740 won't start

[DVPV]

Hello. My Volvo 740, 1988, 2.3i wan''t to start. Problems have begun after repair of brakes, which lasted 2 months. After that the car was not started. It was found out, that the pump in a fuel tank does not work. After its replacement the engine started for 10 seconds and stops. At switching-off the MAF sensor engine works on idle speed (500 rpm). After replacement MAF sensor on good mone, the situation has not changed. I have checked spark, mail fuel pump relay, fuel pump, fuel filter, all is ok. Any idea will be useful.

[Kmaniac in California USA]

Volvo Rule of Thumb: If you replace a faulty in-tank fuel pump, better replace the main fuel pump, too, before it fails. Also, never replace the main fuel pump without inspecting and/or replacing the in-tank pump and inlet filter sock, or you run the risk of rapid, premature failure of the new main fuel pump.

The reason most in-tank fuel pumps fail is because the inlet filter sock has deteriorated, causing dirt to foul and jam the in-tank pump. This same dirt will also start to foul and contaminate the main pump, as well. The inlet filter sock is the only filter protection for both fuel pumps. And this filter is not replaced routinely like the main fuel filter.

If your car is not starting, take a blunt object and tap on the main fuel pump under the car. If it starts right after that, replace the pump as it is contaminate with dirt.

You can search this forum for my experiences with the fuel pumps in my 740.

Let us know what you do and what you find.

[DVPV]

Main pump have 5 atm. pressure ( I have checked on diagnostic equipment). 12 V and ground also ok.

[Kmaniac in California USA]

If you are sure you have both spark and fuel, I can't see a reason why it wouldn't start.

Have you replaced the timing belt recently??

[DVPV]

Engine start, but working only on idle speed ( 500 rpm ) and with disconnected MAF sensor, after acceleration engine die.

[MadeInJapan]

Sounds to me like a bad MAF sensor. See if you can get one off of another car to test this theory.

[Kmaniac in California USA]

Here's another thought. Check, too, for vacuum leaks. You said this happened right after brake work. Could be that the power booster hose was brittle and got cracked during the work. Now the hose may be cracking more. In fact, check all your vacuum hoses and the vacuum reservoir tank for cracks and leaks. A major vacuum leak would have great impact on your idle speed.

[DVPV]

where vacuum reservoir located ?

[Kmaniac in California USA]

The vacuum tank is located under the engine, in front of the crossmember and between the front tires. At least that is where it is on my 740. You will need to remove the splash shield under the engine to see this tank. This tank is used to maintain constant vacuum on the HVAC control panel. If this tank has a major leak, you will not be able to select ventilation airflow through the dash vents or anywhere else as the HVAC defaults to defroster vents only with no vacuum available from this source (a diagnostic hint). There is a large vacuum line that runs from the intake manifold to the tank with one T connector to the HVAC system.

Another vacuum line to check is the vacuum supply to the Idle Speed Controller (ISC). This is another large vacuum line that runs from the intake manifold to the ISC on one side and from the ISC to the plastic air intake tube between the air mass meter and the intake manifold.

Of course, a third vacuum line to check is the vacuum tap for the power brake booster. This is a large line that runs from the intake manifold to the power brake booster.

Check these three lines and let us know what you find.

[DVPV]

Kmaniac in California USA, thank you for avaices. I check vacoom hoses from manifold to brake booster, they are ok. Also was chacked ISC hoses, also good. When I disconnect ISC, idle speed do not change. Is it normal ?