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mgf
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Discussion Starter #1
Morning all,

MGF 1.8 (non vvc)

I've just changed the downpipe and have a symptom where sometimes in second gear when accelerating the revs settle and the speed holds at about 25mph. Going through the rest of the gears everything is fine and it may go an hour before getting this symptom again.

The only thing I can think is the LAMBDA sensor as I needed to use a blow torch to the surround to loosen it. Was pretty careful, but could this have damaged the sensor and would that affect the car in this way?
 

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mg_tf
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I don’t profess to be an expert but I would have thought that while accelerating the ECU would be running in open loop mode and wouldn’t be looking at the Lambda sensor, also if the ECU detected a Lambda issue it would light the EML light and store a code. Have you checked for stored fault codes?
 

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mgf
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Discussion Starter #3
Thanks. I didn't even know the MG had an ODB port.
Will dig out my ODB thing out at the weekend and see what I can find.
 

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mg_tf
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What age is the F? Only the late F’s had an OBD2 port that may or may not work.

Another thing to check is a sticking throttle body; this can be an issue on the plastic throttle body.
 

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Sounds like the O2 sensor/Lambda. My old ZR did the same thing after i changed the cat. The stud on the downpipe snapped so i had to give it a good **** to knock the broken stud out. This from what i can surmise damaged the O2 sensor.



Afterwards the car was doing pretty much what you described, it would hold back, especially in second, although it seemed better once the engine warmed up. It didn't put on the EML, but once i fitted a new O2 sensor the car went back to normal.
 

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mgf
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Discussion Starter #6
Sounds like the O2 sensor/Lambda. My old ZR did the same thing after i changed the cat. The stud on the downpipe snapped so i had to give it a good **** to knock the broken stud out. This from what i can surmise damaged the O2 sensor.



Afterwards the car was doing pretty much what you described, it would hold back, especially in second, although it seemed better once the engine warmed up. It didn't put on the EML, but once i fitted a new O2 sensor the car went back to normal.

That is what I wanted to hear. Same here, no EML light.

We really had to cook the exhaust to get it out so not surprised it is damaged.

Car is 2001, will try a new sensor anyway as if it fixes it will save me no end of time.

Cheers!
 

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Just disconnect it first, It will probably put the EML on but the car should pretty much respond as normal as it will revert to preset values stored in the management system. Fuel economy wont be as good but it should run nearer to normal if the O2 sensor is the issue.


Just remember there are two sensors, there could be a fault with either one.
 

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mgf
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Discussion Starter #9
Was faulty post cat sensor. Replaced and solved issue. Thanks for all your help and suggestions.
 
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