LTFT MAXED OUT

Hi all and happy new year to everyone,


I got a 1995 s1 supercharged Rivi. And I get around 8-9mpg (27l/100km) combined…I get a lean code that comes on and goes away… when I check live data with my Actron 9145 scanner - my long term fuel trim is at 159 or higher (ltft 25% positive)… I have tried resetting it, different Mafs, checked fuel pressure, looked for vacuum leaks, fixed the exhaust leak, but it’s still maxed out… changed my O2 sensor too, it seems to work properly- fluctuates between lean/rich like normal… What else could it be? I read somewhere to check PCM ground, is that something I should be looking for? And where would I locate that ground exactly? I know its under the glovebox but how doni find the ground?

WHen was the last time you changed the air filter?

Any modifications?

You can read the sensors (MAF, O2, etc. ) with a scanner to see if the readings you're getting are reasonable. You'll need the service manual to see reasonable ranges, though I don't have that data for you ATM.

There are two O2 sensors.

Probably the first thing to work on is the peed-a-boo lean code, actually. And maybe your throttle body is dirty. You have to remove it to check, the throat pretty much always looks clean from the inlet side.

albertj wrote:

WHen was the last time you changed the air filter?

Any modifications?

You can read the sensors (MAF, O2, etc. ) with a scanner to see if the readings you're getting are reasonable.  You'll need the service manual to see reasonable ranges, though I don't have that data for you ATM.  

There are two O2 sensors.

Probably the first thing to work on is the peed-a-boo lean code, actually. And maybe your throttle body is dirty.  You have to remove it to check, the throat pretty much always looks clean from the inlet side.

The car is pretty much stock, only a deleted catalytic converter… airbox is stock and the filter was changed recently…
The readings do seem reasonable… 5-7grams/second on maf on idle…
I can upload the live data I am seeing, but I didn’t notice anything other than ltft being high…
One thing which was off was the IAT readings were off, I have ordered that sensor and gonna replace it soon. I believe it reads in fahrenheit while the outside temp on the dash is in Celsius… not sure how that happened, but the car is from Canada and the scanner was purchased in US… Could that be causing such a horrible mpg? I keep reading people getting 20+ mpg city with 3800s…
Also I only have 1 o2 sensor, maybe it was deleted with the cat? Should I really have 2 of them on a series 1?
I disconnected the o2 plug just to see if it improves the mpg… let’s see what comes out of it, but it is getting very difficult to diagnose the fuel trim issue…

BuickRivieraGeorgia wrote:

albertj wrote:

WHen was the last time you changed the air filter?

Any modifications?

You can read the sensors (MAF, O2, etc. ) with a scanner to see if the readings you're getting are reasonable.  You'll need the service manual to see reasonable ranges, though I don't have that data for you ATM.  

There are two O2 sensors.

Probably the first thing to work on is the peed-a-boo lean code, actually. And maybe your throttle body is dirty.  You have to remove it to check, the throat pretty much always looks clean from the inlet side.

The car is pretty much stock, only a deleted catalytic converter… airbox is stock and the filter was changed recently…
The readings do seem reasonable… 5-7grams/second on maf on idle…
I can upload the live data I am seeing, but I didn’t notice anything other than ltft being high…
One thing which was off was the IAT readings were off, I have ordered that sensor and gonna replace it soon. I believe it reads in fahrenheit while the outside temp on the dash is in Celsius… not sure how that happened, but the car is from Canada and the scanner was purchased in US… Could that be causing such a horrible mpg? I keep reading people getting 20+ mpg city with 3800s…
Also I only have 1 o2 sensor, maybe it was deleted with the cat? Should I really have 2 of them on a series 1?
I disconnected the o2 plug just to see if it improves the mpg… let’s see what comes out of it, but it is getting very difficult to diagnose the fuel trim issue…

I can't help you with this - I don't have experience tuning with a cat and sensor delete. Give you a hint though - the upstream and downstream oxie readings can be compared to determine the engine's fuel efficiency and then used to help set fuel trims. You'd need to look in the service manual for details (well, a narrative) on whether and how that's done on the Riviera.