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How to measure pencil coil resistances

24K views 19 replies 3 participants last post by  glenn7 
#1 ·
Hi Folks.

Suspecting coil trouble I am trying to measure the primary and secondary resistances on the ignition coils in my 02 Scenic, which has now had all four coils replaced in the last year.

I can measure the primary resistance ok by putting a meter across the two terminals on top of the coil, but how can I measure the secondary resistance? I'm getting anything from 0.5 to 1.2 ohms across these, although the Haynes manual says should be 0.5, +/- 0.05.

I then tried inserting one meter probe into the sparkplug end of the coil and touching the other probe onto the metal collar where the securing bolt passes through, but nada - tried this on all four coils.

Where is the -ve return on the HT side if not through the securing bolt hole ring?

Haynes manual quotes primary and secondary resistances, so presume there must be a way to do it. Or are they and I being stupid and there is no primary coil because each pencil coil *is* a secondary coil only?

Help much appreciated as ever.

Thanks.
 
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G
#2 ·


PRIMARY RESISTANCE CHECK

Ensure ignition is off
Disconnect coil multiplug
Check resistance between terminals 1 and 2
Should be 0.5 ohms approx


SECONDARY RESITANCE

Ensure ignition is switched off
Remove coil
Check resistance between LT terminal 2 and HT end
Denso coils 5800-8500 ohms
Sagem coils 9000 - 12500
 
#4 ·
I'm getting resistances between 0.5 and 1.2 Ohms on the primary and anything from 11k to 15k ohms on the secondary. These seem to be well outside tolerances.

Two coils have grey tops and are Valeo, two have brown tops and are unbranded.

All four are less than a year old - two just a few weeks.
 
#6 ·
Very poor starting and lumpy initial running - strong smell of petrol at startup. Has previously run ok once this phase overcome, although once again it is misfiring/running lumpily (?) with reduced power. Last time it did this our local mechanic said he got open circuit on two coils and changed them and it did seem better afterwards, but has deteriorated again.

Interestingly and I suspect significantly, it starts *much* better from cold in really cold weather - e.g. frost - than warm. I can't help thinking some temperature info to the engine ECU is out of range.

These last few hot and sunny days it's been a pig to start, needing many cranks of the engine before firing. I can get it to start sooner by pressing on the accelerator but I don't like to do this for fear of sending any more unburnt fuel down to the cat.

TDC sensor has been changed as well btw, as some posters suggested this was a common fault that could affect starting. Made no difference.

It is driving me mad and the car cannot be considered reliable.
 
G
#7 ·
I think a new ECT (coolant temp sensor) will fix all your problems!
Overfuelling is a classic ECT failure sign, which is why your car stinks of petrol and starts nicely when it's frosty.
Should be around £20 from renault. You can use gsf / euro crap rats ones but I've had a lot of problems with their pattern ones for VW's.
2 minute job to fit. Cold engine, unscrew old one (22mm spanner usually) and screw new one in. Be quick on the swap over or you'll lose coolant
 
#8 ·
Thanks Dan.

Is the sensor reasonably 'get-atable' or do various things have to be moved out of the way? Don't mind, just need to know. Is it located near the thermostat? I think I read that there are two sensors in this location, one for coolant and one that does something else!

I've emptied my PM box now btw - they only allow you to store 3 PMs, sent or received, which is inexplicably tight.

Does the replacement need a new o-ring or gasket or somesuch or will PTFE tape do it?
 
G
#9 ·
I havent got a clue where it is on renaults!
It'll be on the side or front of the head in one of the waterways, or coolant hose flange. Get the sensor and then find one on the engine that looks like it!
Shouldn't need to remove anything.
 
#10 ·
ok - I am taking a bit of a chance on this as the Renault dealer's parts dept says there are several on the Scenic (and he didn't know what an ECT was either - me neither - Electronic Coolant Thermistor was my best guess!). He has got one, with three contacts, £22.86, so I am crossing my fingers that it's the right one as it's a 30 mile round trip and I'm going to get it now!

It will be great if it solves the problem as otherwise I do like my Scenic. I guess you've never had to change the ECT on yours?

I will re-post when I've tried it to advise how it goes.

Thanks for your help and advice.
 
G
#11 ·
If you have 3 wires, then i'd say that there is only the one sensor on the car.
Some have a single wire one for the temp gauge, and 2 wire ones for the ect.
But as yours has 3, im guessing one sensor does it all.
Coolant temp sender / sensor, engine coolant thermistor, temp sender.......... they all call it something different but it's the one that controls the ecu fuelling you want!
 
#13 ·
Well, not entirely conclusive - fitted new sensor no problem.

Wouldn't say car started *that* much better (from cold, albeit ambient temp 22 DegC), but maybe ECU needs to 'learn' new sensor state/operating parameters and adapt to it/them. Seemed to be less of a petrol smell around, however.

Will see how the car starts cold again tomorrow morning.

Unfortunately the misfiring did not go away as a result of changing the sensor, so there must still be an ignition or injection problem. :(
 
#16 ·
I ain't saying the Bosch plugs are poor but in my experience I always stick as close to the originals where possible.

Renault scan be quite fickle when it comes to spark plugs.

When it comes to a misfiring petrol engine I always check the colour of the spark plugs and compare their colour no matter how short a time they have been fitted. The colour can give quite a bit of information and rule out some possibilites - helps narrow the search for the problem.:)
 
#19 ·
Fitted new NGK plugs OEM spec and new green-top pencil coils - supposed to be the latest thing and not prone to failure, allegedly.

Made no difference to starting prob.

Traded Scenic in last week for a Kia Cee'd with >3 yrs left on warranty. Relief!

And traded Clio in for an 06 Kia Picanto today.

No more French cars for us!

Best of luck.
 
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