Fuel System: Pumps, Relays                                                                        FAQ Home

1.  Fuel Injection Relay Test.  There are 2 relays inside the fuel injection/pump relay. One of them should turn ON when the ignition is turned on (without turning over the engine), and the other relay (which actually turns the fuel pumps) should come ON when the engine turns over/runs. You can check the 1st relay by putting your fingers on the relay module and turning the ignition on and off repeatedly. You should feel the relay click on every time. If it doesn't, that relay isn't working. And you'll find the car doesn't start if the relay did not come on.
 2. Fuel Pump Diagnostic Tests.  On the 740, the fuse-box + relay box can be pulled out a little to facilitate inserting/removing relay modules. So pull it out as much as the wires will allow. Pull out the fuel injection/pump relay module. Now take a small piece of wire to jumper terminals 30 and 87/2 on the relay board (the terminals are identified on the relay module pins. The 2 terminals are the nearest left and middle right pins on the relay board). This should make the car act like the fuel pump relay is ON.

Now turn the ignition ON (without turning the engine). You should hear a whirring sound right from where you are. That will be the main fuel pump. Now go to the gas tank and unscrew the cap. Put you ear to the hole and you should hear a smaller whirring sound. Or, listen with a piece of heater hose to the tank pump through the gas filler with car running. Should hear a humming. That will be the in-tank pump. If you hear both noises, the fuel pumps should be OK.

To check the pumps individually, you can pull out the in-tank fuel pump fuse after you do the above test, and repeat the test.  You should not hear any whirring at the tank, but you should be able to hear the main pump.

Fuel Pre-Pump Problems. [From RPR ; illustration copyright and used by permission:] 7xx/9xx Volvos are fitted with a fuel pump inside the fuel tank. This pre-pump, also called a primary or feed pump, moves the fuel out of the fuel tank to the main fuel pump. This prevents fuel starvation problems that may occur when the tank is less than half full. If the main pump has failed, the car will not run. If the pre-pump is inoperative, you'll have fuel starvation symptoms. These may include hard starting, louder than normal main fuel pump noise and a loss of power under load. To check the operation of the pre-pump without removing it from the tank, locate the pre-pump fuse. Remove this fuse with the car idling. You should be able to detect increased noise from the main pump and decreased vibration of the fuel tank itself.

[Diagnosis of pre-pump: Are there any short cuts to check to see if the in tank pump fuel pump is working? I opened the gas cap and did not hear any noise.] You should really be able to hear a "buzzing" sound in the fuel tank if the in-tank pump is running. Sometimes a length of heater hose inserted in the filler neck and placed against your ear will help isolate the sound. Try it with the fuse in place and removed and listen for a change in the sound. You might also find another Volvo owner who might let you probe their filler neck with your length of hose and listen to their in-tank pump . Assuming their in-tank pump is working you would be able to determine the sound you are listening for. If you do take it out of the tank:

Replace the short segment of rubber hose with a new section of fuel hose.
Replace the "sock" that is on the end of the pickup tube (about $15 from Volvo)
DO NOT bench test the in-tank pump. When the pump is removed from the tank arcing will occur when powered up and can result in a fire due to the gasoline vapors present. Certainly don't remove the pump from the fuel level in the tank and give it a quick bump on the starter to check out its function- that can result in one hell of a fire (and explosion). The pumps are designed to run submerged in gasoline.

[Car Stalls During Turn: Fuel Prepump Failing.]  [Query:] I bought a used '87 760t. It ran fine when I first got it but after a few months it started stalling when making a left turn. Not every time, but its worse (more likely to stall) if I'm decelerating, in fact I can usually avoid the stall if I slow down before the turn and then give it some gas during the turn. When it does stall it almost always starts right back up no problem.  [Response: MikeW] The stalling during turns is usually indicative of a problem with the in-tank fuel pump. Does it happen when you have a full tank of gas, or only when your down around 1/3 tank or less? Anyway, it sounds like your in-tank pump may be bad, or the rubber hose connecting it with the metal line running out of the tank may have deteriorated, or the filter sock on the bottom of the in-tank pump is plugged.

The little sock filter on the in tank pump intake is blocked with debris
The pipe from the in tank pump has split.

Pour some fuel into the inlet manifold or use ether quickstart. If the motor fires and runs for a second or two then dies, then your electrics are OK but motor will not rev as there seems to be no fuel.
Next, you could replace (or use a spare) the fuel pump relay. Normally, when you switch on the ignition, but just before you actually crank it over, you should hear the fuel pump working, (a faint whine) then it stops (i.e. it is priming the system to pressure) If you hear nothing at all, then the relay could be bad (it is a green bastard stuck in the row of relays (usually top left as you look at it) behind the ash tray. You should remove the little shelf panel to get at it.
Another thing you can do is undo slightly one of the unions in the fuel distributor, using a 12 (or 13mm) mm ring spanner. Normally, undoing one of these, there will be a spurt of fuel. If there is nothing, you have no fuel pressure.
So far it could be the relay or the main pump. You could buy a new relay, slot it in and the car should go. If not, then it is your main fuel pump (or pump wiring, but that is less likely, as the connections to the pump are very solid and durable) You could disconnect the pump wires (you can do this without removing it completely) and get someone to crank while you test voltage across the connectors.
If you have an old relay, you can 'short' it by levering it out of its box and disconnecting the little springs in it. As soon as you put it in (even without the ignition on) the main fuel pump should start to run and keep running and car should start. If nothing happens, then your main pump is well dead. Don't forget to remove the relay and chuck it, or mark on it what you did to it as it would be really dangerous to use otherwise. It is a strictly 'get you home' or diagnostic.
So it's your main fuel pump. The tank pre-pump can be dead (or dying) and the motor will still run if you have more than half a tank of fuel.  Get a new one if you can, or a scrap one from a yard, but test it before you buy it. Order the piece of fuel line from the accumulator to beginning or main engine line from Volvo.

Then disconnect the engine end first as it will be dry. The tank end will spill, so have the new pump ready in position. Cut the old clip off with a hacksaw and use a jubilee clip or whatever equivalent screw clip. Pull the old pump off, whizz the new one on and tighten the clip not too much. Then bolt the pump onto the car. Then push the new tubing onto the accumulator or the old piece on. Its best to buy the new piece. Although it is a pain to undo the union of the short piece with the engine line.

Don't even think of trying to change the tank pump as it is a nightmare if you don't like confined spaces. Also, it is a killer to get the auxiliary tank back on.

[Symptom: Car won't start] I hooked up a fuel pressure gauge and found that no more than 10 psi was generated while running the fuel pump continuously, and the trickle sound got worse. I removed the vacuum hose from the fuel pressure regulator, and found a couple of drops of gas. Just as a check, I turned the fuel pump on for one more second....YEOW!! I could have burned down the whole house with the stream that shot out the front of the regulator. Conclusion: No pressure to injectors, but plenty of raw gas supplied to the intake manifold, thence to the cylinders, and finally onto the ground under the exhaust manifold. No wonder the car wouldn't start. I have a new fuel pressure regulator now.

Noisy Fuel Pump: FPR Faulty.  [Tip from Jeff] I have been fighting a noisy fuel pump, rough idling, and poor performance for the past 3 months and finally solved the problem. It may not be a faulty fuel pump. In my case it was not. I replaced pump and the new one was just as noisy. I checked the in-tank pump and it worked fine. Then I disconnected the outlet or return line from fuel pressure regulator and attached a piece of fuel line to it and stuck it in a bucket. Nothing came out with engine running. The fuel should have been gushing out. I replaced the regulator and I have a totally new car. It runs like a top with no pump noise. So before ruling out pump problems check the regulator output first it is easy and takes about 3 minutes to test.

Pull the fuel pump fuse while engine is running, engine stops with no fuel pressure left in line.
Shut off engine.
Look under the driver side of the car for a small subframe assembly, about 20cm by 15cm or so. It has the filter and main fuel pump on it.
Drop the subframe, unplug the main fuel pump electric connections, disconnect the fuel tank line (plug this one) and disconnect the line to the engine.
Replace fuel filter and banjo gaskets.
Reverse to install.

[Another Tip:] When ever you change the fuel filter get new copper washers from Volvo(less than a buck)!. You'll go nuts trying to find the right size otherwise. (Editor: Wagner Brake sells them as brake fitting copper washers, numbers F17 and F10775.  )  I fought with my filter's leaking connections, replacing the fitting between the pump and the filter which was about $25.00. All I really needed was 2 little copper washers.. The old ones won't crush enough to make a seal.

 Fuel sender unit:

1.      My 88 745 has a plastic tank (love that Swede engineering) and the large knurled plastic ring holding the sender unit in place.  The ring comes off easily enough with a few blows via  strip of oak flooring to the knurls.

2.      I cut the rubber fuel lines since they were obviously on their last legs; these connect the metal outpipes to the metal fuel lines that run under the car.  NOTE:  Volvo uses non-standard 1/2 inch pipes; most auto parts stores only carry up to 3/8 injector hose.  Before you cut those lines have replacements ready.  This applies to the rubber lines running to the main pump and from the fuel filter as well.

3.      I got my old sender unit (the top plate, which was rusted and the pipes cracking) rebuilt at a local radiator shop; they cleaned off the rust and brazed new outlet pipes into place.  Much cheaper than replacing the whole assembly including pre-pump.

4.      I installed the sender unit incorrectly (there is some obstruction in the tank that prevented it from going in vertically; haven't figured it out yet) and now the fuel gauge is inaccurate.  Message:  make marks when removing the unit so you can align it properly.  Allegedly a mark on the top plate aligns with the plastic tank seam, but I couldn't see it.

4. I re-used the original rubber neck seal; no leaks.

Main pump/filter assembly:

1.      Again, 1/2 inch rubber hoses.
2.      I got a Niehoff pump which puts out 90 psi, more than needed.  Price was good and the unit came with the proper fittings for a Volvo assembly.
3.      The little aluminum and neoprene hose connecting the fuel filter to the pump was cracked in my case; I used rubber pressure fuel line with no problem, at 1/10 the dealer cost.
4.      I siliconed over the electrical terminals since they face forward into the slush and grit stream under the car.
5.      All in all, real easy to remove and replace.

Pump Longevity:

[Query:] I have two 740DL Volvo's 1990. One wagon and one sedan.  Had to replace the fuel pumps on both cars. One had 76k the  other had 90k. Is this the norm?  [Response:] If your cars are both Bendix fuel system with the AC (GM parts division) made in USA) fuel pump in tank and no pump underneath floor on bracket next to filter, then yes it is not uncommon.

2 Banjo 'nut' fittings (the ones that actually look like a banjo). Hack apart old fuel lines from an Audi, VW, or BMW from the wreckers to get the ones with the small nipples. Make sure they're the same diameter as your Volvo (see the tip below for Volvo parts needed.)
1 Brass Tee , 3/8" NPT
1 Brass Valve, 3/8" NPT=20
1 150 psi gauge
2 2.5" 3/8" NPT brass extender (pipe w/ both ends threaded)
2 3/8" NPT brass nipples
2" vacuum hose
4 small tie wraps (zip ties)
1 nylon spacer, 2" long, that will accept the 'bored' banjo bolts
some telfon tape for sealing

Banjo Nut - 1" vacuum hose - nipple - extender -tee -valve -extender-nipple-1" vacuum hose - Banjo Nut

Use the tie wraps to clamp the vacuum hose onto the banjo nuts and the nipples. Vacuum host isn't ideal for this, but the tests are short term and a short piece of the hose holds the pressure just fine. The gauge goes on the top of the tee. Be sure to use teflon tape to seal all connections.

One of the banjo bolt goes where your control pressure feed line connects to the fuel distributor. The other one gets bolted into one end of the nylon spacer. The other end of the spacer has the control pressure feed line bolted to it.

Now, follow your Bentley or Haynes directions to test... when placing the tester into the fuel circuit, be sure to orient the valve on the correct 'side' or else you'll only be able to measure system pressure.

Special Volvo Fittings to Make Connection. [Tip from Neal] Here are the Volvo part numbers for two hard to get parts needed to build a fuel pressure gauge assembly:

 9995267-7 Nipple $27.45
 9995116-2 Hose $ 9.30

The nipple is the fitting that connects between the rubber fuel line and the fuel rail. The hose includes the banjo fitting that attaches inline with the nipple. The other end of the hose is an unusual fitting that I imagine could connect only to a Volvo fuel pressure gauge. I cut that fitting off, and installed a 1/8" male pipe thread with barbed fitting pressed onto the hose. The 1/8" male pipe screws into almost any fuel pressure gauge found at any auto store. Make sure you get a gauge that goes to at least 100psi.