View Full Version : TBI data log indicating lean, I think rich....
03-16-2011, 06:10 AM
Started tuning my TBI, and I am very surprised to see the BLM indicating that the truck is running lean, the fuel economy now is 12-13 mpg and the inside of the new tail pipe is sooty looking, and I burn very little oil, so I really expected to see it indicating a rich condition, plus everyone that has a Howell program thinks they run rich.
I checked over my vacuum lines and found no leaks.
My O2 sensor is in the down leg of the passenger side pipe, a few inches below the flapper.
Should I relocate it to behind the Y connection so I know I am getting readings from both sides?
Would I need to get a heated one then? current it is non-heated.
Or I know newer systems us multiple O2 sensors, could I add a second one on the driver side?
Any other thoughts?
03-16-2011, 09:02 AM
How lean? What are your WIDE AVERAGE BLM (Block Learn Multiplier) #'s?
Remember, you're not actually RUNNING lean. It's just telling you that the fuel map is lean for your engine. When you see a lean # in the BLM table, it's telling you that the ECM is ADDING fuel to make the mixture correct.
The second O2 sensor is usually downstream of the cat and is designed to check cat performance. Having a sensor on each side would only be useful in a diagnostic situation. Most stock TBI ECMs aren't equipped to handle two since a TBI, by design, has no way of compensating one side over another.
03-16-2011, 01:11 PM
My primary cruise range is showing 145-155 in the BLM table.
AFR is set to 14.7
I sorta understand the the mixture is lean in that block, but how does that not indicate the engine running lean, unless I adjust the AFR?
For the O2 sensors I was thinking of my buddy's 2000 blazer 4.3, that thing has 4, 1 in each side and the other 2 are fore/aft the cat. I didn't see anywhere in the tune program to add a second O2 but thought it would be neat if you could.
03-16-2011, 03:06 PM
Are they in that range across the board? If so, you could use a bump up in fuel pressure. That's pretty lean. Ideally, you'd want to get within 10% of 128, which is the middle.
If it's only in that range in certain parts of the fuel table, adjust those area only.
03-16-2011, 03:20 PM
Starting to play with the tables, for starters I just smoothed out the curves, it did not change the BLM much, but it did remove most of the spark counts I was getting - there were not a lot, but I only had 1 coming to work this morning.
Here is the BLM log from my Howell program, about 45 minutes of varied driving.
03-16-2011, 08:03 PM
Can you post a screen shot of your fuel map, too?
Some parts look good, others are really out in left field. Usually, if it's less than 118 or more than 138, I will adjust things.
I personally like it within 5 points or less, but that's me being picky.
03-16-2011, 08:31 PM
I don't build tune able fuel injections systems but have made a living diagnosing computerized engine controlled vehicles for years. I don't know everything but have a good understanding of how things work. With that said.
Just something to remember:
An oxygen sensor is just that, a sensor that measures oxygen not fuel. It does not know if you are running rich or lean it just assumes if it measures a large amount of oxygen in your exhaust that you are running lean.
The older OBD I systems were really primitive as far as self diagnosis and adjustments especially without the ability to monitor engine misfires and other "meeting" criteria for setting diagnostic trouble codes and adjusting for out of range sensor voltage signals.
So if you have a computer of that nature and have a spark plug that is producing a weak spark you are not going to have complete combustion. What does complete combustion burn? Fuel and AIR! So the computer does not see the extra fuel only the extra oxygen because as stated earlier that is all that an oxygen sensor does is measure oxygen. It will then assume the engine is running lean and add more fuel which only contributes to the problem, weak spark and extra fuel will make that spark even weaker and the cycle continues until the fuel trim is maxed out and a code is then set.
I am not saying you have weak spark or a misfire or even running rich. I just hope that this might help you remember what you are actually looking at when monitoring oxygen sensor voltages and fuel trim data:D
03-21-2011, 09:25 AM
247pia - I know that the entire engine factors into what the O2 sensor reads, that is why I checked for vac. leaks, thanks for more input, didn't think of a weak plug.
FSJ GUY - The fuel table is the stock Howell, that log is after I smoothed it out.
Update, I pulled some other bins from the internet for comparision and realized that when i bought the kit from Howell it was for my CJ with a nonegr intake and on Thumper I am running a stock egr intake. So although the chevy egr is controlled by the computer, I am playing with the program so it takes it into account. Did a good long test run saturday to get tires for Gonzo and it made a difference, still need to tweak it a little. And now I ordered a VSS so I have another thing to play with in the program :rolleyes:
Bonus I can us the VSS to control my Audiovox Cruise control so I can ditch the magnet sensor.
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