Bad Misfire on Long Trips

**LS1SS** · 11-07-2011, 07:49 AM

This is a problem that has plagued me for the past couple of years and I am out of ideas as to what could be causing it. I have a 2002 Camaro SS with long tube headers, no cats, SLP Exhaust, new coil packs, new plugs, MSD spark plug wires, new PCV valve, and a performance dyno tune. On long trips, > 1.5 hours, the car will start to severely misfire, have limited power, throw SES codes for miss fires and have black sooty exhaust. This in turn fouls out my O2 sensors, which I seem to replace every 6 months due to this issue and seems to be the only way to return the car to normal running status. During this event I get horrible MPG (8-10) and have had a difficult time having a shop diagnose it because of the time it takes for it to happen.

Anyone have any ideas on how to diagnose it or what to replace next?

Thanks

**WS6SP33D** · 11-07-2011, 08:32 AM

Have you checked the pulse rate on all injectors? or checked for a bad injector? Also have you conducted a compression test? Theres only a few things that could be causing this only ling trips and not all trips. Also did you check the ohms on the the new msd wires? Even tho they are new i have seen many outside the rating.

**Knight** · 11-07-2011, 08:54 AM

Have you cleaned the MAF recently? Are you running O2s with the full length harnesses, or extensions or spliced? Why did you replace the coil packs? What brand did you use?

**LS1SS** · 11-07-2011, 10:20 AM

Originally Posted by Knight

Have you cleaned the MAF recently? Are you running O2s with the full length harnesses, or extensions or spliced? Why did you replace the coil packs? What brand did you use?

MAF was cleaned a few weeks after I cleaned and re-oiled the K&N Filter at the beginning of this year. The problem existed before I did that. The O2s are full length from the corvette. The coil packs, AC Delco, were replaced as a last ditch effort to fix this problem with the thinking that they get hot long trips and the old dielectric breaks down causing it to arc out.

The PCV was replaced bc I noticed a larger amount of oil residue in the intake than I expected. I suspect that oil build up in the intake over longer trips through the PCV valve is causing the misfire but I dont know what an appropriate amount of oil is or how to test that theory.

**LS1SS** · 11-07-2011, 10:28 AM

I have not checked the pulse rate, for a bad injector, or compression test. The car dynoed ~365 rwhp and runs perfectly driving around the city. The wires I replaced in 2005 when I did the headers. This problem showed up a couple of years ago so I don't think the wires are the culprit, but what resistance should they be?

**LS1SS** · 11-07-2011, 10:42 AM

The MAF was cleaned a few weeks after I cleaned the K&N filter but this problem existed prior to that.
The O2s are from the corvette so they are full length.
Coil packs were replaced as a last ditch effort with the thought that the dielectric was breaking down over time from extended exposure to heat causing them to arc out. I replaced them with AC Delco coil packs.
The PCV valve was replaced because I noticed more oil residue in the intake than i thought was reasonable. My current theory is that over long trips excess oil is making it into the intake through the PCV causing the misfires and fouling o2 sensors but i dont know how to test this theory.

**WS6SP33D** · 11-07-2011, 10:42 AM

Also like said above please take time and clean you maf if not already

stock LS1 6 in. - 351 ohms
Granatelli 8mm Steel Solid Core Cable - 0.1 ohms
MSD 8.5mm Super Conductor - 71.6 ohms
Accel 8.8 300+ Ferro-Spiral Race Wire - 166.1 ohms
Jacobs Electronics EnergyCore 8.5mm - 178.3 oms
Taylor Spiro Pro 8mm Silicone - 301 ohms
Mallory Pro Sidewinder 8mm Silicone Suppression Wire - 313 ohms
Moroso Blue Maz Spiral Core 8mm - 661 ohms
Magnecor KV85 Competiton 2.5mm - 2053 ohms

**LS1SS** · 11-07-2011, 02:13 PM

I will clean the MAF tonight, it was last done when i cleaned the K&N at the beginning of the year. The o2 sensors are from the corvette so they are full length. The coil packs are AC Delco OEM replacements. I replaced them bc I thought the extend exposure to the heat on long trips was causing the dielectric in them to breakdown which would allow them to arc out. I figured new ones were better than old, probably a bad assumption but its one less thing to be causing the problem.