K Series Starting Issue

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K Series Starting Issue

My car is difficult to start with out touching the accelerator. Once started for the first time it will start again no problem. Seems to idle fine and runs ok. If I then leave it a few mins it will then need the accelerator again to start.

AICV sounds like it is working and I have taken it off to observe it moving, which it is from closed to slightly open when cycling the ignition.

I have reset the TPS and disconnected the battery to try and reset everything.

Any ideas?

Alastair B
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Have you checked the throttle stop position and free movement of the throttle cable cable? Try opening the stop by a quarter of a turn at a time and lock.

SM25T
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Usually means the battery is starting to fail. Mine wouldn't start without a bit of throttle when this happened. Replaced battery, starts and idles on the button.
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I fitted a new battery about 7 months ago and it is kept on a conditioner. It turns over fast and with ease.

The throttle cable is free moving and not sticking. I assume you are talking about the stop screw that holds the butterfly open very slightly. This is tight and fitted with a tamper free cap on mine. I thought this was only to be adjusted with some sort of specialist equipment?

I will try opening this temporarily with a thin shim to see if this has any affect.

Thanks for the suggestions!

revilla
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The throttle stop screw will give you an engine that stalls at junction if too far closed and a very slow return to idle, possibly idle hovering too high and poor engine braking if too far open. And a big on/off power step taking up drive from the overrun. It's a very sensitive adjustment to make it drive nicely. I wouldn't play with it to fix a starting issue, it won't be the problem.

As Ian (SM25T) says, it can be a failing battery. The symptoms are surprising, the engine will still spin over rapidly but the engine won't start without a bit of throttle and you need throttle for a few seconds to keep it going until it settles.

The explanation is that the inrush current as the starter motor first kicks in causes the battery voltage to drop for a tiny fraction of a second, often as low as 5V for a few tens of milliseconds. The ECU sees this voltage on the "ignition sense" input and thinks you've turned the ignition key off. So it recycles the IACV to the correct position for the next start by winding it fully closed to establish the end position, and then open a predetermined number of steps. Once it has decided to do this it completes the process even though the voltage recovers rapidly. Until the IACV recycle has finished it won't idle (as the idle air supply is closed off).

As well as a battery problem, this can be caused by wiring resistance issues and other things.

In particular ... do you know what type of starter motor is fitted? There have been persistent issues over several years with Brise starter motors causing these symptoms. I investigated a couple of cases with an oscilloscope and found that the Brise starters were causing an unacceptable voltage transient even with a healthy battery and electrical system in some cases. At one point I had an engine running in a test rig and a friend had a car with a Brise starter which had these symptoms. We swapped starter motors and my test rig immediately acquired the fault, whereas his car was cured.

What type of battery do you have?

The odd thing is that as you say, there is absolutely no hint from the cranking performance that anything is wrong; the battery is still able to spin the engine over rapidly in most of these cases.

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

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It is a banner battery and quite new. It appears to not be struggling at all when cranking so I had assumed that this is not the issue. I will try connecting a jump starter to see if it starts, will this prove a duff battery if starts or mask something else?

Once I have started it and turn it off almost immediately it will start without any throttle, leave it 5 mins and it is back to needing throttle to start.

I will have to look at what starter it has.....

I was hoping it was just a failing sensor but which one?

Many thanks for your thoughts and help.

john milner
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I have had starting problems caused by a failing crank position sensor. It was playing up intermittently and in the end prevented the car from starting at all. Throttle didn't help with starting though.

Throttle does help with a sticking or failed IACV which I think I have again and need to sort out.

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I have a Brise starter motor fitted.

I have tried a couple of things to see if I can get it to start without throttle when cold. If I connect a jump starter it starts and also it will start if I disconnect the power to the AICV.
 

Does this suggest that I am seeing a dip in voltage too far when starting making the AICV cycle - cutting the air supply at a critical moment?

Any ideas?

revilla
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This sounds like an exact re-run of the scenario I described in some detail in my earlier post. You've pretty much proved it's the IACV that's doing it by "paralysing" it (and it can't be that it's sticking, because you've just made it completely stuck and it fixes the issue).

It just seems as though, even with a perfectly healthy electrical system otherwise, the Brise starter model just pulls too much current briefly for the small battery to cope and you get a transient voltage dropout.

I've come across quite a few cases of this now.

As far as I know the only real solution is to swap starter motor ... a standard Magneton, a WOSP or a Powerlite. For what it's worth I think my friend who had this issue switched to a WOSP and never had the issue again.

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

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Many thanks, I will try a new starter motor. Does something degrade in the started motor making it draw more power over time?

Are WOSP the best to go for and I see that two are listed on their website, any idea which one to go for.

I think I will start with a phone call to Redline.
 

Thanks Revilla for your advice I will post here the result!

revilla
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No, don't think much degrades in the starter, but the battery does.

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