Engine stops when braking

[adurer]

Hello to you,

I am registered now and I need your help.

My problem is this: with car stationary and engine idling, if I depress the brake pedal several times in a rapid succession, the engine will stall. Everything is fine under normal driving conditions, the brakes are strong, braking is easy exactly as it should.

I could not find anywhere a reasonable explanation and cause of this problem.

Can you help, please?

Thanks.

[fordfan]

The cause is likely to be low vacuum in the inlet manifold, primarily caused by using the brakes. However, using the brakes should only cause the engine speed to drop, so you may have an additional vacuum leak or the engine idling speed isn't high enough.

[adurer]

I've attached a vacuum gauge to PCV hose. Idle speed is steady at 800 rpm, vacuum needle is in the green zone (500 mm Hg or -670 mBar). The moment I pump the brake pedal quickly 5-6 times, vacuum is indeed totally destroyed. But HOW it is destroyed so severely so quickly, yet having normal braking when driving, beats me. I want to understand what is faulty and how things happen step by step before buying parts. What more tests should I do?

Edited 9 August, 2012 by adurer

[Phil-E]

I had a similar fault on mine.

I cured it by doing a few things as they all needed doing anyway.

Changed spark plugs, ignition leads (had corrosion on some of them), distributor cap (rotar arm and points were worn down), cleaned and reset throttle body, air filter, oil, oil filter and set valve clearances. I also changed the temperature sensor and thermostat.

I think I also had a vacuum leak somewhere but can't remember where it was. Think this was the main cause of the problems.

Phil

[djaychela]

The brakes use the vacuum from the inlet manifold to provide servo assistance, so although it may be enough to destroy the vacuum the servo may still have enough to allow the brakes to be assisted properly (although if you pumped them a few times they would probably not). My injection felicia used to suffer from this a bit, but it was a faulty non-return valve in the pipe to the servo; when I changed the pipe the problem stopped.

As your car has no injection, it may mean there is some servicing needed - the injection cars can deal with the situation better as they can regulate the tickover of the engine better, with the ECU able to open the throttle to keep the engine running. A non-injection car doesn't have this ability, so if it is borderline then it would be more likely to stall, I would think. Part of the problem here is that very few UK felicias were non-injection (if any, I don't know for sure), so it's unlikely someone here will have had the exact same fault.

[Phil-E]

My injection felicia used to suffer from this a bit, but it was a faulty non-return valve in the pipe to the servo; when I changed the pipe the problem stopped.

Ah yes. That's the pipe I had to replace. My valve had also gone faulty.

Phil

[KenONeill]

Ok, it wasn't on a Felicia, but I've seen a faulty vacumn non-return valve cause stalling on a carburettor engine before too.

Phil's service items can't do any harm, and if it's been a while since they were last done will make the car run better anyway.

Edited 9 August, 2012 by KenONeill

[Phil-E]

My old 1.0l Polo Coupe had the exact same fault too.

Phil

[adurer]

I see that I must go buy a new hose with the 1-way valve.

Here I have a photo of power brake system from Britannica encyclopedia.

Can you explain to me why the bad valve kills the engine, please?

Because I took that hose out and if I blow from booster side, air goes freely, but if I blow from manifold side, air can't pass.

[adurer]

Problem solved with all of you help and some chance.

Having the cause narrowed to 1-way valve (check valve?) I looked closer at that elbow rubber hose coming out of manifold (see photo below) and I saw a long veeeery thin crack on the firewall side (hardest to see). When The hose was pushed with my finger, the crack got bigger, splitting open.

So I guess that when I pumped the pedal, the hose was flexing largely enough for atmospheric pressure to push in and destroy all vacuum thus stalling the engine.

I've put a new rubber hose and now everything is ok. Of course, idle speed drops to almost 700 rpm under heavy pumping, but that's normal for a car without computer under such heavy braking load.

Thank you all and sorry for my English, I am very excited that my problem was solved.

[djaychela]

No worries, glad you got it sorted.

Your English is way better than my Polish!

[KenONeill]

As djaychela says, your English is considerably better than our Polish.

{meanwhile, back at the point}

The split vacumn hose was drawing air into the engine, causing the mixture to get leaner (increasing the ratio of air to fuel), and that alone could cause the engine to die. To make matters worse, when you're on low throttle it could reduce the amount of fuel being mixed into the air i nthe carburettor as well.

[Guest masster]

what is the new hose made from?

Edited 10 August, 2012 by masster

[adurer]

The 'cooked' rubber hose had an almost invisible crack at rest. That was an insidious (?) elbow hose.

One month prior, idle speed was set at 800 rpm and mixture screw was set using an exhaust analyzer at a local MOT facility, then a plastic seal was applied to it. Ignition system was checked with a spark voltage tester (an oscilloscope that shows all 4 HV signals at once)

They made a great job, my engine runs smoothly, fuel consumption is 5.7 l/100 km at steady 100 km/h, 9 l/100 km in city on those very hot days.

So that's why I believe the crack was minor when brakes were not applied.. Only when pumping the brake pedal, I think the crack behaved like a heart valve causing large vacuum leaks.

@masster

The hose was replaced for now with a strong heat resistant acetylene hose. I don't know where to find a similar elbow capable to resist to manifold heat for a long time.

Edited 10 August, 2012 by adurer