FOREWARD
Over the 15+ years that the Volvo 700 and 900 series were in production, many changes were made to the ignition systems, fuel delivery, wiring, clusters, and various other components. These year-by-year changes are often not well documented, and make finding discontinued parts even harder now that many of these cars are reaching the 40 year old mark. In this write-up I will mostly be discussing the fuel system upgrades, and things I have learned along the way with restoring the fuel system in my Bosch LH2.2 powered redblock 740.
This write up, like almost all my others, comes from a personal struggle and a desire for a clear, concise information resource that I could reference for a repair. My 1987 Volvo 740 GLE spent much of its life in Pennsylvania before ending up in my hands in North Carolina. In that time it sat in a covered car port, not moving for the better part of 15 years! As you can imagine, the work to get a car this old and tired back on the road has been no easy task.
In my quest to diagnose a rough running condition, a full teardown and rebuild of the fuel system has quickly turned into a whole ordeal in and of itself. The pump under the car, filter, along with the lift pump in the tank are all original. New injectors will also be going into a cleaned fuel rail.
BASIC INFORMATION
The LH2.2 Fuel System
The fuel system in the LH2.2 (and maybe 2.4 cars as well?) use a basic fuel injection system where a lift pump in the tank sends low pressure fuel to a filter and then to a high pressure pump under the car. The high pressure pump then feeds the fuel rail and the injectors. This 2 pump system works fine when parts are new, but a failure of the in tank lift pump can cause the high pressure pump to burn out or struggle to supply enough fuel to the motor. Additionally, the fuel pump relay in the car can be a sore spot for many redblock owners as a failed one will leave you stranded on the road.
Replacements for the in tank pump, under car pump, filter, hoses and bracket are all readily available. The part that you can NOT buy new anymore is the in-tank assembly that the lift pump bolts into.
The in tank assembly has a few ports on it for the fuel filler port, pressurized fuel, fuel return and breather hoses. It also has the 2 wires for the in tank float as well as power and ground for the lift pump.
The issue now is that these in tank assemblies are no long being produced new or aftermarket. To make matters worse, there are multiple designs of assembly that are only sort of plug and play. This means when you end up in a rusty predicament like me, you better start scrounging the local junkyards.
The under car fuel filter and pump, still attached to the mounting bracket.
Corrosion had rusted out the top of the system leading to leaks and the hoses breaking off the fittings.
Pump Differences Between Years
(Excludes B27, B280, D24T, etc. Only for redblock motors)
Float Style
For the in tank assembly there are 2 different styles of float design. There is the ball style and the tube style.
The older “ball” style float, where the ball floats and swings the arm to actuate resistance to the fuel gauge.
The newer “tube” style float where the inside of the tube houses the float to determine the resistance to send to the fuel gauge.
Fuel Level Sensor Differences:
Lever “Ball” Type Sensor (1982 - 1986)
Empty (0 L) - Resistance: 296(+/- 15)Ω
Full (60L) - Resistance: 36(+/- 2)Ω
Lever “Ball” Type Sensor (1987+) / Tubular “Tube” Type Sensor (1986+)
Empty (0 L) - Resistance: 0Ω
Full (60L) - Resistance: 280Ω
Tubular “Tube” Type Sensor (1988+ (for 760/780 ONLY))
Empty (0 L) - Resistance: 0Ω
Full (80L) - Resistance: 363-370Ω
Upgrade & OEM OPTIONS
Much like a lot of other parts for these cars, replacements are no longer available. This means that you are working with an ever shrinking supply of good, useable ones. I am very lucky to have multiple parts cars I can take from, but even with that they condition of the assemblies can vary greatly. Swapping between these units can be very easy with a few different options:
Easy Wiring Harness Adapter
Thankfully if you have a 1987+ car, the replacements will be easier to find and the gauge should read the same. In all of my searching, not a single ball type unit was available for sale online. The tube style is almost a direct drop in replacement with one small difference. They ball style on my car has a 3 pin bullet connector, where the new tube style assembly used a 3 pin flat blade connector similar to more modern Volvo connectors.
In this situation I made a adapter pig tail using the male end off my old pump soldered to the female end snipped from my parts car. This means there is no cutting or non-reversable damage done to the original wiring harness on my vehicle.
The full harness
“Newer” style blade connector from the pump
Bullet style connector on the chassis of the car.
I also drilled out the pass through hole for the connector, which means I did not have to de-pin the bullet connector end every time the assembly needs to come out. The OEM grommet on the harness of the updated assembly is more than wide enough to still create a water proof seal.
Single Pump Upgrade
One of the most common upgrades for people re-doing their fuel system in the redblock cars is to upgrade to a single pump system. Modern upgrade-style fuel pumps from DeatschWerks and Wahlboro offer a near drop in replacement, and have more than enough GPMs to fully supply the fuel system from inside the tank without the need for the second pump under the car. In my personal experience, the width of these pumps is too large to properly fit inside the plastic carrier on the assembly like the OEM pump did, but modifying the mount to work was very easy.
For my 740 I went with the DeatschWerks 255, which was the recommended pump for the 700 series. It has a basic power and ground wire, and the pickup sock and outlet are nearly identical to the stock pump.
I used a dremel to cut the hard line on the outlet. (This is where the small section of fuel hose mid-way up the hardline is) Doing this cut allowed me to easily mount the angled section of hard line up to the outlet of the pump. Instead of using the plastic “basket” that holds the stock fuel pump, I used 2 hose clamps to attach it to the metal bracket that originally held the basket. This allowed me to finely adjust where the intake sock was sitting, and I tried to line it up as best I could to the bottom of the float.
A soldering iron was used to remove the 2 thin wires from the stock fuel pump. The new hardness from DW was then soldered directly to the top of the assembly where the power and ground are.
The back photo shows how simple the mounting system is. The zip-tie was added to correct some pump angle cause by the alignment of the hose and hardline.
With this single pump setup, the fuel line can go directly to the filter and then the fuel rail.
BjarnTech Digital Dash
The BjarnTech digital speedometer & fuel gauge is an amazing product I recently found thanks to the Volvo 240/740/940 group on Facebook. They are a super easy, drop in replacement for the center speedometer which gives a kmh readout along with fuel level. It is pre-programmed with all the stock ohm ranges for the fuel tank meaning you can upgrade your in tank float to a newer style or one from a 760/780 and still have a working fuel gauge without messing around with decoder boxes.
Currently they do not ship outside of Sweden so you will have to get your buddy to order it and send it over, but I plan on reaching out to see if a special run of US market ones can be made as a NordCarolina exclusive product. Stay tuned for a product review and install guide as soon as I receive mine!