Question about 1998 BMW 7 Series

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1998 BMW 740iL dies and has long cranking

I have a 1998 BMW 740iL with 120 kmiles that has started to occasionally die at idle or while driving, recovering with a restart. Recently, and also for the first time, it has started to also take long (several second) cranks automatically, trying to start, that I stop and restart easily. Any suggestions?

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  • chris_r_webs Jun 11, 2009

    Thanks for the suggestion: you're right, no check engine light. The spraying made a big difference to the engine dying (was twice a day, now once a week) but the long cranking still happens every third time that I try to start. Because the car cannot run without the air hose connected, I could only run the CRC intake cleaner in a few times (1/4 can), stopping & starting in between. I did also buy some air-flow-sensor cleaner and carefully clean that. Could any of this be helped with a new fuel filter (I have one) since it is original? FYI, I changed both cats and all 4 O2 sensors a year ago. Should I persevere with cleaning?

  • chris_r_webs Jun 18, 2009

    Following your thread of a problem with the fuel delivery, I looked at records and realized that the fuel filter was original and had not been changed in 130 kmiles. Changing it last week secured victory over the long cranking – now I have my beautiful, powerful 740iL back.

  • chris_r_webs Jun 18, 2009

    Thank you for the quick response and great suggestions. Simply cleaning the intake and replacing the old fuel filter solved problems that could have cost me hundreds of dollars at the dealer!

  • chris_r_webs Jul 26, 2009

    O.K. my euphoria was short-lived, and the long-cranking and occasional sudden death continued. So, having already changed the fuel filter, I have today now replaced the in-tank electric fuel pump, expecting victory - but the problem continues unimproved. Again, within the last year I have: new O2 sensors and cats, new fuel filter and pump, new spark plugs, new coils, etc. and the car runs otherwise PERFECTLY with strong steady idle with no "check engine" light and no fault codes showing up when I look for any. Any ideas?



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I have been dealing with this issue for years, i assume u have no check engine light on. Before doing any other repairs do this procedure I developed in the dealership shop to repair these stalls near or at idle problems, works most of time is done exactly as described in the procedure.

Here is the common cause of surges, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

Posted on Jun 03, 2009

  • yadayada
    yadayada Jun 12, 2009

    It sounds like u have another issue besides the dirty intake, I believe the electric fuel pump has a defective pressure check valve, to check this problem buy a fuel pressure test gauge from a parts store, on the top of th engine u will find a fuel pressure test port located in the fuel supply manifold to the fuel injectors (manifold goes over the top of the fuel injectors), it will either look like a metal tire valve or an AC charging port, it will have a cap on it, hook up the special fuel pressure test gauge u bought and run engine, verify u have no leaks at the test gauge hookup to the test port, note the pressure at idle and then shut the engine down, the fuel pressure should not drop more than 5 pounds, if it does the built in check valve in the fuel pump is defective and you will need to replace the fuel pump, the pump is located in the fuel tank which u will need to drop down to access pump.

    When the pump dosn't hold pressure it allows the fuel to gravity drain back into the tank, this causes long crank times and start stall conditions, this symptom can be intermittent as it is caused by a sticky check valve ball.

  • yadayada
    yadayada Jul 26, 2009

    carbon deposits on the back of the intake valves can cause this, have a boreascope inspection of the back of the intake valves done, also it is time to take this to a dealer and have a live data exam done with a cold engine to see what the engine coolant temp sensor is doing, u may have dirty fuel injectors as well..


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If the idle is low, you may want to adjust it. Check first the spark plugs, high tension wires and ignition coil if they are still in good condition. You may also want to look at the fuel filter if it needs replacement. At times loos ground wires and leaks in vacuum hoses may be the cause.

Should you experience some erratic idling as well, I would suggest to clean the throttle bodies and Fast Idle Thermo valve.

Posted on Jun 11, 2009


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