I was unclear but I think I did it wrong still. I originally did the test as described and was trying to say that the car appeared to idle normally under all three conditions - with fuse #4 in place, with the fuse removed jumping the left connection, and with the fuse removed jumping the right connection. So in each case I tried to make a connection and then started the car.

However, I repeated the test and I definitely heard the main pump turn on when jumping to the right side of fuse #4 without turning the car on at all. I am not hearing any noise for the left side of fuse #4.

 

the intank pump can pretty much only be heard if you put your ear up against the gas filler pipe with the gas cap removed. and maybe even only if you have less than 1/2 tank.


the driving symptoms of a failed in-tank pump are an engine that is starved for fuel under heavy throttle and high load conditions, like full throttle acceleration in 3rd gear up a grade, if and only if your gas tank is low. when fuel starved, it will feel like all power is gone, but if you let off on the gas it will feel normal again. as the gas goes much below 1/3rd of a tank, it gets worse.

 

Should I simply remove the in tank pump and inspect to see if it's working? Or use a multimeter then? Is there another failure that could lead the seemingly intermittent rough driving I've described? Basically the car will occasionally idle a bit rough while parked - other times it operates silently, and it will sometimes drive with a bit of that same feeling, without effect from acceleration/deceleration. It appears that smooth road either eliminates or masks the rough driving.

Which is why I emphasize that I had suspension work done and that, as a result of an accident, my front right tire is 2 degrees off of alignment due to the frame being bent. I maybe didn't disclose that prior. The front right control arm, spindle and strut were replaced.

Thanks for all your help again. I appreciate it very much.

 

The in-tank pump is easily checked by removing fuse 4, jumpering the right side of fuse 4 to the left side of fuse 6. No need to turn the key or start the car. Put the jumper in place and go back and open the gas cap and listen for a humming in the tank. If you don't hear it then your in-tank pump is not working.

 

problems that occur on rough roads are often due to an intermittent electrical connection or short, the vibration causing the circuit to not make a clean connection. but that wouldn't impact idle when you're stopped.

 

Which could be an indication of a wiring harness issue, like you've said before, I imagine.

I am not hearing the in-tank pump when jumping it, but will try it more over the next week as my gas level gets lower.

Is there a replacement in-tank pump that comes recommended?

 

I'd probably get the best non-Volvo tank pump fcpeuro or ipdusa is offering.

read the sordid story on that cleanflametrap site, many cheaper aftermarket pumps are miswired out of the box, and will SUCK instead of PUMP unless you first test them and if needed reverse the wires.

 

Actually, it is the aftermarket fuel level sending unit that comes wired improperly. I agree with Pierce's recommendation on purchasing from IPD or FCP. I bought mine from FCP and had no problems with it. Check the little rubber hose that connects the in-tank pump to the sending unit and be sure to purchase the correct type of replacement hose - the submersible type. Art Benstein is the keeper of the CleanFlameTrap site. He's over on brickboard.com and extremely helpful in all types of repairs.

 

So I ran my tank down to < 2 or so gallons in the fuel tank and jumped the in-tank pump. I could not hear it on my residential street with the fuel filler cap off and my head next to the tank pipe. However, I did not notice the driveability issues that Pierce described as indicating a bad in-tank pump. I did not drive it too hard, but driving around town, up bridges and such, opening the throttle wide did not cause the loss of power.

Should I assume then that the in-tank pump is in fact bad?

 

That would be a good assumption. Also the hose that connects the in-tank pump to the sending unit may have deteriorated. When replacing, make sure you use the correct type of submersible hose. Regular fuel line hose will deteriorate.

 

Any thoughts on this kit?

https://www.fcpeuro.com/products/vol...n-tank-3507436

 

I would stick with the AC Delco one:

https://www.fcpeuro.com/products/vol...-delco-3507436

Not sure the quality of the kit offered there and whether the hoses they ship are submersible. Since it is shipping with hoses it's size is probably different than the original and needs adaptations to fit it. You should also consider a new sock when you order one. In the cleanflametrap link he specifies what type of hose to get. I was able to find the specific hose he recommended at a local auto parts store.

 

So: i rapped on the top of the fuel pump sender (under the access panel) and I wonder if I perhaps started a stalled pump? My car seems to be driving better after this percussive maintence.

Additionally, today, I tested both the battery voltage to the transfer fuel pump AND the current draw of the trasnfer fuel pump and the preliminary result is that I am in normal range. The battery voltage is 12.7V at the pump's power supply line (yellow-red wire) and the current draw between 3.16 - 2.7A, which, per my Bentley manual, is the average reading for a high-output fuel pump. Since I had the pump replaced in December 2018, it would seem logical that Firestone would have a higher output pump than the original?

I can definitely hear the pump whirring beneath the bung nut with the access panel removed.