Is a positive long term fuel fuel trim OK?
Too much air, too little fuel, a field mouse making the engine bay it home, and things can start to get dicey. This process, known as both short- and long-term fuel trim, is how the ECU keeps track of how much fuel is flowing in. It’s totally fine if you’ve never heard of this concept before—many haven’t.
What causes negative long term fuel trim?
A negative long-term fuel trim means that the ECU has to decrease the injector pulse because the car is running rich. The vehicle needs less petrol in the blend.
How do I reset my long-term fuel trim?
To perform a PCM reset…
- Bring car up to normal operating temp.
- Turn ignition off.
- Remove ECM main fuse.
- Turn ignition to “on”, do not start.
- Wait for system check to complete, numerous errors will be detected.
- Turn ignition off.
- Replace fuse.
- Turn ignition to “on” and wait for system check.
Why is my long term fuel trim negative at idle?
During idle when the throttle plate is closed, the vacuum in the intake manifold is high and very little air flow is entering the engine, so even a small amount of un-metered air will have an effect on fuel trim. This causes the fuel trim numbers to become negative during a boost situation.
What should short term fuel trim be?
The GM system assigns a number between 0 and 255 to define fuel trim, with 128 being the middle point. A short term fuel trim (integrator) reading of 118-138 is considered normal. Fuel trim can also be expressed as either a positive (+) or negative (-) percentage.
What causes negative fuel trims?
A negative fuel trim is considered anything at or below the minus 10 percent threshold. Ron addresses the common issues that can cause fuel trims to go negative. Issues like leaking fuel injectors, a defective fuel pressure regulator and defective MAF sensors will be addressed.
What is a positive fuel trim?
POSITIVE fuel trim values mean the engine computer is adding fuel (increasing the pulse width or on-time of the fuel injectors) to add more fuel to the engine. In other words, it is attempting to RICHEN the fuel mixture because it thinks the engine s air/fuel mixture is running too lean.
What does negative fuel trim mean?
NEGATIVE (-) fuel trim values mean the engine computer is subtracting fuel (decreasing the pulse width or on-time of the fuel injectors) to reduce the amount of fuel injected into the engine. This is done to LEAN out the fuel mixture to compensate for what it perceives as a rich running condition.