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Old 08-07-2018, 01:55 PM   #1
petebee
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Location: Back in NC again...
Default Fuel Issue - FPR or ECU

I am encountering a fuel delivery issue on my recently acquired 91 240 wagon. Twice now I've had the car either stall and refuse to run or barely run enough to make it up a small hill in my neighborhood during test drives. Both times the car was fully warmed up.

I replaced the main pump (it looked like the original pump), in tank pump and strainer. The fuel pump relay was very hot when it decided to run like crap. Note the car has the 561 ECU which I believe is not too reliable.

I plan to get a new fuel pump relay (for insurance) and I do have a 946 ECU in my parts bin. Will that work in the 240 (it was originally from a N/A 940)?

Thanks!

Last edited by petebee; 08-07-2018 at 04:30 PM..
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Old 08-07-2018, 06:41 PM   #2
petebee
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Okay so I went out to test the function of the fuel pumps, and when I bridge fuse 6 to right side of fuse 4 (with fuse 4 removed) I don't hear the in tank pump running. I verified this by doing the same test on my 90 240 wagon and could clearly hear the in tank pump hum. Main pump is working. I checked for voltage at the pump wiring connector in the back and got 10V. So...maybe pump is bad (I ordered the Airtex model that Cleanflametrap recommended on his site) or it is wired backwards. I was very careful when hooking up the wiring that the "+" and "-" labels on both the pump and the wires on the sender were correct. I am getting some success with the sender (a j/y unit that I added due to a faulty fuel level gauge reading) as it does register proper fuel level now.

Would the strain of going up a hill in very hot weather without an in tank pump put enough strain on the main pump, which then added more voltage to the fuel pump relay, heating it up and increasing resistance on old solder joints to the point that the pump would not run? I let the car sit for a few minutes after I struggled to get it up the small hill, and it fired up, got me to my street but started to cut out again on a slight incline as I approached my house.

Guess I'll have to pull out the in tank pump and test for voltage with the sender out of the tank (and away from the fuel source of course).
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Old 08-08-2018, 10:13 AM   #3
EivlEvo
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Why are you so focused on this pump? I'm not saying it's wrong... but what led you there?

What is your fuel pressure at the rail? On a lot of older 240's they've sat for awhile and their injectors end up clogged or gross.

More over... and to answer your question. Sure... a bad pump under high demand can cause issues. How much fuel is in the car? To give you a comparison, on my +t I had no issues with fueling out of boost when my main pump was on it's way out, but in boost below about a third of a tank it couldn't keep up at all.
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Old 08-08-2018, 02:50 PM   #4
petebee
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I appreciate your inquiry. It seems like a vapor lock problem - hot engine, hot climate, car going up a hill with gas tank a bit under half and a confirmed non-functioning in tank pump. I actually think it is the sender not the pump (unless my new pump is bad). I experienced similar issues here during NC summers with my daughter's 240 years ago. It would stall and quit running under hot environmental temps and we traced it to the in tank pump not working. Once it cooled off it ran fine.

I am leaning away from fuel pressure and injector problems as the car runs fine otherwise.
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Old 08-08-2018, 04:20 PM   #5
EivlEvo
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If you're in or near Raleigh and want some help going through things I have plenty of stuff and willingness to assist.

Vapor lock is generally related to fuel pressure but of course can occur with odd things... I might suggest looking at your FPR.
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Old 08-08-2018, 05:10 PM   #6
petebee
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Quote:
Originally Posted by EivlEvo View Post
If you're in or near Raleigh and want some help going through things I have plenty of stuff and willingness to assist.

Vapor lock is generally related to fuel pressure but of course can occur with odd things... I might suggest looking at your FPR.
Thanks for the offer! Good point about the fuel pressure regulator...I'll pull the vacuum hose and see if I smell fuel.
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Old 08-12-2018, 09:07 AM   #7
Lazarus
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Quote:
Originally Posted by petebee View Post
The fuel pump relay was very hot when it decided to run like crap.
Thanks!
What about this? Relays are not supposed to run hot. It may not be the whole problem, but it is part of the problem. This is a common maintenance item.

-L
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Old 08-13-2018, 12:26 PM   #8
petebee
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So I pulled the vacuum hose off of the fuel pressure regulator and smelled gas, indicating a bad FPR. I got a replacement from Autozone along with a new fuel pump relay (the Duralast relays are designed by Wells...which is supposedly a well-built alternative to other aftermarket options). I put in both and the car definitely fired up much more quickly than before.

I also confirmed that the in-tank pump was not working at all, so I picked up a new sender unit from Rockauto. It was strange as the new Volvo sender o-ring that I installed only a few weeks ago had already swollen to a point where I could not get the lock ring to seal at all. Ordered one and it is on its way. I did confirm that the in-tank pump now works by jumpering fuse 6 to 4 and both pumps buzz.

Hopefully this fixes everything once I button up the tank.
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Old 08-15-2018, 09:42 AM   #9
EivlEvo
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Be sure you check the wiring on that sender. They're notoriously wired backwards. So like... be sure your pump is running the CORRECT way.
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Old 08-15-2018, 10:25 AM   #10
petebee
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"+" mark on pump connects to wire that runs up to external harness, "-" mark connects to the ground wire that connects to the ground on the plastic cover of the in-tank pump. Maybe I'll disconnect the feed hose at the main pump and test flow before calling it done!
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