my older Chevy HEI had the module on the distributor. And I had one of those go bad and mess up my timing.

I had an issue like this after some marmots ate up my engine bay when I was weekend backpacking in Yosemite.

The plug wires were bad, but that didnt eliminate the issue and I still got some of that crap, not just misfires but also backfires too. Check your IAT sensor and O2 sensors are functioning correctly. They also ate those wires on mine, and after repairing it runs almost back to completely normal.

Maybe you had a squirrel climb up and snack on some wiring, that happened to my cousin and I had to go fix all the injector wires on her Dodge as they were all chewed through, and she wondered why she had misfires

 

[Biohzd]

Happened to be a compound problem. Replaced things in pairs and finally in triplicates until it started running properly. Turned into: ICM, distributor, two injectors..... Thanks all for your thoughts.