Volvo: 1990 Volvo 760gle problems, mass air flow sensor, volvo 760 gle

Question
QUESTION: Hi Ray,

    I have a 1990 Volvo 760 gle. I'm only 18 and know absolutely nothing about cars. My Volvo has always ran great and now its been stalling on me and all that stuff. We've had to tow it twice, almost three times tonight but we gave the car a 30minute break and it started up okay. We took it to an auto shop and got a diagnostic test on it and they told use nothing was wrong. Apparently there is something wrong if it keeps stopping on me. I can tell when it is about to it seems to kind of register stuff late. Like if I were to push the gas it registers a few seconds late. And then it starts doing that "coughing" thing and stops. We thought maybe some how it fixed its self or maybe it was due to the heat since we live in Las Vegas. But it hasn't been hot the past few times i drove it and it stopped on me. We can't think of anything else it could be, so I was seeing if maybe you could help. Well anyway, I would really appreciate it to hear back from you.
       
       Thanks for your time,
         Tara



ANSWER: Tara,
First you need to find a shop that works on and knows the Volvo's. They do have their own little faults and problems. First thing that I would test is the fuel pump in the tank to be sure that it is working. We call that a pre-pump. That supplies fuel to the main pump. So when the pre-pump fails the main pump has to pull fuel through a pre-pump that is not working and that puts a strain on the fuel system. If the main pump is loud when running that also is a sign of either the pre-pump or bad hose in the tank that connects the pre-pump to the hard line on the sending unit. I would also test the fuel pressure and make sure that the fuel pressure regulator is not leaking. Pressure should bt 42 psi.
Also on a '90 you should be able to read fault codes. I have had a Mass air flow sensor that gives that same kind of symptoms. That being the case and since you have no mechanical knowledge find a Volvo repair shop and have them look at the car, maybe let them drive a few days to see if they can find some fault.

---------- FOLLOW-UP ----------

QUESTION: To date, we have had a diagnostic test run on it, fuel pressures are good, this problem is intermittent. The stalling happens under any circumstances. We believe the fuel pressure to be good, and also the fuel pump relays are good, and everything is normal. Does it need to have a higher octane? After about a half hour it usually runs fine with no signs of troubles. Is there a circuit breaker that I'm not aware of that could be faulty?

Thanks Again

Answer
Tara,
During the time the car stalls is there fuel at the rail, pressure? If the fuel pump relay heats up and opens there maybe a temporary loss of power to the pumps. Now you seem to say the after 30 minutes of running time the car will run without fault, correct? If this is a cold engine condition then look for tune up parts, and check for possible vacuum leaks.
During the "diagnostic test" where fault codes read? Now some things that cause stalling, fuel pump relay, pre pump inop, radio suppression relay (for injectors), power stage, air mass meter, flywheel pick up, fuel pressure regulator, shorted wire harness, clogged fuel filter.
Octane for a B230FT engine is 87. There are not any circuit breakers that control the running other than relays and fuses. Relays sometime heat up and open causing no power flow, then cool off and make contact again.