Question:
The car is running poorly with low MPG and a sooty exhaust. The engine warning light has been showing up after 5 mins whilst standing idle with the engine running for over a year which the dealer states in a sensor and that it will not damage the engine to leave for now. The nationwide garage chain I use for MOTs says its the catalytic converter and lambda sensor and that the emission values show the Cat has failed as well as the sensor. My local Mitsubishi dealer says that cats failing are very rare on this vehicle and that I should try the lambda sensor first! Who should I believe?? the Mot garage will charge £475 to sort while the dealer want £875 for the same work! But the dealer will charge £200 just to test and replace the sensor! If the Cat does turn out to be wrong as well that a lot more money to find. Is there any way to check if the cat does need replacing as I do not have total faith in either establishment!!
Answers:
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Take your car to an MOT station that does not do any repair work.They will give you the genuine reason why your car has failed.You should also have had a print out of the emissions test that was carried out.This should give clues as to why the car has failed.Show it to a qualified mot tester and they should be able to advise you as to what the problem may be.Leap of faith!
You'd have to look at a graph of what the sensor is doing to be sure.
Typically, these systems have two of these sensors- one before the cat and one after. The pre-cat sensor switches from rich to lean rapidly as the engine corrects itself. The cat smooths out this jerking motion and basically homogenizes (spelling?) the mixture, causing the post-cat output to look smoother and change less rapidly and with less magnitude than the pre-cat sensor.
The car will tell a scanner that the cat is bad if the post-cat sensor exhibits a jerky graph similar to the pre-cat, as opposed to a smooth output.
Basically, the post-cat lambda sensor can be giving you the wrong signal if it is bad, and will tell the tester that the cat is bad. However, the test is meant to prove that the converter itself is bad.
I'm assuming the only indication you have is that the car is setting a code for bad cat converter. In my experience, this is usually a problem in the catalytic converter, however, looking at a graph of the sensor's output would clear it up.
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However, sooty exhaust is a result of a drivability problem, and not likely the cat alone. My suggestion is to take it to the dealership and foot the labor bill for them to fix only what they think is causing the problem. The labor will then be under warranty, so if they replace something and it doesn't fix it, it isn't your responsibility to pay for any new parts because you have already paid to fix it.
In other words, let them deal with it. They can't really hold your money responsible if they misjudge.
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Very rarely do catalystic converters need replacement first, unless driving often through water ( causing internal enamels in the cat to crack ) You could take the vehicle to a electrical specialist for a deep diagnostic check as the fault may lie in an ecu or black box as sometimes called but electrical work will accumulate time and labour. If it is a lambda sensor universal ones can be obtained for about 60-100 £ from various sources but check the quantity of wires leading out from it before purchasing.. good luckFord Fusion, Toyota Camry or Corolla, or Honda Civic?
A quick google suggests a Lambda sensor is £51 + vat for one of these. £150 just to fit it seems excessive for ten minutes work. Generally, on an older car like this avoid both main dealers and national chains.1995 gmc jimmy having a hard time starting?
Try the £51 sensor first, then see what happens to the emissions.
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have seen many of these cars having to go back to mitsubishi mostly under warranty as the engine management light comes on and the car runs rough.dont know what they do to them but the fault is known about ask the dealer.
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