K Series Starting Issue

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I have fitted the new WOSP starter motor and the starting issue with the AICV appears to have gone away. Many thanks all especially Revilla. Supplied by Redline, ordered on Wednesday afternoon and delivered first thing next day - great service as always.

I will see how it goes and I may have spare Brise starter motor that would suit somebody without an AICV fitted!

revilla
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Glad you got it sorted. It's quite an unintuitive problem to get to the bottom of, you probably thought I was talking nonsense when I said it was the starter motor Smile

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

anthonym
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Andrew is this relevant:

 It is advisable for the connection to the 'S' terminal to be made as directly to the battery post as possible to eliminate voltage drop in cables

and

Be sure to use cables that are rated to carry adequate current.  If the cables are too small in cross section then there will be a high resistance causing voltage drop and overheating.

That was also what Tim Brise told me to do. Heat would also cause a voltage drop over time.

Maybe you recall how you installed my new engine loom in this regard? (as ever thank you for that).

edit: not important, but interesting to me as the whole lot is being refitted now during chassis refurb.

Does my car have an i a c v ? edit ans = no

has Brise been taken over? edit answer faq = yes

https://brise.co.uk/faq.html

ftaod I have a Brise in my KR500 and have never had this problem.

edit: IT SEEMS throttle boddies means no IACV

... is that tempting fate? I hope not.

anthony

 

ouch! "spikes can also be produced if the engine is stopped with the battery master switch rather than the ignition switch."

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anthonym
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yes my question was rhetorical as you will note by my having also posted that link to the faq.

anthonym
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Andrew iiuc this issue arises when the engine is cold but not when warm? If that's right can it be an ecu mapping question? Even if not, could it be?

I googled:

emerald k6 iacv settings

wondering if this IACV thing can be influenced by the ECU mapping which usually is in charge of most things.

and found this:

Idle Air Control Valve & Cold Start Calibration.

To suit engines using TPS as primary load reference.

http://www.emeraldm3d.com/Emerald/IACV/TPMS/crib_sheet.pdf

page 7

There are two aspects to running a cold engine, initial starting and then the warm up period. For example; the engine may fire straight away but stall after a few seconds of running.

page 8

If the engine fires and then cuts after a few engine turns, you can increase the number of turns that this enrichment is applied for, and/or change the % of extra fuel injected

Whether Emerald or any other ECU I imagine. Any idea how to program a mems? ;-)

Anthony

 

#5

#20

https://www.emeraldm3d.com/software-manuals

revilla
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Hi Anthony,

There are a whole load of different issues being mixed up here.

The cause and effect of a voltage drop depend on where in the circuit it occurs.

If the wiring back to the battery is poor, the voltage measured at the starter or solenoid will be lower than the battery voltage due to the voltage dropped through the resistance of the wiring and connections. That's one kind of "voltage drop". The voltage at the battery itself won't be affected (the voltage at the battery will still go down under load as it would with good cabling due to internal resistance inside the battery, but no more so and in fact probably less so with like cabling as less current will be drawn).

In this case, whether other circuits are affected is a bit if complicated question. Anything wired directly off the battery will not be affected as the voltage drop isn't seen at the battery. However in cars with an FIA switch most of the circuits are usually taken off the starter motor main terminal to out them after the switch. In this case those other circuits will be affected by voltage drops caused by the main motor current draw, but not by issues with the solenoid wiring. In the car we out in a distribution post between the FIA switch and starter main terminal; so it would depend on where the resistance was, upstream or downstream of that list, as to whether other circuits would be affected.

However, the voltage drops we are talking about with the Brise starter are of a completely different nature. In this case there is no problem wit the wiring ... in fact the better the wiring, the worse the problem will be. In this case what is happening is that the starter motor is, for a few milliseconds when first engaged, drawing a very large current - sufficient that the voltage drop across the internal resistance of the battery means that the voltage measured directly across the battery terminals falls to a low level. As low as 5V for a very short time. You need on oscilloscope to see it, not a multimeter, as the voltage only falls that low for milliseconds 

In this case, all other circuits will be affected as everything feeds off the battery, either directly or indirectly.

In the first case, the voltage at the starter would be low but the voltage at the battery would be normal. In the second case, the voltage everywhere would be low.

The starting issues are caused by the transiently low voltage being sensed by the ECU, which reacts as though you had turned off the ignition key. It then recycles the IACV ready for the next start. On a standard K, after switching off the ignition, you can hear an electronic whirring and clicking noise for a few seconds. This is the IACV recycling and is what is triggered by the transient low voltage.

The IACV is a stepped motor. It's not a servo, so the ECU doesn't gety feedback as to its current position. It relies on just telling it to increase or decrease by a number of steps. That all works fine so long as it knows where it is to start with. The only way it can do this is to send it enough "close" instructions to guarantee that it is fully closed, then it knows where it is. That's what you hear it doing, a long string of "close" pluses followed a number of "open" pulses defined by the map which places the IACV in the correct position for starting.

While the ECU is busy recycling the IACV, it obviously can't use it to manage the idle. It will be too far closed to maintain the correct idle speed for most of the procedure, therefore the engine dies immediately after starting ubkess you give it some throttle (the IACV is just a little throttle under ECU control in parallel with the main throttle, and being small only really has any effect when the main throttle is almost closed).

Cars with throttle bodies would not normally have an idle control valve, no. So your car doesn't have one. Everything else about the MEMS3 ECU recovers so quickly from a dropout that you wouldn't notice a problem. By the time you release the key from the start position it would have recovered and would run normally. It's only the IACV recycle that takes a significant amount if time. So without an IACV I doubt you would notice any running issue even if the ECU was getting upset by a transient voltage dropout on starting.

In your case you have an Emerald ECU. I'm not sure whether they contain any filtering on the ignition sense inputs that would avoid them responding to a transient dropout or not, but they mostly get used on cars with throttle bodies so as described above, if they did suffer from the same issue it would probably go unnoticed.

And yes, similar problems could be caused by mapping issues, but that's not the issue here. Startup and warmup enrichment problems would not be resolved by swapping the starter motor. The MEMS ECUs have quite sophisticated startup and warmup corrections which don't tend to need much tinkering with. The Emerald does have various options to correct the startup and warmup enrichment etc. as you have found, but they're just not the issue here.

There is some correlation with engine temperature, and yes cold engines do seem to suffer from the problem more than warm engines, but I think there are two contributions to that:

Firstly, the resistance of copper increases with increasing temperature. A hot engine often means a warm starter motor (you've already alluded to the issues caused by exhaust heat in the starter). This means that when starting a bit engine, the starter will drawn less current from the battery. Intuitively you might expect this to lead to worse starting performance; it does, but a warm engine is easier to start anyway and in this case reducing the current draw will reduce the voltage drop at the battery and therefore reduce the chances of the IACV recycle being triggered, so you will see the issue less on a bit engine.

Secondly a hot engine will turn over more easily, meaning that the starter motor will start turning more quickly. The transient inrush current will therefore not persist for so long and the transient voltage drop will be shorter.

There are two things which limit the current in the starter motor. There is the resistance of the wire coils; this is largely a DC effect and just determines the current through Ohm's law - current is voltage divider by the resistance. But there is also the inductance of the coils, which is an effect connected with the energy stored in the magnetic field generated. This is an AC effect and resists changes in the current in the coils. So when first energising the coils the inductance effect dominates, resisting the change in current and forcing the current to ramp up with time, until eventually the current is sufficient for the resistance to start to dominate, limiting the ultimate peak current. When the motor is turning rapidly, the commutator and brushes are constantly switching different coils on and off rapidly, so the inductive effects are more important as the coils aren't energised long enough to reach the resistive limits. When the motor is first engaged and is only turning very slowly, the coil current has time to ramp up a lot higher.

And yes, you can get nasty voltage spikes if you turn the engine off using the master switch, but again theses are quite unrelated.

In this case, the voltage pulses produced by the alternator windings are loaded down by the battery; if you disconnect the battery with the alternator spinning it has no load and will produce damaging high voltage pulses.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

anthonym
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thanks ever so much for all that Andrew, I'm printing it to read over coffee; looks like it will be fascinating.

anthonym
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guess what? I have made my usual mistake concerning the most obvious. I thought this was all about the alternator and (finally) from your above I see it's the starter. Though I have a Brise starter too. But no IACV.

Q: How long is one turn of the crank when starting?

Q: How long is the transient voltage drop?

How about making the ECU deaf for that time? Just to the voltage drop.

anthonym
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Is this:

The IACV is a stepped motor. It's not a servo, so the ECU doesn't get feedback as to its current position. It relies on just telling it to increase or decrease by a number of steps. That all works fine so long as it knows where it is to start with.

 

about this (page 14 K6 manual):

If using a 4 wire stepper motor then you can also specify whether the Stepper motor should re-sync it’s home position at key-on, key-off or not at all. The re-sync routine is useful not only from the synchronisation point of view but also as it helps to keep the valve’s working surfaces clean and free of deposits.

?