1420Q not running smoothly

[rfgumby]

Hello and good morning,
lately my special started to not running properly. It was just not running on all cylinders. The exhaust is hot for everyone, but it was not running right. I started checking the ignition cables and noticed that for one cable the electric resistance was nearly the double from the other cables. Since I have no grasp of electric systems I'm lost. Could that be the source of the problem?

Thank you and best regards,
Uwe

[EuropaTC]

Hi Uwe,

Sorry to hear of the problems, I'm sure there will be others along later to chip in with suggestions. For now though....

A single high resistance could indicate a problem, assuming you're using suppressed leads rather than the older copper wire with suppressed spark plug caps,  but it depends on the actual numbers because on one of my sets they all vary slightly despite logic saying they should be the same.   The exhausts will transfer some heat to the adjacent ones by conduction, I think you'd need an accurate measurement on individual outlets to determine a faulty cylinder using the exhaust gas temperatures alone.

My first thoughts with any irregular running is to to remove and inspect the 4 spark plugs to see if they are all identical or if one is black/oily/sooty/basically not right 

Hopefully you will find the plug fed by your high resistance lead to be black with all the others a light sandy brown, in which case a new set of leads would be on the list of options. But also check the plug connection/lead connection to the distributor cap and finally the internals of the distributor cap for damage/erosion on that current feed post.

After that it's just a case of going through a system check list. Assuming you have the OEM points/condensor/coil then apart from checking that the wiring circuit shows no signs of broken/loose wires & all have clean connections I'm ashamed to say my approach is to simply replace things one at a time. 

Yep, it's not scientific and is more expensive, but all the parts are available and relatively cheap. Assuming the plugs are new, my order is usually points/condenser together and if that doesn't work then the coil as last option. The distributor cap & rotor arm can be checked visually when replacing the points and any faults are usually obvious, for example there have been cases of some rotor arms which have a riveted arm shorting to earth with the rivet loosening, damage to the central carbon brush in the distributor cap and erosion of terminal posts is easy to spot when it's all apart, etc.
 
Brian

[rfgumby]

Hi Brian,
thanks for your help. I checked the spark plug and 3 are black/sooty and one oily  . The ignition cable with the high resistance leads to on of the black plugs.
I think I will start with the cables (change them) and hope for the best. 

Uwe

[EuropaTC]

black & sooty plugs are not unusual, in fact I was checking my elan yesterday and it was pretty much the same   

It would be worthwhile swapping the plugs around, running the car and seeing if the same cylinder retains the wet/oily plug. If the wet plug moves to another position then it's likely a spark plug problem ?  If not, then at least we've narrowed down the problem area.

I've heard a few comments about plug heat ranges and people using slightly hotter grades of plugs than the original Lotus fitment.  OEM recommendation is NGK BP7's or Champion N7's but I use BP6's in mine which are slightly hotter and they foul up less in the shorter driving I do these days. (the equivalent Champion is N9Y, the grading schemes go opposite ways to confuse us all    )

Brian

[rfgumby]

Hi,
thanks for your help Brian. I opted for the moment to get new ignition wired and a new distributor cap, while I'm at it. Accidentally there was the wrong cap in the package, waiting for the right one at the moment.

Best regards,
Uwe

[rfgumby]

OK, got the new distributor cap and cables. Punt everything together and installed it, looks fine so far. 
No test possible since it was too late and my neighbors don't like the sound of the engine as much as I do. 

Uwe

[rfgumby]

OK, test with the new cap and wires was done ..... and it was ....  Now it runs on just 1 cyl.!
I could  That's the time this hobby makes no fun at all.

Uwe

[EuropaTC]

Ahh, good old Lotus -  Lots Of Trouble, Usually Serious.  One thing you can always rely on is that at some point you're going to scream at the car !   

Well, if it's got worse then it's got to be something recent so all you can do is retrace your steps.  I would have thought it's unlikely to be the HT wires themselves, but there's a rotor arm and the carbon brush inside the distributor cap that can play up. A recent cap I bought had a carbon brush that didn't meet the rotor, exactly how it came like that I just can't imagine, but it did.

It's sounding like an ignition problem though. I think it's best to go back and start from square one. If it's a standard system check the contact breaker points for gap and surface condition. Any build up or burning and I'd replace both the points & condenser at the same time. After that you've done 90% of the system, there's only the low tension wiring (inside the distributor & distributor to HT coil) and the HT coil itself to check if there's still a misfire ?  HT coils do go down, but not as frequently as contact breaker points.

Brian