Rich (negative long term fuel trim) causes

Hi. I have a 96 camry federal 2.2 auto with 307k miles. The short term fuel trim is in stoichiometry but the long term sits around -25. Holding the revs at 2500 improves the long term to -17.

My question is what all could cause this?

I have already replaced all sensors, air filter, purge valve, thermostat, fuel pressure regulator, and the fuel injector cleaning guy said the injectors are not leaking down.
Tested the old and new sensors and all are good. The fuel pressure is also in tolerance.

• This topic was modified 2 months, 3 weeks ago by  Taylor Mauldin.

Topic

[Rahul JonesParticipant]

Try disconnecting sensors like MAF sensor and Throttle Position Sensor then check if the reading changes. Also, you can check if the exhaust fumes reduces or not.

[Taylor MauldinParticipant]

Disconnecting sensors causes no changes

[Rahul JonesParticipant]

Is it possible to share the live data reading from MAF, MAP, TPS, and oxygen sensors?

[Taylor MauldinParticipant]

Have to manually type in. It has a map but no maf.
Engine at warm operating temperature idle 750
Tps 11.4 %
Map 3.9-4.1 psia
Ect 200f
Iat 85f
Oxygen upstream oscillates from .1-.9 back and forth rapidly, upstream short term trim oscillates between 3% rich 1% lean, upstream long term trim -25 % rich, downstream stuck at .115 v sometimes it unsticks and fluctuate between .1-.3 v

[Rahul JonesParticipant]

Is your MAP reading positive on idle? It is supposed to be negative on idle as the intake has vacuum.

[Taylor MauldinParticipant]

The map is reading correctly. 29.4 inhg map atmospheric – 8.0 map at idle= 21.4 inhg vacuum

[Rahul JonesParticipant]

My next suspect would be a stuck open EGR valve. You can plug the vacuum hose going to the EGR and see if that improves.

[Taylor MauldinParticipant]

Plugging the hose made no difference

[Rahul JonesParticipant]

Do you have anything to check the fuel injector pulse duration or through OBD live data? I had a similar issue with a customer’s car where the datas were normal but the engine ran rich and failed emissions. That was caused by a faulty ECU giving longer pulse to the injector.

[Taylor MauldinParticipant]

No, I don’t. The ecu is almost new , it only has 2000 miles on it

[Rahul JonesParticipant]

At this point, I am helpless. Sorry, hope someone from this forum can help you out.

[Author]

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