Question Regarding Fuel Trims

[99 vr4]

You did not mention, what codes did you have?

[BlackSpyderVR4]

Here are the codes: Throwing both codes twice for some reason. P0141 -Heated Oxygen Sensor Heater circuit Bank 1 Sensor 2 and P0156 Heated Oxygen Sensor circuit Bank 2 Sensor 2. So from what I understand both those sensors are just for the Cats. So it shouldn't be affected my fuel trims, correct?

Update: So I went drive around for 30minutes and Idled for 30min. Car dropped the codes and there is no more CEL light. The Trims are a lil better. So my rear and front mid trim are always identical and they settled at -4.10. Which should occur since I increased the MAF Smoothness by 12% and fixed the rear turbo hot pipe and now its running Rich. The Front/Rear Low while better is still way out of sync of each other (Front- (1.9%) Rear-(-11.7)). I'm going to have to go to the shop tomorrow or Friday and just check for vac leaks. Then start from stock rom and take this slow, Im getting to far ahead of myself.

My main questions right now:
1) Why would my front/rear low be so far away from each other?
2) Why are front/rear mid always the same?

Gents thanks for all the help, I do appreciate it.

[mjannusch]

What car is this on? A Spyder?

If so, all Spyders are CA emissions, with the primary O2 sensors reversed on the stock harness compared to a Federal emissions car. That may be the issue why the front/rear low trims are so far out of whack. Check your conversion harness and trace the O2 wiring and see which stock wires go to what pins on the Chrome ECU. Or if you have one of the ECUs that doesn't need a conversion harness, check to make sure the O2 sensor jumpers are set for a CA emissions car.

[99 vr4]

Here are the codes: Throwing both codes twice for some reason. P0141 -Heated Oxygen Sensor Heater circuit Bank 1 Sensor 2 and P0156 Heated Oxygen Sensor circuit Bank 2 Sensor 2. So from what I understand both those sensors are just for the Cats. So it shouldn't be affected my fuel trims, correct?

Update: So I went drive around for 30minutes and Idled for 30min. Car dropped the codes and there is no more CEL light. The Trims are a lil better. So my rear and front mid trim are always identical and they settled at -4.10. Which should occur since I increased the MAF Smoothness by 12% and fixed the rear turbo hot pipe and now its running Rich. The Front/Rear Low while better is still way out of sync of each other (Front- (1.9%) Rear-(-11.7)). I'm going to have to go to the shop tomorrow or Friday and just check for vac leaks. Then start from stock rom and take this slow, Im getting to far ahead of myself.

My main questions right now:
1) Why would my front/rear low be so far away from each other?
2) Why are front/rear mid always the same?

Gents thanks for all the help, I do appreciate it.

Yes the rear O2 would not effect the fuel trims. You need to turn off the periphery bits for the secondary O2 sensors . . . look in the Periphery 2 section.

Ok, the LOW trim is really the idle trim. You will need to add more VE (MAF Smoothness) at the lower air volumes up through 100 hz. It is ok to have up to +25%.

You also should have changed the MAF Size, Adder, and Scaling size for the ECO MAF.

After you flash the changes, reset the fuel trims by pulling the storage connector (or battery ground) for a few seconds. After 10 minutes of idle, you will see the new LOW fuel trims which should be closer to normal. The front may be + and the rear may be -. This is OK, as long as they are close in value. Mine sit at +2 front and - 2 rear.

Greg, correct me if I am wrong here.

What car is this on? A Spyder?

If so, all Spyders are CA emissions, with the primary O2 sensors reversed on the stock harness compared to a Federal emissions car. That may be the issue why the front/rear low trims are so far out of whack. Check your conversion harness and trace the O2 wiring and see which stock wires go to what pins on the Chrome ECU. Or if you have one of the ECUs that doesn't need a conversion harness, check to make sure the O2 sensor jumpers are set for a CA emissions car.

You should have been shipped a CA harness. But if you want to check any way, pin 75 of the stock harness should go to pin 71 of the new ECU. Pin 76 should go to pin 72. All pin numbers are as viewed from the wire side of the connector.

GEN1 GEN2 Connector.JPG

On the 98/99 ECU, it is the 30 pin connector, the one all the way on the right as viewed from the wire side. Pin 71 is the first pin on the left, top row, as viewed from the wire side.

[BlackSpyderVR4]

It appears the pins are good. I did adjust the MAF Size, Adder, and Scaling correctly for the EVO MAF. Have all the Peripheries set up properly for VAC Delete and so I don't throw CELs for the secondary O2's. So we just recently had a cold front go through EL Paso and temps dropped. Last night I hammered the car from 1-2 and the car started to rapidly backfire once hitting boost at about 11PSI (Sounded like machine gun) I'm guessing this is spark blowout (any other ideas). It appears my mid fuel trims have settle to 2% Rear and 4% Front so thats good. But the Low Fuel trim is still way off at -12 Rear and 6 Front. So the next step I will be replacing Spark plugs, while I do this will do compression and gaskets.I might go ahead and replace the front and rear O2 sensors as well. After that Im all out of ideas what is causing this low front/rear discrepancy. You fine gentleman have any other ideas or can diagnose the problem?

[BlackSpyderVR4]

Ok, been playing with the tuning a little. The front and rear low are always 13% apart. If the front is +5% then the rear will be -8%, if front is +12% rear will be -1%, etc. The mids are great they are about 4% apart. Have them at +2 and -2. I pulled the front spark plugs and they looked great. So how can the front and rears be good on the Mid and bad on Low? The only thing I know of that affects Low's more then the Mid is Vacuum Leaks.

[99 vr4]

Ok, been playing with the tuning a little. The front and rear low are always 13% apart. If the front is +5% then the rear will be -8%, if front is +12% rear will be -1%, etc. The mids are great they are about 4% apart. Have them at +2 and -2. I pulled the front spark plugs and they looked great. So how can the front and rears be good on the Mid and bad on Low? The only thing I know of that affects Low's more then the Mid is Vacuum Leaks.

Or the MAF or any other intake leak...

[BlackSpyderVR4]

but the intake pipe y's after the MAF. So any issues with the MAF would screw up both O2's correct? The car is running to smooth for there to be a MAF issue I would think. I will keep eliminating things as I go. The first will be the rear plugs, then rear sensor since its easy to get too.