Fuel System: Pumps, Relays                                                                        FAQ Home
 Volvo Maintenance FAQ for 7xx/9xx/90 Cars                                                                                                                     Version 5.0
Fuel Pump and FI Relay Diagnostic Tests

Symptoms of Bad Pump Relay 

Fuel Pre-Pump Problems

Fuel Pump Noise

Fuel Main Pump Problems

Failed Check Valve

Pre-pump Outlet Hose

Fuel Pressure Regulator and System Pressure

Noisy Fuel Pump: Bad FPR

Fuel Filter Replacement

Airbag Deployment While Changing Fuel Filter

Fuel Pump and Sender Replacement

Fuel Pressure Test Tool

Fuel Pump and FI Relay Diagnostic Tests.  Here is a procedure to test the operation of the fuel injection relay and the operation of both fuel pumps.  The 3 main things to check in the fuel circuit are the fuel pump relay, and the 2 fuel pumps. CAVEAT: The main fuel pump is not designed to be run without the in-tank pump "on", so get the second part of this test over quickly.  You should not need to keep it running in this condition for more than a few seconds to complete this part anyway.

Symptoms of Bad Pump Relay. [Symptoms:] 89 740 died & started 10 min. later. My '89 740 did the EXACT same thing for a while. When it acted up it did have spark. It seemed to be related to getting hot. It would die in motion, or when hot, it would also refuse to restart 'til it rested for 10 min. As far as driving it, not much you can do, just be prepared to pull over and give it a rest for 10 min. When it acts up, as the key is turned "ON", listen, the fuel pump should normally be heard to come on for about 1.5 sec. If it's not coming on, I'd bet on the relay. [Diagnosis:] After replacing the fuel pump relay ($38 at dealer), it's been 100% fine. [Editor's Note: See the note on "Headlamp Circuits/Relay Won't Function" in the Electrical: Lighting section for more relay information.]

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:

[Symptoms of worn fuel pre-pump:] My experience with a worn fuel pre-pump is that it will cause the engine to miss and lose power under conditions of high flow (high throttle and high rpm). The problem grew worse very gradually (over 10's of 1000's of kms). It certainly wasn't going to leave me stranded anywhere. [Another example:]  My wife drives an '83 760, which I have maintained as needed.  Recently, the car started to vapor-lock in warmer weather, and/or when the fuel level dropped to around a 1/4 tank or lower.  Oddly enough, when I refill the tank, the problem seems to go away.  [Test Tip:] As far as a definitive test goes, I guess it would be necessary to set up a pressure gauge and flow meter as well as a valve in the circuit that would allow a specified volume to flow while reading pressure, but see the above fuse and noise procedure for an alternative.

[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.

Fuel Pump Noise. Fuel Pump Noise.  [Query:] My car is running perfectly but whenever the fuel-gauge drops to around 25%, noises coming out unexpectedly, but after refuelling the noise will suddenly disappear.  Does anyone could tell me what's wrong with my car?  [Response 1: Michael Pardee]  Sounds like the hose on the in-tank fuel pump has a hole in it. That is very common, and if the hole gets much worse, it will not be able to run below 1/4 tank at all. Fortunately, it's an easy fix.  [Response 2: Peter James] I would agree with that and/or the intank pump has failed and you are
now stressing the main pump, which in turn can lead to premature failure of the main pump.
[Response 3:] Are you sure it's the in-tank pump, not the main pump down by the rear wheel arch that is making the noise? Most commonly this pump makes this noise not because it is failing, but because the in tank pump is not supplying the fuel to it for some reason. It won't do it any good to operate in this condition, and when the main pump fails, you're stuck at the roadside. The most common causes of in tank pump woes are not failure of the pump itself, but two other possibilities: Both require the pump removed from the tank to rectify unfortunately.

Fuel Main Pump Problems. [Symptoms of dead main fuel pump:] car won't run. [Diagnosis:]  If you can't wait or have no cash, your can cut your old line off and move the accumulator about 1.5 inches forward on the new pump. Then take off the old pump, (Three bolts its in a cradle, 13 mm I think)

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.

Failed Check Valve. [Symptom:] My '84 244GLE is equipped with B23F engine and LH Jetronic 2 fuel injection, she doesn't want to start (read run) the first time -though cranks fine- when it has been sitting at least 6 hours. The car will start without hesitation on the second try. [Diagnosis:] It sounds like a classic case of failed fuel pump check valve, on the main pump under the car, left side, just ahead and inboard of the left rear wheel. They cost about $14 at the dealer and are fairly easy to install. Just go buy one at the dealer and they'll show you in the parts book where it goes.

Pre-pump Outlet Hose. Don't let those guys charge you $200.00 for working on your pre-pump! Most likely the small piece of rubber fuel line between the in-tank electric pre-pump and the metal output tube has eroded and needs replacing. This is not a difficult job but requires getting under the car to detach the pre-pump output line from the main fuel pump inlet hose. Then the rest of the pre-pump removal can be done from inside the trunk.
Fuel Tank Line Clamp Recommendations.  [Query:] Which clamps work best on fuel lines inside tanks?  What's their projected life span ?  [Response: Jim McDonald] Breeze clamps; about 250 years if you get all stainless ones, somewhat less in plain steel.

Fuel Pressure Regulator and System Pressure. What about the pressure regulator concept? Very unlikely. But I'll give you good advice, install an in-line fuel pressure gauge (liquid filled). It'll save you from guessing on your problem as to fuel pressure and clogged lines or filter. I've got mine from Summit part #SUM-800160 (60psi) $19.95.

[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: Bad FPR.  [Tip from Chris Daunhauer ] My fuel pump noise (both the old one and the new one I installed) turned out to be caused by a faulty pressure regulator up at the injector rail NOT by a bad pump. Parts counter man insisted that from my description of the problem I had a bad pump in the tank. He was wrong. Bad regulator was not letting excess pressure bleed off back into the fuel tank causing external pump have to work too hard. Thanks for the 2 suggestions, guys, they were both right. The electric pump delivers about 10 times as much gas to the injectors as they need. Excess is routed back to the tank. Could have been either a clogged return to tank line or faulty regulator. In my case it was the regulator.
Here's what I learned....
If the external electric fuel pump is noisy, pull the return line off the pressure regulator. Install a spare length of hose on the barb and run the other end into a can on the ground. Start the engine. Fuel should be rushing out of the hose leading into your can, even at idle. If this excess fuel that the injectors aren't using is NOT (mine was not) rushin out, there's a good chance your fuel pressure regulator (about $60) is stuck closed.
Volvo mech said he's put pressure gauges on cars w/ stuck regulators and the needle goes off the scale.

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.

Fuel Filter Replacement. [Query:] The time has come for the fuel filter to be replaced. Rather than pay the dealer an arm and a leg, I'd like to replace it myself as I have done with my 200 series. Has anyone replaced a fuel filter on this model and year (1995 940)? Where is it located? Tips?
[Response 1: John B] It should be the same as the 7xx cars: [More Fuel Filter Replacement Tips]  Any tips to make fuel filter replacement easier?  [Response 1: Neos] Don't do it the way I did. I did not raise the car (740) high enough, and doing so caused me to not have the best of angles (and room to work) to hold all in proper position. I almost broke the line (toward the front of the filter) that goes over to the pump. It is real easy to start it bending to the point of having a kink if not careful.  [Response 2:  Robert Abel] I've done three in the past 1 1/2 years. One was easy,and the other two were pains in the butt because the nuts were so tight. I actually ended up cutting one end of the filter open because the nut began turning inside the filter.  The more of the work you can do on the bench instead of under the car, the more pleasant this task is. Remove only what is necessary to take the pump and filter cage off, then do the remainder on the bench. If you have an impact wrench, you will likely avoid the problems I had.  Having a fire extinguisher around is probably not a bad idea.
[Response 3:  Philip] I take somewhat the opposite approach from Robert. During my first few changes, I removed the filter from the bracket and then tried to disconnect the lines; it was very difficult.  Now I try to leave the filter in place as much as possible, although I find that I do need to loosen the bolts to the cage a little to get my wrenches in there. After the lines are off, I loosen and push out the filter. When I put it back on, it is difficult to get the right angle of the rubber line around the cage unless it is one of the last things tightened.

[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.

Airbag Deployment While Changing Fuel Filter.  [Tip from Abe Crombie] There is a Volvo SB out on precautions when changing fuel filters.  The SRS Airbag system is powered anytime the key is in position I or II. If you are listening to radio while changing fuel filter and you are using air impact tools there are real risks of deploying airbag as you re-install the fuel pump/fuel filter bracket. The hammering of air impact tool on bolts securing this bracket which is very near crash sensor location in floor pan on inside of car, can cause a deployment. This sounds like someone found out about this the hard and expensive way.  The bulletin only mentions 700/900 series but the 240 crash sensor is not too far away from the same location. LEAVE KEY OFF WHEN CHANGING FUEL FILTER!! If you need tunes get your rhythm somewhere else besides the car radio.  [Comment: S. Ringlee] By extension, then, if I use impact tools on such things as suspension bolts or anything else likely to jolt the body while the ignition is on, the same result may occur. $2500 lesson (bags, sensors, seat belts, glass, speakers, heaven knows what else.) Your advice is great: listen to a boom box and NOT the car radio while banging on the car. Thanks for the tip.

Fuel Pump and Sender Replacement.  [Tips from David Schermbrucker]

 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.

Fuel Pressure Test Tool. At last check, Volvo wanted $600 for the pressure rig to test control, =
system, and residual pressures. I built one for much less ... here's how. Parts needed: Now, hook them up in this order:

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.

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