Fiesta 1.25 Zetec 'Missing'

[mckln335]

Hi Chaps,

Recently bought a Fiesta 1.25 Zetec 1997. Runs as sweet as a nut apart from when i hit 4,000 rpm, the engine seems to 'miss' and lose power. Also, it seems to be absolutely drinking petrol. I have changed the spark plugs and the air filter, this hasnt solved the problem. Could it possibly be the ignition leads or something more serious like the injection system?

Any help would be much appreciated

Cheers,

Mark

[richyrich86]

Im no expert but its possible its the oxygen meter in the exhaust.

My thinking:
the meter looks at the amount of unburnt oxygen coming out of the engine and feeds it back to the ECU. I think there is an ideal level which the engine tries to maintain, by increasing fuel amounts. if the sensor is down, the ECU will be getting an incorrect reading so throwing fuel into the engine, and hence bogging it down. (fuel burns only when mixed with air).

[mckln335]

Would it pass the emissions test if it was doing this? Because it did pass the MOT on Saturday.

Cheers,

Mark

[Zad]

MoTs are done with the engine running at idle, or at not many revs. It sounds like you are getting problems at higher revs, which wouldn't have shown up on the exhaust gas analyser. Also, the catalyst will be converting any unburned hydrocarbons. Running rich does sound like the cat sensor (or cabling) is on the way out. Time to say hello to the local garage and get their advice before the excess fuel makes your catalyst go phut.

[SwissCamel]

Had a 1.25 Zetec once upon a time. Drove it hard, and used to get some truly shocking mpg. Average of about 33mpg, and on one late night motorway blast covered 170miles and returned 26mpg...

[mckln335]

Zad said:

MoTs are done with the engine running at idle, or at not many revs. It sounds like you are getting problems at higher revs, which wouldn't have shown up on the exhaust gas analyser. Also, the catalyst will be converting any unburned hydrocarbons. Running rich does sound like the cat sensor (or cabling) is on the way out. Time to say hello to the local garage and get their advice before the excess fuel makes your catalyst go phut.

Thats a good point. It is booked in for a diagnostic test tomorrow morning so we shall wait and see what happens.

[mckln335]

SwissCamel said:

Had a 1.25 Zetec once upon a time. Drove it hard, and used to get some truly shocking mpg. Average of about 33mpg, and on one late night motorway blast covered 170miles and returned 26mpg...

I would hate to find out what my mpg is then. I do around 15 miles a day, and havnt been driving it hard since i found out about this fuel problem. From wednesday last week to wednesday this week i put 70 quid of fuel in!

[_Al_]

I just bought a 1997 1.25 and it's very similar. If you rev it slowly through the range it's fine, but if you floor it it'll really struggle between 3,200 and 4,500rpm then pick up again. I'm also getting dire fuel economy. 22mpg on the motorway. Exactly the same as my MR2 Turbo!

[mckln335]

Hi Chaps,

Mechanic said on saturday afternoon that it is the Mass Air Flow Sensor.
He hooked up the machine to the ECU which came back saying that the mixture was too lean. He checked the voltage coming from the MAF and it gave a reading of 3.5V, whereas the bloke said it should be at least 4V.
I shall get this changed and see what happens.

Cheers,

Mark

[mckln335]

Job done, changed the MAF and the car accelerates smoothly once more. Hopefully this should sort the fuel consumption out as well.

Cheers for your help guys,

Mark

[mckln335]

• *Update***

Right, well the problem of the car missing is completely sorted now.
However, it still seems to be using a heck of a lot of fuel.
I worked out the fuel consumption the other day and it was only doing between 28 and 32 mpg! Would the chap who did the diagnostic test have to maybe reset the ECU to tell it that the car is now taking in the right amount of air therefore fuel?

Cheers,

Mark