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Wrong.

The accumulator is not the CPR.

The CPR is mounted at the engine and regulates the regulating pressure which gives feedback to the fuelpressure regulator within the fueldistribitor.

The accumulator is mounted at the fuelpump and must be seen as a device which holds the fuelpressure in the system when the engine is stopped. Like a pressurebuffer.

Thanks Peter,

Can you tell me where the CPR is located? Think I read somewhere that the intake has to come off to remove it?

When you have the fueldistributor three black fuellines are located. One is going under the intakemanifold (coldstart injector) the other two are going towards the CPR. This one is located next to the ignition and under the thermostat housing.

It's on the block just above the ign distributor. Looks like this:

Thanks! You guys are just great

Wonder if it can be bought new original? Found it at W&N but would rather not buy anything from them again:

http://www.wallothnesch.com/warmlaufgeb ... 12-24.html

You must look if you have the one with only the fuellines and electricconnection or also additional a vacuumline attached.

The picture of W&N is the one with vacuumline and the picture in the post is the one without.

The dealer is asking around 500 euro for it.

They foul internally. As far as I know the E21 always needs one with the vacuum line.I think I have an overhauled example for you. Perhaps we can think of some kind of trade hehehe

They're fairly easy to strip down and check, I did it with the one on my Golf GTI:


Took about 5 minutes to strip it down to its component bits:



The casing and seal:








The feed and return pipes feed into this block, which has a diaphragm that's acted on by a fixed rate spring, but assisted by an electrically heated bi-metalic spring:



Regulator block:




The diaphragm:



End cap:



The spring and push rod:



The Bi-metalic spring:



The spring heater element:



Plug retaining clip and seal:



The spring is electrically heated. In its cold position, the control pressure (which opposes the injector pressure fuel circuit) is lowered to increase the fueling to the injectors. This is done by the bi-metalic spring opposing the coil spring, aleviating the pressure on the diaphragm, and effectively bleeding off the control pressure in the metering head, richening the mixture. The heater element warms the spring to realease the coil spring, and so leaning the mix as the engine warms up. It only recieves this electrical input for a short time after start up, and from then on, the heat soak from the engine keeps the bi-metalic spring in the required position.




The reassembled warm up regulator



It's dead simlple, it's only weaknesses are failed heater element, which makes cold starting difficult, and rust in the diaphragm block, caused by water in the fuel. This one seems ok inside.

Thanks for a clear explanation and that pretty much covers it. There are a few more causes of issues though. Internal fouling, bi-metal defective or dislocated, membrane stuck due to rust of fuel residue, membrane ripped, rubber o-ring dried/aged/worn to an extent it doesn't close anymore, inlet filter fouled or damaged, membrane pin dislocated. I've even seen two previously 'overhauled' WUR's that had the bi-metals fitted the other way around!