many codes missing bank 1

[brocsbar]

98 blazer 176k miles got codes 131 o2 sensor both are new bank 1s1 and b2s1 b1s1 shows no activity (they are bosch) sometimes runs ok but some times falls on its face code 300 mult misfire it is missing on #1 #3 #5 quite a bit (got new cap rotor wires. also code 404 EGR 719-TCC , 1133 and 1381. where to start? naturally im a guy doesn't want to spend much

[82Stang]

Getting a code for O2 sensor doesn't necessarily mean an O2 sensor. Sometimes it means 'look upstream'. As in, to the upper intake and surrounding sensors and components and vacuum. Could be a faulty EGR valve or IAC etc. Blazers are also notorious for fuel line leaks in the intake, they are in my 1993.

Multiple misfire, if you have new cap/rotor and wires, it could be a bad coil. Or suspect wiring.

I'd do the EGR first, used because new is $$, get a used one from a U-pullit or boneyard to try. Might make it run better.

[brocsbar]

what would make the whole bank miss? plus something must be going on with the o2 cause it doesn't hardly cycle on the scope

[viggy58]

clogged exhaust? collapsed valve? mixed up firing order on the cap? did you use a/c delco cap and rotor?

clear codes, then post back with the exact order they show up.

[82Stang]

Originally Posted by brocsbar

what would make the whole bank miss? plus something must be going on with the o2 cause it doesn't hardly cycle on the scope

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.

[brocsbar]

Someone else put on a cap rotor wire o2s plugs and already tried to fix to no avail so im not sure what they used but from my xperience most people (not myself as I put the good stuff on my stuff) go cheap I will post back in a few days what I find.

[82Stang]

Originally Posted by brocsbar

Someone else put on a cap rotor wire o2s plugs and already tried to fix to no avail so im not sure what they used but from my xperience most people (not myself as I put the good stuff on my stuff) go cheap I will post back in a few days what I find.

I used to use the 'good' stuff myself, but with the lack of quality of parts these days, I save my money and go cheap as long as all things are equal.

[old_master]

As mentioned, low fuel pressure can cause O2 sensor DTC's along with a host of others. Quick easy test is to check fuel pressure and leakdown. Takes about 15 minutes and tells you immediately if there's a problem. Key ON, engine OFF, fuel pump running: Pressure must be 60PSI to 66PSI and must remain above 55PSI for 3 to 5 minutes after the fuel pump shuts off.

[brocsbar]

hopefully ill get the blaz back later in the week and ill def do leakdown and get vacuum readings...im thinking intake...and i got a used EGR to try