Saxo misfire between 3,500 and 4,000RPM

watsoft · Post by **watsoft** » 20 Apr 2006, 13:17

I've a MKII Saxo 1.1 that's done 172,000miles and for the main part it's been pretty good.

The problem at the moment is that it runs fine until I get between 3500 and 4000RPM and then it starts to stutter. It also runs fine above this RPM.

My initial thoughts were the spark plugs, but they look fine (light brown deposit). I've let the car tick over whilst I jiggle all the wires I can find, but it doesn't object and continues to tick over in the usual way (revs increasing and decreasing slightly). There's no smell or signs of leaking petrol and whilst I haven't replaced the petrol filter recently, I wouldn't have thought it cause these symptoms. There are no signs of corss-contamination between oil and water. I've also checked sensor connections and they all look reasonable.

I tried to check the coil pack as per the haynes manual, but it's a bit vague as to which pins to connect the multimeter probes. I'm not sure if the values specified match those of the MKII coil pack as I had to make do with a MKI manual!

When the problem happens a fault code is registered, but it seems to clear itself without having to start the car 3 times. Can a cheap fault code reader be purchased for the MKII? My local Citroen dealer is useless and I know it would be a waste of time getting them to trace the fault.

Thanks in advance for any advice.

drpau · Post by **drpau** » 20 Apr 2006, 14:38

How about your HT leads?

watsoft · Post by **watsoft** » 20 Apr 2006, 15:39

I don't have any, I've got a coil pack that sit's above the injectors and feeds each of the spark plugs. The only external connection is a 4 pin plug which I assume is an LT feed and timing signal...I gather from the Haynes manual.

I've had to replace the coil pack before, but the symptoms were very different...I turned a corner and my engine died! Very scary as I'd only just changed the timing belt the week previous. I was so happy that it was a £60 fix and not a engine rebuild!

PowerLee · Post by **PowerLee** » 20 Apr 2006, 17:39

Does your coil pack have SAGEM on it?

If it does THROW it in the bin & fit the latest ELECTROFILL coil pack & a set of Citroen spark plugs

watsoft · Post by **watsoft** » 20 Apr 2006, 20:23

Thanks for the advice PowerLee, I'll check soon as monsoon season is finished here in Grimsby! Where on the pack will the name printed? I doubt this is a genuine part as I took it to a Citroen specialist when the first coil pack failed at around 70k.

A mate of mine suggested that it might be the throttle sensor as it works in a similar manner to a Scalextric controller (not literally) and with me doing mostly motorway miles he believes that the rheostat might have started to fail around the RPM where the engine sits 2.5hrs each day! Makes a bit of sense to me, but if anyone could confirm it would be appreciated.

pugxpert · Post by **pugxpert** » 20 Apr 2006, 20:33

pin 4 is 12v supply pins 1+2 go back to ecu these are earthed by ecu to fire coil (primary circuit) and if your a late type pin 2 is phase detection info to ecu for cylinder refrence. can check the resistance between 4+1 and 4+2 should be the same around 0.8ohm also if you have a scope you can see a duff sagem or electrofil coil, have a look at www.peugeotmt.co.uk have some scope imagery on there for coils.

AndersDK · Post by **AndersDK** » 20 Apr 2006, 23:24

The scope option is for the few owning a scope. The ohm's checking wont tell you a thing really. 0.8 ohm is the same as a shortcircuit reading using any standard hobby multimeter.
The only sensible thing you can check on a HT coil is if it's disrupted or not.

You can check if the coil and/or the HT cables are arcing using the stoneage trick : run the engine in total dark hood open looking over the ignition system. Any visible arcing at all is a fault. You may even see a faint arcing from inside the coilpack - i.e. the coilpack looks like its faint blinking. I have a feeling that this is the problem with the Sagem units.
PS : Sometimes you can see a faint blue'ish corona light on the HT cables. Not necessarily a problem.

If nothing found then start your troubleshooting replacing the plugs.

mezuk04 · Post by **mezuk04** » 21 Apr 2006, 07:45

Does your coil pack have SAGEM on it?

My old USB Modem had SAGEM on it.......never did like that modem

pugxpert · Post by **pugxpert** » 21 Apr 2006, 07:57

you can definetly check your coil primary windings with an ohms meter ignition coil is very low resistance 0.8 ohm i would check it out anyway even though anders says not to bother if your resistance is high on one side of the windings your coil will pack up underload,you cant always see the coil arcing and does your car misfire by just reving up sataionary? i bet it is when you are driving with engine under load, just get someone to drive your car at night with you strapped up under bonnet looking for a blue flash! if you kmow someone with same engine in peugeot or citroen just swap there coil onto your car and try it! i would put money on that it is the coil.

watsoft · Post by **watsoft** » 21 Apr 2006, 08:57

Thanks all, you've given me some quality info!

I only own a hobby multimeter, but my mate has a very expensive one, so we should be able to get a reasonable reading.

pugexpert, the engine runs fine up to 3500rpm and fine after 4000rpm, but the fault can be experienced with or without load. The first time I noticed it was when I accelerated back up to motorway speed after some roadworks, but it happens when I drop in speed or maintain a speed that puts me in that rpm band. I've even replicated the problem on the drive, but it only appeared once the engine was up to temperature (could have been coincidence).

I'll do the suggested checks this weekend and keep you posted.

AndersDK · Post by **AndersDK** » 21 Apr 2006, 14:54

AndersDK wrote:... 0.8 ohm is the same as a shortcircuit reading using any standard hobby multimeter.
The only sensible thing you can check on a HT coil is if it's disrupted or not.

pugxpert wrote:... you can definetly check your coil primary windings with an ohms meter ignition coil is very low resistance 0.8 ohm i would check it out anyway even though anders says not to bother if your resistance is high on one side of the windings your coil will pack up underload ...

Yeah we seems to disagree a lot here dont we P.expert 8)

watsoft · Post by **watsoft** » 20 Jun 2006, 08:40

I bought a cheap fault-code-reader which identified a problem with injector 3. I've wiggled the wire and the problem has finally gone away!

If you want a cheap reader for your car check this link: http://www.frenchcarforum.co.uk/forum/v ... hp?t=18813. It works fine for post 2000, but you could contact the dealer for a suitable reader for pre 2000 cars (All dependent on make and model).