Deteriorating Starting Performance

Talk about the E-Type Series 3
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panamacarrera
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#1 Deteriorating Starting Performance

Post by panamacarrera » Thu Sep 22, 2022 3:10 pm

My SIII OTS has always started well, give the fuel pump some ticks to fill the carbs, turn the key and she'd quickly fire into life. But in the last week or two that's changed.

Now, after letting the fuel pump run for a short while, the engine will fire sweetly on the starter motor but as soon as the starter is disengaged, she dies. It will do this three, four or five times (enough to get the Missus asking me if the car's OK?), before eventually starting.

The car does this from cool, warm and hot so I don't think it's a problem with fuel vaporisation. Once started she runs normally.

I've run the car on E5, so I don't think there's an issue there.

I'm sure it's a fuel issue, but i can't imagine what would cause the symptoms.

Gents, any ideas, please?

Nigel
'71 S3 OTS

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MarekH
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#2 Re: Deteriorating Starting Performance

Post by MarekH » Thu Sep 22, 2022 4:40 pm

Dear Nigel,

The only "fuel" difference between starting and running is the use of the choke.

To start a car you need more air and more fuel than you do to keep it running. So logically, that'd be where to start looking. Assuming you are not delivering enough fuel via the choke, or the throttle is not correctly set, then after four or five attempts, there may be enough fuel splattered over the inside walls of the manifold that some of it reaches the cylinders in the quantity needed to keep the car running above 120rpm.

kind regards
Marek

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panamacarrera
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#3 Re: Deteriorating Starting Performance

Post by panamacarrera » Fri Sep 23, 2022 8:36 am

Thanks Marek
What you say is correct, and I will check the choke linkages and cable today, I'll let you know what I find.
But it doesn't explain the problem when the engine is at operating temperatures.
'71 S3 OTS

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#4 Re: Deteriorating Starting Performance

Post by MarekH » Fri Sep 23, 2022 11:04 am

It's still true for a hot start, but the magnitude difference is not as great. Starting an engine is a very heavy load, whereas idling the same engine is a lighter load.

For a fuel injected engine, about 20-15mSec worth of fuel at very low temperatures is needed per cylinder, but only 7mSec of fuel is put in when starting a fully warmed up engine. By comparison, the fully warmed up idling engine sees ~4.5mSec.

Carburettored engines are no different to this, but the figures get painted using a very broad brush, so it is often much harder to tell whether something is correctly sitting the sweet spot or just working just within acceptable limits.

kind regards
Marek

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tinworm
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#5 Re: Deteriorating Starting Performance

Post by tinworm » Mon Sep 26, 2022 5:06 am

Sounds like a possible electrical fault maybe - ballast resistor circuit ? - if you have one that is.

Barrie
1968 E-type roadster, 1964 E-type fixed head 1995 Ferrari 355 1980 Ferrari 308 1987 V8 90 Landrover 1988 Bedford rascal van 1943 Ford GPW

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#6 Re: Deteriorating Starting Performance

Post by MarekH » Mon Sep 26, 2022 12:00 pm

If the resistance in the wiring/connectors or through through the ballast resistor is excessive, then starting performance will be impaired.

The ballast resistor circuit has two components:- during normal running it lowers the voltage (and controls that voltage) to the coil; during starting it allows for full voltage to the coil.

If you measure the resistance (or the voltage drop) in the whole circuit from the coil to the battery positive in both cases then it ought to flush out whether the circuit is capable of providing higher starting voltage as opposed to lower running voltage. (Obviously disconnect the white/red wire when doing this.)

When I purchased my car, the PO recommended a starter pack as the only reliable way to start it. It turned out that one of the wiring connectors at the ballast was hanging on by just a couple of strands of copper. Once this was fixed, starting became "normal".

kind regards
Marek

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