Will only start after ignition key is released?

[Penelope Stopit]

rdl001 said:

Hi Pen and Belle,

I was testing the voltages last night with my trickle charger still plugged in, so this may explain my high voltages.

on retest,

When I test between (+ coil terminal) to (engine ground) I see:
Ignition on, 12.3 volts
Cranking, 8 volts

When I test between (+ coil terminal) and (- coil terminal) I see:
Ignition on, 0 volts
Cranking, 1.7 volts

When I test between (+ battery terminal) and (- battery terminal) I see:
Ignition on, 12.3 volts
Cranking, 8.1 volts

Does that make more sense?

Lovely, yes the charger was upping the voltage

Ok you've found something

Cranking, 8 volts @ Coil +ive

Cranking, 8.1 volts @ battery

Losing 0.1 of a volt through all those cables and the ignition switch is nice, very nice, there is very little loss of voltage

The problem is that the 8.1 volts measured at the battery during cranking is far too low

There should be approximately 9.6 volts or higher at the battery when cranking

If the battery is fully charged and left to stand for 6 hours, the battery voltage should hold at 9.6 volts when cranking

Try this................

Charge battery and leave it to cool down for 6 hours (cold UK winter should do the job)

Then....

Crank the engine over once for 7 seconds

Wait 1 minute

Crank the engine over again for 7 seconds

Wait 1 minute

Crank the engine for a third time and measure the battery voltage while it's cranking

Battery voltage at third cranking should be 9.6 volts or higher

If the fully charged battery voltage is dropping down to 8.something volts it is definitely faulty

The thing is, there is nothing to say that the engine will start as normal once you replace the faulty battery (if it is faulty), you need to go one step at a time

Wouldn't surprise me if a good battery sorted the problem, 8 volts at the coil is very low, but.............

[rdl001]

Okay, understood.

It just seems strange (or coincidental) that after I have changed the ignition coil and ignition module that I then have a suspect battery?

Note: I have just put a feed from the positive battery terminal to the positive coil terminal and she starts when cranking, as she should.
Does that tell us anything?

By the way, thanks for all your help so far

[Penelope Stopit]

rdl001 said:

Okay, understood.

It just seems strange (or coincidental) that after I have changed the ignition coil and ignition module that I then have a suspect battery?

Note: I have just put a feed from the positive battery terminal to the positive coil terminal and she starts when cranking, as she should.
Does that tell us anything?

By the way, thanks for all your help so far

Glad to possibly be of some help

Yes that tells us much

Ok, we don't know what the voltage differences were this time when you jumped from battery to coil but it has proved that a slightly higher voltage did the job

The new module may need a higher voltage than the old one needed to run it, that's assuming that the module is supplied by the same cable/circuit which it very likely is

You have two choices

Check the battery and replace it if it's faulty as it will only get worse

or

Use jump leads and a known good battery to prove that all is well with a higher battery voltage

Whatever, that battery will need replacing soon if it's faulty

There is only one other possible cause and I very much doubt it, it's possible that interference from something is being picked up by the coil positive cable, this is highly unlikely

Edited by Penelope Stopit on Thursday 5th December 21:02

[Loubaruch]

Have you measured the voltage on the ignition feed on the ignition switch while cranking? Still a possible reason.

[Penelope Stopit]

Cranking, 8 volts @ Coil +ive

Cranking, 8.1 volts @ battery

[Loubaruch]

Fair enough Penny, I missed that!

[rdl001]

Update:

At the start of this thread I said that I had fitted a new Bosch Coil (TVR E0057) and Ignition Module (TVR E0411) from TVR parts Ltd, which cured my 'poor performance at higher RPM'.

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks, showing 9.6 volts at the coil during cranking.
Does this mean that the 'copied part' (TVR E0411) from TVR Parts was drawing too much current and not giving sufficient voltage to the coil.

I have yet to test the car on the road, but it seems that the Ignition Module (TVR E0411) from TVR parts is not compatible with the coil they sell?, or is it just a quirk of my engine?

[TwinKam]

...or... more likely that the new module faulty (yes, it does happen).

[Paulprior]

i put a new module in mine last year, really bad kangarooing, swapped it for another of the same and all ok since

[Penelope Stopit]

rdl001 said:

When I test between (+ battery terminal) and (- battery terminal) I see:
Ignition on, 12.3 volts
Cranking, 8.1 volts

rdl001 said:

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks, showing 9.6 volts at the coil during cranking.

I'm curious as to how the coil supply is 9.6 Volts when the battery voltage was measured to be 8.1 Volts during cranking

[CAPP0]

rdl001 said:

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks

[rdl001]

Penelope Stopit said:

rdl001 said:

When I test between (+ battery terminal) and (- battery terminal) I see:
Ignition on, 12.3 volts
Cranking, 8.1 volts

rdl001 said:

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks, showing 9.6 volts at the coil during cranking.

I'm curious as to how the coil supply is 9.6 Volts when the battery voltage was measured to be 8.1 Volts during cranking

Could the module have been dragging the voltage down?

[Penelope Stopit]

rdl001 said:

Penelope Stopit said:

rdl001 said:

When I test between (+ battery terminal) and (- battery terminal) I see:
Ignition on, 12.3 volts
Cranking, 8.1 volts

rdl001 said:

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks, showing 9.6 volts at the coil during cranking.

I'm curious as to how the coil supply is 9.6 Volts when the battery voltage was measured to be 8.1 Volts during cranking

Could the module have been dragging the voltage down?

No it couldn't

It's not possible to have a higher than battery voltage @ any circuit supply

Best put it down to one of TVR lifes mysteries

[Steve_D]

Penelope Stopit said:

.....Best put it down to one of TVR lifes mysteries

Penny you're getting way too mellow these days. What happened to ripping the OP a new A hole?

Steve

[Oldred_V8S]

CAPP0 said:

rdl001 said:

I have now refitted the original Lucas ignition module, and the car now starts perfectly as soon as it cranks

Just goes to show how the experience of someone who owns or has owned one of these vehicles will always trump the self appointed "experts" whose skills amount to Google and cut and paste.

[semaj]

And for the hard of learning, if it ain't broke leave it alone! I cannot believe how complex some people make a simple diagnosis job, surely logic says put back the bit you changed as the first step! Ok I'll get my coat!
Lucky it was not at our local 'specialist', that would have cost you about £400!