Low Fuel Trim won't go down

[ChvyKc]

I am in the process of tuning my car right now and I can't get the FTRL on my MMCD to go down. It is at 139 right now and no matter how low I turn the AFC it stays right there. You can tell the car is leaning out because the O2 voltage is staying at zero and the car starts to sound like it has cams in it. It started out at 109.3 and I couldn't get it to go down and I turned the AFC richer to see if that would change it and it went right up.

Does this fuel trim take a while to go down? I am reseting the ECU right now to get it back to 100 and see if I can't keep it there.

Any help will be appreciated.

David

 

[project_tsi]

Have you checked for boost leaks lately? It may be a boost leak and its making your trims whack. I believe the ecu will automatically compensate for up to 30% difference. In order for the ecu to reset all its trims, you need to go out and drive for about 30min or so, until the ecu enters its open loop, or it might be closed loop, I forgot!

 

[steve]

Reset the ECU.
Set your base fuel pressure to 36 psi with the hose off.
Set the SAFC low corrections to -18
Start the car and wait for the O2-R and O2 Feedback to start cycling.
If the O2-R doesn't go to 0.8v or more within a few mins replace the O2 sensor.
If the O2-R doesn't start cycling by the time the raditor fan turns on take more fuel away.
On a 91+ it should go into closed loop with coolant temps around 86F. 90 cars wait until the temp get higher.
If the coolant and air temp sensors before starting the engine aren't close to outside temp check them and fix.

Steve

 

[ChvyKc]

I don't get any kind of cycling on my O2-R. It stay at 3.49 at all times. I get a reading on the O2-F though. I bought the cable that I am using for the diagnostic port off of another guy. I am not for sure if they are even tapped into the right tabs on the diagnotic port.

I am extremely frustrated with this, if anybody can help, please do.

David

 

[steve]

I don't get any kind of cycling on my O2-R. It stay at 3.49 at all times.

What version of MMCd are you using?

Steve

 

[ChvyKc]

1.5d is the version that it said that I downloaded. I just got a new PDA and I downloaded MMCD Friday night and loaded it on the logger that night, so it should be the newest version.

 

[steve]

If you got it from the MMCd sourceforge site that would be 1.5d. The the latest version of the original version and now several years out of date. I can't remember anymore how it has the O2 sensors labled. Clearly it shouldn't 3.49v. On versions that show two O2 sensors one is the right one and the other is reading a location in memory that isn't an O2 sensor on our cars.

Steve

 

[ChvyKc]

Yeah, it has another label that is O2-F and it reads like it is suppose to except for the fact that it doesn't read the same thing that my 02 voltage gauge reads. Like right now, the logger reads 0.91 which should be a little lean but not by much and my gauge reads .96 which is really rich. The car actually runs like it is really rich. It wants to pop and buck like it was before when I was overflowing the stock regulator.

When I lean the car out so that the gauge reads between .92 and .93 then the car runs right and pulls really hard. While the gauge is reading that, the logger is reading .87 which should be to lean.

I don't understand how the logger is reading a litle bit leaner than it is suppose to be but the gauge is reading right. Since I have the gauge tapped into the O2 sensor wire going into the ECU could it be degrading the signal going to the logger?

 

[v8s_are_slow]

what are the other trims at? are you watching your O2 trims as you adjust? if you're resetting the ecu and then turn it back on, watch the O2 trims for the short range. it should be cycling around 100. the fuel trims are long term. O2 trims are the short term (helps to give you an idea as to where your trims will be in the long run as you adjust). the trims take awhile to adjust but the low is the quickest out of them. i've had to drive 2 or 3 days sometimes before my trims will adjust.

 

[ChvyKc]

what are the other trims at? are you watching your O2 trims as you adjust? if you're resetting the ecu and then turn it back on, watch the O2 trims for the short range. it should be cycling around 100. the fuel trims are long term. O2 trims are the short term (helps to give you an idea as to where your trims will be in the long run as you adjust). the trims take awhile to adjust but the low is the quickest out of them. i've had to drive 2 or 3 days sometimes before my trims will adjust.

I was watching all 3 of the fuel trims that MMCD has. The medium and the high one would stay at 100% and the only time that the low one would change was when I richened the car back up, then it would change really quick. The O2FT was another thing that was screwing with me. It would cycle between 80% and 120% except for when I came to a stop and then it would just count up to 167% for a couple of seconds. After a couple of seconds, it would go back down to 100%. I can lean the car out at idle to were it sounds like it has cams in it and the O2FT will just sit at 100%.

It was like the car would stay at 100 while the car was reving down and as long as I didn't push the clutch in it would stay at 100 but as soon as I did push the clutch in and let the car idle, it would just start counting up to 167%. It's not like it jumped up there all of a sudden, you could watch it count up.

 

[v8s_are_slow]

you don't watch the trims on a decel. only at cruise, or for the low trim, at idle. if it's climbing to 167% and then right back down to 100% i wouldn't worry too much. especially if it's an O2 trim that you're talking about. the low trim isn't as important as the mid and low's but of course you don't wanna run it extremely lean either.

 

[ChvyKc]

you don't watch the trims on a decel. only at cruise, or for the low trim, at idle. if it's climbing to 167% and then right back down to 100% i wouldn't worry too much. especially if it's an O2 trim that you're talking about. the low trim isn't as important as the mid and low's but of course you don't wanna run it extremely lean either.

At idle, the O2 fuel trim down't move at all no matter how much I lean the car out, it will move up if I richen the car up. I had the car at the point to were it almost didn't have enough fuel to even run at idle and I let it set there and run for 30 minutes and none of the fuel trims moved and the O2 trim didn't move either.

 

[v8s_are_slow]

okay what about your O2's? not the O2 trim, but your O2's. at idle and with the car warmed up, it should be cycling up and down. at cruising speeds with a steady pedal pressure it should be cycling. how old is your O2 sensor?

 

[ChvyKc]

okay what about your O2's? not the O2 trim, but your O2's. at idle and with the car warmed up, it should be cycling up and down. at cruising speeds with a steady pedal pressure it should be cycling. how old is your O2 sensor?

The O2 sensor has less than 10,000 miles on it, so it should be good. The voltage on the O2 voltage gauge cyles, but I didn't check to see if it was cycling on the logger, it never occured to me to do that. I was only logging O2 voltage at WOT. The only thing that I was looking at when I had it at idle was the fuel trims, but like I said the gauge was cycling at idle so I didn't think to check it.