F.A.S.T./O2 over correction problem

[njrob6]

F.A.S.T. QUESTION:

Has anyone out there have ever had a problem running where the EGT meter is reading way lean, over 1600 degrees, but the 02 sensor is pulling out fuel? Thats whats happening to me, it's pulling out like -10% of fuel but my EGT meter (brand new Fluke) is reading over 1600 degrees. And this is at 15lbs of boost using 115 octane gas. Anyone have any ideas?

Rob

 

[NastyGn]

Well I would want to ask what is your fuel/Air ratio where this is
happing? It to may be to lean then the 02 will try to pull fuel out to hit the A/F ratio set reguardless of what the EGT is reading.

Take Care

 

[njrob6]

My target air/fuel ratio is 11.5, my actual ratio is about the same.
This is a tough one

Rob

 

[meach13]

I HAVE SEEN A CAR BE TO RICH AND IT CAUSE THE EGTS TO BE HIGH
WITH -10% O2 CORRECTION SAYING TO ME THAT THE CAR IS TO RICH
TRY TO FINE TUNE THE VE TABLE AND AND SEE WHAT IT DOES

 

[NastyGn]

Originally posted by njrob6
My target air/fuel ratio is 11.5, my actual ratio is about the same.
This is a tough one

Rob

My next question would be first what timing are you set to
on the Fel-pro in that area and next have you used a timing
light to make sure the fel-Pro and motor show the same timing?

If the timing is to low you still have a flame from combustion in
the header and it will not burn up all the fuel, there four giving
you a high EGT (beacuse it sees direct flame) and a Rich 02
sensor (reading the unburnt fuel)

Just some suggestions

Good Luck

 

[norbs]

You may want to turn down the O2 gain setting, what you might be seeing is a general trend in o2 correction from ealier frames in the log. I have noticed the o2 correction tends to lag a bit behind. Turn down the o2 gain see if it helps.

 

[njrob6]

The timing in that area is at 24 degrees. I havent checked the engine with a timing light to see if it's the same as the car thinks it is. I'll do that next.

Rob

 

[njrob6]

NORBS:

What do you mean by O2 gain settings? You mean the O2 correction values?

Rob

 

[njrob6]

MEACH 13:

How do you get lean EGT readings when a car is overly rich?

Rob

 

[10SV6]

EGT is just the temperature of the exhaust gas. You can't use it as a steadfast rule for rich or lean.

Timing will change EGT. A generalization is that added advance will lower EGT until detonation starts. A rich, retarded tune will have high EGT because fuel is still being burnt in the headers - combustion is still occuring after the exhaust valve opens.

EGT is just another tool to use in hitting the tune. The spark plugs are your window into whats actually happening in the cylinders.

 

[norbs]

i mean the o2 gain, not correction. See diagram below

 

[Craig Smith]

Originally posted by njrob6
F.A.S.T. QUESTION:

Has anyone out there have ever had a problem running where the EGT meter is reading way lean, over 1600 degrees, but the 02 sensor is pulling out fuel? Thats whats happening to me, it's pulling out like -10% of fuel but my EGT meter (brand new Fluke) is reading over 1600 degrees. And this is at 15lbs of boost using 115 octane gas. Anyone have any ideas?

Rob

Where do you have your EGT probe located? I have seen people move the probe as little as 1/2" and see 200 degree differences in the readings. EGTs all by themselves are not the greatest thing to tune by because so many things can effect EGT.

Craig

 

[njrob6]

The EGT is located in the collector of the header right before the turbo.

Rob

 

[njrob6]

Can somebody who runs a Buick GN, with 83lb inj. and a T-76, send me a file of your tables. I'd like to compare my VE #'s to what you may have.


Thanx,

Rob

 

[Craig Smith]

Nothing wrong with 1600 degree EGTs in the collector of a turbo motor. You should expect these temps to be much higher than on a n/a motor. I believe Lance would tell you that his EGTs were often at 1800 degrees at the end of a pass.

Look at the demo file on your C-Com disk. The demo file is a Turbo V6 with a T-76 turbo running 26 psi or so of boost. Plenty of other things can effect what your VE numbers will be, but maybe this will give you a good idea. Bottom line is that your VE numbers should be set so that the target a/f ratio matches the actual a/f ratio as closely as possible.

Craig

 

[njrob6]

Ok, I made a few changes and the car feels way better on the street, going to the track on Wed to see the results. I changed the crank sensor because it was giving me a very erratic reading with the timing light. I also found that I need to adjust the crank reference angle by 4 degrees down to 6 degrees. I also closed the gap on the plugs to .028 from .032 that made a huge difference on a miss i had top end. Lets see how it runs at the track.

Rob

 

[Craig Smith]

If you find performance increases in closing the plug gap, you need a stronger ignition. I assume you are using the stock Buick ignition... the answer to this problem (assuming it is a problem) is an MSD DIS-4. I think it would be worth looking into. Hope this helps.

Craig

 

[njrob6]

I just happen to have an MSD,just havent put it in yet. I will now. What plug gap you think I should start off using? Im think like .032 and see how it runs? I have the gap at .028 right now w/o the MSD.


Rob

 

[9SECVSIX]

Rob. Send me a personal e mail and I will return it with my GCT.

 

[njrob6]

oK, this is what I found out so far. I have a top end miss that I always had.The car ran 10.3's with a miss going all the way down the track. Thats probably why the O2 is always pulling out fuel, it's because of that miss i have alot of unburnt gas giving me a rich A/F ratio. I went over my whole ignition system, everything checks out ok. I have a feeling it's my valve springs. Im using Crane 99838 springs, I just ordered a set of K-Motion 750's, lets see if that solves my prolems.

Rob