Had two minor issues over summer that I want to try to sort:
1/ Occasional slight misfire / lumpy idle
2/ Increased radio interference with engine revs
Everything seems okay with radio aerial, earthing etc, and so I’m thinking HT leads could be causing both issues? As they’ve never been changed in my ownership (15 years) I’m thinking they’re probably original, so worth doing.
First thought was OEM, but local Mazda dealer quoted £88+VAT for a set, and I can see lots of branded aftermarket ones priced between £30 - £60.
I’ve read a few reports of new sets of leads not being same length as originals and not fitting neatly (MX5 Parts and others). I’m looking for a recommendation from anyone who’s recently changed HT leads on their Mk1 and happy with fit and performance of your replacements.
A quick way to check if the insulation around coil, leads and plugs is OK is to run the engine in the dark with the bonnet open and have a careful look.
If you can see blue flashes floating around the leads etc that is leakage, lost spark energy.
While that is a classic sign of duff leads, a less likely possibility is because a plug has gone high resistance and the spark is simply finding an easier way to ground.
Years ago at a main service I treated my old bitsa to some nice new very expensive “Sparkrite” leads from Halfords. Alas, they were useless with blue light everywhere, and the ten year old leads went back on, no problems. Money back after a quick demo in their car park!
A decade ago on my old Vextra it was a brand-new plug causing the problem soon after a main service, and eventually it broke down the coil-pack, the ancient leads were OK. New plugs (again) and new coil pack.
As Richard explains, these are relatively easy to check out and I would be very surprised if the original leads are the problem. Having said that they have obviously been on the car for a while, so a possibility. I don’t think original mazda leads can be beaten; if you are lucky they may be equalled.
If the misfire is happening when the car is warm, a good chance that is is coil pack related.
Radio interference comes from unsuppressed power; again, could be coilpack.
Dearer is not always the better, stay away from the magnecor leads, we have dealt with lots of issues with them on our own roadsters and owners roadsters that come here for help.
M-m
Checked things out under the bonnet in the dark last night. Only sparking I could see was a a blue glow which seemed to be right at the bottom of the connector of HT Lead no.3 where it connects to coil pack.
Watched a couple of videos this morning on testing leads with a multimeter. Managed to remove Lead No.3 (took some moving) and tested resistance as per videos but can’t get any reading at all (meter just sits at 1). Decided to remove another Lead to compare results, but up to now remaining ones won’t budge off coil pack. Tried a piece of cord looped round connectors (which is what moved first one), but no joy.
Any suggestions for removing HT connectors from coil pack?
You have obviously found your problem.
Whilst the HT leads should not fall out of the coil ports, you should not have to wrestle with them.
There has been water ingress and corrosion, hence the issue and difficulty in removal. You should see nice shiny silver port bases on the coilpack; what can you see?
Assuming I am correct and there is corrosion, the leads will be compromised and require replacement. You may be able to restore the coilpack ports with a dremel or similar.
Original Mazda leads usually seal well, so I would be surprised if well fitted Original Mazda leads have contributed to this problem. Perhaps the OP would be kind enough to send a photo of the coilpack ports with leads removed and another of one of the HT lead ends, the end that goes into the coilpack port.
Agree with MM on the Magnecor leads. Not that good new and not a robust product from my experience. They are 8mm, look good and are expensive but I would not fit them to my cars; a good used set of original 7mm boring black leads every day of the week.
That looks like an original Mazda HT lead to me.
Good photos but the flash or reflected light has obscured corrosion detail from my eyes anyway. I think I see that the bottom part(aluminium) of the port in the coilpack is showing oxidation?
The HT lead also looks stained with corrosion. Both these should be clean looking shiny metal.
By the way for removal I usually twist the lead head slightly and pull at the same time.
If the ports have oxidised it will be much harder for the electricity to flow, as it has to jump past the non-conductive oxidation to get to the conductive metal below. This will result in higher voltages, weaker spark and heat/light generation.
I suggest this will have stressed both the HT leads and the coilpack over time and created your running issues.
You could try cleaning everything up for a short term test but as already suggested, the best way forward once this is confirmed as the cause is replacement of the coilpack and HT leads.
Further update. Managed to get remaining connectors off coil pack to inspect other ports and leads. Took a bit of prising at the bottom of the rubber boots to free them as they were stuck tight to ports, before pulling off from top. Other than the first lead I removed (sparky one pictured above) all other ports are perfectly clean and shiny.
Having removed all leads, I was also able to test and compare all four with multimeter. Sparky one faulty (must have a break), but other three checked out fine.
The core of the coil pack that was cruddy seems to have cleaned up well with Dremel tool (as recommended by Rhino666).
So, looks like one dodgy lead may have caused running issues and deterioration of coil pack port. Don’t really want to try going for a test drive knowing I’ve a dodgy lead, so back looking at options for a set of new leads now, which is where the thread started.
Very happy to report that cleaning the coil pack port and the one replacement HT Lead cured the misfire and lumpy idle. Been for a spirited spin and everything is back to smooth progressive power through all the gears .
Big thanks to Rob (Rhino666) for his advice and supplying me with a lead to try .
Still got the radio interference, so some further investigation required for there, but that’s another story, and perhaps another forum topic.
Very pleased that the running issue has been resolved but a little disturbed that your radio is still getting interference.
In the old days of a single coil unit and associated distributor/rotor arm, etc, radio interference was expected if a suppressor or suppressors were not fitted.
More modern coilpacks have largely consigned this problem to history.
Your current issue implies damage to the coilpack to be honest as I cannot suggest where else the leaked power, causing this issue could be coming from.
You could well be right about the coil pack, but the port cleaned up pristine, and with the replacement lead the car now idles and runs perfectly, which was my main concern. It really does feel so much better
As suggested by Richard I’ve just been out in the dark looking for sparks again, but this time didn’t find any. I read on another thread a fine mist of water can help show up any issues too. which I tried but again no sparks from the leads or the coil pack.
It’s possible that something’s going on with the coil pack that I can’t see, but before going for a change, I’m going to have another look at the radio / aerial / wiring / earthing set-up.
I was thinking that both the running and radio interference problems started around the same time but with the car being used so infrequently this year, and even then not always using the radio, that might not be the case.
I did find today that the interference did not show up playing a CD, only on FM radio - which may be a clue?
Anyhow, I’ll have to either fettle the radio, fit a replacement coil pack, or just dig out my old CD collection
it works
.