Hello guys!

Currently own 54 plate Fiesta Zetec S with 1.6 petrol engine.

Writing here hoping someone will lead me to a cause of the stalling issue. Hoping to fix it without chucking too much money and avoiding garage charges etc.

Now the issue is exactly that:
Whenever driving in 5th gear and breaking (not a gentle braking) with clutch DOWN the engine stalls after a while (with all the lights flashing on the dash and power steering doesn't work as well), but then on releasing the clutch pedal it jump-starts again with no problem.
I've tried different things in hoping that this will take care of it but to no avail:
1. Changed PCV hose and PCV valve replaced by new ones (although the old hose wasn't visibly split and old valve had still rattling ball inside of it)
2. Throttle body was taken out and thoroughly cleaned (wasn't too bad as well tbh)
3. Took out the T-MAP sensor and cleaned it as well.
4. Flushed the PAS fluid and replaced with a fresh one (initially I thought that the problem is with power steering because at that point I didn't know that the engine is stalling)
5. Fuel filter and spark plugs were changed during major service in December last year.

Now, I do not know what to do next, and were to look.
I'm coping with this issue for over a year now, it didn't really bother me because I just made a habit of breaking without depressing the clutch pedal until the speed drops to around 40-35mph and then it's absolutely safe to do it because it won't stall. It also won't stall on any other gear (1-4) - although I think the problem is with the speed rapidly dropping from 60mph, not the gear selected. It also won't stall if breaking without hammering the brake pedal (ie "gently").
The reason why I want to fix it is because I'm planning to sell my car this year and do not want for anybody to inherit this problem, because it could be dangerous for the person not knowing about it (no PAS etc). Also it's quite irritating because once in a while I forget and depress the clutch pedal before the roundabout approach etc and loose all the power steering and have to release the clucth pedal to jump start the engine again.  

I was thinking about doing next steps as:
1. Put in the new T-MAP sensor?
2. Put in the new sensor which is attached to a throttle body (sorry don't know the name of it)?
3. New coil pack with leads?
4. Investigate possible vacuum leak?
5. Do not waste money on unnecessary parts and take the car to a garage? 

Now, couple notes to add:
- Car never had a problem starting cold/hot, the idle is spot on (around 1100 cold, 7-800 warm) and not jumping.
- When watching the revs during "stalling procedure" - driving 60mph + clutch down + brakes down - revs drop to around 700rpm then after couple seconds they drop to 500rpm - then almost instantly - 0rpm and engine stalled.

Thank you for any info you might have!
 

3 hours ago, AlexGnok said:

driving in 5th gear and breaking (not a gentle braking) with clutch DOWN the engine stalls after a while

On a petrol engine, the manifold vacuum operates the brake servo. A faulty valve in the servo could, when braking, allow so much air in that the engine stalls. If the fault only and always happens under heavy braking, then this is almost the only link.

It should be possible to test this while idling stationary, by jamming the brakes on hard.

Another test is that after stopping the engine, you should get 2 to 5 actuations of the brake before the servo runs out of vacuum (so to speak), and the pedal gets very hard.

7 minutes ago, Tdci-Peter said:

If the fault only and always happens under heavy braking, then this is almost the only link.

Thank you, I'll investigate it.

But, thinking about it - if i don't depress the clutch pedal, I can brake in any way I want, really harshly (almost emergency stop) braking.

But I'll give it a try when stationery and idling and see what it does.

4 hours ago, AlexGnok said:

if i don't depress the clutch pedal, I can brake in any way I want,

With the clutch engaged, and in gear, it is not possible to stall. Excess air does not matter then as the fuel is cut-off, since the engine is in over-drive (being driven by the wheels, not by its fuel). So I could be wrong (not the 1st time!), but this seems to be pointing to stalling due to excess air, rather than some odd electrical/electronic/software problem.

It is always a worry on modern cars that odd symptoms arise because of some sort of wiring problem or software glitch! Sometimes I wish for the simplicity of the earlier cars I had, with no electronics whatsoever. But, in reality, carbs had some quite complex problems, and those old cars did not give 100+ HP combined with 54MPG on a decent run, that I just got with my current Focus.

12 hours ago, Tdci-Peter said:

It should be possible to test this while idling stationary, by jamming the brakes on hard.

Another test is that after stopping the engine, you should get 2 to 5 actuations of the brake before the servo runs out of vacuum (so to speak), and the pedal gets very hard.

Just tried it this morning. 

No matter what I  do with the brakes while car is idling, it does not affect the engine. 

And when the engine is off it takes around 7 "pumps" of brake pedal to make it almost rock hard. Is it supposed to be like that? 

Any more ideas what should I check? 

3 hours ago, AlexGnok said:

No matter what I  do with the brakes while car is idling, it does not affect the engine. 

And when the engine is off it takes around 7 "pumps" of brake pedal to make it almost rock hard. Is it supposed to be like that? 

That is good news in a way. Changing the brake servo is a pig of a job, it usually means emptying and re-filling the a/c system. With the braking system in good condition, and no air in the hydraulic system, there is little movement of the master cylinder, so the vacuum "stored" in the servo will last for more brake pumps. So that sounds good, also.

I have read through the quite comprehensive initial report you gave, again. I don't have a clear simple answer!

The only other link I can think of between heavy braking and the engine, apart from the servo, is the pressure in the fuel lines due to the G forces. The fuel return line back to the tank will be positively pressurised. Maybe some minor fault in the fuel rail regulator or pump could give fuel starvation under sustained G force due to deceleration.

I would use a Ford specific diagnostic system like Forscan to hunt for any error codes, that might give a clue. Unfortunately, Ford do not usually fit pressure sensors to petrol injection systems, so fuel pressure problems can be hard to diagnose.

With regard to selling the car, if it was going to a dealer, I would not worry at all. Many cars are handed to dealers with much worse faults. If a private sale, then if the prospective driver took it for a test, it is likely to soon be apparent if they tend to do clutch down braking. I have a feeling that driving instructors teach that the car should be kept in gear with clutch engaged for as long as possible, only using neutral or de-clutched at low speed, for that very reason. And some car handbooks also say the same thing, I believe. I tend to coast in neutral for shortish distances where junctions are too close together to be worth changing up, but do have a slight guilty feeling about what an instructor would say if he was watching me! My lessons were a very, very long time ago now.

6 hours ago, Tdci-Peter said:

That is good news in a way. Changing the brake servo is a pig of a job, it usually means emptying and re-filling the a/c system.

AC doesn't work anyway ) Tried to get it regassed at halfrods this summer, but they couldn't do it. They recharged it, but I haven't paid for it because it didn't work in the end. The couldn't tell why, which was no surprise for me.

6 hours ago, Tdci-Peter said:

The only other link I can think of between heavy braking and the engine, apart from the servo, is the pressure in the fuel lines due to the G forces. The fuel return line back to the tank will be positively pressurised. Maybe some minor fault in the fuel rail regulator or pump could give fuel starvation under sustained G force due to deceleration.

I would use a Ford specific diagnostic system like Forscan to hunt for any error codes, that might give a clue. Unfortunately, Ford do not usually fit pressure sensors to petrol injection systems, so fuel pressure problems can be hard to diagnose.

Yeah, it could easily be some fuel issue. I was thinking about clogged injectors etc but my thought didn't go as far for fuel rail or fuel pump )

Probably will try and use some kind of scanning tool hooked up to my phone.

What about pressure sensors and stuff like that in Ford's next generation? I was looking to buy Ford MK7 ST as my next car. 

6 hours ago, Tdci-Peter said:

With regard to selling the car, if it was going to a dealer, I would not worry at all. Many cars are handed to dealers with much worse faults. If a private sale, then if the prospective driver took it for a test, it is likely to soon be apparent if they tend to do clutch down braking.

Never thought about part exchange to be honest, don't know why. Are they not checking the vehicle before taking it from you? 

This car is cheap anyway, so even without them checking, they would probably give me around 300£ I guess (that's what Autotrader shows me for part ex, and around 900£ with private sale).

Definitely will not be selling privately without telling about issue in advert. I'm just not kind a person like that (pointing at the previous owner who sold me this car without telling a word about it) 😆

It will either go cheap with mentioning the issue, or part exchange it, or keep it and then scrap it. Still am hoping to fix it though 🙄

6 hours ago, Tdci-Peter said:

I have a feeling that driving instructors teach that the car should be kept in gear with clutch engaged for as long as possible, only using neutral or de-clutched at low speed, for that very reason. And some car handbooks also say the same thing, I believe.

I'm in UK not too long, didn't have the driving license so last year had to take the test. And my driving instructor told me right away: "When braking - clutch down all the time, remember that". So that's what I was doing. Now, driving my car I realise that it's not the best idea, because you're having less control over the car and putting more strain on your brakes by eliminating engine braking.

6 hours ago, Tdci-Peter said:

I tend to coast in neutral for shortish distances where junctions are too close together to be worth changing up, but do have a slight guilty feeling about what an instructor would say if he was watching me! My lessons were a very, very long time ago now.

That's what I am doing as well, from time to time. During test it would be bad though, marked under the "control: clutch" section because of the coasting ))

34 minutes ago, AlexGnok said:

What about pressure sensors and stuff like that in Ford's next generation? I was looking to buy Ford MK7 ST as my next car. 

As far as I can tell, the conventional petrol engines (1.6 tivct, 1.8) do not have fuel rail pressure sensors, not on the mk3 Focus anyway, which is relatively up to date.

All common rail diesels (eg TDCI) will have a sensor, and as far as I can see, all the GDI (gasoline direct injected, or Ecoboost) engines will have this sensor.

I had a quick look on the internet about clutch use during braking, there was some discussion, but the consensus seemed to be to only put the clutch in to change gear, or when the rpm dropped near to stalling point.

Some sites claimed that putting the clutch in saved fuel! This has been complete nonsense since carburetor engines became obsolete. All electronically controlled injection engines (petrol or diesel) will turn the fuel off completely in over-run. In fact, the engine uses more fuel if coasting in neutral, or with the clutch down, as it has to idle.

The most authoritative looking site (never can be 100% sure of anything on the 'net!) was this one:

https://www.drivingtesttips.biz/what-is-coasting.html

For a scanning tool, have a look at: https://tunnelrat-electronics.fwscart.com/

And for the software needed, look at: http://forscan.org/download.html

This is a dedicated Ford system that will find any codes that exist. It also allows live logging of data. It would be possible to log a stall during braking, but I am not confident that the log data will give a helpful result, cause and effect are very difficult to distinguish sometimes.

 

5 minutes ago, Tdci-Peter said:

For a scanning tool, have a look at: https://tunnelrat-electronics.fwscart.com/

And for the software needed, look at: http://forscan.org/download.html

This is a dedicated Ford system that will find any codes that exist. It also allows live logging of data. It would be possible to log a stall during braking, but I am not confident that the log data will give a helpful result, cause and effect are very difficult to distinguish sometimes.

 

Thank you, will definitely have a look!