What do you think would cause this???

[ski_dwn_it]

Ok a little background for you.

The car is a vette with a 434ci motor, n/a, 11.5:1 compression and runs 10.0X@135MPH. The 60' times are always in the low 1.3X when it trips the 60' beams with the front tires. And the car leaves rediculously hard, very violent but straight as an arrow.

Yesterday (2nd time out this season) the car started off running great. The 60' times were 1.33X and the car ran a 10.24 which was expected for the 3k DA weather. Right where I expected it to land.

On the third run the car on the launch left like a snail. It barely pulled the front about 4" and 60'ed in the 1.42 range. To me it felt like as mentioned a snail leaving compared to how it normally feels; which usually it feels like you got rearended by a semi at 40mph when you mat it. I ran the car about 4 more time and the end MPH was exactly where it should have been, but the 60' all felt like I had No Gearing in the car or the way it would feel if you raised the rear gearing.....no snap.

Couple of questions and scenerios I want to ask about.

First thing that came to mind problem wise was the fact that lately I have been getting an open pump error on my LM1 that is tied into my DFI system. This has been happening more and more. Plus to me it seems that it takes a long time to heat the O2. Do you think the problem is a lazy or bad o2?

I did not have my laptop with me - DUH. So I did not have a good way to diagnose it there. This morning first thing I probably have some mad neighbors because I was out there at 7am with the car on the trailer idling it and pulling numbers. No codes were set, but I am not sure if the 02 is a code in DFI that will clear itself?

Also something else that I noticed with my tune is the Acceleration modifier changes gradually with temperature and flattens out at about 200F. I am thinking for consistency purposes I would want to flatline this between about 120+ since I usually try to keep the car around 130-150 when staging. If that is different throughout the temp range I might get varying results - RIGHT? ( I don't think this is the problem though with the soft launches, but something I wanted to make sure I was thinking correctly about).

Lastly, on the launches I have noticed in the past that the AFR overshoots the desired fuel I have set pretty much. But I just left it go because the car is like a rocket off the line - is this modifier where I would dial that in?

Sorry for all the questions. The main this I guess I am asking is there is any way to tell if the 02 is flaking out causing my problem. My fear is the converter might have broke and not be giving out any multiplication.....

Any assistance you can give would be appreciated.

Here is a video of the car leaving normally....

Video of Run1 - Photobucket - Video and Image Hosting

Video of 10.08Run - Photobucket - Video and Image Hosting

 

[norbs]

I would try a new o2 sensor, and race the car again with no other changes, if it ran strong before on the same tune its should run the same with the same program. The acceleration modifier acts as the main pump shot as in a carb. Most engines can tolerate more fuel when cold then warm so thats why it probabaly less when it warms up slightly.

Your error code on the lm-1 wont be picked up on the dfi right away. When the lm-1 goes into error mode it sets a constant voltage (sepecified in the lm-1 programmer setup)for the output. WHen the dfi sees the o2 sensor voltage not changing over time then it sets a code.


The converter maybe on its way out, it maybe a good time to check it out and get a ptc converter in there if your not using one.

 

[ski_dwn_it]

Norbs.

Thanks for the help man. you are always one that I can count on for good info.

Where do you think the cheapest place is to get a new sensor. Summit has them for 79beans.

Do you think the car would run any better in Alpha-N? How would you recommend I start with that strategy? I will not do it until this is resolved as i do not want to add more variables to the problem. Just something to think about I guess.

Out of curiosity. when it defaults to the given value if the 02 is not working what is that value? Is it just a 1 multiplier as the car did not change a bit on the topend, but the tune is always within a percent or two correction when it is working...so i would not expect much a change. Just curious if that is the case.

Its always something.

i just spoke to a very reputable tranny builder and he told me to take the car out get it in high gear and floor it. If the car converter only flashes to about 3000-3200 its likely the converter. If it goes up to normal, then its highly likely its the 02 or something else.

Thanks again for the help.

Regards,

 

[Craig Smith]

I think you broke your stator in the converter as well. On a few other notes...

Accel DFI's version of Alpha-N is very different from most other implementations I have seen. Their method continues to use a MAP vs. RPM table for fueling, but they have another table in front of it that you set to correlate a throttle position to an engine load value. Real Alpha-N in my opinion allows for direct pulsewidth control as a function of throttle position; this method merely equates a throttle position with a user-selectable engine load value and sends it through the speed/density algorithm for fuel calculations. In short, you wouldn't be any better off with Alpha-N in this instance.

I also don't think the Acceleration modifier will make a difference from a consistency standpoint, unless you have a horribly noisy MAP or TPS signal. The a-mod is used to increase or decrease asynchronous/transitional fueling, which are, for all practical purposes, not a factor in down-track performance.

Bosch O2 sensors are good items to keep spares of as they are cheap and not terribly robust. If you run closed loop with one, I'd certainly keep one in the glove box.

But you definitely need to (and will, I'm sure) look on the laptop and see what it's telling you. My money's on the stator.

 

[ski_dwn_it]

I think you broke your stator in the converter as well. On a few other notes...

Accel DFI's version of Alpha-N is very different from most other implementations I have seen. Their method continues to use a MAP vs. RPM table for fueling, but they have another table in front of it that you set to correlate a throttle position to an engine load value. Real Alpha-N in my opinion allows for direct pulsewidth control as a function of throttle position; this method merely equates a throttle position with a user-selectable engine load value and sends it through the speed/density algorithm for fuel calculations. In short, you wouldn't be any better off with Alpha-N in this instance.

I also don't think the Acceleration modifier will make a difference from a consistency standpoint, unless you have a horribly noisy MAP or TPS signal. The a-mod is used to increase or decrease asynchronous/transitional fueling, which are, for all practical purposes, not a factor in down-track performance.

Bosch O2 sensors are good items to keep spares of as they are cheap and not terribly robust. If you run closed loop with one, I'd certainly keep one in the glove box.

But you definitely need to (and will, I'm sure) look on the laptop and see what it's telling you. My money's on the stator.

Thanks fellas for the help. I have another question on another board where I am talking with a trans guru....hoping its not the stator...but when I came back into the pits and everyone came over asking what happened....the first thing I said was the stator. FIgures since I was just about to pull the trigger on a vacuum pump and front and rear brakes for it. In preparation for some juice *maybe*.

Where is the best (cheapest) place to get the sensors Craig?

Thanks for the info on all the questions I have....you guys are a wealth of info and help.

 

[norbs]

The voltage you specify when you run the lm-1 programmer software, in the advanced section of the wideband voltage setup graphs. See below

http://www3.sympatico.ca/norbz/lm1.JPG

Its usually set for High Impedance, which means it floats as if it were not there in the circuit or 0 volts. The dfi will see 0 volts and assume its lean and add a bunch of fuel to compensate. But as soon as it flat lines it will set a code after 32 seconds and go to open loop anyway.

By changing it from high impedance to a set voltage you can reduce the fuel it adds or subtracts when the sensor on the lm-1 goes into error mode. What this value should be is up to you. Heres the chart. Just remember it has to show leaner so the ecu adds fuel, not rich as it will subtract fuel on an error condition.

http://www.innovatemotorsports.com/resources/SampleAnalogOutTable.pdf

 

[Craig Smith]

The dfi will see 0 volts and assume its lean and add a bunch of fuel to compensate. But as soon as it flat lines it will set a code after 32 seconds and go to open loop anyway.

I think you may have mistyped that. The DFI's 0-5V input should be configured so that 0V = 10:1 AFR and 5V = 20:1 AFR. A higher voltage is therefore a leaner a/f ratio. Opposite of how a narrow band works where 0V = lean and 1V = rich.

 

[norbs]

Ya Craig your right, what was i thinking, so the dfi would pull fuel if you had a lm-1 set up by factory default on the error code, not a good thing. To make it go full rich on an lm-1 error code you would enter 5volts on the lm1 setup correct? As the ecu would think the sensor is showing 20:1 at that point and add fuel to compensate

 

[JimP]

I can't help you but I hope you keep the underneath clean since people are getting a real good look at it.