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Strange ignition lead resistances


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It's wet and windy here in Lincolnshire so I thought I'd have a potter in the garage with the Esprit.

I have a mild misfire issue at idle so I thought I'd inspect the ignition leads.

They look in good condition although not new.

The connectors at each end are bright and shiny as are the terminals on the coil packs.

I measured the resistance on each lead and was surprised to see such a difference in each one.

Now, I was expecting to see the longest one (No.1) have the highest resistance and the shortest one (No.4) have the lowest, but the range seems too much considering the relatively minor differences in lead length.

The resistance readings are as follows;

No.1   13.48 k ohms

No.2   12.95 k ohms

No.3   8.61 k ohms

No.4   7.74 k ohms

As you can see, the difference between 1 & 2 is reasonable enough, as is the difference between 3 & 4.

But the gulf between 1/2 vs 3/4 seems disproportionate.

Thoughts welcome and experience on correct Esprit lead resistance.

Regards,

Andy.

 

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Good thinking to replace suspect ignition leads in any modern technology car, including your SE. The OEM system is of high energy design and will light off the charge effectively so long as components

I can't offer any technical expertise here Andy, only a suggestion that worked for me.

I bought a cheap set of leads from Ebay (100% silicone 8mm) that were not much more than £10. They arrived in 2 working days, I fitted them to the car and they've been on there since. Also, check the plug gap as one of mine had closed after I'd dropped it and failed to notice before inserting.

I've bought magnecor and others before costing £80-100 and not really noticed the difference, although there are, as it's about increasing the spark quality at the plug. Having said all that, you have an SE and mines just the N/A and this makes a difference on the lead quality required.

Hoping you find an answer to the misfire

 

Sorry, checking my ebay I was wrong on price - they were £25 - but extremely good value.

https://www.ebay.co.uk/itm/LOTUS-EXCEL-ESPRIT-2-2-TURBO-8MM-RED-SILICONE-IGNITION-HT-LEADS-WIRES-MLR-WI/401547900477?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

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Having said that, just found these containing substantial detail on leads at just £12.95 (you could pay that for one)

https://www.ebay.co.uk/itm/HT-Leads-Ignition-Cables-Set-fits-LOTUS-ESPRIT-S2-2-2-80-to-88-910-CI-Quality/233590222825?epid=2082819873&hash=item36630fefe9:g:s0wAAOSwefNfMnOh

Rgds

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Good thinking to replace suspect ignition leads in any modern technology car, including your SE. The OEM system is of high energy design and will light off the charge effectively so long as components are in sound nick AND no fault to ground is permitted. Seems it is wise to dress the plug boots at either end with silicone dielectric grease against that occuring.

Cheers

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46 minutes ago, sailorbob said:

Magnecor give the resistance of their KV85 wires as 72 ohms per cm (2.2K ohms per foot) +/-10%.

Thanks Derek,

So roughly measured, my longest lead (No.1) is 120cm and the shortest (No.4) is 90cm.

That equates to 8.6 k ohms and 6.4 k ohms respectively.

It will be interesting to see if those high readings on my present No.1 and No.2 leads is causing the issue.

While the resistance readings indicate some probable degradation, I suspect new leads will make no difference to the slight mis-fire.

Andy.

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Are your leads all the same type? It may seem a daft question but the Magnecor Electrosports 70 & 80 wires have a resistance of 98 ohms per cm (3K ohms per foot) +/-10%.

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Thanks Tom, Interesting data.

Slightly puzzled by the 1500 ohm difference between lead 2 and 3, while 3 and 4 only have a 60 ohm difference.

I'll report on my new leads when they arrive.

Thanks again,

Andy.

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  • 2 weeks later...

So, The puzzle continues.

After looking on ebay, I thought I'd try the Lucas leads on offer for £20 delivered.

They eventually arrived this morning so I set about them with my multi-meter.

The set consists of 2 leads at 905mm long and 2 leads at 1005mm long.

The 905mm leads measure 19 k ohms and 29 k ohms.

The 1005mm leads measure 20 k ohms and 27 k ohms.

It doesn't make any sense. What on earth is going on?

Also, the coil end fittings are the wrong type so I'll be returning them.

Andy.

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