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Discussion Starter · #1 ·
Hey all,

My cousin just bought a 1996 C1500 pickup with the 350SBC. The MIL light was on, so we pulled the codes, it had a bank 2 too rich code and a cylinder 3 misfire code. We did a tuneup on it, then erased the codes. He drove it around town for a while, then it threw another code, misfire on cyl 3. So, what's going on? We're pretty clueless as to what's causing a misfire code...other than the cylinder actually misfiring...
 

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P0303 DTC code

Well cylinder misfire codes can be difficult to diagnose since there are many factors that contribute to the misfire condition. Here is a good overview of the P0303 DTC code from obd-codes.com :
P0303 Code - Cylinder #3 Misfire

Technical Description

Cylinder #3 Misfire Detected
What does that mean?

A P0303 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #3.
Symptoms

Symptoms may include:
  • the engine may be harder to start
  • the engine may stumble / stumble, and/or hesitate
  • other symptoms may also be present
Causes

A code P0303 may mean that one or more of the following has happened:
  • Faulty spark plug or wire
  • Faulty coil (pack)
  • Faulty oxygen sensor(s)
  • Faulty fuel injector
  • Burned exhaust valve
  • Faulty catalytic converter(s)
  • Running out of fuel
  • Poor compression
  • Defective computer
Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

btw: I remember something about corroded injector connectors being a problem on GM vehicles. The recommended fix was to clean the connections and apply dielectric grease to prevent corrosion.
 

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Discussion Starter · #3 ·
Well, a full tune-up has been done since the truck was bought, including spark plugs, wires, rotor, and cap, we then reset the code and it returned. I guess the next place to start looking would be the burnt exhaust valve and screwed up fuel injectors....

As a side note, the tach on the truck was working oddly, the tach reading was jumping all over the place, then after the tune-up, it ceased working completley. Still haven't figured that one out yet....
 

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Hmm....two problems, same cause?

Hmmm....tach quit working. Sounds like an electrical issue. I mentioned in my previous post that GM had trouble with corrosion on the injector connectors. Maybe you've got something to look at there that is common between the two issues.
 

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Discussion Starter · #5 ·
as for the tach issue, I'm 98% sure it's the actual instrument cluster dieing, as the code reader my uncle has can read the current RPM off the computer as well as other data and the tach reading from the computer reads perfectly.
 

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It could be as simple as the sparkplug gap being to small. You can pick up a sparkplug gapper (or what ever it is called) for like a dollar. Also check the insulator in the boot and see if its still there or broken.
 
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