Peugeot 106 Intermittent Misfire and Hesitation

[Pete731]

Hi All,

Newbie to the forum here so please be gentle with me

As the title says I have a 106 Independence with around 90k on the clock. The problem actually started last winter. When it was cold the car would hesitate slightly the first couple of times I accelerated away after starting but would then be ok for the rest of the journey.

Spring and Summer came and the problem went away.

Now it has returned but much worse. Sometimes, when I first start up and pull away it feels like the engine is completely cutting out for a split second then is ok again, like a large hesitation. It might do this once or twice and then is ok for the rest of the journey, except that sometimes I can feel an intermittent miss if I hold it on part throttle. If I give it more throttle the miss goes away.

The engine warning light has not come on.

I let my local mechanic have a look at it and as a starting point he changed the fuel filter and plugged in a OBD scanner, which showed there was nothing to report.

On the way home the engine faltered so much I didn't think I was going to make it home. Then over the next few days it was perfectly fine.

So it would seem I have to start changing sensors. Any insights on which one(s) to replace first?

(I believe there are 2 temperature sensors. The blue one for the dash light and the green one for the ECU, except on mine both are coloured blue.)

I might also try reseating all the sensor connections (probably the first thing to do).

Thanks for any help.

Pete

[CitroJim]

Hi and welcome to the forum If your 106 has the same Bosch monopoint injection as the Saxo and late AX then your problem is very likely to be a mucky throttle pot. They ate not individually replaceable as they are part of the throttle body but with extreme care they can be cleaned quire successfully.

I've done this on my erstwhile Saxo and an AX.

If you can confirm you have the Bosch system, I can supply more details of how to do the job. Can't right now as I'm on my 'phone...

[Pete731]

Hi Jim,

Many thanks for your quick reply.

I have attached photos of the ecu and throttle body.

I think that from the numbers on the ecu label that it is a Bosch one. I didn't unscrew it from the tray.

[Stickyfinger]

I agree with Jim....it was a problem that "our" little AX had for a while.....it has not missed a beat since the reason was finally tracked down

[CitroJim]

That's the multipoint injection system and unfortunately what Both I and Alasdair said above does not apply. That said, I'd still very much suspect the throttle pot as a potential cause.

I'd also look for any air leaks between the air intake and the end of the inlet manifold, especially the various vacuum pipes such as those going to the brake servo and crankcase ventilation system. I have known those crack, allow air in south of the throttle butterfly and resulting in a dangerously weak mixture.

I have reached my limit here as I have zero experience of this injection system. Sorry.

[Pete731]

I had a look at any hoses connecting to the throttle body. The only thing I could find was some deterioration on the hose going to the servo but I think it is airtight. Might replace it as a matter of course. Had a look with the engine running too. Nothing obvious. Next step, replace the throttle position sensor.

[ozvtr]

The engine temp sensor that the ECU uses is on top of the thermostat housing. If the coolant temp on the dash indicates about half way when the engine is warmed up then the sensor is OK. The other "blue" sensor (if it has one) is under the thermostat housing. It's the over temp sensor. It doesn't do anything until the cylinder head temp reaches 120'C.
I'm not familiar with the cable operated throttle. So I cant comment on the TPS.
The TU3 is a very simple engine and doesn't have many sensors. There's the Manifold Absolute Pressure sensor on the inlet plenum, but that's very reliable. The crank angle sensor on the bell housing. If that's not giving correct information the engine ECU will shut down the engine.

Have you replaced the spark plugs? I had a similar problem with my C3 and the TU3 engine. VERY hard starting when the engine was cold, particularly on winter days. But ran perfectly when warmed up and summer days. I tried EVERYTHING, including the injectors and coil pack! I literally have a "spare" car to swap parts on! Cleaned and gaped the plugs. Electrodes looked good. No change. Then I replaced the plugs...now starts and runs perfectly. I had never seen this before. All the spark plugs I have used in all my cars were replaced because the electrodes had warn down! Not because they developed a fault. Yes the plugs were the correct spec (Bosch FR7DC) and the plugs had only done about 30000KM. The strange thing was that the engine didn't fire on any cylinders when it was acting up. Leading me to believe all 4 plugs were faulty.

[Pete731]

Many thanks for the info ozvtr.

Since it is a poverty spec 106 it doesn't actually have a temperature gauge, just a warning light - but that has never worked while I have driven the car. The fan does seem to run normally, though.

The spark plugs were changed when the problem first started several months ago.

However, the problem has now become much worse over the last couple of days. The engine was constantly cutting in and out on my short trip to work this morning so much so that I won't use the car any more except from taking it to my local mechanic. The engine has also started to stall when at idle. I have asked him to change the TPS and both temperature sensors. I will leave the MAP sensor for now, as you say, they are very reliable.

I have been told the TPS has to be coded to the ECU but that can be arranged.

I will let you know what happens.

[Pete731]

I had another look around the engine bay this afternoon and became quite excited when this came apart in my hand especially as it appeared to be part of the coil pack.



It had previously been repaired by having insulating tape wrapped around it. However I now know that it is just a radio interference suppressor. I tried to solder the earth terminal back on with no luck so glued it back together It should last until a replacement arrives although I am not really using the car at the minute. And I can always turn the radio off.

[ozvtr]

Coil pack is the next thing I would look at (if you haven't already) but I know that they are expensive.

Earlier models didn't have that suppressor. Just an earthed shielding around the coil pack low voltage wires. I have seen faults in that shielding cause induced problems with the "fly-by-wire" throttles. But not always!
That suppressor and the earthing crimp lug get mangled by gorillas who cant remove the locking nut from the coil pack retaining stud. You need a very thin 10mm spanner to get the two apart.

[Pete731]

Thanks ozvtr.

It occurred to me afterwards that since the suppressor casing was damaged exposing the capacitor inside that perhaps if moisture got inside the casing it could potentially be shorting the coil pack out. Or perhaps the capacitor itself had become damaged.

I decided to tie the remains of the suppressor out of the way and give it a go. No misfire (so far). I have now pressed the car back into service.

And there is no interference on the radio

I have ordered a replacement capacitor so will probably fit it anyway as it should only be a quick job.

I should mention that I did unplug the coil pack to get better access to tie the suppressor up but the plug did seem to be seated correctly etc.

And I see what you mean about needing the thin spanner.

[ozvtr]

Are you saying that "fixing" the suppressor has stopped the misfires? Actually, did you disconnect it?
In that case it's more than a radio suppressor! I would be interested to see if the misfires come back if you connected the suppressor.
I have a 2003 C3 with the TU3JP (KFV) engine. It does not have the suppressor, just an earth wire. I am currently "doing up" a 2005 C3 (TU3 blah blah) and it does have the "suppressor". I am very interested to see how you go with this.
I will also look at the circuit diagrams to see if the suppressor is on the diagram for the 2005 model.

[CitroJim]

Are you saying that "fixing" the suppressor has stopped the misfires? Actually, did you disconnect it?
In that case it's more than a radio suppressor!

It's quite possible it's acting in a similar way to the condenser (an old term for a capacitor) in a traditional points (contact breaker) ignition system.

It will certainly cause problems if it's physically damaged, can thus absorb moisture and become electrically leaky as a result.

This capacitor is present on many 90s-2000s PSA vehicles, including the V6 ES9 engine... My Base Model AX has one fitted and that has no radio. It was missing on my blue AX and although the radio suffered no interference whilst it was missing, I did replace it.

It'll be there for good reason as the radio equipment fitted OE by PSA to those vehicles need no help to have any sources of local interference supressed.

[Pete731]

I am off on Friday. I will reconnect it and see what happens.

[mickthemaverick]

If it is the same as it used to be the suppressor was fitted to prevent interference on the AM bands rather than FM so you probably don't use that now anyway!!