Random Misfires Code
10-04-2011, 08:36 PM
#1
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Random Misfires Code
Alright opti-spark gurus. My 1996 LT4 car threw this code. I reset the code and inspected visually. I noted the sparkplug wires looked pretty shabby, with a few burned looking spots. I ordered a set of Taylor Spiral Pro 8mm red wires (and a fuel filter on general principles). I am at 65001 on the odometer. Car threw the code again today (I actually felt the stumble this time). I am thinking I may need a cap and rotor (maybe just replace the opti). I can use a lift at Quantico. As I understand it I am looking at replacing the water pump, coolant, opti, wires, and plugs. Looks like @$500-600 in parts and a bunch of work. Any other causes of that code other than failing opti? Could it just be wires? Is it absolutely essential to replace the whole opti or is the cap and rotor enough? I drive less than 5k a year. 
10-04-2011, 11:19 PM
#2
A lot of things can cause a random misfire code to set (fuel system, ignition system, engine internal, etc.). Given the shaby spark plug wires you noted I would first replace those along with the spark plugs if they are original as this needs to be done anyway. If this fixes your problem (and it can) then your good to go. If this does not invest in a Factory Service Manual. The manual has a detailed fault tree for chasing down this issue.
The opti can cause this issue but so can a number of other things.
The opti can cause this issue but so can a number of other things.
10-05-2011, 03:57 AM
#3
Any decent OBDII scan tool will allow you to monitor misfire count by cylinder number in real time, drive the car with the tool connected and see if you can isolate which cylinders show the highest misfire counts. Once you have that information carefully inspect the wires and plugs in those cylinders.
10-05-2011, 07:47 AM
#4
Mine will do the same thing right after I fill up the tank at a different station than the one I usually go to.
Most of the time I run Sunoco 93 but every once in awhile I run Shell 93. The stations by my house seemed to be ok but others will cause the code. I’ll throw some sea foam in the tank and wait a couple of days, the light goes off and everything is fine.
Also when they change from summer to winter blends it seems to take it awhile to get used to the change.
96 LT-4 with 89,000 miles
Most of the time I run Sunoco 93 but every once in awhile I run Shell 93. The stations by my house seemed to be ok but others will cause the code. I’ll throw some sea foam in the tank and wait a couple of days, the light goes off and everything is fine.
Also when they change from summer to winter blends it seems to take it awhile to get used to the change.
96 LT-4 with 89,000 miles
10-05-2011, 08:28 AM
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PG- thanks for that, I was worried about Sea Foam and the injectors. Sea Foam will go in tonight. I will change the plugs and wires in a few weeks as well as the fuel filter and an oil change and we'll see where she sits. I truly hope to wait on the opti. Just seems like an atrocious amount of work, and there are a few less challenging things I would like to tighten up first. Is $70 reasonable for OEM Delcos? Any as good/better alternatives for less dinero?
Last edited by 1stVetteC4; 10-05-2011 at 08:36 AM.
10-05-2011, 07:41 PM
#6
Le Mans Master
Out here - at least in the not too distant past, it was allmost always the injectors and the cause was MTBE (thankfully now banned) which was being used as a fuel additive. To avoid a CA recall, GM issued a 200k, 10 year extended warranty for all injected vehicles (CA only). I'd have them cleaned (which is what the Dealers did under the extended warranty) as that often makes it go away.
