Just over a week ago a car ran into the back of my XK8 whilst I was stopped at traffic lights, not too much damage fortunately but it will be needing a new rear bumper. Shortly afterwards it felt like it wasn't going to start but then did and ran perfectly. Now, to get it to start I generally have to press the accelerator a little and it can take while to fire. I took it to have a diagnostic check to see if anything showed up (initially there were a few things so they were cleared and I went back today, a couple of days after they were cleared) and there were two things, one is that the catalytic converter on one bank is performing below requirement, possible cause is fracture so hopefully that is going to be replaced under insurance. The second was in the "flight recorder" test which showed that the inertia switch had been activated. It was something I had wondered about but my knowledge was that they were either on or off, and mine is certainly pressed down as it should be to run. Could it be that it is slightly sticking or might there be something else causing the problem? Obviously need to get it sorted but would be good to get this done quickly and I'm quite prepared to have a go myself if it could be something straightforward to fix. Anyone got any ideas?

 

At least you should have no problem with the insurers with someone running into the back of a stationary vehicle at traffic lights.

Inertia switch is a safety device and is either ON or OFF. It has to be reset manually. If it had tripped in the accident you would have had to reset it. Flight Recorder only tells you it has tripped but not when.

Did they give you the actual 'few codes' before clearing them and the further codes when you went back? The actual codes - not what they described them as.

Graham

 

That is what I thought about the inertia switch, and it didn't activate when the car was hit. Just seems odd that it was showing in the flight recorder status.

Most of the codes which showed up related to when I had coil pack fail a few months ago, they showed them being unplugged whilst I found the failed one. I have a print out of it but not to hand.

The only fault now showing is the catalytic converter not working to requirement, it says which bank and gives possible causes including fracture so the insurance company have said they will replace it.

 

Possibly the switch has been triggered sometime before you got the vehicle.

They unplugged coils to find a failed one? The usual method is to move the suspect one and recheck DTC's to see if the code changes to match (each cylinder sets an individual code).

With a damaged Cat, the fuel trims will be all over the place. The problem will very likely to disappear with a replacement Cat and a hard reset.

Graham

 

Thanks for the reply Graham.

I was the one who unplugged the coil packs to find it myself, pretty easy to do really when one cylinder is down and saved another drive to a place to have the codes read when it wasn't running properly.

What do you mean by a hard reset?

 

Not a good plan to run with a deliberate misfire. You need a code reader at minimum with these vehicles.

A 'hard reset' removes (almost) everything form memory, particularly fuel trims.

Disconnect the battery negative terminal, and short it to the positive terminal for 30 seconds to reset the electronics.

Graham

 

On the basis it already had a misfire and I needed to sort out what it needed as quickly as possible (and I'd only had the car about 3 weeks at the time so hadn't even considered a code reader at that stage) disconnecting a coil plug for a couple of seconds to see if it affected the running.

Thanks for the info on the hard reset.

 

Running with a misfire for a few seconds, minutes, or even a couple days (short drives) shouldn't do any longterm damage, but extended misfires sends too much fuel to the cats and plugs them up, if you want to see if it truly is your cat, then with a normal OBD2 scanner, you can monitor the voltages, if you're downstream sensor (B1s1 or B2S2) is over 1 volt (if i remember correctly) its showing the cat damage. I've seen two cat's with this problem, and one S2 sensor was reading 0.7v, the other was like 1.9, or higher. Swapping it with the other sensor on the other bank resulted in the same cat voltage spike, meaning it was the cat, and not the sensor itself being bad.

 

A damaged cat will not affect fuel trims. Trims are only affected by upstream sensors. Cat efficiency is only determined by downstream sensors.