Hi,

My Bravo 1.2 16v developed a strange problem. When I try to pull of hard from a junction engine sounds like its running on 3 cylinders and sporadically catches on. Sometimes it backfires. This is not the case if I accelerate with minimum input or at high rpm. Problem seems to be related to air temperature. Near or below 0 C it runs almost fine but not perfect. Also its less noticeable with cold engine.
Iv'e changed sparks, cables and coil but problem remains. Also tmap sensor looks fine. If warmed up by hand ntc changes resistance and reading fits specifications. Resetting ECU doesn't fix the problem.
Any ideas?

tepaks said:

Hi,

Iv'e changed sparks, cables and coil but problem remains. Also tmap sensor looks fine. If warmed up by hand ntc changes resistance and reading fits specifications. Resetting ECU doesn't fix the problem.
Any ideas?

Click to expand...

has it generated ANY codes..??

sounds like 1 of the Temp sensors - does it start well hot OR cold ?

Charlie

varesecrazy said:

has it generated ANY codes..??

sounds like 1 of the Temp sensors - does it start well hot OR cold ?

Charlie

Click to expand...

Thanks for the reply. No there are no error codes. Temperature reading from ECU is ok. Engine starts with no problems regardless hot or cold. Only strange reading comes from MAP sensor when the engine is not running. It reads 850 mbar?!? So I swapped air temperature and pressure sensor. No difference.

Coils/leads/plugs ok....
If you can, measure the resistance of injectors. If one visibly off, it is going to die.
I think the ecu drives coils in pairs so ecu should be fine.
What colour is your coolant/oil? (headgasket)

Neverth said:

Coils/leads/plugs ok....
If you can, measure the resistance of injectors. If one visibly off, it is going to die.
I think the ecu drives coils in pairs so ecu should be fine.
What colour is your coolant/oil? (headgasket)

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You are right. Coil is a dual one, driving 2 cylinders in pairs simultaneously.
Resistance of all four injectors is the same, 16.1 ohm to be exact. Once again, when idling or under low load engine fires on all four without any problems.
Coolant is is bright, translucent yellow, and not boiling. Tester shows -20 deg C. I guess gasket is fine. Tomorrow I'll measure compression and fuel pressure just to be sure.
Oil level is fine and its translucent light brown ( coffee ) as you can expect from any normal running engine. Definitely not burned brown/black.
There are no signs of above normal oil consumption. Exhaust fumes are normal ( slightly white when cold, colorless when engine is running at 90 deg C ) Definitely not blue or black. But there is a noticeable smell of unburned fuel after provoked fault ( rapid, aggressive revving up ) accompanied with occasional backfire. Sparks also show signs of to rich mixture ( black fluffy outer ring ).
I'm very confused sins ECU shows no error at all and usually most ECU report ignition error when lambda detects to rich mixture.

p.s. exhaust fumes tested at constant 2500 rpm are within expected/accepted values for this type of engine. But than again this doesn't prove anything sins engine is running fine at any constant rpm or under light load and/or light acceleration.

I've just came back from friends garage.
Compression on all four is >17 bar measured 3 times on each cylinder.
Fuel pressure 3,8 bar and stable
New air filter
no difference
:bang:

Try the crank/timing sensor, had similar before and turned out to be that.

blackmagic11 said:

Try the crank/timing sensor, had similar before and turned out to be that.

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What symptoms did your engine had?

Well when You did everything and nothing works it's time to start from square one.
That's is exactly what i've done. Ignoring every thing I've learned about this car and ignoring all advices I've received, I've just started from the beginning just as if I was confronted with this car for the first time.
Having all symptoms in mind, I've swapped the sparks and HT cables again.
Nothing chained.
Then I swapped the ignition coil again with a brand new one.
Result:
Engine purrs like a happy cat once again!

Congratulations on figuring it out and fixing your car... these engines are fantastic when they are running right.

What you have seen is a typical problem with modern cars... a simple fault somewhere will screw other things up and make strange symptoms somewhere else. So if the fuel is not burning right then the engine management / lambda sensors will see a mixture fault and try to compensate, and then everything goes in a loop giving confusion.

I recently sorted out a long-standing problem on my Tipo ie where it would run really badly during warm up (revving and falling, not pulling) and generally being down on performance. It was like that for years! It was all due to bad (very old) spark plug leads, the car idled OK but wasn't burning cleanly on 2 cylinders so the mixture was rich and the ECU got all confused.

It was only when I overhauled the cylinder head and cambelt and put it back together that it ran really badly - so just disturbing the leads etc made them finally fail completely.

Obviously plugs and leads are traditionally the 1st things to change, but these days it's easy to imagine that these parts last a very long time and a funny engine fault is probably due to something complicated (e.g. a sensor).