I will start a new thread since it seems you guys were correct and the fuel pump was not the real culprit

 

In my case (or in the case of one of my 240s a 1989 wagon), I had a loud humming noise coming from the main pump, which was accompanied by loss of power when for example trying to maintain speed going uphill (as if not enough fuel was getting to the engine) but only when the tank was less than half full. Naturally, I thought it was the in-tank auxiliary pump as it's well know than when it fails you get the symptoms I was getting. Well, the in-tank pump has been replaced now twice and I know the second one in pace now works fine, as proven by a good flow of fuel from the connection to the fuel line when tested, a flow that stops when the corresponding fuse is removed. Yet the main pump was still humming very loudly. The main pump has been replaced now twice too, and while it was quiet to begging with, it began to hum little by little as the previous pumps....the loss of power, although not that noticeable now, is still present when the tank is less than half full. It is frustrating. It cannot be either one of the pumps as they both have been replaced twice and the problem necessarily has to be between the two pumps or before the main pump. The fuel filter after the in-line main pump is fine (and it would not produce these symptoms anyway). Any ideas or better solutions than constantly filling up the fuel tank and/or waiting for the main pump to fail completely? Thanks!!

 

is the fuel pressure correct?

 

The fuel pressure regulator was also replaced (even though the previous one was still operating well)....assuming that the two fuel pumps and the pressure regulator are fine, why would the problem of losing power while under load occur only when the tank is half or more than half empty? Wouldn't this mean that the issue is before the main in-line pump and not related to fuel pressure between the in-line pump and the engine?

 

when you serviced the in tank pump, did you also replace the connection hose, and the 'sock' ?

 

The whole ensemble was replaced...the fuel gauge was not working and replacing the sender was the first thing I thought of doing. Because of the "stuttering" under load, the idea was to replace everything, including the sock filter and the hose. The in-tank pump actually "spits" a nice stream of fuel at the exit level when tested.....

I got this second 240 (a 1989 wagon) a couple of months ago, believe it or not with only 57K miles. It was stored in a garage since 2005 (the re-registration list of fees was one page long.....). Of course I imagine that such long hibernation is the reason of the troubles (I should have thought about it and before even driving it again should have cleaned well the tank...). I've heard of cases where the main pump and the filter had to be replaced several times in a row and every time there was a lot of "dust" clogging the parts. Perhaps I should try to use one of these fuel cleaner solutions? Do you know of any such product that might be of help in this case?

 

the big problem is, a lot of replacement parts today are junk. I'd rather rebuild an original pump+sender assembly then install some chinese thing in its place.

 

But if that was the case for any or the two sending-pump sets installed there would actually be no fuel pumped through the spigot when testing it....on the other side, I know that at least one set is OEM...

I wonder if I could get any benefit from adding a fuel cleaner solution to the gas....are these products any effective? which one is reliable and good for volvos 240?

By the way, I checked the fuses, took out #4 and jumped from left #6 alternatively to right (empty)#4 to test the in-tank pump and to left #4 to test the main pump. In both cases the pumps sounded steadily and nicely as many times as I tested them. Then I used a different 8 amp fuse for #4 and still got the same problems.....

 

a fuel pressure test would pretty much prove the fuel delivery system is working perfectly. the pressure should be 42-44 PSI relative to manifold vacuum if the vacuum line is connected (typically about 35 PSI at idle with -9 PSI vacuum), and 42-44 psi total if the vacuum line is disconnected. if pressure is good, then you need to look at something else, if its wrong, then you need to figure out why.

 

The mechanic I ask for help for the things I cannot or don't dare to do myself (too many..), a Swedish guy who worked for the original Volvo company for over 20 years, told me the pressure was fine....thougn I'm thinking that perhaps when he doesn't suspect something is wrong he tells me it's fine without checking...in any case, how do you check the file pressure (I know the basic concept but not the type of pressure gauge you can use, etc)?

Today I drove without the fuse #4 and it doesn't make any difference in noise or performance. It is beginning to lose power now even with a full tank and on flat terrain when pressing on the gas pedal suddenly.....I'm beginning to think the problem is either that the line between the two pumps is clogged, the fuel check valve is failing, or something else beyond the pumps. Checking the fuel pressure on delivery to the injectors makes absolute sense.....I'm afraid the problem is looking to be far more complicated than I thought, which is concerning...

Thanks for all your comments and help!

 

A fuel pressure gauge is connected with a T between the fuel hose and the injector rail.

anyways, maybe your problem isn't fuel delivery at all.

 

open up your relay box and look for the "Fuel pump " relay and while the cars is parked and idling jiggle the relay and if the idle gets normal there's your problem

 

a 240 doesn't have a relay panel, they are scattered all over behind the dashboard. the fuel pump relay is behind the glovebox.

 

and you can hear it clicking perfectly well, and the pumps actually respond and begin to work. A faulty pump relay would make the pump stop working albeit intermittently and the car might either stall or not start at all. I doubt it would directly impact the idle, which is otherwise perfect on the car...

 

Pushing the brake pedal? Two possibilities: this would affect the engine vacuum from the brake booster; it would affect the electrical system, from power draw of the brake lights. In some strange way, either path could possibly affect other systems.

 

yeah, if the brake pedal is causing bogging, I'd be looking at the vacuum lines, and brake vacuum hose, and the one-way vacuum valve at the brake booster

 

After replacing and measuring a bunch of other parts/systems, I'm presenting my case again in search of ideas and help!:

I recently bought an 89' 245 with very low mileage (57,000 miles, had been in storage for 10 years) and I quickly noticed a loud main fuel pump (like a loud flying mosquito buzz; I also have a 89' 244 and I can't hear the pump at all). A new pump had been installed shortly before I bought the car. A few days later, I realize now when the tank was emptier, the car couldn't go faster than 20-25 mph on the freeway (even on flat sections). The check engine light came on for only a few seconds but never again. After stopping for a while, the car ran almost normally until the mechanic shop. For the new few weeks, the in-tank pump (main initial suspect) has been replaced twice (now it's a Bosch, and it's wired correctly, spilling plenty of fuel when tested), the main pump has been again replaced (also a Bosch), and so have been the fuel filter, the fuel check valve, the fuel pressure regulator, and the fuel pump relay. The check engine light never appeared again, and the ECU shows no codes (1-1-1). Both pumps work as evidenced by testing with the proper combination of jumpers between fuses #6 and #4 and listening to both of them starting, as well as checking the in-tank pump spilling a good fuel jet stream, and measuring the fuel pressure on the line right before the engine (which is fine). Yet the main pump continues to be exceedingly loud and the car hesitates under load when the tank is low in gas. The rubber mounts below the pump are intact. The air filter is clean and almost new. Next think to check was the MAF sensor: I found a used one for testing purposes and replaced it. I thought initially that the pump noise had decreased but it was wishful thinking, it is still loud and with a buzzing pitch audible both inside and outside the car (while I can't even hear the pump on my 244 when lying on the floor near it). The idle is steady and smooth and when the tank is full or near full the car drives perfectly and accelerates with no problem even on steep uphills. Any ideas about what to do next?

Incidentally, even though the two MAF sensors are identical outside and have the same Bosch part number, their filaments inside are quite different: the one originally on the car has the trapezoid layout, whereas the one I bought used has like a holding Y-shaped part and a filament joining the two tips of it. Can anybody explain whether Bosch manufactured the same part with different filament types?

Thanks!!!

 

I can only hypothesis that your new main fuel pump is a noisy one.

the MAF should have NO effect on fuel pump noise, its purely about telling the ECU how much air mass is coming in, so it knows how much fuel to inject.

 

I replaced the main fuel pump on my daughter's 240 and even though the new pump stated it was Bosch, it made much more noise than the original pump on my 240. I don't know if the quality of the replacement pumps are as good as the originals.

As far as the car bogging down when the tank is empty, since the car sat for a long time, it may be necessary to replace the fuel filter multiple times as you work out all the crap in the tank from the old fuel.

 

Thank you Pierce and Act1292 for your helpful comments. The MAF replacement was done only because of the hesitation when gong uphill above 2000-2250 rpm...I thought that because the MAF controls the air/throttle it might be a factor when the engine is under load (besides, I just paid $17.50 for the MAF including shipping, and replaced it in less than 10 min). I have thought that perhaps the pump--Bosch and all-is noisy and also certainly about the issue with the deposits on the tank having to slowly be pushed through the fuel pump, filter, etc. It's just the fact that the three factors (noisy pump all the time, hesitation only under high load and hesitation under high load only when the tank is less than half full) are combined and still present after replacing so many things that bugs me and my curiosity....