4 CEL codes, sometimes flashing...

[alchemist1]

My 98 Suburban (251,000 miles) has been running bad the last couple of weeks and is throwing a CEL, and scanning it shows four codes:
P0420 (Bank 1 catalyst effciency), P0430 (bank 2 catalyst efficiency), P0135 (O2 sensor bank 1 sensor 1), and P0305 (cyliner #5 misfire).

Occasionally, the CEL will actually flash instead of staying on. I replaced both O2 sensors, pre-cat, as I knew at least one was probably original. Also ran a can of Seafoam thru the gas tank on Sunday and it ran a little better on the highway going to Raleigh. But Monday ran like crap again. I'm thinking two things: Injector clogged or malfunction AND/OR catalytic converters are toast. I found the universal Magnflows for close to $80 each.


Any ideas on these symptoms? I've never seen a flashing CEL previously.

[99'HEARTBEAT]

Here is Information on the Trouble Codes.....P0135......P0305......P0420......P0430,

Trouble Code.....P0135 may mean that one or more of the following has happened:

• O2 Heater element resistance is high
• Internal short or open in the heater element
• O2 heater circuit wiring high resistance
• open or short to ground in the wiring harness

Trouble Code.....P0305 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

Trouble Code....P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

Trouble Code....P0430 may mean that one or more of the following has happened:

• The catalytic converter is no longer functioning properly
• An oxygen sensor is not reading (functioning) properly
• There is an exhaust leak

Regarding the Flashing CEL....Check Engine Light,
......Light Flashing -- A Misfire Condition has been detected.....A Misfire increases Vehicle Emissions and may Damage the Emission Control System on your Vehicle. Dealer or qualified service center diagnosis and service may be required.

.....Light On Steady -- An Emission Control System Malfunction has been Detected on your Vehicle. Dealer or qualified service center diagnosis and service may be required.

[alchemist1]

Here is Information on the Trouble Codes.....P0135......P0305......P0420......P0430,

Trouble Code.....P0135 may mean that one or more of the following has happened:

• O2 Heater element resistance is high
• Internal short or open in the heater element
• O2 heater circuit wiring high resistance
• open or short to ground in the wiring harness

Trouble Code.....P0305 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

Trouble Code....P0420 may mean that one or more of the following has happened:

• Leaded fuel was used where unleaded was called for
• An oxygen sensor is not reading (functioning) properly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings

Trouble Code....P0430 may mean that one or more of the following has happened:

• The catalytic converter is no longer functioning properly
• An oxygen sensor is not reading (functioning) properly
• There is an exhaust leak

Regarding the Flashing CEL....Check Engine Light,
......Light Flashing -- A Misfire Condition has been detected.....A Misfire increases Vehicle Emissions and may Damage the Emission Control System on your Vehicle. Dealer or qualified service center diagnosis and service may be required.

.....Light On Steady -- An Emission Control System Malfunction has been Detected on your Vehicle. Dealer or qualified service center diagnosis and service may be required.

Yup, I know all about the CEL codes and what they mean, but just wondering, can the fuel injection (CSFI, and all its shortcomings) cause the misfire? I am thinking yes.