Stephencs601

Did a dyno Sunday and found I am running very lean in my mixture. Anyone have ideas on how to correct. There is a loss of hp because of this situation

duggee

try vacuum lines and any other sources of leaks in the intake

Stephencs601

It was thought that maybe a sensor is giving a false reading. car runs great otherwise and passes NYS inspection with ease.

Stephencs601

Anyone else out there have any ideas. I am down about 50 hp from what I should have. Vacuum was good. Car runs good otherwise, but performance from the dyno shows only 185 hp

hacker-pschorr

Do you have a previous dyno chart showing 50hp more than this one? What correction factor is this dyno using? Why kind of dyno is it?

You say vacuum was good. Did you hook up a gauge, if so how much vacuum is it pulling at idle? Where was the gauge connected to?

The #1 sensor I would check is the WOT switch on the side of the throttle body. Simple on/off switch that tells the computer to go rich. Easy to check with a meter, there are two switches down there. The other (lower one) is the idle switch. As long as you are down there, check them both.

Them temp II sensor on the front of the motor in the coolant bridge is directly related to injector duty cycle. I suppose if it were showing less resistance than it should, the car would be lean. Once the car is fully warmed up you can test the resistance of this sensor, compare that value to the WSM.

The AFM is a bit trickier to test. Since the car drives fine. I would doubt that is the issue.

Stephencs601

I am not sure of the Dyno and the test was done twice. We did not hook up a vacuum guage since the car was not running rich and did idle very well. I can fax you the results if you wish.

hacker-pschorr

I was just curious if you had a before / after to compare since different correction factors alone could eat up 50hp on a dyno chart.

Stephencs601

I never did a Dyno prior to yesterday. The car should have somewhere around 200-234 hp, I am at 187 max.

hacker-pschorr

234hp is at the flywheel. If your car is an automatic you can expect a 20% or so power loss to the rear wheels. Reason why I asked what kind of dyno since most dyno's do not calculate flywheel hp. Even the ones that do, unless you ask for that "test" you are showing rear wheel hp numbers.

234hp - 20% = 188rwhp. Right on the money. If you car is a 5-speed it should make a bit more.

Stephencs601

Ok, that makes sense. Then the hp is right on because we were using the rear wheel hp readings. The only thing is, the test did show a lean mixture. Also, there were other 1984's there and they produced higher hp and a richer mixtures. Though, most cars did show a leaner mixture but more hp.

hacker-pschorr

I would check the WOT switch. IIRC when activated the computer enrichens the mixture by 12%. Sure other sensors have a play in this, it is the easiest (and cheapest) one to test & replace.

On the side of the throttle body are two switches. The lower one is idle, upper one WOT. Use a meter hooke dup to both terminals of the switch. As you open the throttle the switch simply closes. If there is no change, order a new one. As long as you are in there, check the idle switch to. Same test, except it closes when the throttle is closes.

Stephencs601

Hook up an ohm meter to both connections and see if there are any changes. Now where exactly is this switch. Is it under air breather?

hacker-pschorr

Closed throttle should be no reading (no current going through).
Once the switch is activated, you should be reading zero ohm's.

The idle switch is the opposite.

AO

Out of curiosity, how lean is "lean"? Are we talking readings in the 15's? 16's?

Not sure what a stock 84 should run but since we're talking stock, I would think it would stay in the 14's, maybe into the high 13's.

hacker-pschorr

There you go again Andrew, asking the most obvious question