I own a 1987 Volvo 240 GL and have had it for about 2 months now. I live in Hawaii so there's not a whole lot of options as far as 240s go, and I had seen an ad for a very good condition one not too far from my house. Before I got the car I was waiting for "the fuel pump" (their words) to be replaced as the car had a no-start condition. I never saw the car failing to start though so from what I learned later I have no clue what was causing that to happen, if it was happening at all..
When I asked which pump it was they said it was the secondary fuel pump and also the sock filter (the in-tank one). Having owned a 240 before, I knew that the car would still run without it functioning so I dismissed it as a case of them not knowing the car too well. Anyway that's it for the backstory, I've never had an issue with the car not starting but after buying the car there was a strange case of severe hesitation whenever I tried to accelerate. It would only happen if it was hot outside (never happened early in the morning or late at night) and when I eventually got up to speed the car would be fine until I had to stop and then start accelerating again. The hesitation is hard to describe but the engine RPM would get to about 1,750 before dipping well below idle speed and then shooting back up again. It would repeat that cycle in rapid succession maybe 4 or 5 times before I eventually got going. If I was going uphill, even the slightest of inclines, and accelerating there was a chance the car would quit altogether and wouldn't restart until it was back on level ground.
After a lot of diagnosing and thinking about the only repair i was aware of, I decided to unplug the power for the in-tank fuel pump (which I was pretty sure wasn't even functioning anymore as I couldn't hear it)
As soon as the pump was unplugged the car would run perfectly fine. I can stop mid-drive and plug it back in to cause the problem again. Where I've disconnected it is in the trunk under the plastic panel/cover on the left side, it's a yellow/red wire running into a black one (sedan trunk).
I've been running the car with the in-tank pump disabled but I would like to fix it before the main pump decides to give up altogether. The strain put on it can (and will) cause premature failure. If I do figure out the issue, I will replace the main pump because I don't trust it too much.

Something to note is that I did test the fuel pump relay and eventually replaced it and the condition still persisted. I am very confident that I've isolated the issue to the secondary pump and was wondering about actions to take next.

I have wanted to open up the fuel tank and check the pump myself but I have been very busy and haven't done many repairs (voluntarily, at least..water pump broke a week ago but that's a story for another day).
When I do get around to opening it up, is there anything in particular i should be looking for? I have a digital multimeter so I can test the pump that way as well.


Yes I did check the forum and I did see a very similar case to mine with very similar symptoms, but it seems they solved the problem by running the tank empty and refilling with good gas. I've run the tank to empty before and the problem is solved by unplugging a wire (which shouldn't magically change the condition of the gas)

I appreciate any and all help, this is the first time I've resorted to asking a forum directly because my situation is so specific that I wouldn't even know how to look it up like all the other repairs I've done.

One explanation which could sound good to some is the pump was replaced using one of the aftermarket sender units that were wired backward a decade ago. One might think this would cause it to pump backwards, but no, it is a centrifugal pump, and regardless of which way the impeller turns, the output is at the edge and the input at the center.

Nonetheless, I have no alternative explanation to offer, so I am one curious to know what you find. Indeed, very curious. I hope you don't find rust.


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Art Benstein near Baltimore

In The Tank

I'll start out by saying, no matter what, the OP should check the wiring of the pre-pump as it was recently installed and the symptoms are consistent with fuel starvation. If simply disconnecting the pre-pump at all improves things then that would pretty much isolate the problem and warrant inspecting the installation. I doubt it's a split rubber pick-up hose as the symptoms of such are typically noticed as being associated with going around a tight bend or up a steep hill with the tank 1/3rd full.

Now, Art, as to your comments about centrifugal pumps, that got me thinking it through in more detail as I'm quite sure the pre-pump was the entire problem with the car I worked on. You're absolutely right, now that I think about a reverse spinning impeller, the flow is still being pulled in from the center and pushed out to the side, just swirling in the wrong direction to work with the pump head design. It actually has to fight against the pump head design, but nonetheless will end up still flowing in the normal direction, albeit at a greatly reduced rate and the more efficient the pump head design, the worse it's likely to be. Doing a bit of reading on some pump engineering sites, seems the flow rate of a reversing centrifugal pump is reduced in the order of 70%.

Now I'm trying to visualize how that effects things when it's two pumps in series, as is the case here. On the surface, you'd think a pre-pump providing only 30% of flow would still provide a bit of boost. Then I thought more carefully about what might be going on in the head of the pre-pump. Okay, so here's an argument I will present to you. If the main pump is pulling fluid through the auxiliary pump and the auxiliary pump is just sitting there floating free with no power to the motor, the impeller will be encouraged to start spinning in the normal direction and the tighter the pump cavity, the stronger the effect will be. Now if you then power that auxiliary pump, it now has a bit more to fight against to turn the impeller in the opposite direction than if the main pump wasn't drawing fluid through it. Those pre-pumps are not exactly powerful in comparison the the main pump, just there to provide a little extra boost. Now, with both pumps running in that last scenario, and the impeller effectively getting closer to standing still or even turning in the normal direction if the main pump is really winning, then a stationary (or extremely slow) impeller actually becomes a minor flow restrictor, with flow through the impeller happening much as if the pre-pump was seized. The delivery out from the main pump will then be less than if it was just the main pump running on its own with no flow restriction back at the pre-pump. The result is the increased possibility of fuel starvation at the fuel rail during heavy demand, such as what was observed with the car I worked on. I'd say QED, but I know you're already trying to formulate a counter argument -laugh.

All I know for sure is that I admit reverse wiring the pump and just fixing that ended the hesitation and bucking during acceleration under load as would normally be associated with fuel starvation. When I worked on the car, everything seemed good to go when I was finished and ran the engine up to speed with the hood open. The next day, the owner noticed major problems when accelerating up a hill and took the car straight to a Volvo shop to figure it out. They're the ones who isolated the problem to the pre-pump and immediately recognized the reverse wiring when they looked. I quite imagine they did their diagnosis at the fuel rail and noticed the pressure either rise or fail to drop when the pre-pump was de-energized. The owner was told the pump was mis-wired and running in reverse, which was correct, which both the owner (and later I) assumed meant the flow was reversed and the pumps were fighting each other, which may or may not have been true based on my above argument. Whatever the case, simply re-wiring the pre-pump ended the problem and my reputation suffered in the eyes of the owner. That is until the day I quickly diagnosed a bad AMM by simply disconnecting it to get it started in limp home mode.

Art, I look forward to your usual good critique of my thoughts. I actually quite enjoy such banter with you as I often find it most educational. It's a rare day you're incorrect.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

My 240 pump still ran but fuel was intermediate. Running pump must be good said my brain. Replaced.the pump and all is good. I just had to know why the pump ran. Dremel Tooled cut the pump housing off and found that the motor did run fine only the coupling between the rotor that pumped the gasoline and the actual pump motor has bent prongs and engaged the rotor immediately. Eventually the rotor stop turning completely when the coupling prongs broke completely. Hard to believe a rotor pump a 1\4" wide by 1 -1\2" tall can pump over 150 psi. So pumps can sound like their.working ,but failure can be illusive.

Hi Dave,

Gotta admit, I dashed off the post you reference before reading your replies. Yes, I checked all four of them, afterwards. Sounded like I was refuting your theory, but really I admitted I don't know what the trouble is, and I'm curious to find out what solves it. And it sounds to me like you know already.

Most definitely OP needs to check the polarity and fix it if it is wrong.

I don't understand how any amount of positive pressure could inhibit the flow of fuel over none at all, but then again, I learn something new every day. This begs an experiment for sure. Now did I save any old, but still working tank pumps?

Today was our day-delayed Thanksgiving down here in the States. Nice to see the lineup of family 240's one of which was proudly shown after being detailed inside and out. Hope your 940 fleet is doing well.
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Art Benstein near Baltimore

Don't be irreplaceable. If you can't be replaced, you can't be promoted.

Yes, an experiment is warranted, especially if the OP confirms my suspicions. I expect you to get to it as soon as your family Thanksgiving feast is fully digested and you can lay your hands on the requisite pumps for testing. Perhaps with enough lubrication one of your relatives will volunteer their 240 while they're with you -laugh.

In case some of our American cousins reading this aren't aware, up here in the frozen north Canada celebrates Thanksgiving way back on the second Monday of October, making for a normal 3-day long weekend. It gives rise to an interesting benefit for our local turkey producers in maximizing production. Canada apparently exports some 50 million pounds of turkey annually, most all of it to the U.S. market. How much of that is gizzards, I have no idea. After gearing up to fatten Canadians with turkey for our Thanksgiving, they get to keep the production up as they re-focus on the American Thanksgiving market, adding whatever excess is left over from Canada into the supply line. Then they get to turn around yet again and focus production back on Christmas in Canada, where turkey is far more traditional than in the States, again adding any overproduction intended for the U.S. back into the supply line. There's one more flurry of feathered activity at Easter where they're having increasing success replacing the traditional ham here with cheaper by the pound turkey.

And to finish off my holiday banter, there's Black Friday. There was no Black Friday retail blowout in Canada until only the past five or so years. Our retail blowout has always been Boxing Day, the day after Christmas as a federal stat holiday here unlike yours. It's nice to have a paid day to recover and exchange all your unwanted presents. In more recent years that extended to become Boxing Week sales, where you get to pick up all those now discontinued electronics and winter clothing at below wholesale prices that some fool presumably bought at list price the week prior. Then along came the Internet and Cyber Monday. I certainly remember the first Cyber Monday sale with FCPEuro way back when -I probably still have some of those parts in my stock. Of course, with most of our population close to the 49th parallel, we've always been bombarded with American Black Friday TV ads. It took a suprisingly long time for our retailers to figure out they were missing an opportunity, but it's a big deal now with both e-tailers and retailers. I just got back from a minor flurry of Black Friday madness myself, didn't quite make it to the below half-priced motor oil. The ads for pre-Boxing Day sales are now starting to appear even before Cyber Monday is over. It was getting harder and harder for Canadians to distinguish themselves both culturally and economically from Americans, but as long as you've got a guy like Trump running the show, well, let's just say we're not overly worried about maintaining our identity or our sanity -no offense intended to long time GOP loyalists.

Art, my best to you and yours for the Thanksgiving weekend, and as well to all our brickboard followers. Let us all take a moment to be thankful to Jarrod for his renewed efforts to continue and rebuild our little corner of the Volvo world here -all donations will certainly be greatly appreciated.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

This is the OP, I finally got the email that lets me login to my account. Thanks for the feedback, both of you. I thought I might've had enough time to check things out but I ended up busy. I'll definitely be checking the wiring to see if it's wired backwards. Definitely makes a bit of sense that the in-tank pump would end up like that with the whole black power wire thing going on. It might be a little while before I can actually open up the tank, because I'll be busy working until next Friday.. I have opened up the little inspection cover though and everything on top of the tank looks to be in good condition.

Your symptoms very much remind me of the last time I put a new in-tank pre-pump in a 240 for someone else a few years back, a job I had done a number of times before. The car started and more or less ran okay except for horrid hesitation during low speed acceleration. Turns out I'd simply wired the pre-pump backwards. It's real easy to do. As I vaguely recall, the black wire I assumed was for ground (as is the norm in auto wiring) was actually for power. I had known that from my early 140 years, just totally forgot it when I went to help someone else. Rather embarrassing for a supposed Vovlophile.

Sorry, about that. Brickboard server must have been having a major hiccup. First it wanted me to log in to post a reply, but the login links at the top of the screen aren't visible in my browser (still aren't)and then the screen froze and I couldn't get any pages on brickboard.com to load, just kept timing out. Then I started to get server errors. I kept trying different browsers, same thing. Somehow I must have managed to post anonymously. Oh well, it's hopefully all there, probably with different typos in each post.

Your symptoms very much remind me of the last time I put a new in-tank pre-pump in a 240 for someone else a few years back, a job I had done a number of times before. The car started and more or less ran okay except for horrid hesitation during low speed acceleration. Turns out I'd simply wired the pre-pump backwards. It's real easy to do. As I vaguely recall, the black wire I assumed was for ground (as is the norm in auto wiring) was actually for power. I had known that from my early 140 years, just totally forgot it when I went to help someone else. Rather embarrassing for a supposed Vovlophile.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Your symptoms very much remind me of the last time I put a new in-tank pre-pump in a 240 for someone else a few years back, a job I had done a number of times before. The car started and more or less ran okay except for horrid hesitation during low speed acceleration. Turns out I'd simply wired the pre-pump backwards. It's real easy to do. As I vaguely recall, the black wire I assumed was for ground (as is the norm in auto wiring) was actually for power. I had known that from my early 140 years, just totally forgot it when I went to help someone else. Rather embarrassing for a supposed Vovlophile.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Your symptoms very much remind me of the last time I put a new in-tank pre-pump in a 240 for someone else a few years back, a job I had done a number of times before. The car started and more or less ran okay except for horrid hesitation during low speed acceleration. Turns out I'd simply wired the pre-pump backwards. It's real easy to do. As I vaguely recall, the black wire I assumed was for ground (as is the norm in auto wiring) was actually for power. I had known that from my early 140 years, just totally forgot it when I went to help someone else. Rather embarrassing for a supposed Vovlophile.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

If it is definitely something to do with the in-tank pump, the third part back there that should be replaced is the small rubber hose. I can’t say that a bad hose would cause your specific issue. It has been way too long since I owned a 240. Maybe someone else will chime in? However, I do know that it is SOP to replace the pump, sock and hose when replacing the in-tank pump. That is exactly what I did on my 90.

My one other related thought is to check the condition of the wiring at the fuel sender. I had to replace the sender also due to rot.

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Will I buy another Volvo??? We'll see....

Thanks for the reply, I'll definitely take a look at anything that looks out of place or rotting.
I just don't know how and/or why the in-tank pump could cause that issue..
When I do find the time to take a look at it (maybe this Thanksgiving weekend?) I'll try to post an update on the situation.

You might want to test the fuel pressure regulator before opening up the tank. When bad, they have been known to cause irregular running problems.

Also changing the fuel filter might help. Cheap too...:)

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Will I buy another Volvo??? We'll see....

Check out Art's Clean Flame Trap pix and notes on the intank pump

http://cleanflametrap.com/transferPump.htm

Thanks, I've checked out that page and it's been helpful in learning about the pumps.
This is the OP, I finally got the email that lets me login to my account.