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Pierburg 2E2 fault finder and overview - rough draft (LONG!)

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Chris Mancuska Message 1 of 1 , Dec 23, 2002

Hi all,

here's a rough draft of my setup guide for the 2E2 carb - can you check it for sillies, etc...... I'm going to take a load of underbonnet pictures to back it up and stick it up on the web somewhere.

THE PIERBURG 2E2

Introduction.

This is an overview and common fault finding guide for the Pierburg 2E2 carburettor, commonly fitted to Pre 1991 1.6 and 1.8 engined VW models, such as the Golf, Jetta, Passat etc. All references to left and right are as for a person looking at the engine bay from the front of the car - the battery is therefore on the right.

This carb has a reputation for being difficult to set up, and for being unreliable in use, and is frequently replaced by Weber carbs of a similar size. This carb IS complicated, with 6 electrical attachments and 7 vacuum connections, plus being plumbed into the engine cooling system of the car - but there are only 4 systems that can actually go wrong in normal use - this guide is designed to let you decide whether your carb really is worn, or just set up incorrectly, as I believe the reputation for premature wear is groundless, and stems from inexpert fiddling.

Part 1 - The Mistake in the Haynes manual and on the bonnet diagram.

On the inlet manifold, there is a vacuum supply to the advance retard mechanism, brakes, the choke pulldown unit and the (carb) three point unit. Part of the system consists of a vacuum store (a green globe) and two non return valves, which look like inline fuel filters, and are half black, half yellow. One of these is usually fitted the wrong way round, because of a series of mistakes by VAG and Haynes.

Follow the vacuum pipe from the green vacuum store, to a t piece that goes into the carb, and then to a non return valve. The YELLOW end should point towards the vacuum store, not (as shown in Haynes and on the underbonnet diagram) the black side.

A symptom of this is the choke pulldown unit not working, the idle being very low when the car is cold, poor performance when the engine is cold, constant stalling when cold, etc etc....

Go outside and FIX THIS NOW - it's free and takes an instant.

Part 2 - Airbox and associated plumbing.

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The standard intake system helps prevent carb icing on cold damp days - you may want to experiment with non standard intakes in a quest for more power, but I'd keep the standard one somewhere, for when temperatures drop below 10 degrees C.

The airbox is vertically split in line with the air filter. The rear of the airbox is clipped to the top of the carb, and the front is bolted to a mount which is in turn secured to the engine using some of the front camshaft cover studs.

Just behind the air filter, on the inside left of the airbox is a thermovacuum control device (TCD) This device has two attachments for vacuum hoses on one face (sticking out of the airbox via two small holes) and a brass heatsink

on the opposite face. The function of this device (one of two on the induction system) is simple - when the air as sampled by the heatsink is less than approximately 17 degrees C, the two vacuum hoses are linked, and air can flow from one vacuum hose to the other. Between 17 and 20 Degrees C (sampled inside the airbox in this case) the device starts to close the link between the hoses, and above 20 degrees C the hoses are isolated.

The hoses attached to this device:

1) A BLACK tube (3.5mm diameter) travels down the inlet tube away from the airbox to the mixer unit - it attaches to a vacuum controlled flap in this unit.

2) A CLEAR tube (again 3.5 mm diameter) loops round the LHS of the carb and is attached at the rear of the carb, low down.

The mixer unit has two air intakes - one from the front of the engine compartment (cold air) and one from a heat exchanger bolted to the exhaust manifold (hot air) via a 50mm flexible metal foil connecting pipe

The function of the TCD in the airbox, the vacuum supplied from the carb attachment and the vacuum controlled flap in the mixer are to try to make the temperature of the air entering the airbox between 17 and 20 degrees C at all times (unless ambient air temperature exceed this obviously).

The only moving parts in this system are

1). The vacuum controlled flap in the mixer (detach the airbox end of the vacum tube and suck on it - the flap should be heard moving inside the mixer unit) The mixer casing can be split and the internals freed up if need be.

2). The TCD - stick it in the freezer for 20 mins - you should be able to blow through the tubes, and then warm it up - the tubes should become isolated.

Symptoms of problems with the Airbox and associated plumbing:

Travelling on the motorway at a steady speed, the car will falter and stumble, possibly to a standstill - after waiting for a few minutes, you can drive off as if nothing had happened. This is carb icing and will occur most often on cool damp foggy days. Some cars suffer, some don't when the airbox is modified......

Part 3 - Hot water and it's function There are three outlets on the head for hot water to escape - One (RHS of block) is for hot water supply to the heater, one (Front of block) is the main thermostatically controlled route to either back to the bottom of the block or to the radiator.

The third outlet is at the rear of the head, and supplies hot water to the inlet manifold, the automatic choke mechanism and then to the expansion element, and then back to a T piece in the heater return hose, and back to the bottom of the block - this is the outlet we are interested in.

In many of the 2E2 equipped cars I've so far seen, this hot water supply is blocked by a swelled gromit between the head and the inlet manifold. This basically means the choke will never heat up, and never turn off.

This gromit seems to fail after the engine has been allowed to run low on coolant - which would probably make sense to a lot of owners who had problems with the heater matix a few years ago......

To check this pipe for blockage - run car until temperature gauge is at normal operating temperature, and test the temperature of the autochoke casing - the aluminium tubular casing on the RHS of the carb with two water hose

attachments, one hose coming from the inlet manifold. This casing should be scalding hot - too hot to touch for more than a second. If not - then you have a blockage.

A new manifold gasket is £6 from VAG, and the gromit is £1.52, but the job of replacing them is quite lengthy, and dirty - most cars with failed gromits will also have had a failed camshaft cover gasket too, so the engine will be filthy.

You will need a 1/4 inch driver set, a 6mm Allen key and a 6mm allen key bit for the driver. Tape the extensions and sockets etc together so you don't lose tools between the exhaust and inlet manifolds, and use a mirror and a torch to find the 6 bolts securing the manifold to the head. The carb does not need to be removed from the manifold for manifold removal.

For replacement, temporarily glue the bolts into the the manifold holes using silicon sealant or similar, and stick the new gasket to the manifold using a very thin film of instant gasket. Get the manifold in the approximate correct position and attach it to the head using the far left and right bolts - this makes all the bolt holes horizontal so the chance of losing a bolt in between the manifolds is minimised.

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the chance of losing a bolt in between the manifolds is minimised.

Use the mirror and torch trick to tighten the bolts - you will find number 4 from the left particularly difficult to get a tool on (and even to see!)

To set the auto choke, run car (with the airbox off) till the temperature needle is just out of the white cold engine zone. Loosen the three autochoke mounting bolts and rotate the unit until the choke flap in the carb just goes totally vertical. Job done!

Part 4 - The infamous (and non existant) Waxstat or expansion element.

This thing gets so much stick!

Description:

This is a temperature dependant plunger mechanism, mounted to the front of the carb just to the right of centre. It has a hot water supply from the thermochoke unit and returns water to the return pipe for the heater via a t-piece.

As the temperature of the unit rises, a plunger extends into the choke body and presses against a lever mounted on the end of a shaft, which turns and moves a cam that the idle stop rests on, visible on the RHS/ front of the carb, to the left of the throttle cable attachment.

When the unit cools a spring moves the cam back to the cold (fast idle) position - you are supposed to help this by pushing the accellerator once before starting the car.

Basically they cost 41 quid and last 40000 miles.

After you have corrected the non-return valve error in the vacuum supply to the choke pulldown unit, you will probably find that your car now ticks over fast when cold. If this does not slow down when warm (and you've unblocked the hot water supply from the inlet manifold so the choke works etc) then you now need to purchase a new expansion element and stick it on.

There is a small screw for adusting the cam position on the shaft located to the left and towards the front of the car, of the throttle cable attachment - the stop should just be held off the cam by the three point unit when the engine is fully warm.

Part 5 - Electrical connections.

There are many. Basically there are three heaters, a fuel cut off solenoid, a temperature time device (whatever!) and other bits, depending on what model your car is. As long as the connectors are clean and the carb well earthed, you will never get any problems. Promise.

Even when they do malfunction, with the exception of the fuel cut off valve, you would be hard pressed to notice, but: -

Here are a couple of checks for the paranoid:

1), When the ignition is turned on, an audible click should be made by the carb. (Fuel cut off)

2). When ignition is turned on, engine cold and not running, the choke flap should move slightly all by itself. (Thermochoke heater element)

3). The inlet manifold heater can only be checked if you remove the manifold - it's accessed from the underside of the inlet manifold so is inaccessible in situ, but the part throttle channel heater (front LHS of the carb) can be removed and checked easily.

4). Get out more - seriously. You are spending far too much time on this car.

Summary of Checks:

Before throwing away the 2E2, do the following:

1). Standardise and repair all air inlet hoses, make sure TCD on airbox works, check and replace all split or loose vacuum control hoses, check flap in air mixer for movement.

3.5mm internal diameter fuel hose is perfect for replacement vacuum hoses, and 50mm metal foil ducting is what you need to replace the hot air duct if needed.

2). Turn the non return valve on the line to the vacuum store around so the yellow end faces the store. (Opposite to bonnet diagram!)

3). Check hot water supply to carb really is hot. Will need to remove manifold and replace gromit and gasket if not.

4). Set autochoke so it goes off at the right temperature.

5). Check expansion element for correct operation as engine warms (tickover should drop)

6). Check and clean/replace electrical connections, etc.

Overview of carb operation.

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Starting:

On initial starting the choke flap is almost fully closed. After a few seconds the choke pulldown unit opens the choke slightly so the engine does not strangle. The waxstat or more properly the expansion element is holding the throttle slightly open, resulting in a high tickover speed.

As the engine warms, the hot water flowing round the autochoke body, helped by a little heater element (After 1985!) built into the autochoke warms a long spring which expands and starts to open the choke flap.

Meanwhile the expansion element is pushng the throttle stop cam round, so the throttle is closing, so the tickover steadily drops.

If the tickover drops too low, the three point unit (four point if you've got air con!) moves another throttle stop to open the throttle slightly. The same unit compensates for air conditioning, drag from automatic gearboxes, etc,

and stops the engine stalling while on tickover. The unit also cuts off fuel to the idle jets when the car is on the overrun, to prevent unburned fuel being dragged though a possibly fitted catalytic converter.

When the car is fully warm, the idle should be controlled by the three point unit - it should be off the throttle stop provided by the expansion element cam.

Common Symptoms.

(Turn that one way valve round first - it masks loads of symptoms)

High tickover when hot

1). Waxstat (expansion element) broken.

2). Inlet manifold water feed blocked. (expansion element not expanding because it is not being heated).

Stuttering on part throttle at speed.

1). Carb icing due to air mixer malfunction, or ducts missing.

2). Inlet manifold water feed blocked (choke still on)

Ridiculous fuel consumption, smell of petrol outside (particularly after reversing)

1). Thermochoke broken (never seen a broken one!) OR

2). Inlet manifold water feed blocked (again!).

Backfires on overrrun, stalling etc.

1). Three or four point unit broken - VERY rare, good job because they are 150 quid!

2). Air leak after carb - flexible mounting can perish......

Any other problems:

You haven't turned that one way valve round yet, so you don't know!

Copyright Chris Mancuska 2002 - All parts of this document can be freely distributed, as long as the authors name stays attachedto the work.