1995 L300 running rich

Submitted: Thursday, Feb 13, 2020 at 16:53
ThreadID: 139675 Views:601 Replies:3 FollowUps:0
My mate has an old Mitsubishi L 300 that, by the sounds of it, is running rich ( I haven't seen it yet .. going to catch up tomorrow) Can anyone tell me if there is a sensor in the exhaust that could be the cause of the issue? He has tried all the usual suspects, blocked air cleaner, dodgy fuel etc. however as it is injected, I figure it must have some sort of sensor to tell the processor when the motor is at running temperature and adjust the fuel delivery accordingly. She's an old girl with around 260,000 kms on the clock.
I'm a retired tractor mechanic and not really familiar with older road vehicles.
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Reply By: HKB Electronics - Thursday, Feb 13, 2020 at 17:08

Thursday, Feb 13, 2020 at 17:08
EGO sensor (exhaust) is normally only used to tune the mixture when engine is running at a constant throttle setting, should not cause issues accelerating etc. Would cause issue at constant speed, idle etc.

MAF sensor in the intake also used for main mixture management, try unplugging it car will normally run ok without it plugged in, at least the cars I have do. Computer reverts to fixed look up tables if it gets no info from the MAF.

Coolant sensor temperature could cause you grief it is out of wack, there will probably be two, one for the temperature gauge if there is one and one for the engine management system, temperature gauge may read ok but engine computer may be getting different info.

Other one that can cause misfire is crank angle sensor.

Try scanning with a reader and see what fault codes are present. If you don't have one check the usual things first, spark plugs, leads, coils etc. Also fuel pump t that age.


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AnswerID: 630030

Reply By: RMD - Thursday, Feb 13, 2020 at 19:18

Thursday, Feb 13, 2020 at 19:18
It will have an oxy sensor in exhaust and if it is operating ok but engine running rich there may be either an air leak in exhaust system which sucks in air past manifold gasket and makes the oxy sensor think it is running lean, if so the ecu will richen the mix. Also the intake side may have an air leak which is admitting air unmeasured by the airflow meter and that will cause some problem. A split vacuum hose to the fuel regulator will make the fuel pressure to injectors to be elevated/more than needed and therefore forcing more fuel per unit time through the injectors, ie, rich.
AnswerID: 630036

Reply By: qldcamper - Sunday, Feb 16, 2020 at 16:51

Sunday, Feb 16, 2020 at 16:51
If there is an oxy sensor try removing it and burning off any build up with an lpg torch, was a trick back in the day if the sensor strayed out of operating range.
AnswerID: 630083

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