Cold start issue (for a change!)

Cold start issue (for a change!)

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QBee

Original Poster:

20,904 posts

143 months

Tuesday 25th July 2017
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You can only do about two or maybe three fully cold starts per day - the heat stays in the block for ages, as does pressure in the fuel rail.

Classic Chim

12,424 posts

148 months

Tuesday 25th July 2017
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^^^ good point. Probably only two this time of year so a long winded affair if your trying to even out cold starts.
I remember being a bit concearned the mapping was being done in summer and might be a bit off come winter but Jay assured me it wouldn't make any difference and I must say he was right. Having mapped them during the winter months these mappers are bound to have the relevant data to get it right any time of year.

I still can't work out why it starts so well in winter, no choke effectively but it doesn't seem to make any difference, steppers do a job, Mbe does iwithout that stepper and still it runs excellent cold. I can only assume the air temp sensor coupled with mass air pressure in manifold sensor then pretty quick reading lambda sensors adjust cold idle as soon as it senses the ambient temp and air mass coming into the engine so a matter of milli seconds after turning over its adjusting mix and timing to compensate cold or wet air and aiding firing. Good firing from cold an engine should idle instantly if the oils not to cold and you have a good mixture it doesnt need raised idle after a few seconds firing as that's warmed the burn area. You just hold the idle slightly higher for about 5 seconds as it clears its throat and will idle in - temperature conditions from then on.
I do have mechanical sympathy so you'll not catch me running a cold engine on idle straight away as I always run it upto 1500 revs and get some oil splash over the cam before letting it idle. The Mbe secret is in using fast changes to cam timing and valve opening/ overlap to soften compression and ease pistons up and over at low revs I think. You don't need much power at low revs on tickover if the timing is helping to spin the engine over easier. More efficient. smile I think that's how it works. These new Ecu are making the engines feel far more refined I know that thumbup

QBee

Original Poster:

20,904 posts

143 months

Tuesday 25th July 2017
quotequote all
The map is set to enrich the fuelling on start up from cold - simple as that

QBee

Original Poster:

20,904 posts

143 months

Tuesday 25th July 2017
quotequote all
PYNEY said:
Hi QBee I'm also having the same problem as you in the last couple of months ?
I have a standard 4.5 but the same issue ? car runs fine apart from cold start turns over longer than normal
will be interested to know your findings or I will be calling mat

cheers keith
The car needs to keep pressure in the fuel rail between uses for a quick start up from cold.
I am starting to suspect, following a chat with Jools, that the issue may be one of the components that maintain fuel pressure letting pressure out. The car is going to Mat Smith tomorrow, as I have to go there anyway with my Saab (for a service), so will park the TVR on my trailer tonight and tow it over in the morning, to give him first dibs on tomorrow's cold start

PYNEY

1,048 posts

217 months

Tuesday 25th July 2017
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Keep us posted qbee will be interesting to find out what it may be , all the best keith

pb450

1,301 posts

159 months

Tuesday 25th July 2017
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QBee said:
The car needs to keep pressure in the fuel rail between uses for a quick start up from cold.
I am starting to suspect, following a chat with Jools, that the issue may be one of the components that maintain fuel pressure letting pressure out. The car is going to Mat Smith tomorrow, as I have to go there anyway with my Saab (for a service), so will park the TVR on my trailer tonight and tow it over in the morning, to give him first dibs on tomorrow's cold start
Two for the price of one. (well, probably not!) Smart thinking there Anthony.

Classic Chim

12,424 posts

148 months

Tuesday 25th July 2017
quotequote all
QBee said:
The map is set to enrich the fuelling on start up from cold - simple as that
No tming advance then?

QBee

Original Poster:

20,904 posts

143 months

Tuesday 25th July 2017
quotequote all
Classic Chim said:
QBee said:
The map is set to enrich the fuelling on start up from cold - simple as that
No tming advance then?
Pas un scooby, mon ami (as they say in the Sarf de France)

Classic Chim

12,424 posts

148 months

Tuesday 25th July 2017
quotequote all
QBee said:
Pas un scooby, mon ami (as they say in the Sarf de France)
smile
I wish I was buddy.
No worries wink

Pupp

12,206 posts

271 months

Wednesday 26th July 2017
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It may be the tank or a union to the tank is weeping, but that's not the problem as neither the outlet or return have any ireal nfluence on fuel pressure seen by the injectors. In fact I doubt it's fuel pressure related at all.

I'd try a new set of plugs in it...

Classic Chim

12,424 posts

148 months

Wednesday 26th July 2017
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Hmm fuel line, that's obvious really yes

He uses Iridium plugs I think.
Can the flame be getting blown out on start up with a Turbo or is that just plain stupid biggrin

Pupp

12,206 posts

271 months

Wednesday 26th July 2017
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Classic Chim said:
Hmm fuel line, that's obvious really yes

He uses Iridium plugs I think.
Can the flame be getting blown out on start up with a Turbo or is that just plain stupid biggrin
Might be obvious but no-one pointed it out until well into page 2.

Nothing stupid about the turbo connection but I doubt that it will be producing enough puff on cranking to affect spark energy and ignition of the charge, although increased cylinder pressures created by FI engines can and do cause problems when significant boost levels are used.

However, if the plugs have been cold fouled repeatedly, perhaps by lots of cranking with a depleted battery using whatever current it can produce to keep the starter moving at the cost of spark energy, then a slightly less than ideal mix might well fail to be ignited. Doesn't have to be much off at all and the fact a small gel battery is being used under the hefty load of spinning up a cold V8 leaves precious little to energise the spark. Plugs that have been cold fouled are difficult, even impossible to 'clean' in my experience. Not sure I'd be running 6s in a turbo but that's another debate (unless they've been cooked and ruined that way but they would have obvious damage and deposits if so)

QBee

Original Poster:

20,904 posts

143 months

Wednesday 26th July 2017
quotequote all
Car spent the day with Mat Smith.
Before I headed for work he plugged his pressure gauge into the fuel rail - I had loaded it onto my trailer last night, and unloaded it this morning without starting the ignition.
No pressure shown, so he disengaged the immobiliser and turned the key.
3.5 bar pressure in the fuel rail the instant the pump started to prime.
So no problem there.
He left it for the morning to see if it decayed over time. Apparently not much.
When I got back this afternoon the car had been on the ramp, boot bung removed, 52mm socket bought, weeping union on the bottom of the tank tightened to solve the leak I had had since the body off refurb over the winter. The starring issue is much more recent, post a battery change.
He then looked again at the starting while his colleague James sat watching the Emerald display on his laptop. Only odd thing they noticed was a momentary voltage drop to 9v on turning the key.
Car fired up almost instantly, as it did when I loaded it back on the trailer at 6.30 to bring it home. So problem apparently fixed.

So we are officially puzzled. I will see what the next few cold starts bring. We cannot see how the weep could be the cause.

Classic Chim

12,424 posts

148 months

Thursday 27th July 2017
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The weep is before its pressurised.
Fouled plugs wink

Flooded. Big V8 but not really RV can flood very easily.
And when they do can then wash the bores which drops compression and car wont start until you've turned engine over enough to remove the excess fuel and re oiled the bores to get a compression ratio that supports firing.
This can take some time cranking engine to achieve this compression.
If it's severely flooded possibly through fouled plugs failing to fire mix, in some cases you have to remove fuel pump fuse and turn engine over with WOT for bloody ages to remove fuel. Leaving it some time can do it via evaporation but re gaining that seal between rings and bores with new oil to gain the correct compression can take a lot of cranking.

My Jag V8 did it when I started it cold and switched it off only moments later. That was it flooded.
Mine took far more than a few minutes to rebuild compression. I used easy start and nearly blew the plastic inlet manifold off the car the second time it did it, what a flame filled backfire that was. nearly had bonnet off
Did it smell of fuel in the engine bay when it's not starting, it should be if there's fuel there.
Goodluck smile