I have a LEAN problem.....

[vetteboy86]

I hooked the software up to the car tonight, and I could monitor various charateristics. I was really intrested in the O2 voltage. I noticed it didn't move very much, I thought it would go low, then high over and over if the car was running right. I hooked my brothers car up, and it did move low to high. I then discovered a variable called fuel mixture status. I noticed his went rich lean rich lean, and did that over and over. I know this is normal. I looked at the graph, and it looked like a PWM waveform, very normal.

I hooked mine back up and found this variable, and all I see is lean all the time. I watched the computer while my brother adjusted the fuel pressure. We turned that thing every which way, and the lean condition did not go away. In about 15 minutes of run time, it was rich maybe 10 seconds, and that is probably too much. There was about a 5 second period when it went back and forth.

Here is the question, what is causing this. I can adjust the fuel pressure up and down, although the needle isn't very steady.

Any suggestions???

 

[Hrtbeat1]

Are you in closed loop? Are you idleing in the driveway? With the 383 what size are your injectors? I think I read on another thread you are using Accels.

With that software watch the Oxygen sensor voltage ... it should fluxuate between ~.05 volts and ~.96 volts ... ideally. Another thing to watch is the Oxygen sensor transitions ... they should gradually increase from 0 to 256 then start over again. (A nice slope on the chart mode) With those injectors watch the Injector Pulse Width, on the Chart display the PW should follow the throttle position % and the Engine speed (not exactally but increase Throttle = increase PW) At idle the PW should be somewhere around 2.5 milliseconds and vary between 1 and 4.5 mS depending on throttle. (This was on a L98, ported plenum, siamesed runners and Hotcam) You should see the PW drop rapidly as you go from partial throttle to coast then it will pick back up to ~2.5 mS.

 

[Hrtbeat1]

One more thing I thought of. Are you using a heated O2 sensor? With the readings being as low as they are .220 V - .08 V maybe you need a heated sensor. Just a though.

 

[vetteboy86]

The mixture reads lean regardless of driving habits. At idle, cruising, or WOT. The O2 voltage is very low. The heated O2 is something I can try this weekend, it wouldn't take long to install, I put one on my bros car.

I might try to give you a call, or email you sometime today or tomorrow. I will play with that software some more, I just want to get the car driveable, and then go with burning some new PROMs.

I was curious that changing the fuel pressure had no effect on idle quality, and the mixture stayed lean regardless.

The injectors are 24 lbs.

 

[Hrtbeat1]

For the most part what I've seen the only way to determine what the correct pressure is for your car is at WOT, when the computer goes into open loop. The injector PW will stay the same but the higher pressure will allow more fuel to flow. You need to do some tests, I used a G-tech and timed 30-70 MPH acceleration. It took several runs. Basically what I did was time a run, increase the FP by 2 psi, time another run, ect. ect. At some point your 30-70 time will increase when it does back down 1 psi and try again.

A word of caution if you are indeed lean you don't want to be doing WOT runs. Rich you end up buying spark plugs, lean you end up buying pistons, valves, head gaskets, ect. Let's get it running right before you go doing the WOT tests.

Try that heated O2 sensor and see if that helps. I am available just about anytime untill Monday evening, you have my number, give me a buzz.

 

[Vettelt193]

The mixture reads lean regardless of driving habits. At idle, cruising, or WOT. The O2 voltage is very low. The heated O2 is something I can try this weekend, it wouldn't take long to install, I put one on my bros car.

I might try to give you a call, or email you sometime today or tomorrow. I will play with that software some more, I just want to get the car driveable, and then go with burning some new PROMs.

I was curious that changing the fuel pressure had no effect on idle quality, and the mixture stayed lean regardless.

The injectors are 24 lbs.

Are you running a 383 motor as someone mentioned earlier, or are you running a stock rebuild?

24# won't do it for a 383... even a stock LT4 runs 28#

The computer will only adjust so much before it stops increasing the pulse... increasing the pressure helps, but the pressure is more along the lines of fine tuning once the proper injectors are picked... so if you are running a 383, 24# injectors, and stock tune you will have a hell of a time getting the car to run right IMHO.

 

[Moonunit 451]

On a stock tune that may be true, but there are a lot of guys that run 24# injectors with very good results on 383's.

I think you are on the right track with the O2 sensor .

 

[Hrtbeat1]

Formula for determining injectors

Here is the formula for determining the proper size injectors to use.

Injector size (lb/hr) = (Engine HP at the flywheel X Brake Specific Fuel Consumption) / (Number of injectors X Duty cycle of injectors)

When figuring the injector size it is important to be realistic in the HP figure used. For the most part 85% duty cycle is as much as you want 90% at the most. This means the injector would be open 85% of the time ... 90% of the time at most. Injectors are rated at 100% duty cycle (static flow) or always open.

BSFC ... Brake Specific Fuel Consumption is the lbs of fuel an engine consumes per HP per hour, or how efficiently the engine can convert fuel to HP. Here are some generalizations for determining BSFC.

Low to medium performance street engines: 0.50
Performance engines with good heads: 0.45 <---- ie Corvette
Race engines with very efficient heads: 0.40 - 0.45
Turbo or Supercharged engines: 0.55 - 0.60 <--- richer air/fuel ratios

Let's guesstimate that with Craig's increase in displacement and porting of the heads he is somewhere around 350 HP ... quite an improvement over stock but easily attainable.

(350HP X 0.45 BSFC) / (8 injectors X .85 duty cycle) = 157.5 / 6.8 = 23.16

I don't know of any manufacturer that makes a 23 lb injector so you would round up and viola 24 lb/hr injectors. Right where he is at.

 

[74bigblock]

It's Not Bacon....

It's new Sizzle LEAN

 

[vetteboy86]

So you guys think that the first place to start would be with a heated O2 sensor? I am also concerned about my fuel pressure readings. Cant figure out why the needle on the guage is jumping so much.