1996 Long Term Fuel Trim

[TMack409]

I've always been curious about why Bank 1 seems a bit out of kilter with respect to bank 2's seemingly normal readings...but I am not throwing codes so I've never really dug into it very deeply.

Today I thought I would dig down a bit - with your help and perhaps find out what the deal is.

At idle, in neutral, the B1 LTFT reads -4.68. Then at almost exactly 1100RPM, the B1 LTFT drops quickly to -.87 and remains there thru out the rest of the RPM range.
The mysterious 1100 RPM remains the consistent shift point.....in neutral......

However, when I put the car in D with foot on the brake and then the shift from -4.68 to -.87 occurs with even the slightest application of my foot on the gas pedal.

On the surface, this appears to be a vacuum leak. But that shift from -4.68 to -.87 is so quick and so sudden, that I am not so sure about a vacuum leak.

FYI - I swapped the Oxygen sensors around last year while messing with this "problem" and it made no difference.

Is there a known problem area with Bank1- Regards vacuum leak? Intake manifold? Fuel Injector seals? To be sure, I've checked all the vacuum hoses for leaks a dozen times or more.


Your thoughts?

[Qslim]

Originally Posted by TMack409

I've always been curious about why Bank 1 seems a bit out of kilter with respect to bank 2's seemingly normal readings...but I am not throwing codes so I've never really dug into it very deeply.

Today I thought I would dig down a bit - with your help and perhaps find out what the deal is.

At idle, in neutral, the B1 LTFT reads -4.68. Then at almost exactly 1100RPM, the B1 LTFT drops quickly to -.87 and remains there thru out the rest of the RPM range.
The mysterious 1100 RPM remains the consistent shift point.....in neutral......

However, when I put the car in D with foot on the brake and then the shift from -4.68 to -.87 occurs with even the slightest application of my foot on the gas pedal.

On the surface, this appears to be a vacuum leak. But that shift from -4.68 to -.87 is so quick and so sudden, that I am not so sure about a vacuum leak.

FYI - I swapped the Oxygen sensors around last year while messing with this "problem" and it made no difference.

Is there a known problem area with Bank1- Regards vacuum leak? Intake manifold? Fuel Injector seals? To be sure, I've checked all the vacuum hoses for leaks a dozen times or more.


Your thoughts?

I think you're touched in the head and having too much fun with your scanner.
It's always been my experience on the *MZ-FE engines that when a genuine lean or rich condition is present, the system always detects it in bank 1 first (PO171, PO172), and I remember hearing a few other guys comment about it too over the years. But, I never cared, mostly because this little tidbit has no bearing on how the thing works in regards to it's use. There's probably an answer somewhere in the corner of the mind of an engine management software engineer in Japan, though.
As far as your fuel trim "problem", I think you should back away from the scanner and go to a ball game or something. Fuel trims under 8% or so either way are perfectly acceptable, and the condition you're describing is probably related to some preprogrammed response to a shift in calculated load. Or not. Either way, there's no point in probing for problems if you have no light or driveability concerns. Take up model rocketry or something. Build a kite.

[TMack409]

Originally Posted by Qslim

I think you're touched in the head and having too much fun with your scanner.
It's always been my experience on the *MZ-FE engines that when a genuine lean or rich condition is present, the system always detects it in bank 1 first (PO171, PO172), and I remember hearing a few other guys comment about it too over the years. But, I never cared, mostly because this little tidbit has no bearing on how the thing works in regards to it's use. There's probably an answer somewhere in the corner of the mind of an engine management software engineer in Japan, though.
As far as your fuel trim "problem", I think you should back away from the scanner and go to a ball game or something. Fuel trims under 8% or so either way are perfectly acceptable, and the condition you're describing is probably related to some preprogrammed response to a shift in calculated load. Or not. Either way, there's no point in probing for problems if you have no light or driveability concerns. Take up model rocketry or something. Build a kite.

Thanks for the response Qslim! I have a full time hobby involving my 1985 Jaguar, but once in awhile I get caught up :-) That would have been today ;-)

[Qslim]

Originally Posted by TMack409

Thanks for the response Qslim! I have a full time hobby involving my 1985 Jaguar, but once in awhile I get caught up :-) That would have been today ;-)

Hah! I bet it IS full time. I've heard Lucas makes (or made) only the best electrical systems...