fiat brava rattles and accelerates poorly

[natscape]

hello everyone! i'm sorry for the long post but i'm trying to give as much info as possible.

my fiat brava -99 1.244 cc has recently started shaking/rattling while stationary and driving in low gears. i suspect it rattles when in higher gears as well but obviously it's less noticeable. it's quite hard to start but it does start every time. when i start the car, it revs up, then falls, then revvs up again. this all happens in a matter of seconds while the key is in. it starts better when the engine is warm.

the first thing i did was to go to a garage, and here's what they said.
i need a new coil pack apparently, because it keeps misfiring on one of the cylinders.

i dunno if its relevant but just for the record, 2 months ago i've had the lambda sensor changed (new one), the CATT changed, the sparkplugs and the exhaust (i THINK it was just the rear part because if the whole exhaust had been changed i guess the costs would've been waaay beyond my budget). the air filter and the oil filter changed too.

furthermore, the garage said that if the problem is only with the coil pack then a new one should fix the problem. however if the problem was with the ecu then it'd just mess up the new coil pack.

there are 2 things i dont understand.
1. if the coil pack is what delivers the spark to the sparkplugs, how can the WHOLE pack be responsible for only misfiring on one cylinder? i thought that if the whole pack was bust then it wouldnt deliver any sparks and the car wouldnt start at all???
2. how can the ecu be at fault for the coil pack only delivering the spark to 3 of the 4 spark plugs?

the garage gave me a quote for 130£ for a new coil pack.
does the diagnosis sound right to anyone??

i hope i got all the terminology right. will be very grateful for any suggestions and second opinions!

natasha

 

[Agile]

This is the problem with modern cars!

The complexity is beyone many people including the garages as well.

I know nothing about your car but suppose the ECU will be responsible for the spark timing and in an extreme case might be the cause.

Also, like you, I would have expected the coilpack to be very unlikely to be the cause.


My suggestions are:-

1. Distributor cap cracked/arcing ( if there is one! )

2. Spark plug leads Try measuring their resistance.

3. spark plugs or their gap.

4. burnt valves/seats.

5. cylinder head gasket leaking.


Suggestions:-

Try to identify which cylinder by pulling off one plug lead in turn.

Then swap that plug for another and see it it remains that cylinder at fault.

Tony

 

[^neo^]

If it has coil 'packs' then it has no distributor, so most of the above advice won't really be relevant unfortunately.

Instead of a seprate coil, distributor and spark plug leads each spark plug has it's own coil pack (basically a coil which fits directly to the top of the spark plug) which is controlled by the ecu.

If it does have spark plug leads, then it's probably got a ecu controlled coil which sends a signal to the coil to tell each plug when to spark. Usually the whole coil will die rather than just one section of it though.

Not sure what system your car has though, probably the seprate coil packs.

 

[Agile]

This one seems to have a single "coil pack" with ignition leads. See this description I have lifted from fiatforum.com where more information can be found. After reading this description it does sound as if it could be the pack at fault but measuring as suggested might indicate if thats the problem. But it could also be the ignition leads or valve seats I expect.

It sounds very easy to fit if you can get one yourself.

Tony




HT is where the plug leads jopin the coil. if you remove the plug leads you should see each HT output is numbered 1-4, representing each cylinder. the way the coilpack works is using 2 internal coils, each one discharges to 2 cylinders. when i say a "coiled pair" i mean 2 HT outputs (such as 1&4) that are common to one internal coil. if you test the resistance across these 2 HT outputs you get an idea of the conditon of the shared discharge circuitry. if you measure 1&4 then compare it to 2&3 and both are very similar then you know the discharge circuitry will provide an even output for all 4 outputs, important for even running.

there will be 3 pins on the LT side of the coil (iirc), LT is the side where the connector is plugged into the coilpack. its how the coilpack is powered. the 3 pins are for earth (1) and power to the coils (2). you need to determine which pin is earth (do a continuity test on connector pins to determine coilpack earth pin) then test resistance between each of the other 2 pins and earth. the 2 results you get will give an indication of the conditon of the coils. a coil with less resistance will hold less charge and cause low sparking on 2 cylinders (the most common coil problem).

 

[natscape]

gentlemen,

many thanks for your inputs.

i'm gonna ask another garage for a second opinion with your suggestions in mind, if nothing else then to learn what all this car business is all about.

if you are all mechanics or just very interested in cars, in your experience, which cars are the easiest to maintain and don't f*nny about as much as fix-it-again-tomorrows (FIATs) do?

thanks
natasha

 

[Agile]

gentlemen,

if you are all mechanics or just very interested in cars, in your experience, which cars are the easiest to maintain and don't f*nny about as much as fix-it-again-tomorrows (FIATs) do?

thanks
natasha

I am a gas boiler engineer and neo says he is a steel fabricator! But cars are a bit like boilers in the way they burn fuel and just another machine anyway.

Many modern cars seem to be designed to be very difficult to repair. The question would really be which one is the least difficult to repair!

Its less important how difficult they are to repair. Whats more important is how OFTEN they break down!

Tony

 

[^neo^]

VW all the way for me.
Easy to fix if they do go wrong, parts are cheap, and generally a nice drive

 

[wotan]

If it has coil 'packs' then it has no distributor, so most of the above advice won't really be relevant unfortunately.

Instead of a seprate coil, distributor and spark plug leads each spark plug has it's own coil pack (basically a coil which fits directly to the top of the spark plug) which is controlled by the ecu.

If it does have spark plug leads, then it's probably got a ecu controlled coil which sends a signal to the coil to tell each plug when to spark. Usually the whole coil will die rather than just one section of it though.

Not sure what system your car has though, probably the seprate coil packs.

Not so, on the Vauxhall vectra 2.5 V6, the coil pack consists of six indivdual coils all potted together, any one of them can fail, the system operates on what is known as waste spark, when the plug fires it's a cascade of sparks rather than one single spark as in common distributer systems.
I speak from expierence, expensive to replace, I have never heard of a faulty coil pack causing damage to the ECU.

Wotan

 

[bongos]

I had a similar problem on my '99 Golf. One coil had to be replaced and it cost about £50 IIRC - I'm sure Fiat spares will be cheaper than Volkswagen

I would expect you could just replace the faulty coil rather than all of them but I don't know the setup on the Brava so I couldn't say if its the same as mine. At my garage they simply connected their computer to the ECU and it told them which cylinder the fault was with, which they then replaced. Not a big or expensive job.

It's becoming quite common now I think too as RAC/AA carry spares in their vans for some cars that have notoriusly unreliable coils. Might be worth a second opinion from another garage to make sure they don't replace more than needs doing.

 

[Agile]

If you read the description that I posted above you will see that the Fiat usit is a single unit with TWO coils that sparks two cylinder at a time. One will be firing and the other evacuating.

It might be the same as the one in my Laguna which has a similar arrangement.

The Laguna one is a mounting bracket with two identical coil units which each feed two cylinders in the same way but each individual coil unit can be changed on its own.

Tony

 

[TicklyT]

I went down the 'It's always the coil pack' route a while back trying to diagnose a misfire on a Renault...... In the end it turned out to be the crank position sensor.