tech2

this rules out anytime of vacuum leak as the fuel trim is rich, not lean. Since its cutting fuel on both banks look at things that would effect both banks ie. bad maf, high fuel pressure, flex fuel sensor askew (don't think 2500's have flex fuel). 2 bad pre cat 02 sensors, cracked, leaking exhaust manifolds on both banks



does it run smoother during open loop operation?


misfires will skew ft data so don't let it mislead you.

I just read the other post from the link. did you test for injector leakdown? what is the system fuel pressure?

dougx

No exhaust leaks It does run smoother in open loop before it's warmed up completely. Cylinders 4 and 6 actually flood and #4 has been fouled. Fuel pressure was 60 psi, may be a little more my gauge would not seal completely. I did pull even bank injectors out and tested @ 75 psi with no leakage and activated them. All had good pattern. No flex fuel on this truck.
Here is some sensor test data. If I need to test each I will.

At Idle readings. closed loop.
Air flow rate .77lb/min
O2 sensor 1 bank 1 .15v
O2 sensor 2 bank 1 .80v

O2 sensor 1 bank 2 .70v
O2 sensor 2 bank 2 1.11v

Front O2 sensor .67v
rear O2 sensor .79v

air fuel ratio 14.60

Readings at 2500 RPM air flow 3.87 lb/min
O2 sensor 1 bank 1 .80v
02 sensor 2 bank 1 .50v

O2 sensor 1 bank 2 .38v
O2 sensor 2 bank 2 .92v

Front O2 sensor .19v
Rear O2 sensor .51

air fuel ratio 14.60
I have a noid kit coming to test injector activation

Thanks...

tech2

when warm and in closed loop at 2500rpm ,the pre cat 02 sensors should be switching from 0.2 to 0.8 volts fairly quickly.
the02 are ignored in open loop; so if its running better in open loop disconnect both precat 02 sensors and see if that makes a difference. it will set dtc but we don't care about that right now. it it clears ups and runs better, replace both pre cat 02 sensors.

dougx

You are right, it does run better with the O2 sensors disconnected. I disconnected them right at the header pipe coming from the ex manifold and are before the cats. Rpm 1750- 2000 seems to run smooth and the throttle from a start is better, it used to feel like it had a dead spot, but still has pronounced miss at idle. I will also pull plugs on cylinders with the most misses and make sure they are not fouled. This truck did have some very stale fuel in it. Which could explain the O2 sensor damage I would think.

dougx

I'm waiting on the sensors to get here. Will post results once in. I found some new Ac l Delco ones for $23 each.

dougx

I got the new o2 sensors and installed them. Unfortunately there is no change.I have not yet checked to see how quickly they change voltage. I will do that tomorrow..