740 & 760 Very hard cold start in a 740 b230f.

Hi all,

Since December, I've been experiencing a very hard cold start on my 740. Cold, as in more than 12 hours.

This is how it would go: I would start the car in the morning, i can feel its very hard to crank but once it comes to life the RPM is very low (below 500) and fluctuates quite heavily. After 3 - 4 seconds of this, the car either stalls and i have to crank it again, or the RPM jumps up to 1.5k and drops back down to around 950 on a cold idle and the car runs fine after that. When the engine is even slightly warm, say after 5 hours of not running, it will start first time. But any longer than that, and its very hard to start.

Out of suggestion, I've replaced the fuel filter with an OE one, replaced the fuel pump check valve, and put in some injector cleaner in a full fuel tank. The external fuel pump is working correctly and has been checked.

But what i have noticed is after i've put the fuel injector cleaner in and put some oil flush for an oil change, this started occurring about a week later. I don't know if this is a coincidence, but maybe the cleaner loosened some gunk up and caused a build up?

My mechanic checked the fuel pressure regulator and that's not the problem. He suggested replacing the fuel line from the filter to the fuel rail, but will this really fix it? The line is not frayed or anything and seems unlikely.

Comments

  • What year model is your 740?

    Where are you based?

  • SLT16SLT (@SLT16) Gold Coast

    Its an 87 740. LH 2.2. I'm on the gold coast.

  • Check the IAC valve next, it can become blocked and not function properly on cold start

  • SLT16SLT (@SLT16) Gold Coast

    Cleaned the IAC just a week ago, and also cleaned out the oil trap box and the flame trap.

  • There is an idle adjust, also the throttle closed switch (TPS)

    Also the engine coolant temp sensor (ECT) and then the air mass meter (AMM)


    Lastly..... what voltage is battery dropping to while cranking?

  • SLT16SLT (@SLT16) Gold Coast

    The TPS is working as i've already tested it. Idle is adjusted and is running at 750 rpm when engine is at operating temp.

    Not sure about coolant temp sensor and MAF. What is the correct procedure in testing those?

    I'll also connect a volt meter today and test the battery as you suggest.

  • When you cleaned the iac how did you test it?

  • The AMM cannot be tested reliably, aside from swapping to another AMM meter, pn 0280212007

  • SLT16SLT (@SLT16) Gold Coast

    I haven't tested the IAC. What voltage has to be between which pins? Also i just remembered i swapped the mas air meter over in the past while testing another issue and it is perfectly working, as i know for a fact my 2nd one is a good working condition spare.

  • You could easily disconnect the electric plug and try it one morning with it not working, I’m not sure what the range is for testing. But I would clean the insides first, you will need to remove it to clean it

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