1995 L300 running rich

Submitted: Thursday, Feb 13, 2020 at 16:53
ThreadID: 139675 Views:6959 Replies:4 FollowUps:0
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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

Reply By: Don H7 - Wednesday, Feb 26, 2020 at 14:17

Wednesday, Feb 26, 2020 at 14:17
We removed the plugs and performed a compression test ... tricky position to have the gauge sealed adequately however it has 160 psi across the board however I believe they would be better than that as the gauge rubber is old and hard as well the difficulty in accessing the spark plug holes. There were no auto shops open in town on the weekend so my mate had to purchase and fit the new plugs after I left. He then followed up with a thorough search of the air intake from the air cleaner to the throttle body and notice a lead loose and possibly not contacting a sensor in this area. He fitted it securely and straight away noticed improvement. He even disconnected this lead while it was running to notice a difference in idle speed after a few seconds. He seems confident of the remedy. Thanks to all for your ideas and suggestions.
AnswerID: 630222

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