1 year ago, new spider distributor cap, wires, plugs--running great. 6 mo ago pack rats ate 6 wires to the computer, fixed--running great Last mo cold starting rough but fine when warm. I have headers and can feel right cylinders cold and it runs like a 3 cylinder engine. Ideas?

 

To clarify, 2,4,and 6 cylinders with badly fouled plugs--thought I was smart, cleaned plugs and put in a new O2 sensor=no better. Help, please

 

Did you use ACDelco cap and rotor? These vehicles don't like aftermarket cap and rotor.

 

Do you have a scan tool?

For this discussion, "scan tool" = dedicated scan tool or ([PC or tablet or phone] app with [OBD-II->USB cable or OBD-II->bluetooth or OBD-II->WiFi adapter])

 

Forgot to mention--no codes! After new O2 sensor and cleaning plugs with propane torch, still only running on 3 cylinders

 

Stupid me! I said no codes in mistake because when I checked my battery was too low. Got a new battery 2 days ago, fully charged, now is almost discharged when I went back to check the codes. Where do I look for trouble? Sorry for giving you bad information. Can the two problems be connected? Can I just pull fuses with multimeter to look for drain?

 

Be sure to fuse protect your multimeter, and use the "high amperage" plug for the probe. Most multimeters don't do anything over 500mA on the "normal" probe connection, and often they only do 5A or 10A maximum on the high amperage connection.

The problems might be related. You do need to check for codes (both current DTCs and pending DTCs), but that wasn't the only thing I wanted to check with the scan tool. If your scan tool can get to the Mode 5 O2 sensor monitor data, that might tell you something. I'd also watch the graph for the O2 Sensor (bank 2 sensor 1) and the short and long term fuel trims on bank 2 while it's running (live datastream, AKA mode 6).

I suspect you will find a wire crossed with power (possibly crossed to the "keep alive" power to the PCM since you're having battery issues). The most likely culprit is the O2 sensor. If 12V battery voltage gets crossed on the signal of the O2 sensor, the PCM could read that as excessively lean, and it would dump as much fuel as possible in (very high positive fuel trims) to compensate, but that won't lower the O2 sensor signal because the O2 sensor is connected to power. You could also have a brand new, BAD O2 sensor. That happens. "New" is not the same as "good."

The other possibility is that power is crossed onto one or more injector wires, keeping one or more injectors constantly open. To foul all three plugs, it would have to be all three injectors, and that should result in hard starting issues, in addition to the misfiring. If that's happening, you'll see low voltage on the O2 sensor (rich), and very negative fuel trims (as the PCM tries to lean the mixture, but can't because the power is getting to the injectors when the PCM has them "off").

 

Much appreciated--waiting for the battery to charge. I guess what bothers me is why wouldn't the car run for even a little bit with clean plugs?

 

My scanner only does trouble codes and pending==shows no codes! (multimeter to 10 amp only) Boy that battery drains fast.

 

Check for pending codes after running, but before battery dies. Dead battery will clear any current or pending codes.

You could also check for voltage at the right side O2 sensor with the engine off (battery still charged and connected. There shouldn't be battery voltage anywhere on the O2 sensor connector when the engine is off. You can also back probe the O2 sensor with your volt meter on the tan and purple wires. There should never be battery voltate on either of those, and the voltage across them should cycle/oscillate when the engine is running.

If you don't mind tripping a SES light and another DTC, you could also try starting it with the right bank upstream O2 sensor unplugged.

If the O2 sensor is faulty or the wiring is messed up to that sensor, it can cause it to run super rich and misfire, even with clean or new plugs. The fouled plugs aren't causing the problem, the problem is causing fouled plugs.