brake related running problem? wierd | Technical matters | Back Room Forum

Sat 1 Jul 2006 19:57

brake related running problem? wierd - steveo3002

car is a 1989 16v golf k jet

wierd one this...i had a leaky brake pipe fitting, so i was sat in the car with it idleing and repeatedly pressing the brake pedal to see if i could make it leak again

anyway as i pressed the pedal on/off a few times the engine began to splutter and carried on doing so until i stopped pressing the pedal...i let the engine clear and then braked again same thing happened

cant really figure out whats happening there...some kind of vacumn problem? otherwise the car runs and brakes fine

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Sat 1 Jul 2006 21:03

brake related running problem? wierd - Armitage Shanks {p}

Weird! Sounds like something to do with the servo ie a leak is that is unbalancing air flow to the engine, making it weak or rich and upsetting the running.

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Sat 1 Jul 2006 21:20

brake related running problem? wierd - Aprilia

If you're repeatedly prodding the brake pedal then you will be reducing the inlet manifold vacuum ( the inlet manifold vacuum is what 'powers' the servo). If just one push on the pedal causes problems then you may have a servo fault or a faulty valve in the servo vacuum hose.

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Sat 1 Jul 2006 21:46

brake related running problem? wierd - steveo3002

aprilla ...are you suggesting it may be normal if i repeatedly press the brake?? i was pressing it alot , but didnt expect it to affect the running

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Sat 1 Jul 2006 21:50

brake related running problem? wierd - Dynamic Dave

Aprillia is correct.

Basically you affected the air / fuel mixure by taking extra air from the manifold to replenish the vacuum in the servo by repeatedly pressing the brake pedal.

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Sat 1 Jul 2006 22:01

brake related running problem? wierd - Altea Ego

yes if you pump the pedal repeatedly on most cars at tickover the revs drop and go a bit screwy;
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TourVanMan TM < Ex RF >

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Sat 1 Jul 2006 22:08

brake related running problem? wierd - Number_Cruncher

>>Basically you affected the air / fuel mixure by taking extra air from the manifold to replenish the vacuum in the servo by repeatedly pressing the brake pedal.

[Pedant Alert!]

Yes, but the flow of air is in the opposite direction. Air enters the servo via a little sponge filter that surrounds the brake pushrod, and, eventually, end up entering the inlet manifold.

[ / Pedant Alert!]

This extra air reduces the inlet manifold vacuum, *and* by-passes the air flow meter, so the K Jetronic system knows nothing about it - so the mixture is weakened.

If the pedal is pressed and held, there shouldn't be any constant flow of air through the servo, just a slug of air for each instance the pedal is pressed.

Number_Cruncher

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Sat 1 Jul 2006 22:30

brake related running problem? wierd - Aprilia

Very comprehensively and accurately explained, N_C !

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Sat 1 Jul 2006 23:12

brake related running problem? wierd - steveo3002

cheers lads....was woried id have spend even more £££££ for a minute

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Sun 2 Jul 2006 01:22

brake related running problem? wierd - Dynamic Dave