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91-95 Jeep 4.0 Adjustable Fuel Pressure Regulator
Recently I started a search for an adjustable fuel pressure regulator for my YJ. As many know there is typically only one place to go for these. I found an alternative that is a fraction of the cost. As it turns out SpaPerformance makes an adjustable fuel pressure regulator for Chryslers, which works great for the 4.0 Jeeps.
Below, pictured is the Spa VLRPF231, Chrysler Adjustable Fuel Pressure Regulator, compared to the OEM YJ fuel pressure regulator:
Jeep Adjustable Fuel Pressure Regulator

Just like the alternative to this option, you do need to make a minor modification to the retaining bracket. Be careful with this bracket. It is no longer manufactured, so you can not get a new one (Take your time). The modification is minor. In the image below notice I have removed the lower half of the bolt hole. It allows the bracket to clear the vacuum line. It's still a little tricky to get everything in place, but it works. Also this was a test fit. The bracket is just steel, I would recommend painting it after cutting it.
Fuel Pressure Regulator Installation

Adding a washer to the retaining bolt would be a good idea just as cheap insurance after cutting out part of the hole. Also keep in mind you will need a fuel pressure gauge to complete this installation. You can rent these from most Auto Parts Stores or buy your own. If you are going to have an adjustable regulator it may not be a bad idea to own one, and they aren't horribly expensive. The Jeep fuel rail doesn't require any special adapters for most gauges. The regulator is adjusted with the vacuum line disconnected.
Jeep Adjustable FPR Installed

Couple quick things to keep in mind. The stock injectors for a YJ are rated 21 pounds at 39 PSI (Stock Fuel pressure). Also remember that adjusting the fuel pressure will change your injector flow rate. See the image below for an example on how fuel pressure will affect injector flow rates.
Injectors flow rates vs Fuel Pressure

As for why? This is primarily going to be for those running different injectors, or modified motors. If your Jeep is stock, the OEM fuel pressure regulator will be just fine.
Related Topics: | Jeep Fuel Injector Tech |
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