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Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 21865
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Mitsubishi 2.4 GDI: Morning,I am having a proper headache

Customer Question

I am having a proper headache with my 1999 Galant 2.4 GDI. Hopefully you can advise me as to fix it or euthanize it!. The flex connection on the exhaust started to leak and threw P0170 faults at me so replaced the pipe. It ran ok for months now I have P0170 and P1221 coming up. It is fine when it is cold then after a couple of minutes it starts to oscillate between 850/1250 ish RPM. This is followed by a "click" like a relay from the dashboard around the area of the R/H side of the radio. as this happens, pot No:1 goes dead. I have checked the OBD readout and the short term fuel trip drops and satys at 0.0% while the long term is at -7.0%. Does this sound like anything you have encountered before? I have changed the MAF and cleaned the throttle body butterfly.
Submitted: 2 years ago.
Category: UK Car
Expert:  Matt replied 2 years ago.
Hello Bryn
an exhaust leak then can make it runn very rich as the exhaust oxygen sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.
So I'd suggest repairing the exhaust leak 1st and if the issue persists then replace the O2 sensor
Customer: replied 2 years ago.
Hi Matt..... the exhaust was replaced... as in the description of the fault. Any other ideas?... I am curious to know what is behind the dash towards what sounds like the right hand side.... as the a "click" which sounds like a relay?... is heard the no.1 pot starts to misfire. As soon as the engine cools it runs fine. The short term trim value drops to 0.0% as the misfire on 1 occurs.
I hope this might help.... as well as the rest of the explination in the previous message.
Expert:  Matt replied 2 years ago.
as the short term trim is dropping to 0 then this indicates that the ECU has stopped using that sensor, either its dropping into open loop ( full throttle ) or the sensor signal is faulty and is being discounted by the ECU
this is why I suggest to check over the sensor wiring etc
Customer: replied 2 years ago.
Hi I had a closer look at the car tonight and have found the following:
From cold:- ( Idling fine )
Short term trim: -3.2 to -4.8
Long term trim: -4.7
RPM 1000
O2 sens 1: 0.030
O2 sens 2: 0.031Warm (approx. 60 sec)
Short term trim: -4.8 raising to -25.0
Long term trim: -4.7
RPM: dropping to 960
O2 sens 1: rising to 0.300 on idle (0.800 when revved)
o2 sens 2: slight rise to 0.120 approx. ( 0. 210 when revved )When it goes into fault:
Short term trim: 0.0
Long term trim: -4.7
RPM: starts hunting around 650 to 1000 for approx. 10 sec then jumps to 1340 and stays there. It also kills pot 1 (which is ok until this point.. also at this point there is what sounds like a relay click located around the RH side of the radio / AC display)
O2 sense 1: 0.220
O2 sense 2; 0.0
It is driving me mad.... so hope you can figure this one out for me.Thanks Bryn
Expert:  Matt replied 2 years ago.
This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.
As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.
Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.
The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine
Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty
Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.
This leads them to be quite intermittent in the case of mild leaks
Expert:  Matt replied 2 years ago.

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