Peugeot 106 Intermittent Misfire and Hesitation

[ozvtr]

Electrical "noise" that came over the radio (in the olden days, LOL!) was mostly solved by going to resistive spark plug leads instead of wires. I should know, I lived in that era . Today the resistors to stop massive current inrush in the secondary side of the ignition are in the spark plugs, (most systems don't even have plug leads).

The condensers in the Kettering ignition were to stop the points being damaged by the back EMF arc over from the primary of the coil when the points opened. The ignition would still run without one but your points wouldn't last long.

Alternators typically made the most electrical noise in the power system and capacitors on the field windings or B+ terminal were usually the answer.

I am interested to see if this "suppressor" is causing the misfires or not. To my knowledge, it's only a shield around the low voltage coil pack wires...but why? Yes, it could be for radio noise suppression. But as I have said, the loss of this shield has effected other systems in the engine bay before. The other thing is that I am assuming it's connected to a shield...I could be wrong (gasp!). I know it's a shield on the earlier, models but is it a shield on later models? It may be de-coupling the positive supply of the coil pack?? If it's breaking down, that would explain the misfires.

[CitroJim]

I am interested to see if this "suppressor" is causing the misfires or not. To my knowledge, it's only a shield around the low voltage coil pack wires...but why? Yes, it could be for radio noise suppression. But as I have said, the loss of this shield has effected other systems in the engine bay before. The other thing is that I am assuming it's connected to a shield...I could be wrong (gasp!). I know it's a shield on the earlier, models but is it a shield on later models? It may be de-coupling the positive supply of the coil pack?? If it's breaking down, that would explain the misfires.

I'm intrigued too... As said, if it was sufficiently physically damaged to allow an ingress of moisture and thus as a result became electrically 'leaky' then that could conceivably cause an issue.

[ozvtr]

I have looked at both the Mk1 and facelift TU3JP circuit diagrams and there is no sign of shielding or a suppressor connected with the primary of the coil pack.
The only shielding in the diagram is around the knock sensor wiring.
Looking in my 2005 car, the engine has both the green/yellow earth for the shielding AND the "suppressor like" device.
I have an old loom that was on one of my C3's engine. The loom was hacked up by some monkey at some point, so I replaced it. I have since pulled it apart, that's how I know about the shield.
The shielding is only around the feedback line to the engine ECU. There is nothing on the coil +ve power line.
My contention would be that there is a splice in the power line and this decoupling capacitor is attached to it, as there is only one power wire at the grey connector of the coil pack.

OK. A bit more digging shows it to be a FACON 2.2 micro farad capacitor. It seems to have been used by PSA in their engines for a while now. And typically used on the ignition coils and alternators as suppressors.

So, if it is connected to the power line of the coil pack and it goes "leaky", that would result in misfires...I suppose.

[Pete731]

I had a go at reconnecting the suppressor but due to the physical state of it could not get an electrical connection at the earth terminal end despite my best efforts.

In the end I snipped it off and took it apart further. There was no evidence of dampness within the plastic casing. My multimeter does not have the specific ability to test capacitance so I just used the resistance setting to put a voltage through it and watch the numbers go up until it went open circuit. Then I swapped to probes over and repeated the exercise. The cap acted as expected but I realise that this would only be a basic test and would not be totally exhaustive in determining its health. So the cap seems to be ok as far as it goes.

The only other thing I did the other day besides disconnecting the suppressor was to unplug the coil pack so I took the connector off again and inspected it more closely. It all appears as it should with shiny connectors and no sign of any corrosion.

I can only conclude the suppressor assembly was still faulty somehow shorting the coil pack or there was a bad connection at the coil pack plug which unplugging it and plugging it back in resolved.

I only wish that testing would have produced more conclusive results.

If the fault returns the coil pack would be no. 1 suspect as this is the only area I have messed with.

And the radio seems fine on both FM and AM

I have a replacement suppressor and will fit it when I get hold of the correct crimp terminal.

[CitroJim]

Very interesting Pete Yes, that capacitor was more or less behaving as I'd expect to when tested using a multimeter. For a temporary replacement you can always use a standard 0.1 microfarad 400v or 630V polyester film capacitor as a substitute.

These days, modern car electrical systems are generally very 'quiet' from an interference point of view and modern car radios are also much more resistant than their forebears.

I have many 'happy' memories of working on supressing cars of the 60s and early 70s some 50-odd years ago when a basic Radiomobile or Motorola radio was installed in them... That was when Radio 1 was on 247 metres Medium Wave and Radio Luxembourg on 208 metres was the only station to listen to in the evening...

Those were the days Arm yourself with a fistful of suppressor capacitors along with new resistive HT leads and if luck was on your side you might even succeed!

[ozvtr]

I have 2 C3's (on the road) with TU3JP engines. Both "hunt" when the car is doing about 60Kmh (about 35MPH). Both of them! So there is a production flaw in the circa 2003 TU3 engines. The ECU's are the "fly-by-wire" Sagem units. I am assuming that, in that era (2005), Peugeot went to the fly-by-wire throttles? I know that around 2003 the Peugeot versions of the TU3 had cable throttles.
Neither throw up a fault code, so the engine ECU's don't "think" that there is a problem! The hunting is very pronounced. Not bad, but certainly noticeable.
I can not find any faults with the engines. When I bought them, they both had the usual head gasket failure and I replaced the gaskets. One needed the head decked, new exhaust valve seats and a valve job. So I consider both engines and electrics as serviceable as 22 year old engines could be.
I am currently working on a 2005 C3 (yes TU3 engine). In good condition for a 20 year old car. But again requires a head gasket and some other bits and pieces. I guess fixing C3's is a hobby by now !

As I have mentioned before it has the "upgraded" suppressor mod. But I am very interested in any improvements that Citroen might have made to the platform, namely the engine and gearbox ECU firmware. And if they solved this hunting problem? Why did the early versions not have the suppressor but they installed it on later versions? The 2003 cars DO NOT suffer any radio interference on either AM or FM and the CD players perform fine. So why install this suppressor?
P.S. I bought this car from an auction, unregistered. So I haven't really driven it yet.

[Pete731]

Just wanted to add that I fitted the new suppressor today and all is still ok (so far).

[Pete731]

So after some months of running ok the misfire returned!

The only other thing I did last time when fitting a new suppressor, to replace the disintegrated one, was to unplug the coil pack to get better access. So this time I unplugged the coil pack, gave the contacts another spray with contact cleaner and plugged it back in. He presto, no misfire.

So I am now convinced the problem all along has been either a dodgy contact on the coil pack itself or a connection at the end of the loom where it plugs into said coil pack.
Might replace the pack first and see how it runs then if that doesn't cure it re end the loom with the coil pack plug.

On another note, now the ignition barrel has lost its return spring from when you start the engine back to the 'running' position, so I have to turn it back manually. I sometimes lose the indicators and radio etc. if I haven't moved it back to the exact position. Am I correct in thinking that the return spring is in the plastic bit that plugs into the lock barrel? Meaning that I only need to replace that instead of the whole lock (and save having to get new keys reprogrammed)? I see that the original Peugeot key has a small screw so the blade that would come with a new barrel can be swapped into the old key holder to save reprogramming but most of the replacement ones available now don't seem to have this.

[CitroJim]

Sorry to hear the misfire has returned Pete... It may be the coil, especially if it happens when the engine is hot... Coils are often OK when cold and give issues when hot.

The ignition lock return spring is usually inside the lock barrel itself. If you have a spare handy, you could try carefully disassembling the assembly and seeing if the problem can be solved. Nothing to be loose really! The spring may be a little flat coil spring.

I once successfully dismantled, cleaned and reassembled one of my AX door locks...

[ozvtr]

So after some months of running ok the misfire returned!
So this time I unplugged the coil pack, gave the contacts another spray with contact cleaner and plugged it back in. He presto, no misfire.

I suspected an ignition problem but not a contact problem. Good job.
I have 4 C3's (it's along story) all used when I bought them, all with the TU3JP engine. I don't think any of them have the OEM starters or coil packs! I don't know why. 4 out of 4?

On another note, now the ignition barrel has lost its return spring from when you start the engine back to the 'running' position, so I have to turn it back manually.

You can try removing the steering wheel shroud and spraying a "water displacing spray", like WD-40, directly into the key hole. The mechanism can get gummed up. Put a rag under the barrel to catch excess fluid so it doesn't run everywhere. It may take a few tries.
If that fails and you need to replace the lock, it's a pain in the bottom! Yes, you only need to replace the barrel and the key blade but the barrel is held in with a security screw, which will need to be drilled out. The head of this screw is snapped off during installation. So you need to treat it like a broken screw.

[Pete731]

You can try removing the steering wheel shroud and spraying a "water displacing spray", like WD-40, directly into the key hole.

Great. I did try a small amount of WD-40 but I will give it a good go.

the barrel is held in with a security screw, which will need to be drilled out.

That's what I was afraid of. And there I was hoping it would be a nice simple job! Definitely trying the spray method first.

[Pete731]

Just wanted to report back on this. Since I gave the coil pack a good wriggle in an attempt to seat it right down the misfire seems to have gone away. The disintegrated suppressor seems to have been a red herring. Should the misfire return the steps I will take in order of priority are, take the coil pack off and refit it, followed by replacing it followed by replacing the plug and end section of the loom that plugs into the coil pack. Finders crossed it keeps on going as it is.

Thanks for everyone's help with this.

[ozvtr]

The disintegrated suppressor seems to have been a red herring.

The engines before 2005 did not have this capacitor, but they installed one from 2005 on. I have taken another look and it's not connected to the shield because the shield wire is also there. It's connected to something else. I would assume it was installed to fix some sort of problem...but what problem? As I said it does not appear on the circuit diagrams.
Strange!

[Pete731]

The disintegrated suppressor seems to have been a red herring.

The engines before 2005 did not have this capacitor, but they installed one from 2005 on.

That's interesting. Mine's a TU1 dating from 2000 however I take your point re the capacitor being fitted for a reason. Anyway, it now has one of correct value fitted.

[ozvtr]

That's interesting. Mine's a TU1 dating from 2000 however I take your point re the capacitor being fitted for a reason. Anyway, it now has one of correct value fitted.

I might have to caveat what I said. The engines are in Citroen C3's and they are TU3s (but I don't think that should make a difference). I own two 2003 examples and two 2005 examples. That's how I know, but it seems Peugeot and Citroen were doing things differently?!
So Peugeot had the suppressors in from the beginning but Citroen didn't install them until 2005? I would have assumed these cars were built from a pool of common PSA parts.

"Curiouser and Curiouser" said Alice.