Brava 1.4 SX acceleration problems (flat spot?)

[Sue]

Hi,
I have recently purchased an older Brava 1.4 SX (N reg, 1996). It has only done 55k and looks in very good condition.

I am now experiencing a problem whereby I seem to loose acceleration for a fraction of a second through each gear. It happens nearly all the time. I have had a Electronic Diagnostic done on the car but it has shown no fault.
The spark plugs have been changed and I have had new leads, but the problem is still there. Anyway one got any suggestions!!!



Regards,
Sue.

 

[Anonymous]

Mines the same it seems to varie to on how long i've been driving the car that day.

 

[Sue]

Will this flat spot (if that's what it's called) be doing any damage? What is the most likely cause? Is there anything I can do, or my Hubby's mechanic friend, to locate the problem and fix it?


Thanks,
Sue.

 

[Stu]

try an ecu reset. take battery off for an hour,replace, then start car and leave to idle for 5 mins at least. Then drive car reasonably hard right through the rev ranges whilst the ecu re-learns. It will take about 200 miles for the settings to stick AND this technique will use more petrol in the short term but hopefully it will sort ya problem, Also , bang some redex injector cleaner in the petrol for good measure!

Hope this helps

Stu

 

[Sue]

Hi,
I tried the ECU reset but it made no difference. I put some Redex in and this changed the problem slightly but didn't fix it.

The coil has been changed as has the air filter but I still have the problem.

I think the Redex did some good, as the problem has changed in the sense that the loss of power usually isn't as dramatic as it was, although I would say it happens more frequently now.

When I use the car first thing in the mornig it seems OK for a while so I assume the problem occurs as the car warms up. Also, there seems to be a lot of air in the petrol tank. When I take the petrol cap off there is a huge rush of air, never noticed this with other cars.

Any help or suggestions greatly appreciated.


Thanks,
Sue.

 

[Waderider]

Flat Spot

My S-reg 1.4 does this too. ECU reset, injection cleaner, service, nothing has fixed it. I call it personality.

 

[Anonymous]

I get this all the time, is the rush of air not going into the petrol tank?

Since the tank is an airtight unit as the fuel get used there is no air to replace the volume of fuel that has been burned. So if you use a full tank of fuel the effect will be more pronounced.

 

[Waderider]

I think that would be a bit of a myth anon. The fuel system is constantly pressurised at 1.1 bar, there is a vent on the filler union to allow air in, and there is a fuel vapour system on the car.

 

[Matt]

So what is the "wooshing" air phenomenon then? This great mystery is gonna keep me awake until it is solved.

 

[Matt]

I take it the vent on the filler cap is somekind of pressure valve, ie, over 1.1 bar and it opens.

 

[Waderider]

Fuel system

I'm sitting looking at the workshop manual, it doesn't describe what pressure the relief valve works at, but says the filler neck is "union with vent and pressure relief valve". Likewise it shows a "fuel evaporation control circuit", which basically is a breather pipe from the fuel tank to the throttle body. So the fuel lines are pressurised by the fuel pump, and manifold intake vacuum will cause a similar vacuum in the actual fuel tank.

So the petrol tank should suck air in when you remove the filler cap. Sounds feasible to me anyhow!

 

[Matt]

ok, I'm starting to see now, but I think I may have been mistaken the way the air must be going. If the tank is pressurised above 1 bar then that would mean air/gas would have to be pumped into the tank and so when the cap removed the air would rush out. On the other hand, if the air was rushing in then that would mean it was a vacuum (which is what I assumed it was).

Well, looks like this has been solved, well done that man.

 

[Waderider]

System pressure

Only the fuel lines and pump forward are pressurised, the tank isn't (not by the fuel pump anyhow). Otherwise when you switch the ignition on it would take an age for the fuel system to allow the engine to start, because the fuel pump would have so much volume to get up to working pressure.

Sorry Sue, it appears your thread has been hijacked.

 

[Matt]

lol, sorry Sue, you did raise the issue

Does this mean we don't know why there is a pressure difference in the tank then?

 

[Waderider]

No, there is a negative pressure in the tank caused by the fuel vapour system sucking vapour out using inlet manifold vacuum, and of course fuel being used. The negative pressure is regulated by a air inlet valve in the filler neck, and when you remove the filler cap air shall rush into the tank to equalise to atmospheric pressure.

I have to add I'm getting all this out of the workshop manual, and I've never had to look at my cars fuel system.

It's all in here:

http://www.babarmalik.com/Vol1.pdf

Under the section specific to the 1.4 engine fuelling and ECU.

 

[Matt]

So I was pretty much correct to begin with, just didn't mention the fuel vapour system.

lol, seems almost like a waste of a good thread.

 

[Sue]

OK, thanks for that, I think

The reason I mention the air in the petrol tank (rushing in or out) is that it is quite severe compared to other vehicles I have had and/or filled up.

The petrol cap is not the original one I assume as it is a big green thing. It seems to fit OK but I wondered if it was maybe causing a problem?


Thanks,
Sue.

 

[Waderider]

Petrol cap.

Well, I doubt if it is causing THE problem, as my car, with the standard cap does it.

But it may be A problem, as the manual doesn't state were the relief valve is, might be worth going to the scrappies for a specific one.

 

[Ash]

get the cam oil spray bar checked sometimes these get blocked and kill the cams.

 

[twilight]

The "L" (or "λ") sensor

Well I had about the same problems for quite long time in my 1.4 SX.

No matter what I tried, nothing seemed to resolve the problem.

Not until I read in the fiat puntoclub.gr a suggestion about taking off the "L" sensor plug and see what happens.

I can say that the car was running perfectly with no issues.

So I realised that I had to change this sensor and I did. It cost me 110 euro. The brand is NGK and I noticed better consuption than before.