Cat Heat Sensor and lumpy idle (V6 1997)

paulmorgan · Post by **paulmorgan** » Sat Feb 23, 2013 4:25 pm

Since having the timing belt changed my v6 Bongo has been lumpy at idle, especially once up to temp. Seems almost like the idle revs are set too low as it's smooth enough whilst driving - just feels like it's about to stall when sat in traffic. The rev counter sits at about 500 rpm or slightly less when warm. I've also noticed a bit of a squeak - sounds a bit like it's coming from a belt pulley. Should've taken it straight back but not had the time and have done about 2000km since the belt was done.

What things will the garage have had to remove/replace and adjust whilst doing the timing belt? I'd like to be on confident ground if trying to argue that they shouldn't charge me for putting it right...

Is there an easy tweak for the idle revs that I can do to see if that helps?

Also just had the cat/exhaust Heat warning lamp come on - and stay on despite a two hour wait for it to cool. Light was still on despite it being down to ambient temp. I've disconnected the sensor. Presumably the sensor has failed. Worth getting a new one? Easy to fit? Cheap alternative parts available? Does it feed into the ECU at all (and affect the fuel mix)? I'm thinking of getting an emissions test done just to make sure the Cat is OK. Could this be linked to the lumpy idle (above) or just a coincidence?

teenmal · Post by **teenmal** » Sat Feb 23, 2013 4:35 pm

Hi,it sound like the engine is not firing on all 6 cylinders,it could be dumping unburnt fuel into the CAT.It is not advisable to mask this by adjusting the tick over speed,you need to get this matter investigated asap.
If it is dumping fuel the CAT will get Red Hot.
Good Luck.

paulmorgan · Post by **paulmorgan** » Sat Feb 23, 2013 4:45 pm

teenmal wrote:Hi,it sound like the engine is not firing on all 6 cylinders,it could be dumping unburnt fuel into the CAT.It is not advisable to mask this by adjusting the tick over speed,you need to get this matter investigated asap.
If it is dumping fuel the CAT will get Red Hot.
Good Luck.

Thanks for the reply. Why would the CAT heat lamp still be on when it's cold? Could it have got so hot that it killed the sensor making it read hot even when cold?

teenmal · Post by **teenmal** » Sat Feb 23, 2013 5:00 pm

That's a strong possibility,you need to get the engine running problem checked out.

windywatson · Post by **windywatson** » Sat Feb 23, 2013 6:22 pm

Hi,

Cam belt replacement on the V6 is quite a big job, as there are a lot of pipes & drive belts to be removed in order to do the work. It is possible that the belt could have been fitted slightly out, say by one tooth. If you study the engine drawings you will appreciate that there are quite a few cam belt pullies to align correctly, having 2 banks of double over head cams.
I had a car in the past where this had happened on a belt change and whilst this wasn't enough to cause engine damage it ran resonably with the exception of lumpy tickover and the preformance lacked edge.
With regards to the CAT over heat warning, that may be coincedentail as the vehicle is resonably old and if the engine has not been running correctly the sensor having now been overheated for a long duration may have finally packed up.
The squeaking could easily be one of the belts driving, air con, altinator, power steering etc, or perhaps one of the cambelt tensioners.

Hope this helps give you some ideas what to look for.

Cheers

Cheers

Post by **g8dhe** » Mon Feb 25, 2013 11:28 am

Ah Ha, just had exactly the same happen! Belts changed last week and the first long run found the engine causing vibration as we paused at junctions and roundabouts, but not consistently.. Suspecting the idle controls as well, there is an ISC solenoid at the back offside of the engine, but just about to go and look at the manual to see what the adjustments are before going to talk with the garage. There doesn't seem to be any mis-firing merely judder and shaking at low rev's when idling also the idle rev's seem to change between pauses but consistent when just sat stationery.

Post by **g8dhe** » Mon Feb 25, 2013 5:37 pm

OK well the Air Adjustment Screw which sets the idle speed is shown below reached from the drivers side, but you need to put the ECU into Test mode to feel the change I found, Earth the TEN connection and if you have a Rev. meter then use it as well with NO loads A/C off, Lights off etc. then 680-720RPM

I found a single turn, anti-clockwise, increased it sufficiently.

haydn callow · Post by **haydn callow** » Tue Feb 26, 2013 8:13 pm

I think you will find the light stays on whilst cold is because when it came on it get so hot it melts the heat sensor.......this then shorts it and the light comes on.......you now need to replace the sensor and the light will go out......had exactly this problem on a mx5 and it also was caused by unburnt fuel entering the cat causing it to overhear

Cat Heat Sensor and lumpy idle (V6 1997)

Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)

Re: Cat Heat Sensor and lumpy idle (V6 1997)