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Inconsistent AFR's with megasquirt 1/2.2


78zstyle

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I have a simple 2.2 set up for fuel only. When tuning, lets say im at 30 KPA and 3k RPM, ill get it dialed into a nice 13.5-14.0 AFR. Later I come back to this cell in the VE table, but im running insanely lean! Like 16-17! This is under the same conditions.. Is there something I'm doing wrong that is causing this?

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Sounds like a fuel temperature problem to me. I bet that when you noticed AFR going lean either:

 

A.) The fuel tank had gone from fairly full to almost empty

 

Or

 

B.)The the car had sat for a while allowing the fuel rail to heat soak.

 

As gasoline heats up it expands (becomes less dense) so even though the volume of fuel injeced at each squirt remains the same, the mass of fuel varies based on temperature. Solutions would be better heat sheilding around fuel lines and tank, or a returnless system like modern cars have. Id kind of like to see a fuel temperature compensation feature be added to future megasquirt codes, increasing/decreasing injector PW based on fuel temperature.

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Take a data log and see if any of the sensor readings are different between the two.

 

I will do this tomorrow morning on my way to school.

 

Sounds like a fuel temperature problem to me. I bet that when you noticed AFR going lean either:

 

A.) The fuel tank had gone from fairly full to almost empty

 

Or

 

B.)The the car had sat for a while allowing the fuel rail to heat soak.

 

As gasoline heats up it expands (becomes less dense) so even though the volume of fuel injeced at each squirt remains the same, the mass of fuel varies based on temperature. Solutions would be better heat sheilding around fuel lines and tank, or a returnless system like modern cars have. Id kind of like to see a fuel temperature compensation feature be added to future megasquirt codes, increasing/decreasing injector PW based on fuel temperature.

 

Yes to A. What do you recommend for heat shielding?

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Aluminzed steel, aluminum sheet, aluminized heat tape, etc. There are numerous ways to shield the fuel rail and the gas tank. None probably work as well as asbestos, but that is hard to come by these days. You can't escape the fact that the intake manifold and fuel rail sit directly on top of the exhaust manifold (unless you swap in a different motor) so you just have to do what you can. Wrapping the exhaust manifold or header, using the factory heat shield or a custom one, and using heat tape or wrap on the fuel rail and maybe even the bottom of the intake manifold will help a lot. Also check to see how close your exhaust system comes to the gas tank. If it is pretty close, you may want to put some shielding their too. And the same goes for if your exhaust system comes close to the fuel lines in the transmission tunnel.

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DEI makes a great heat blanket with a mylar surface on one side the help reflect heat. Add that to the stock heat shield and it makes a huge difference.

 

Header wrap as mentioned and a heat blanket around the inducer side of the turbo as well as the down pipe makes a significant difference as well

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Aluminzed steel, aluminum sheet, aluminized heat tape, etc. There are numerous ways to shield the fuel rail and the gas tank. None probably work as well as asbestos, but that is hard to come by these days. You can't escape the fact that the intake manifold and fuel rail sit directly on top of the exhaust manifold (unless you swap in a different motor) so you just have to do what you can. Wrapping the exhaust manifold or header, using the factory heat shield or a custom one, and using heat tape or wrap on the fuel rail and maybe even the bottom of the intake manifold will help a lot. Also check to see how close your exhaust system comes to the gas tank. If it is pretty close, you may want to put some shielding their too. And the same goes for if your exhaust system comes close to the fuel lines in the transmission tunnel.

 

I took the heat shield out of the tranny tunnel that goes over where the catalytic converter used to sit (I have a custom exhaust).. thinking maybe that would help along with the other suggestions. Still going to do the data log to make sure.

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I took the heat shield out of the tranny tunnel that goes over where the catalytic converter used to sit (I have a custom exhaust).. thinking maybe that would help along with the other suggestions. Still going to do the data log to make sure.

 

That will have a minimal impact in comparison to the other mods... it's more for keeping heat out of the car interior by that point....

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Which intake air temp sensor are you using? Where is it located?

Sensor heat soak can make the ECU think the air is hotter than it is - therefore less dense than it is- and it will pull fuel accordingly.

 

Sam

using the gm iat sensor from diyauto

 

here is my datalog: notice my o2 readings are whack.. while watching in megatune if i was cruising megasquirt said like 4.9 afr, and if i blip the throttle it went to what it really was then back.

 

link to datalog: http://www.2shared.com/document/nlYXyIYL/datalog201203301350.html

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The link you provided wants me to install 3rd party download software which I do not want. Attach the log to a post in this thread.

 

Which O2 sensor / WB controller are you using?

The MS, AFR gauge, and AFR sensor controller should all be grounded at the same location.

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Are you running Acceleration Enrichment? If so noise in your map/tps could cause erratic pulse widths.

I am indeed. I believe i had this problem before adding that to my tune. I could be wrong though and i will test this tomorrow.

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Can you point me to a time in the log when it is behaving correctly and also when it is behaving incorrectly? I don't see any big issues in the attached scatter plots. **Edited: because I grabbed the wrong log file from my download folder***

 

I assume you have a turbocharger and are running about 15lbs 5 lbs of boost? If either is incorrect, your MAP sensor needs to be calibrated.

 

Are you seeing the problem in a AFR gauge or in the tuning software interface? It is not hard to get the gauge to read differently. Make sure the LC-1 output to the gauge is configured correctly (if you have a gauge - which on is it?)

You really need to ground everything at the same location. Otherwise, you will be chasing your tail. Also, be sure to run all sensor grounds back to the same place as well.

 

Sam

post-250-069339000 1333309140_thumb.png

Edited by Sam280Z
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Can you point me to a time in the log when it is behaving correctly and also when it is behaving incorrectly? I don't see any big issues in the attached scatter plots. post-250-069339000 1333309140_thumb.png

 

I assume you have a turbocharger and are running about 15lbs boost? If either is incorrect, your MAP sensor needs to be calibrated.

 

Are you seeing the problem in a AFR gauge or in the tuning software interface? It is not hard to get the gauge to read differently. Make sure the LC-1 output to the gauge is configured correctly (if you have a gauge - which on is it?)

You really need to ground everything at the same location. Otherwise, you will be chasing your tail. Also, be sure to run all sensor grounds back to the same place as well.

 

Sam

78zstyle - I am running 6 PSI. I got my wideband to read correctly now.. I had to mess with the LC 1 output.

 

I can't really tell in that graph where it happened, but I can tell you that the problem started in the first couple minutes, then went away for a little.. then came back.

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