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MIGClub Member
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Discussion Starter · #1 ·
DIY Fuel pressure regulator

For injection engines only, these can be used to increase the fuel delivery to the injectors. This is only desirable when other modifications have been done to the engine, for example an induction kit, or an exhaust system. Fitting one to a standard engine will only cause to whole system to run rich. It may cure flat spots, but you are getting around the problem that has caused then, not fixing the problem.

If you imagine squeezing a hosepipe as water tries to escape, your hand is acting as a restriction, which builds up pressure upstream of the point at which you hand is. The more you squeeze with your hand the more the pressure increases. By adjusting your grip on the hose you are able to regulate the amount of pressure in the hose.

This is exactly how a fuel pressure regulator works. From the factory, it is manufactured to a specific pressure. After market items are adjustable, this allows you to increase the pressure along the fuel rail, in turn delivering more fuel through the injectors.

You may well have heard of "FSE Power Boost Valves". These are adjustable pressure regulators designed to replace the standard regulator. These kits can be expensive due to the alloy blank that is fitted instead to the original item. They can cost up to £125 and the fact is these FSE kits are not worth the money.

I work as a Hydraulic Engineer doing consultancy work for major water companies, hence I know a little about this subject. Going back to the hosepipe, imagine you have one hand squeezing the hose, generating a pressure of 20psi. Without letting go with the first hand, then you do the same with the other hand downstream of the first, only harder. You will see that the pressure rises higher than 20psi, even upstream of the first hand.

What I am trying to say here is that, it you have two pressure regulators, the pressure will be dictated by the one creating the greatest flow restriction. Hence, if you leave your standard pressure regulator on and fit an adjustable one down stream of this point, you will be able to adjust the pressure higher than standard, but never lower. This is good as it safeguards the engine from running to lean due to incorrect set-up of the adjustable regulator.

Going along with this theory, all you need to fit an adjustable fuel pressure regulator is the regulator itself, such as one made by Weber, and two jubilee clips. It fit it in place, cut the fuel line downstream of the standard regulator, and fit the regulator at this point using the jubilee clip to secure it.

It is important that the correct pressure is set. The fact that the old regulator is in place will stop you from running too lean, but you could still run too rich, causing excessive fuel usage, emissions and even excessive piston ring wear. If you look at your standard regulator, you should see its pressure rating stamped on it. If this happens to be 40psi, then try setting up the regulator a little higher, such as 43psi. It is best to have this done on a rolling road so that emissions can be checked, but this will add to the overall cost.

Vauxhall for some reason made the pressure measuring point valve some stupid size, so standard pressure gauges will not fit. It may be a good idea to see if a local garage will lend you an adapter, or see if you can buy one from Vauxhall.

To check the pressure, you first need to depressurise the fuel rail. Do this by removing the fuse for the fuel pump, found in the main fuse box marked in the lid as “FI”. Once removed, try starting the car until there is obviously no fuel in the fuel rail. Connect an accurate pressure gauge using an adapter, to the fuel rail. Start the engine and check the reading on the gauge. You can adjust the pressure as described in the instructions that came with the regulator, usually by turning a bolt at the top of the unit. Once the required pressure is achieved, fit the lock nut onto the adjustment bolt to stop it from moving.

All parts needed for this modification are available for places such as Regal and Demon Tweaks, both give discounts to MIG members.
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