Hi all, so I've had my mk1.5 Focus 1.8 petrol for a few weeks now and as of last night it has developed a problem.

When the engine gets up to normal operating temp(half way indicated on the temp gauge) it starts to loose power and will not rev. Sometimes it cuts out altogether sometimes it will continue to idle, but will not rev.

If you leave it for a few minutes it will run again, but only for a couple of miles and then back to this.

The longer you leave it not running, the longer it drives as normal until it starts again.

Other info, not sure of its relevance;

No EML, when's diagnostic scanner is plugged in its showing no faults either, but it is only a basic scanner.

Fuel level is just below a qtr of a tank.

Before this there was an intermittent fault of p0133, slow response O2 sensor bank 1 Sensor 1.

Can anyone offer any help?

That fault could be fuel pressure meanin new pump,map sensor or possible intake leak I would be betting on fuel pump if u can get pressure check should be 3.8 bar

I had a tiny thought in my head it could be that, but then quickly put it outta my head!

Fairly expensive I'd imagine?

Is there such a thing as a fuel pressure tester or how would I check the pressure?

Oh, I'm guessing it would need to be tested whilst the problem is occurring?

U can buy I pressure tester but doubt they cheap test is pretty easy do to car pumps not cheap for genuine but u can get cheaper ones

A friend of mine has a snap on scanner and is going to check the live data for the fuel pressure :)

Anyone else have any further ideas?

Have u checked anything yet to rule out stuff

Had a look round the intake area and the fuel hoses at the engine, but nothing obvious

all the symptoms you have given point to an exhaust blockage

It has a full s/steel system except for the cat, seems to be good pressure from the tail pipe?

I had a mk1 1.8 Mondeo that had a blocked cat and it was different as in it had no power at all, neither warm nor cold

is that a new system, or old

not saying this is your problem, but the symptoms perfectly match a blocked exhaust

Ah right, the system has been on the car for a while, a few years as far as I am aware

unless new, the fact its stainless is immaterial, blockages will be internal.

gasses are escaping, but not fully, hence why car runs ok when cold, as engine warms up the pressure builds up to the point its creating back pressure, when thatr happens, car loses power to the point it doesnt rev or dies.

leave the car for a few minutes, some of that pressure gradually releases...hence you can then drive a short distance before problem recurs...longer you leave the car, further you will get.

the code that was flagging previously was an early sign of the problem

most common areas of blockages is the cat or the rear silencer...though blockages can occur anywhere in the system

if the cat has broken up, it can send pieces further down the system so it may even be blocked in the pipework between silencers.

by the way...blocked/collapsed cats dont always give themselves away with the rattling

That sounds logical enough! Will start removing it bit by bit from the rear then :)

Oh, just thought, sometimes when trying to get the car to rev there would be the odd backfire, could this happen with a blocked exhaust?

Yes definitely I think Wase right say ur cat stuffed an backfire dead give away ouch not cheap fix

The only thing that bugs me about this theory is if it was blocked to that extent, why would it still tick over at normal idle speed? Surely if the engine was being choked that much it would die altogether?

This is her on tick over at cold:

Just checked the vacuum hose from the manifold to under the coil pack and yes it is closed over, but opens under throttle

We'll u did say at times it can cut out so it not completely blocked but more u drive it will just keep gettin worse like has it just been gettin worse over last few months

Like anything, the less work the easier it is!

So when you sit at idle, the car is ticking over, no real pressure going in or out, just enough to keep it ticking. Then as you run the car, the more revs, the more work the car does, the more work, the more pressure of combustion and exhaust gasses going out. Your then creating a bottle neck effect!

Imagine this. You get on a bus, everyone casually walks on or off as they see fit. No pressure, everyone moves, no bottle neck. now, set one of the seats on fire. All of a sudden you have increased the pressure, everyone is running to the door trying to get off the bus before you all cook. All of a sudden there is a bottleneck and no one can get out.

This is pretty much whats happening it seems!

Easy to test for

All you need to do is remove the front sensor, keep the electrics connected and tie it up out of harm's way...

Way I would do it, is loosen the sensor then just nip it back up...take for run till symptoms develop, when still hot taking the necessary precautions, remove the sensor but keep it plugged in, tie it out the way and run again, if power returns you have a blocked exhaust.

Be warned though, doing this makes exhaust a tad noisy :)

Just back from my local mechanics who plugged I his snap on diagnostic computer and it was the no1 o2 sensor :)

very unusual symptoms of just a bad 02 srensor (though suggestion earlier you found split in vacuum hose too, so the combined might give something like your experiencing)

be interested to know if this has cured all the problems, not easy diagnosing over www, can only be suggestions...but those symptoms you originally typed scream a blockage in exhaust, a blockage will damage 02 sensors so i would take this for a long test run because if it does turn out to be a blockage, you could ruin the new sensor if not dealt with sooner rather than later.