nsimmons

I was trying to tweak my idle with a stock o2 sensor tonight

Initially the car was idling around 1000 and was showing a 0.06-0.09 voltage i lowered the idle to around 600 and it began to cycle from 0.250-0.650.

After playing with the mixture and idle speed i was able to get a very smooth running engine with a snappier throttle idling around 700.

What im confused about is the o2 sensor voltage is now 0.1-0.12 showing a lean condition. I cant richen the idle enough to bring the voltage up.

If i drop the idle a little lower it cycles around the 250-750 range but then its idling very low with a noticible lope. Also when my fan kicks on the idle drops slightly and the voltage stays in the 0.8-0.9 range. Quickly returning to the lean condition when it shuts off.

Im concerned about idle hydrocarbons as i need to get it through emissions by saturday. My initial reaction is its better to be a little lean with a higher idle than stoich with a rough idle.

Thoughts on this or advice?

Damon

Are you sure you're actuall in closed loop? The ECM, even on a computer controlled carbureted 3rd gen, tries for stoich (~.450mV) at idle at part throttle. It's always going to bounce up and down quite a bit, but in closed loop it's always going to try for this voltage on average. Is the computer still operating your carb?

nsimmons

sorry no computer, its a non cc qjet, with a 214/224 cam, hence the lope.

Last time i took it though emssions the timing was very retarded and after i noticed the boosters were dripping due to the throttle plate plate being open so far. Ive sinced fixed this, and since it passed no problem everywhere but idle hydrocarbons i have hopes for it.


Going to try again in a couple hours.

nsimmons

3 tests and all the tweaking i can think of and it made no difference

i tried adjusting the timing from 22bdtc to 42btdc leaning the mixture, increasing the idle, made no difference
still failing idle hydrocarbons

readin 1500-1700 max 344

I quit, its going to a shop tommorow, worst case i can at least get a conditional pass good for a year

Damon

That is WAY high. Sounds like your QJet is running real fat at idle for some reason. The cam alone isn't big enough to tank the emissions that bad by itself- I've passed with bigger.

Do you run a cat? A fresh cat can cover up a multitude of tuning sins.

nsimmons

Yeah theres a cat, but i have no idea how old it is, thats what im suspecting.

tom3

AIR system - air pump - working right? Thinking it should be pumping at idle. Maybe at higher idle it shuts down? Just thinking.

nsimmons

There isnt one, previous owner removed it. The cat is all it has for emissions, but i passed a crossfire vette with an identicle engine and nothing but a cat a couple years ago, no problem.

8Mike9

I'd suggest a heated O2 sensor to get a bit more accurate at idle condition.

nsimmons

Case anyone was interested. Verdict from the shop was an internally leaking carb, warped surfaces. They suggested a 400 dollar new qjet. I'm going to pick up an edelbrock, and run with that.

I have a spread bore performer, is an adapter needed for a 600cfm performer? Or a better suggestion?