88 350 tpi formula

iTrader: (9)

well here goes another beat to death topic but,
my car drops out of closed loop at idle and runs really rich. the o2 is saying lean. I think the exhaust flow is the problem because of the high flow with headers no cat and so on. will the heated o2 help?

also there seem to be no vacum or exhaust leaks. the fuel and so on seem to be in check.

72LT1VETTE

Check for leaking injectors. At idle the injector firing is slowed way down. If a few are leaking fuel into the cylinders the O2 senses a rich mixture and tries to compensate but can't fire the injectors any slower. You will get code 33 or 34 (can't rem which) kick it in the butt and all is well until you idle again or slow down for city traffic. Also check coolant temp sensor and thermostat sticking open. Temp sensor controls open/closed loop based on engine temp.

Doctor J

IIRC, an O2 sensor needs to be about 350 deg C (min) to operate correctly. If you are too far from the exhaust ports, the sensor will be too cold to work right. A heated sensor corrects this, and will also get up to operating temp in a minute or so after startup- reducing the open-loop cold idle time.

I recently used this part # in long-tube headers:

AC-Delco # AFS74 is a three-wire heated sensor. The GM long# is 25312179.

AFS74: 1995 CHEVROLET S10 PICKUP V6 4.3L 262cid GAS FI N Engine VIN = Z

These are about $30-35 from- http://www.rockauto.com/ .

I have used rock and they have excellent prices on parts (delivery can be a little slow). Also, enter four digit Discount Code "8940" on the "Please tell us how you heard about us" line of the shopping cart, receive an immediate 5% discount on that order until 31 Jul 02.

Two extra wires of the sensor connect to 12v source and ground.

HTH

DrJ

kane91z

id use the heated GNX sensor - my best friend put one on his GN and the cars idle drastically improved - I was planning on doing this but my camaro has been broken since last june

I believe you can get one from gmpartsdirect.com - if that place still exists - I have the part number around here somewhere if you need it -

12 Sec GTA

Kane, I'd appreciate that PN if you could find it

kane91z

sorry my internet has been on the fritz for the last month - it seems i only get 2 hours of service a weeks - anyways ill ask my friend if i can get a hold of him - i can't seem to find where i put my file containing all the part numbers of things i wanted to buy.

86TpiTransAm

Actually, the O2 sensor has to reach 600 degrees for the ECM to go into closed loop.

The exhaust is at it's hottest point when accelerating and at it's coldest point when at idle. At idle, it's possible for the exhaust temps to drop low enough to cause the ECM to go back into open loop. This is especially true with headers. Due to the design of headers, the air is even cooler at idle than with regular exhaust manifolds and this is why alot of people with headers use a heated O2 sensor. Even those people that have headers but are not experiencing open loop at idle, should switch to a heated O2 sensor. Even though the ECM isn't going back into open loop at idle, the lower temps of the O2 sensor can still cause a slightly erratic idle. Also, during initial engine warm-up, it takes the O2 sensor longer to heat up with headers and this causes the ECM to run in open loop even longer than needed which is just causing a rich condition and wasting fuel. A heated O2 sensor will heat up quicker and cause the ECM to go into closed loop quicker, thus increasing fuel mileage as well as engine performance.