been having problems today, engine management light came on this morning but thought nothing of it as been having problems recently!

last friday the light came on for no apparent reason, was the day after i had the cambelt changed so took it in to get it read just incase and it was 27 counts of faults on coil pack 1. the guy said it possibly could be the pack on the way out or most probably the spark plugs so changed them and its been fine!

today the light came on again for no apparent reason but later in the day the reason came aparent! i keep having a sudden juddering and loss of power, both when accelerating and sat at lights idling. it feels like one of the cylinders isnt firing but dropping the clutch and a tap of the gas sorts it!

so im a bit puzzled! we had this a few months back and some redex in the tank seemed to sort it. im thinking along the lines of the coil pack going and keeps stopping firing? or could it be something less expensive!

27 counts of coil 1 faults? what do you mean

Dont you mean the error counter was at 27(it counts down the way)?

the guy said the coil pack had sent a fault 27 times!

If you have a multimeter you can check them yourself. Check them when they are cold and then again when the engine is hot (ignition switched off of course or you will get a perm checking the HT side ) they should give more or less the same reading from each one.

TBO check it sooner rather than later it has been known for failing coil packs to fry the ECU

wont the coil packs fry a multimeter? or you do them a special way?

With the engine off there is no power supplied to the coils

You need to check the resistance accross the LT side first. Unplug the small single plug on each coil and touch both pins with the multimeter the reading should be between 0.5 and 0.6 ohms (when cold)

Then unplug the two HT leads and do the same this should be 6.6 to 8.1 ohms (when cold) if you get higher of lower readings then the coil pack is NFG

if you check them with the engine hot the readings should be about the same on the two coil packs.

cheers allan! dont suppose you know which is numbered one and two? the error was for coil pack one but dont know if thats the front of the back pack

Not 100% sure but I think it is the back one the one that feeds the spark plugs for cylinders 1 and 4

Then unplug the two HT leads and do the same this should be 6.6 to 8.1 ohms (when cold) if you get higher of lower readings then the coil pack is NFG

Click to expand...

you mean connect the multimeter between the 2 connections?

yep

You do not check a coil with resistance,the 'consumer' (in this case the coil must be 'working' at the time of test or you will get false readings.Coils tend to break down under load so resistance tests are useless.

p.s.coils do not send faults to ecu,how can it(they)?

Sorry mate but

a pro may do it that way if he has the equipment but if I rember my degree level physics and 5 years working with industrial transformers I can tell you if you have been given an indication that there is a problem by a "Pro" then you can veryfiy this yourself if the problem is as bad as indicated

Resitance does very under load but static resistance especially on the primary side of a simple dc step up transformer (a coil) has a huge effect on the output voltage frequency, increased resitance of the LT side will reduce output voltage.. Fact

Now if you want to talk about AC transformers that are finding there way on to more sofisticated cars then that is a different matter

You are right there is no feedback to the ECU it is my understanding that the ECU logs the fact that there is high resistance.

A resistance check (on both primary & secondary windings) on a ignition coil will only prove a open circuit,nothing else! As I stated since coils faults are normally due to breakdown under load resistance checks are useless,unless of course you have a open circuit in the windings however this would be obvious as the coil wouldn't produce a H.T. output,i.e.no spark.

p.s.I have been a auto electrician for 19yrs (with many different manufacturers) so I know about coils

OK not getting into an argument here, you deal in small coils i deal in big ones

all i'll say is section 5B of the Haynes if you have a coil that is NFG and you have been told there is a problem with one this will help identify the potentially duff one.

The coil can 'send' a problem to the ECU in as much as the unburnt fuel gets picked up by the lambda sensor and because the system can't sort it, it throws the light on.

This is a common cause of misdiagnosis. Code reader says lambda faulty. Change lambda, fault remains.

Cheers

D

The coil(s) on a cinq/sei do not send any kind of error to the ecu.If like the scenario you stated that unburnt fuel passes through it would trigger a lambda sensor but this error would also state top/bottom limit,looking at the integrator (or voltage)would confirm/dismiss a lambda fault instantly,its not a common misdiagnosis its 'poor' diagnosis.
Misfire would bring up a generic error code(3000-3004)if vehicle had a misfire (post 2001) or knock sensor error.
Allan....personally I dont give anytime to Haynes manuals,my argument is that checking a coil by resistance is not a good way to diagnose this part,the only sure 100% way of checking a coil is under load,end off.

OK how do you check this as a DIY machanic then?

Beside resistance checks on primary & secondry windings (as already mentioned) for open circuits there is little you can do beside substitution(probably the quickest method assuming the subsituted coil is known to be good),unless you have suitable Kv measuring equipment.Flashing 'neon' type in-line testers are good for quick monitoring of HT spark but will not show up & light intermittent misfire plus problem could be in the lead.

...to correct my self earlier,P0300(multiple generic)to 0312(for 12cyl cars)are the correct misfire error codes.

right finally got round to measuring the coil packs this is what i got

FRONT

primary - 0.8 ohm
secondary - 7.39 Kohm

REAR

primary - 0.9 ohm
secondary - 7.34 Kohm

now haynes says the primary should be between 0.5 - 0.6 so you think both of them are going?

anyone?