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.

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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

  • Have you pulled the cold start sensor up in the head under the no 3 inlet. Hard to get to and even see but I had the same issue with my 740 b230 changed the sender problem gone. Just an idea that worked for me

  • That's the cold start injector

  • A 740 doesn't have the same set up as the bosch k. The sender for cold start is up under number 3 inlet tube at the rear of the head. When it is crook the car won't start cold but will hot. When I did a recent engine swap on my 740 I forgot to change the sender and had the cold start issue until I took the one out of the old engine and swapped it. Bugger of a job had to us a die grinder to modify a 3/8 drive socket so it would fit over it. A swivel and a couple of extension bars and you can get it out.

  • That's the coolant temp sensor for the ECU. We were getting confused with the cold start injector which lies in the manifold not the cylinder head

  • Correct a Mondo cobber

  • SLT16SLT @SLT16 Gold Coast

    Yes I did the coolant temperature sensor, genuine Bosch.

    Still no difference.

    What i have noticed is, when you unplug the sensor on a cold start the car starts with no trouble.

    I know its not the wiring harness because it was completely redone in 2012 by a reputable individual.

    What are the consequences if i drove with it unplugged for easy cold starts?

  • What fault codes do you have?

  • SLT16SLT @SLT16 Gold Coast

    This is LH2.2, there are no electronic diagnostics.

  • edited May 29

    If your problem is only surfacing when cold, and everything works perfectly once warm, that is a clue. When you disconnect the connector for the coolant temp sensor the ECU is not getting the required signal to add extra fuel injection during cold cranking and running, it's like a choke, helps with cold running


    Try what you suggested and see

  • Sorry.

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