fiesta starting problem

That's the one. Just couldn't think of it at the time.

I had EXACTLY the same with my L plate 1.1 fiesta.

Just solved it last weekend, was really bugging me.

New set of leads, helped New plugs, helped Clean the lambda sensor - covered in soot, perfect !!!

Only takes 3 mins, and free, right at front of engine on exhaust

Now ideles perfect, starts without throttle, never misses, starts every time and hopefully will get through emissions this time on mot!

Is this common? I replaced the downpipe on my car recently and the sensor was nice and clean - just a light brown colouring on it.

Mined ewe, you're talking about a Ford. Does it use oil?

Si

Apparently so

Oh yes, not too smokey, but drinks it

I am surprised a clean or dirty oxygen sensor could make any difference. It is 'turned off' at cold start and during warming up anyway. The ECM then assumes a default O2 sensor output of 450mV and allows ad hoc matching of air and fuel mixture until the engine is warmed up to operating temperature of at least 60ºC. I assume the Fiesta runs fine once it's warmed up (so that the battery is resurrected every time!).

I would suggest something simple to do in the first instance: Clean the throttle body again, if "another sensor at bottom off carb" refers to just this one. Clean the Air Flow Sensor, or if you are not light fingered, replace it. They are at least both easy to do. Check the output signals in various operations from the Throttle Switch and the Throttle Potentiometer (Position) Sensor. All can be completed in an hour with a DVM. Disconnect the battery and reconnect to reset the ECM When you are in luck and the engine fires up eventually, take a long ride without a break (1 hr drive or 50 miles) of varying driving modes, town traffic, motorway, uphill...etc. to retrain the ECM. It is likely that its additional adaptive mapping (in coping with the worn out engine) is all but wrong and possibly you have spurious sensor readings logged in too producing grossly inappropriate ejector responses. That can explain why it is so difficult to cold start the engine, and quenching its thirst with a bit of petrol works. Do it soon for what you are doing at the moment is poisoning the catalytic converter.

There you go then. Check the breathers and o2 sensor regularly and hope it passes the hydrocarbon test next MOT! :)

Si

I believe the Mini also had an SU carb. and cat. for one or two years. I also heard it had a negative effect on performance.

Well, maybe there's some reason the fuel isn't getting up there, like air getting in through a poor fuel hose connection somewhere.

This is more likely to be a problem with a mechanical fuel pump up near the engine rather than with the electrical sort which is usually somewhere near the fuel tank.

If you take the spark plugs out and look at them after unsuccessfully cranking it for a while and they're /not/ covered in petrol, then fuel supply could be the problem.

If all the easy things are OK-- there's fuel and sparks and the spark is at the right time (it sounds like the spark side of things is probably OK), then you have to wonder if there's a mechanical problem with the engine itself, like low compression.

If you see oil on any of the spark plugs, that's a pretty clear sign of trouble. You really need a compression tester, but you can tell a certain amount just by taking the plugs out and putting your thumb carefully over each spark plug hole while someone turns over the engine on the starter; if one or two cylinders feel like they're puffing out the air a bit less vigorously than the others then you've got problems.

If the compression improves after putting a bit of oil in the cylinders, then it's probably rings-- the oil kind of helps them seal a bit better temporarily. If not, then it might be valves or head gasket, which are a bit easier to fix (but still quite a big job).