Hello again all,

Here is a link to problems leading up to what I think has been the problem all along...
https://volvoforums.com/m_96451/tm.htm

My 88 760 Turbo gets down to about 1/4 to 1/2 a tank of gas and starts to run crappy and will eventually not run at all. I know its not out of gas. Actually one thing thatsucks is that prior to having work done on my car my gas gauge worked perfectly, now it doesn't show full when I do fill it all the way up and sometimes it does after being on for at least a 1/2 an hour or so.

Anyway both fuel pumps are suppose to be new...I know the one is working under the car..I can hear it. From myprior post and talking with "Tech" I'm thinking that the pump in the tank is not working or maybe doesnt have power to it??? Don't know for sure. I'm going to work on it this weekend. Im not to up on electrical problems , so my question is about testing power going to the pump.
Questions:
1. what kind of tester do I need to check power to pump?

2. should there be power to the pump always when the key is turned on?

3. Or maybe the question should be how to test pump with a tester??

Well I hope thats clear enough, I'm going to take the carpet out of the truck and the access door to the pump and fuel gauge sensor. I'm hoping to be able to fix whatever is wrong with the sensor as well without having to buy a new one. We'll see. Thanks in advance. Bunky

 

1. Voltmeter, multimeter or 12volt test lamp.

2. Yes.

3. Stick with 1.

Two wires on the pump: pink (live)and black (earth or ground). Switch ignition on, touch both, at the same time,with the leads on the meter or the test lamp and you should get a reading.

 

Thanks Bill....I think I've found the real problem. The mechanic who changed the in tank pump put the damn sensor unit back in wrong. Instead of the sensor unit or float/pump being down toward the bottom of the tank they had it postitioned almost sideways.

I didn't discover it till today , because I went to the junk yard and got one out of a newer 91 940 ...same sensor and pump anyway and noticed right away that the position of the sensor unit was different and of course after I got it out I could see clearly this is probably the problem of the car starting to stumble and quit shortly after using about a 1/4 tank of gas aftertopping off the tank. Heres some pictures..
This is the way I found it once I took the access panel off. When I installed the new one I had to turn the unit about a 1/4 turn clockwise for the sensor/fuel pump to be at bottom of tank. Why the mechanics who installed it in the first place didn't see this is beyond me...anyway I just want my baby back on the road.

This is the unit I pulled out of a 91 940...I think it was a 940 , I saw so many Junked Volvos today I was going nuts. Anyway I did install the newer unit since I went to the trouble of pulling it out of the car at the junk yard. Cost $27.50 American dollars. I hope this does solve the problem I've been having and I did take it for a test drive for about 10 miles or so around town...will do more tomorrow and so on.

Thanks again Bill of Durham your a "Prince".

 

Just one minor, possibly major, point. Did you put a new sock filter on the replacement unit? If not I would suggest you get one ASAP and put it on or you risk damaging your main pump.

By the way Durham is the Land of The Prince Bishops.

 

I did put a sock on the replacement pump....actually that is a picture of the old one which didnt have one on it. I looked in the tank the best I could to see if one was floating around,didnt see it though. Again thanks for all you help.

 

Ok....I think I still have a problem.The car is running still since I found that the last mechanics that worked on it installed the fuelsensor/in-tankpump in sideways.So its picking up fuel now,but Im not getting any power to the in-tank pump, I'm 99.9% sure. The main pump just sounds noisier than normal as well. I am getting power to the fuel sensor though so I know my tester is working. The in-take fuel pump is NEW as well. Also when I take the fuse out of the panel and turn on the key I'm not showing any power either with the tester. Another thing that concerns me is that on fuse 31 which is the in-tank fuel pump and the "lambda sensor" if this Lambda sensor is not getting power as well, what would be the syptoms of this? All I know about the Lambda sensor is that its on the exhaust somewhere under the hood but I haven't really seen it yet or know how to test it for power.

Again this is a 1988 Volvo 760 Turbo Intercooler Sedan 4cyl. with two fuel pumps, now it is my understanding that when the car is running that "both" of these pumps are alway pumping. Am I right about that? If that's the case can I re-run a new wire from the fuse panel and that wouldn't conflict with anything? Usually Bill of Durham comes to the rescue so I'm hoping Bill that you can answer this question as well.

It just seems to me that if the pumps do run the whole time when the car is running that running another wire from the fuse panel would be OK?....But if the power comes through the ECU and is regulated by this , I don't know if bypassing it would harm anything. Let me know.
thanks , bunky

 

My wiring diagrams and fuse list show that fuse #30 is for the in-tank pump and Lambda-Sond. Fuse #31 is for the fuel pump relay which runs the main pump.

However, to answer the questions: if the Lambda-Sond is not receiving power/not working itshould illuminate the Lambda light on the dash. On US models I think that is the Check Engine Light.

Both pumps should be running when the engine is 'on'. The in-tank pump basically primes the system and the main boosts the flow to the required pressure. Running a new wire from fuse #30, or #31 if that is how it is on your car, should present no problems. Both fuses are ignition controlled and the in-tank pump is not directly connected to the ECU.

The main pump is probably noisier because it is doing the work of both pumps.

 

hey bill,
Thanks again for the quick response, you are right about the fuse numbers. With key on and I test the #30 fuse slot I get no power. I also don't have any check engine light either so I'm assuming that the Lambda-Sond is working?

But I think you answered the main part of the question. I can run a new wire from the fuse panel to the in-tank pump. That seems to be my easy fix, well sort of, still going to be a challenge running and hiding the wires, but thats my problem (haha). Anyway thats my project tonight it looks and thanks again.
Denis (bunky)

 

Before going to the trouble of hiding wires etc why not run a wire from the battery positive to the pump to see if it does work?

 

Bill, I have done that already and the pump works. But the positive wire originally feeding the pump doesn't and it doesn't at the fuse panel as well. Its so hard to work at or behind the fuse panel , so I think I have found a "unused accessorie plug" that is under the drivers side / behind radio that I can use to feed the pump. It cuts off by the ignition and back on when the key is turned on, so I think this is my answer? I still will need to run a positive and ground wire up to that dash area though, that's tonights project. Last night I was trying to figurea way to not have to do this ,but I don't see any other way now. I also didnt get to spend alot of time last night working on it because wife had to work late and I had Daddy duties.

Of course if you have any suggestions , I'm all ears.....let me know....thanks again Bill.

bunky