Boost Control Frequency Valve
replacing on a 1992 Lotus Esprit SE
by Lotus Esprit World
This guide will show you how to remove and replace a Boost Control Frequency Valve on 4 cylinder injection cars. This valve is part of the system that controls the boost from the ECU. Without this the Esprit will only boost to the maximum set by the wastegate (ie mechanical boost). This valve helps the ECU to control how much boost is given.
BCFV were a requirement when electronic fuel injection was introduced 1989 model year, USA and Europe. Lotus refer to it as the GMP4 system, before GMP4 it was carburettors or Bosch K jetronic on USA cars. V8 also has one, BCFV part numbers are the same (A082M6420F) for the V8 but plumbing and controller differs for twin turbos.
If you have any boost problems, either too much or too little. Removing this valve and replacing it with a pipe, will stop the ECU from having any control over boost. If you still have a problem with the valve removed, then you have a mechanical boost problem, which is probably a wastegate issue. If without the valve you get the amount of boost set-up via the wastegate, which is 0.65bar for most Esprits, then you have an Electrical boost issue.
We were getting too much boost throughout the rev range, giving us a very fast car, but at full throttle the ECU was cutting boost for safety, giving us a very stuttery car on full throttle. Not Good! We tested our Esprit without the valve and using our digital boost gauge found we were getting exactly 0.65 bar a full throttle! You could also use FreeScan to check the boost, as the strandard gauge isn't that accurate and hard to read. So it was an electrical problem! First stop, replace the valve, which is only around £15. Once this was changed, our boost problem was gone!
Here's how we did it.
This job is not difficult and should take under a couple of hours to complete.
You will need the following parts:
New Boost Control Frequency Valve
New pipes (if needed)
New clips (if needed)
You will need the following tools:
The valve is situated in the rear compartment behind the engine. Remove the six screws holding the panel in place.
You should now see the fuses, relays and valves. The boost valve is on the far left of the panel. First unclip the connection to the ECU.
You can then remove the screw holding the valve in place. Then loosen the clips holding the valve pipes to the incoming connection. Once both of these has been loosen, you should be able to remove the valve from the car. To test for a non-electrical problem, fit a short pipe to the tow incoming pipes. This stops the ECU from controlling any boost. You can now drive the car to see if you're boost issues are still there.
We checked our pipes coming from the wastegate to the valve. Once had been damaged on a jubilee clip from another hose. We decided to replace them. The original pipe is 0.6mm, but we used a 1/4" fuel pipe, which will do the job. We removed the two pipes and cut two new pieces to length. We also replaced the old clips, which had rusted badly with new jubilee clips.
It's a simple set up in to the panel. Two short pipes attached to the wastegate and come into the side of the panel. The red arrows point to the two connections. You can see the pipe that comes into the bottom of the panel still fitted. We removed these old pipes and fitted the new ones.
Make sure the connection is tight, as any leaks will effect the system. The new pipes are fitted and the connectors are pushed into the panel.
New time to fit our new Boost valve. Christopher Neils supplied ours at sort notice. Talk to Paul or Mark in their Parts department. We removed the pipes from the old valve and check to make sure they were ok. We then fitted them to the new valve. This is a very simple task require just a small normal screwdriver.
Reattach the valve to the pipes and make sure all connections are nice and tight. Then reconnect the ECU connection and replace the panel cover. You now have a new valve fitted and are ready to test the cars boost again.
This is a very easy part to fit and if it's not working properly you'll see a big difference with the new part fitted. As we said above, all our boost related problems disappeared once this new valve was fitted. A great fix for £15 and about an hours work. Nice to have the Esprit working properly again!
We've sent our valve off to Lotus so they can take a look and see what the problem was with it. Remember our Esprit is now 13 years old, so valves, relays, sensors can all fail after this amount of time. So keep an eye on your Esprit and you can check some of the sensors and valves using readings from freescan. Make sure your Esprit is working as it should.
This mod was performed by LEW on their 1992 Esprit SE.
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