I have a Fiat Bravo 1.8 HLX N reg 1996 only done 38000,the car has always
been ran on normal 95 ron texaco unleaded,and the last 3 months or so the
engine has started pinking (pinging) it's been to a local garage who's had
it on a bosch kts diagnostic computer and found no errors or faults,the only
thing out of spec was we took the car for a drive with the KTS connected and
went hard through each gear ie about 5-5500 rpm's and he noticed the
injector pulses were only 11ms for which he said should be 14ms min and more
like around 18,i've been told since from other people that it's just a red
herring with injector pulses as they constantly change? i did however a few
days ago try texaco super unleaded and the pinking vanished,what's the
reason for it not liking normal unleaded anymore? it's not carbon,it's had a
treatment of ecotek's powerboost foam,hardly nothing came out the
exhaust,it's had treatments of redex and stp complete fuel system
cleaner,but it just won't run on unleaded anymore.all sensors have been
checked,he said ignition timing can't be adjusted because the ECU controls
ignition and air/fuel mixture ratios,i changed plugs a couple of weeks ago
to no avail,then decided to change plugs again but for champion instead of
NGK and noticed small yellow deposits on the plugs ceramic insulator,does
this indicate anything?
This may not be that easy to get to the bottom of.
Pre-ignition (pinking) is affected by fuel mixture being too lean (or badly
atomised), too much ignition advance or local hot spots and fuel octane
rating. Hot spots can be cooled by more fuel, cooler and continual air
intake and colder running spark plugs. Systems with 'knock' sensors use the
sensor to provide feedback on the ignition advance.
The recent evelvated ambient air temperature could be the cause if your car
was running close to the limit to begin with. New plugs of the same type
would eliminate plug degradation if the condition persists. This would only
leave timing, fuel mixture, fuel octane, knock sensor and other hot spot
I don't believe your car has a knock sensor but I could be wrong.
On the ignition timing front it is not unkown for the TDC sensor to be
incorrectly set. This will never show on any diagnostic kit as this kit
uses the TDC pulse as a point of reference. To check the TDC you need to
either get physical and/or us a traditional strope timing light.
The fuel mixture Lambda sensor could be defective sending incorrect fuel/aix
miture readings to the ECU. This can be check by the usual MOT emission
tests which measure the fuel/air ratio. If this is Ok then we are down to
the delivered fuel based on the Lambda signal to the ECU.
With fuel mixture/atomisation one has to assume that the injector pulse is
correct and that the injectors are varnished or otherwise clogged and need a
good clean to restore the all important 'mist' spray as opposed to a
possible non atomised jet. You could try running a fuel injector cleaner
through the system a couple of times to see if that cures the problem.
A clogged air filter can also effect the mixture.
A defective air flow meter would also upset the fuel mixture. Not all fuel
injection systems have a 'flow meter' but use other methods to determine air
flow rate. e.g. the ECU calculates the flow rate base on engine volume,
rpm and air temperature. Here you are really at the hands of the diagnostic
equipment. Same goes for the knock sensor.
If the problem still persists the one could try colder running plugs.
As you say this problem has only recently occurred the only other variables
(beyond car variables) are the air temperature
and the fuel octane rating (try other 95RON makes like Esso, Shell etc.)
I'm sure I've missed something so hopefully somebody else can pick up on
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.