Coil resistances?

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richtbiscuits
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Coil resistances?

Post by richtbiscuits » 27th November 2017 - 10:44pm

Hello all, I'm wondering if anyone might know about coil resistances. My FI 412 has been running rough on and off lately and I noticed it was accentuated in wet/damp conditions leading me to think ignition. The distributor cap had deposits on all four contact points and there is erosion of the leading edge on the rotor arm. I've cleaned them up while I await replacements. Could a poor coil be responsible for this kind of wear/damage? I checked the resistance in the coil today. It's a Bosch coil, part number 0221119027, and the resistances measured were 2.9-3.0 and 7640 ohms. I found one site online which quotes the resistances as 3.4 and 7790 ohms. Does anyone know if these are correct or if the readings my coil shows indicate whether it is okay or compromised? Any other suggestions for rough running in damp conditions? All advise greatly welcomed. Thanks.
'72 412 LE Variant
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miketyp3
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Re: Coil resistances?

Post by miketyp3 » 28th November 2017 - 8:05am

To me it sounds like the condenser may be on its way out.
Mike

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purplepeter
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Re: Coil resistances?

Post by purplepeter » 28th November 2017 - 9:41am

I'd agree with Mike but would add the question that if You think it's accentuated in damp conditions, is the car garaged?.. You might consider a can of Holts Damp Start, which forms a sealing/insulating layer over the entire ignition system

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 28th November 2017 - 7:00pm

Thanks for the suggestions. The car is garaged at night and the worse times have been after the car has been sat out all day in the wet and damp at work. It tends to run okay in the morning, if it's dry. I've got a condenser around the place somewhere so I'll replace the existing one and see how we go. Would a poor condenser lead to the engine hunting at idle? The revs have always rhythymically increased and dropped despite all attempts to cure the issue. I changed all the vac hosing for new and checked the auxiliary air regulator, as Clymer suggests that can cause hunting at idle, but no joy. Any thoughts?
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miketyp3
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Re: Coil resistances?

Post by miketyp3 » 29th November 2017 - 9:44am

It wouldn't directly, but it would cause the heavy pitting of the points and distributor contacts that you are seeing, which in turn wouldn't help with slow running - possibly having the effect of advancing and retarding the ignition.
On its own the hunting does sound like an air leak somewhere, which I guess could also be temperature dependant.
I'm no expert on FI, but I guess it could be a fuelling issue (pressure sensor?).
The first step as always though is to get the ignition spot on, then look elsewhere.
Mike

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 29th November 2017 - 8:43pm

Well, I found various condensers of which none have the same part number as the one currently fitted. I always thought they were much of a muchness but apparently not. One wont fit, a square and circle thing, and the other two have different part numbers. All start 1 237 330 but the last three digits differ: 220 on the fitted one and 168, 170 and 251 on the others I have. Any idea which should be fitted on a type 4 engine? I suppose it would depend on the distributor but I can't find any info on the intermerweb regarding distributor number and correlating condenser numbers. Coincidentally, I inspected the points and they look fine, contrary to the damaged rotor arm and cap, but there is some scoring on the cams of the distributor shaft.
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Re: Coil resistances?

Post by miketyp3 » 30th November 2017 - 8:30am

I don't know either... I think for the sake of a fiver or whatever they are, if there's any doubt I'd go and buy a new one.
http://www.vwtype3and4club.org.uk/_docs ... rtswap.htm
Its probably worth treating it to a new cap, rotor arm and points at the same time.
There's really no point looking for faults elsewhere or tuning a car until you can be certain the ignition is as good as it can be.
Mike

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 30th November 2017 - 3:03pm

New points, rotor arm and cap were already ordered. I've ordered a condenser now too after finding some info on the old timer website. Soon as they get here I'll fit it all and see how it runs. It's in for MOT next week so I'll get them to do the valve gaps and timing while it's there. Thanks for all the help and advice.
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937carrera
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Re: Coil resistances?

Post by 937carrera » 30th November 2017 - 11:33pm

ETKA says the VW part number is 311 905 295 C or B. Cross referencing to Bosch part numbers the C item is the one ending in 220.

Fit the new components by all means, but I suggest that you keep the existing condenser - Editors view I seem to recall is that the old ones are much better than the modern versions.

The resistance readings don't seem too far out from spec, have you put a plug on one of the leads to see if there;s a nice strong blue spark, or a weak yellow one ?

I
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 1st December 2017 - 11:31pm

I got the Bosch one ending 220 after lots of cross referencing. The old one doesn't look terribly old given the appearance of the green wiring. I'll hang onto it. Car running okay now with the cleaned up cap, rotor and a blob of grease on a small bit of exposed wire on the condenser, although it's still hunting. I'll fit the new parts when they're all here. I haven't pulled a lead to check the spark but I'll do that this weekend as I'm going to be tinkering anyway since the gearshift to second, either up or down, is rather hit-and-miss and clunky/noisy.
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937carrera
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Re: Coil resistances?

Post by 937carrera » 2nd December 2017 - 8:38am

Sounds good :)

If I recall correctly hunting is an indication of an air leak, most probably at the auxiliary air valve
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 2nd December 2017 - 4:00pm

I suspected an air leak too so I changed all the vac hoses, which did help but didn't fully resolve the issue. I've fitted a different auxiliary air valve without any change and neither of which showed a problem according to the test in Clymer. Changed the MPS too for a spare, again no change. Only thing I can think is a poorly adjusted throttle switch but I'm not sure how it'd cause hunting. Very puzzling.

As an aside, I also found today that the blower fan in the engine compartment doesn't run. I connected a spare but no joy. Is this blower linked to the eberspacher system or does it run independently? The eber is currently unplugged under the car and the fuel line plugged. Currently all I get is a slight waft of warm air down by the seat when I turn the dash switch, operate the levers and open the vents up. It's not really cutting the mustard for autumn/winter driving, especially in damp conditions when the interior mists up!
'72 412 LE Variant
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937carrera
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Re: Coil resistances?

Post by 937carrera » 2nd December 2017 - 4:23pm

IIRC the blower fan and Eberspacher are independent. Type 4 engines / heat exchangers are nowhere near as good at transferring heat into the passenger compartment as the vertical engines.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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937carrera
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Re: Coil resistances?

Post by 937carrera » 2nd December 2017 - 4:25pm

Quick thought - are the injectors properly sealed in the heads, no opportunities for air bypass ?
David
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Re: Coil resistances?

Post by Editor » 12th December 2017 - 2:56am

Some of the Type 4 ECUs have a rich/lean knob on the top edge to adjust the fuel mixture. Hunting can be the sign of a weak mixture. If yours has one, the knob clicks as it's turned, so you could see if that makes any difference, but note where you started so it can be put back in the same place.
Hunting on FI Type 3s is sometimes due to timing not being adjusted correctly, as it's sensitive to rpm and manifold vacuum, but I'm not sure how differently the Type 4 behaves in that respect.

Compared with the Beetle engine, the flat Type 3 and Type 4 engines have always seemed sensitive to very humid days - There used to be silicone sleeves sold to put over the plug insulators. If the distributor cap has gone matt on its surface, change that.

Coil resistance sounds OK.
Dave.

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 15th December 2017 - 10:29pm

Thanks for the advice. My ECU does have an adjusting knob on it and it is currently turned all the way down as it used to run really rough. I will revisit it though as there have been changes since. My car is pretty thirsty though, doing all of 16-17 mpg on average over the last six months. I wonder whether this is an ignition timing thing given the hunting and poor mpg when mixture adjusted to lean as can be.

On the plus side, my car has a nice new MoT certificate. It initially failed on an inoperative handbrake on the off side but Dave and his team at Kingfisher have fixed it for me along with an oil leak between the engine and 'box, which turned out to be loose plugs on the oil galleries, and a gear stick adjustment. Very happy driving home today!
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937carrera
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Re: Coil resistances?

Post by 937carrera » 16th December 2017 - 9:01pm

richtbiscuits wrote:
15th December 2017 - 10:29pm
16-17 mpg on average over the last six months.
When I had a 412LE as a daily driver I only used to get 17-18 mpg (generally enthusiastic driving) :badgrin:

Good news on the MOT :thumbsup:
David
1974 412LS Variant
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Re: Coil resistances?

Post by Editor » 19th December 2017 - 1:35am

Check the charging voltage at mid-range rpm. It's a common problem on the FI that gives poor mpg when the regulator is not giving the right sort of output. Somewhere in the region of 14 Volts is OK. I'm not sure what your Type 4 alternator has by way of a regulator. With low supply voltage, the FI automatically richens the mixture.
Short journeys and cold weather can return pretty poor mpg, and if the car is sitting with petrol evaporating, that doesn't help either, but if you're doing decent length journeys at modest speeds, that does sound a bit on the low side.
Dave.

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Re: Coil resistances?

Post by richtbiscuits » 20th December 2017 - 11:52pm

Apologies if I sound a bit thick but where do I check the voltage, at the battery? I have installed a new alternator (nut fell off shortly after I got the car back on the road and it destroyed the thread on the old and tired one) and I tried a new voltage regulator some time ago on one of my many efforts to resolve the hunting issue. I do do a lot of short, from cold, journeys so I expect the mpg to be down but I suppose I thought it might just be a little better than it is. I did wonder about evaporation - I once spent hours trying to get my beetle started after a couple of months storage only to find the tank dry!
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Re: Coil resistances?

Post by Editor » 23rd December 2017 - 1:36am

With a Type 4 it's not as easy to get access to the battery, being under the front seat ISTR. The regulator output would be an easier point to try. Essentially as you speed up the engine you should see a decent voltage rise. A fully charged battery has a voltage of around 13.2V or so when not being charged, so expect around a volt more than that. It's not that critical, but worth checking at some point. You're probably not going to get decent mpg with short journeys in cold weather.
Dave.

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Re: Coil resistances?

Post by 937carrera » 23rd December 2017 - 11:17am

It's not too bad chacking the battery voltage on a type 4. Backrest forward and pull the height adjustment lever; that will allow the seat to tip backwards and stay there.

Regular routine for me as i disconnect the earth when the car is not in use. Saves the battery discharging because of the clock.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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richtbiscuits
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Re: Coil resistances?

Post by richtbiscuits » 28th January 2018 - 7:56pm

Update to the long running hunting issue. I changed the points today and set the correct gap and the car instantly sounded different with no rise and fall of idle rpm. Went out for a drive and it's a totally different car. It picks up revs quick and gets down the road no problem. There's no stuttering at constant speed and comes back to idle smoothly when I lift my foot. A lesson, if ever one was needed, in doing the simple things first to resolve a running issue before looking for the more severe! :D
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937carrera
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Re: Coil resistances?

Post by 937carrera » 28th January 2018 - 8:07pm

That's good news, thanks for the update as we all walked with you up the garden path :)
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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