Odd O2 readings
Thread Starter
Drifting
Joined: Jul 2001
Posts: 1,296
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From: Largo Florida
Odd O2 readings
Last week I noticed a BLM split when I was scanning with Autotap. It was not running right too. I noticed that throughout the rpm range at steady cruising the LTFT were way off bank 1 to 2. For example bank two was -15% and bank one -5% (didn't used to be that way). At idle they are within a 2-3% difference. For some time I have suspected something was not quite right with bank two. I figured I blew a header gasket so I replaced them as well as glued around the O2 bungs because they looked like they may be leaking as well.
Got it together today and the BLM split is unchanged! I plug up the two vacuum accessory lines and the canister purge line too. Still ran bad.
Things I have replaced over a number of months:
I have replaced the O2s twice already so their good. Injectors replaced a little while ago too. Plugs all looked the same and normal (3rd set). On the second opti and plug wires. Replaced MAF, both coolant sensors, IAT, TPS, MAP. Cleaned IAC. New coil and ICM. Resealed intake. AFPR, high volume fuel pump, fuel filter, PCM, cleaned TB.
Using LT1 Edit, I put in a stock program with idle speed, timing bumped at idle, and injector constant changed but this time forced open loop. For the first time in 6 months the car drove super smooth without any bucking! Plus it feels like I have another 20 ft/lbs TQ from idle to 1500 rpm. This smoothness lasted for about 45 minutes and the bucking came back to maybe 5-10% of what it is normally. Been driving it most of the day and the bucking is almost unnoticeable. Bear in mind I have an aluminum flywheel that allows you to really feel the engine. I have always heard that an LT4 Vette with the hotcam can run on the stock program with no drivability issues.
I figure I have fried my O2 wiring to the PCM somehow and that is what is the cause. However, the O2s look like they are active with Autotap. I did not see any burned wires when I was under there but something is wrong. The O2 wiring to the PCM from the connector has 2 blacks and a tan and purple wire. How so I test these?
Maybe you guys have other suggestions to remedy this problem?
Got it together today and the BLM split is unchanged! I plug up the two vacuum accessory lines and the canister purge line too. Still ran bad.
Things I have replaced over a number of months:
I have replaced the O2s twice already so their good. Injectors replaced a little while ago too. Plugs all looked the same and normal (3rd set). On the second opti and plug wires. Replaced MAF, both coolant sensors, IAT, TPS, MAP. Cleaned IAC. New coil and ICM. Resealed intake. AFPR, high volume fuel pump, fuel filter, PCM, cleaned TB.
Using LT1 Edit, I put in a stock program with idle speed, timing bumped at idle, and injector constant changed but this time forced open loop. For the first time in 6 months the car drove super smooth without any bucking! Plus it feels like I have another 20 ft/lbs TQ from idle to 1500 rpm. This smoothness lasted for about 45 minutes and the bucking came back to maybe 5-10% of what it is normally. Been driving it most of the day and the bucking is almost unnoticeable. Bear in mind I have an aluminum flywheel that allows you to really feel the engine. I have always heard that an LT4 Vette with the hotcam can run on the stock program with no drivability issues.
I figure I have fried my O2 wiring to the PCM somehow and that is what is the cause. However, the O2s look like they are active with Autotap. I did not see any burned wires when I was under there but something is wrong. The O2 wiring to the PCM from the connector has 2 blacks and a tan and purple wire. How so I test these?
Maybe you guys have other suggestions to remedy this problem?
