My problem started with the fuel pump making a buzzing noise, got on the freeway and it stalled while i was accelerating. luckily i chugged home on the side streets going 30. we decided to replace the fuel filter and pump. after about a week it started making the same noise and the car would stutter and hesitate off the line. we replaced the filter again and the problem went away for a few days...we then decided to empty and clean the gas tank and replace the filter again. now the same problem is happening again..we have pour seafoam in the tank and engine, replaced the spark plug, spark wires, distributor cap and rotar. car still runs but stutters off the line and at high speeds.

so my question is what might the problem be and how can we fix it? fuel injectors dirty? maybe fuel system relay?
thanks

 

You keep saying fuel pump in the singular...you do know there are 2, right? Describe the stalls. Is it immediate and immediate restarts or do you have to wait 5-10 minutes? When it restarts does it start cleanly as if there was no issue or does it chug for a minute and then smooth out?

 

yes i know there are two. the main on underneath is one making the buzzing sound. after the stalls it will start up but i have to give it some gas and it will chug a bit after for a while. and hesitates fairly often when i accelerate.

maybe the pump in the gas tank is a problem?

 

Could be the pump has failed, the filter sock is clogged (doubtful since you were just in there), the rubber connector between the pump and the gas line on the sending unit has rotted and failed allowing pumped gas to just spill back into the tank, or...the connector in the trunk that goes to the in tank pump has corroded or otherwise failed. Generally, when the rubber connector fails the car will run better with a full tank than with a half tank or less. Lack of sufficient fuel flow from the lift pump will indeed make the inline under car pump noisy and will effect drive-ability. Use a length of vac hose as a stethoscope and have someone turn the key on while you listen through the gas filler to see if you can hear the intank pump fire up. If not, start digging in the trunk and trace the wiring from the tank sender back to the drivers rear fender well. There is a 3 wire connector there. The heavy red wire is the pump power lead. Disconnect the connector and make certain the connector is nice and clean as opposed to looking burned or corroded. Assuming it's ok, double check to make sure the wire gets power when the key is switched on. Assuming it does and the pump doesn't run, it's safe to presume the pump is dead.

 

I would indeed check the in-tank pump. WHen it fails, it can cause the main pump to work too hard and cause it to make a lot of noise and eventully fail. Use the link below as it has a good explanation on how to troubleshoot the in-tank pump.

In the Tank - 240 Volvo Tank Pump and Sender

Oops - The last link is good for 240. 740 is similar but the fuses are probably different. Symptoms I described are the same though. Also, I think the turbos have a different (high volume pre-pump) so if you need to order a replacement, make sure you get one for the turbo.

 

I have a 90 740 Turbo that I've just replaced the fuel pump intank, now the car had a bit of hesitation in first gear and will not go into full boost until I shift into 2nd. The mechanic removed the fuel tank before he realized he didn't have to. Can that cause the gas to go bad. Before the fuel pump went bad the was running excellent. Need help please

 

just to confirm it was the in-tank pump and the was working great for a month new there is a new problem which i will probably make a new thread for. thanks for all the help guys

 

So, I was trying to replace the in-tank fuel pump and I ended up completely disintegrating the connector. It must have been rusted into one solid piece. Now what do I do? Can I buy this connector at the dealer? Any other suggestions?

The car is a 1989 740, non-turbo.

 

can we get a photo of what broke ?