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I have bought a Mk1 Cabriolet that has been sitting for over a year. I am trying to get it road worthy.

So far so good, but I am having an issue with the engine and braking:

The engine stalls when I slow down, even a little. At first I thought this might be something to do with the brake booster vacuum hoses but the issue does not happen when I reverse and brake. In fact, I can reverse, lock up the wheels and the engines is happy. Nor could I find any indication of a vacuum leak - no whistling and all the hoses seem intact.

The engine idles, starts and accelerates fine and the brakes feel fine.

I'm not sure if its a petrol issue either. I've replaced the old petrol that was in the tank with new, fresh petrol and when the engine dies it just stops - doesnt sputter out like theres low fuel.

Would anyone know what could be causing this?

More info:

Model year is 1993, manual transmission. Engine is the 1.8lt, 8 valve, with the Bosch K-Jetronic injection system

I also tried slowing down and braking in neutral - the problem still occurs. Its almost like the loss of forward momentum triggers it.

VIDEO OF PROBLEM (turn up volume a little)

BETTER VIDEO

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Does it start right back up? –  Paulster2 Jun 29 at 18:25
    
@Paulster2 yes it does –  MeltingDog Jun 29 at 22:23
1  
I know what the issue is, but it's just not popping into my head. I have heard of this happening with other cars. I am thinking it has to do with the Idle Air Control (IAC) valve, but not sure. The reverse thing is throwing me off, that's for sure. –  Paulster2 Jun 29 at 23:00
    
@Paulster2 oh man if you remember anything else please let me know! Im stumped! –  MeltingDog Jun 29 at 23:57
    
Is this a manual? If so, does the stalling happen when you depress the clutch and slow down at the same time? –  Zaid Jul 2 at 20:10

3 Answers 3

Problems like this are addressed in Charles Probst's excellent reference, Bosch Fuel Injection & Engine Management.

From what I can gather, the Mk1 Golf utilizes a basic K-Jetronic system illustrated in the diagram below1 (which operates on the principle of continuous injection).

Continuous Injection System Schematic

The stalling symptom is an indication that the air-fuel mixture is not being metered correctly. Given that this happens on coast-down, it seems that the amount of fuel is not dialed back quickly when the throttle plate closes, resulting in too much fuel and not enough air, causing the engine to stall.

According to the troubleshooting guide, there could be many causes for this. Based on your symptoms, I would consider the following to be prime suspects:

  • Sticking/binding control plunger

    The plunger is what governs how much fuel goes to the injector from the fuel distributor. If it is sticking open, this would explain the symptoms you're experiencing during coast-down.

    Since the sensor plate is mechanically linked to the plunger, it is possible to test if either sensor plate or control plunger is binding by lifting the sensor plate to see if it offers resistance.

    It is possible to clean the control plunger in case it is sticking due to fuel residue/impurities.

  • Faulty fuel distributor

    As far as I can tell, there is no test outlined in the book that allows one to determine if it is at fault. If it is at fault, the only remedy is to replace it since it is calibrated when manufactured.


1 : http://www.spannerhead.com/2012/01/30/atomizing-fuel-continuous-injection/

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Good answer Zaid - definitely sounds plausible. The early Bosch FI systems are a little bit of a PITB. I hope this helps the OP. –  Paulster2 Jul 7 at 23:03
    
Wow lots of good info! Thanks heaps for this! With the plunger sticking, is this basically causing the engine to flood? –  MeltingDog Jul 8 at 0:32
1  
@Paulster2, one needs to remember that this technology comes from an era when it was considered a step up from carburetion; the K-basic systems didn't even need lambda sensors! As electronic controllers became more commonplace, the mechanical fuel distributor gave way to an electronic equivalent (KE-Jetronic, that's what the "E" stands for). Fascinating stuff, definitely not the usual run-of-the-mill question :) –  Zaid Jul 8 at 2:49
    
@MeltingDog, if by flooding you mean that the air-fuel mixture is too rich for ignition to take place then yes, that is the hypothesis. –  Zaid Jul 8 at 2:54
    
@Zaid ah thanks, yes that is what I meant. I also put a new video up the top that demonstrates the problem better. –  MeltingDog Jul 8 at 2:57
up vote 1 down vote accepted

I eventually found the issue: the fuel lifter pump was faulty. For those that dont know, the Mk1 has 2 fuel pumps - the main one underneath the car (or, on some variations, in the engine bay) and a 2nd 'lifter' or 'transfer' pump that sits inside the fuel tank and can be accessed by removing the rear seat. This 2nd pump's bearing were gone. The primary pump had enough power to run the car but I guess the g-force under braking overrided the fuel pressure provided by the single pump.

Anyway, replaced the lifter pump and all is well.

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Anything from OBDC? Sometimes it will record a pending fault that will not light up the "Check Engine" light. If you don't have an OBDC reader, most parts stored will read it for you. Check the Idle Air Control Valve by disconnecting the air hose going into it and plugging the hose. If it stops stalling, that's the problem, try removing the IAC assembly and cleaning.
If it still stalls, reconnect the IAC hose and clean out the air intake pathway, check air filter, etc. Clean the throttle body with intake cleaner, including the flaps/springs/etc. Clean the Mass Air Flow sensor with MAF cleaner (that is very sensitive to the solvents, make sure you are using real MAF cleaner) If it still stalls, check fuel filter, replace if it hasn't been replaced in your maintenance window. If it still stalls, it could be transmission sensors (if auto-tranny), load sensors, etc.

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Thanks heaps for these suggestions. Sadly, there no ports for an OBD device - it basically uses the same engine as a mark 1. This might be a dumb question but do you know where I could find the IAC valve? I have workshop manuals but they actually make no mention of it. –  MeltingDog Jul 7 at 0:24
    
The car has no MAF's –  Zaid Jul 8 at 3:12
    
@Zaid ... The car has no electronic MAF as we know them today. It does have a sensor which measures the amount of air flowing into the engine. In the image you posted above, it's labeled the Air Flow Sensor. –  Paulster2 Jul 8 at 10:34
    
@Paulster2 : You're right, my earlier comment was referring to hot-wire MAF's which this answer was alluding to. –  Zaid Jul 8 at 10:43
    
@Paulster2 : I believe the air-flow sensor on the car is closer to a volumetric air-flow sensor than mass air-flow since I don't see any temperature correction taking place here. –  Zaid Jul 8 at 10:50

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