hi all,
i have a 91 740 wagon(regina) i came to this site for help in replacing my in tank fuel pump (which had died) and once i replaced it my car was running like new, but only for two days. after the 2nd day it staid on for 15 minutes then died then only a few minutes then it would die, now it only stays on for about 2 seconds then it dies.

the one thing i notice is that when it used to stay on for a few minutes if at any time i pressed the accelerator it would die immediately which makes me feel like it's a vacuum leak, but i can't find one

things i've replaced so far:
in-tank pump
fuel filter(and fuel line from filter to engine)
fuel pump relay
fuel pressure regulator
spark plugs
spark plug wires
i also made sure that fuel was reaching the engine(not pretty though).

any thoughts on what this could be?

 

Change the diffuser relay on the watercoolant compartment.Common fault and could be your problem.

 

watercoolant compartment...do you mean the coolant reservoir? also, what does the diffuser relay do?

 

Yes.And Its got to do with the gas from fuelpump and the engine firing.You can open the relay and solder the dots on it

 

oh ok thanks. i'll check it out and report back my results.

 

ok, so i replaced the diffsuer relay but still the same problem, i've been searching for a vacuum leak but still no luck finding one. it stayed on for about 5 seconds, but as soon as i pressed the gas petal it died (even if i don't hit the gas it still dies a few seconds after it's started)

i feel like there is something on the car (probably something inexpensive and easily over looked) that i'm missing, but given the symptoms i'm at a loss as to what it could be.

 

Bad luck.Anyway,were the fuel and diffuser relay new?
You say fuel is reaching the engine (not pretty though). What does it mean?Are you sure the fuelpump is working and fuel is coming through to the engine?
If the answer is yes to both of the above,then I would suggest you to replace the MAF massairflow sensor just behind the airfilter cause that could be the fault.They are pretty expensive so try changing with another from a friend to see if that is your problem.You can also do the diagnosis at the box inside the engine room and see if you get a code.Check the volvo manual to find out how to do this diagnosis.You could also disconnect the massairflow sensor from the airfilter clean the connecting points with electronic cleaning oil and then connect and start the car and see what happens.Also try starting the car without the airflow sensor (when its disconnected) and see what happens.

 

unfortunately there doesn't seem to be a maf on my car. i think my specific version of the wagon did not come with one.

also, yes to both your previous questions(i removed the hose on the fuel injection rail and plenty of gas came out, and the diffuser relay was new)

 

Then I think you have a temp sensor for the intake air just near the air filter and it may be faulty.Also I would suggest you to do a diagonostic test at the box and get the fault codes.Check out here below how to do it.You may get a code for this sensor.

Engine and OBD DiagnosticCodes

You may get 122 code