Peugeot 306 Cabriolet 2.0 8 valve running super-rich!!

18 months ago the wife's 1994 306 Cabriolet started to run really
rich, took it to an independant garage who replaced the Lambda sensor.
All seemed well for a while. Then it started running rich again, took
it back to them for MoT and they did something to sort it, not sure
what. Now it's running like the choke is out (I know it hasn't got a
choke) but you know what I mean. The yellow engine warning light is
now on almost permanently, the car is doing about 19 to the gallon and
I'm worried it's damaging the cat, cylinder bores etc. The car drives
horribly, and it's smelling very sooty. The local Peugeot dealer
charges labour at 70 quid an hour pls VAT, but I just don't trust them
not to sell me loads of expensive parts I don't need. By the way, the
place I originally took the car to have full diagnostic equipment but
said there was nothing held in the memory relevant to this problem. I
am reasonably mechanically minded and would be prepared to look into
this myself. Where should I start? Tahnkyou for any tips. Ian.

 

Can anyone give me some help with this please? Thanks. Ian

 

This might sound condecending.... but is the air filter housing/pipes etc.
clear of debris?

 

Thanks for the tips mindwipe, and I don't think you're condescending
Sometimes it's the obvious that gets missed. I'll give it a look
tonight, the temp sender is my prime suspect. The guage never gets
much above 80 if at all, although I believe this may use a different
sensor/sender unit? Cheers. Ian.

 

OK. Tonight I checked that the air tubing to the air filter was
completely clear, it was. The air filter was pretty grubby, so I
removed it and went for a drive without it - same problem was there,
jerky running, smoky (huge clouds when I booted it,) but no yellow K
light on at all - the wife said it was on permanently earlier today
when she drove it. Hoovered out the cr*p from the filter and refitted
it. Then I disconnected the battery and quickly reconnected 'cos the
alarm kept going off. Disconnected the ECU for 10-15 mins. Went for
a dive, no K light and no jerkiness, seemingly problem solved.
Nowhere near as much smoke on hard acceleration although I noticed a
bit when revving it in the driveway. Just as I pulled in the yellow
light came on again!
Not sure which is the coolant temp sensor - is it the one under the
intake manifold in the side of the block with green connectors? -
impossible to get to I fear without removing intake manifold or
starter motor :-( Anyway I think I have made some progress, and
hopefully I have proved the ECU is OK (it's a Magnetti Marelli one.)
Not sure what to check next, but as ever any tips or advise gratefully
received. Cheers, Ian.

 

yes the connector is green too cos peugeot techs are a bit thick(only
kidding as i was one)
check the terminals in the block connector too and trace the wiring as far
back as you can for damage
as a rule a bad connection to this sensor will give a minus C reading at the
ecu which will induce a cold start scenario i.e over fuelling

 

Thanks for the reply. Sorry to be thick, but where exactly is the
coolant temp sensor? There is a sensor underneath the intake
manifold, going into the side of the cylinder block, which has a black
wire coming out of it (maybe a black sleeve, it's hard to tell) coming
up to a green connector block which is mounted on a kind of
bracket/clip thing near the manifold (just to the left of the manifold
as viewed from the front.) Do the sensors themselves go wrong? If I
need to replace it it will be very difficult due to the position of
the sensor and lack of room. How can I test the sensor while it's in
place? I tried a multimeter across all 3 terminals in its connector,
open circuit. Cheers. Ian

 

round back of thermo housing

 

An update for those kind enough to have given me some advise over the
last week or so!

This week I have replaced the old air filter and have fitted correctly
gapped new Champion RC9YCC spark plugs. The car definitely fells like
it is running running better. After resetting the ECU last week the
fuel consumption improved to 23mpg with very average driving. I'm
hoping that with the new filter and plugs yesterday it will improve
some more.
I'm convinced that the car is still overfuelling to some degree, you
can smell it! When you come to a standstill in neutral the revs will
hover at about 1100-1200 for 3-4 seconds then drop down to a
reasonable tickover at around 900rpm. It didn't do this before. The
yellow K light hasn't come on for ages so I'm not sure of the next
step. I have heard you can get the ECU tested, maybe that's the way I
should go. Anyone know where to go for that? Thanks. Ian. ps the
air filter is now a K&N panel type