Xantia V6 broken exhaust (update: and rough low rpm running)

[addo]

Your "worst" coil result is within 5% of spec; that is - to me - acceptable. A dying or duff coil will show charge times 50% different.

Behaviour noted with the poor terminals was: Loss of power under load, overheating, near-stall when fans came on, uneven idle, excessive toggling between fan speeds, near stalling when pulling away from a stop. All of these were intermittent, and nearly every time I exchanged a component with new genuine or OEM, I thought the problem was fixed, as for a while it seemed better. I would not say all these symptoms were caused by the terminals, but most of them abated significantly or vanished once the electrics were fixed.

Considering I paid $370 for the coil pack, $180 for the stepper motor, $55 for the CAS, $60 for plugs, $50 for the thermostat, $112 for the FPR, $180 for the fuel pump, I have some justification to be butthurt when people keep repeating my mistakes despite attempts to pass on hard-earned experience... In the end I was skewered by the battery cable shedding all its insulation; clearly to keep driving would have been stupid so I had to pay local parts prices for cable and terminals in order to fix it promptly.

[Mandrake]

Your "worst" coil result is within 5% of spec; that is - to me - acceptable. A dying or duff coil will show charge times 50% different.

I agree that the charge times don't really show anything out of the ordinary.

Bear in mind though that coil charge times can only tell you about the health of the primary coil and the magnetic circuit, it tells you nothing about the secondary side of the coil and won't detect secondary faults, as I've already shown by confirming that the charge times do not change when a plug lead is disconnected or shorted to earth.

All they're testing is the time it takes for the primary current ramp to build up to its maximum, low inductance for example due to a shorted turn on the primary would show up as a charge time that is too quick. A high resistance joint in the primary may show up as a charge time that is too long.

Coils can fail through an internal breakdown of insulation on the secondary side which flashes over when the secondary voltage is above a certain threshold, for example lets say 10,000 volts. With the plug lead connected the spark voltage may only reach a few thousand volts at idle so the spark fires normally, open the throttle wide so higher spark voltage is required and it flashes over inside the coil instead of jumping the plug. This won't be reflected in the charge times at all as the primary side doesn't know whether the spark jumped in the plug, internally in the faulty coil, or from a faulty plug lead to earth...

Behaviour noted with the poor terminals was: Loss of power under load, overheating, near-stall when fans came on, uneven idle, excessive toggling between fan speeds, near stalling when pulling away from a stop. All of these were intermittent, and nearly every time I exchanged a component with new genuine or OEM, I thought the problem was fixed, as for a while it seemed better. I would not say all these symptoms were caused by the terminals, but most of them abated significantly or vanished once the electrics were fixed.

Considering I paid $370 for the coil pack, $180 for the stepper motor, $55 for the CAS, $60 for plugs, $50 for the thermostat, $112 for the FPR, $180 for the fuel pump, I have some justification to be butthurt when people keep repeating my mistakes despite attempts to pass on hard-earned experience... In the end I was skewered by the battery cable shedding all its insulation; clearly to keep driving would have been stupid so I had to pay local parts prices for cable and terminals in order to fix it promptly.

Point taken, I do definitely agree that there is an intermittent electrical fault that I haven't located yet but have disturbed on numerous occasions, even if it isn't all of the problem. Whether its the battery terminals I'm not sure, I will replace the negative when I find one I'm happy with, but it could just as easily be my spade terminal which I am going to remove soon and replace with a crimped butt joiner, or it could be a corroded earth where the ECU earths to the engine/chassis. I will do some further investigation.

[Mandrake]

Simon, have you checked SEDRE? Pretty sure that'll give you a good idea where the Ecu is grounded (Using The "Installation" diagram). Pretty sure one of the sections in SEDRE is "general earthing points" too so might give you an idea of where the ones that are used on the engine (of course the engine is one big hunk of metal so really any bolt on it turns into an earthing point but you're really only interested in the ones used )

Pretty sure your favourite youtuber has a video on ground noise testing using a scope with the differences between a good and bad ground

Hi Ben,

I'm well versed in the electrical side of testing for bad grounds with a scope etc coming from an electronics background, my problem is reading automotive circuit diagrams which are very different to normal electronics ones, trying to figure out what the numbered boxes on the diagram are, where they are physically located on the car, and identifying which of the bundle of 5 green wires is the one you're looking for!

[CitroJim]

my problem is reading automotive circuit diagrams which are very different to normal electronics ones, trying to figure out what the numbered boxes on the diagram are, where they are physically located on the car, and identifying which of the bundle of 5 green wires is the one you're looking for!

Simon, have you ghot the complete set of injection-related diagrams for your car?

You should have the schematic, the harness diagram and the location diagram.

If not I'll supply and I'm also happy to give a short tutorial on how to read them. Once you know how it all makes perfect sense

[Ben82]

Simon,

Taken a look on SEDRE, guessing my way through the options for your xantia.

Someone (Jim?) can tell me that i'm completely bonkers and incorrect with this, but to me, from:


Shows me that there are 3 potential earthing points on the "20 MOT" harness: MM05 (via ME05 or ME05A) and MC16.

Then this:


Shows me that the ECU from pin 2, is connected to MM05 via ME05A (and pin 19 is connected to MM05 via ME05) ... Next up the installation, then points to where MM05 is:


So from that it should be at those two points?

EDIT: spotted another grounded pin (19) so updated the above

[Northern_Mike]

Behaviour noted with the poor terminals was: Loss of power under load, overheating, near-stall when fans came on, uneven idle, excessive toggling between fan speeds, near stalling when pulling away from a stop. All of these were intermittent, and nearly every time I exchanged a component with new genuine or OEM, I thought the problem was fixed, as for a while it seemed better. I would not say all these symptoms were caused by the terminals, but most of them abated significantly or vanished once the electrics were fixed.

Considering I paid $370 for the coil pack, $180 for the stepper motor, $55 for the CAS, $60 for plugs, $50 for the thermostat, $112 for the FPR, $180 for the fuel pump, I have some justification to be butthurt when people keep repeating my mistakes despite attempts to pass on hard-earned experience... In the end I was skewered by the battery cable shedding all its insulation; clearly to keep driving would have been stupid so I had to pay local parts prices for cable and terminals in order to fix it promptly.

Point taken, I do definitely agree that there is an intermittent electrical fault that I haven't located yet but have disturbed on numerous occasions, even if it isn't all of the problem. Whether its the battery terminals I'm not sure, I will replace the negative when I find one I'm happy with

So you're going to not replace the one part that's the cheapest and easiest to do, which has been proven by others to be the cause of similar problems on many different vehicles.. yet your going to go delving into other wiring you know nothing about?

Yes. That makes perfect sense

[CitroJim]

Ben, spot on completely with your reading and interpretation of the three diagrams

[Ben82]

Ben, spot on completely with your reading and interpretation of the three diagrams

Thanks Jim Good to know my reading of the diagrams is getting better... the resource I posted in the Useful links section has been invaluable with learning ( http://peugeot.mainspot.net/wiringall/index.shtml" onclick="window.open(this.href);return false; )

[Mandrake]

So you're going to not replace the one part that's the cheapest and easiest to do, which has been proven by others to be the cause of similar problems on many different vehicles.. yet your going to go delving into other wiring you know nothing about?

Yes. That makes perfect sense

Mike you're making it sound like I'm wilfully ignoring a battery terminal whose guilt in the proceedings is a foregone conclusion, but its not the case at all.

In fact on Saturday I made a special trip 12 miles each way to a far away Halfords to get a battery terminal since none of the local ones had them in stock and I wanted to get it done the same day. When I got home and looked closer at the terminal I realised it wouldn't work as the hole for the cables to go into was too big when there are only two cables on the negative terminal, so on Sunday I went back again 12 miles each way to swap it for the other type which should have had a smaller hole but I'm still not very happy with it.

If I was happy with the terminal I would have changed it already last weekend. Once I cut the old terminal off if the new one won't fit satisfactorily then all I've achieved is putting the car off the road, and if its marginal I could just end up introducing another poor electrical connection. So I'm looking around to see what other terminals are available first. If someone has any suggestions of somewhere other than Halfords that do good battery terminals I'm listening...

The other point is that just because addo had a faulty battery terminal doesn't automatically mean that its my problem. If the Lexia voltage reading from the ECU is accurate I definitely have a voltage drop problem - 1.1 (cold) to 1.3 (hot) volts drop between the battery posts and the engine ECU is quite bad, however NONE of that voltage drop is between the battery negative post and the negative terminal, or between the negative terminal and the negative cables, I've already checked.

As soon as I can find a new battery terminal that I am happy with which won't make my problems even worse I will replace it, however I do not believe the negative terminal is causing the symptoms, especially when there are no difficulties with cranking speed.

[Mandrake]

Thanks Ben!

That Peugeot link you posted is excellent, I'll study that in detail later tonight. Those diagrams you posted and the tracing you did is also extremely helpful. In fact I think you might have just woken me up to where the problem could be!

Those two earth wires on the top of the front cam covers I'm well aware of, but for some reason I've never connected the dots and traced them to see what they connect to. In hindsight its obvious that they're the earthing points for the ECU.

Looking at the diagram and referring to the pinouts of the ECU, one of them, ME05 is used as the earth point for most of the sensor cable screens including the crank shaft sensor, oxygen sensor, and the knock sensor and here's the kicker - its also the earth return (via transistors inside the ECU) for the injectors!!!

The voltage drop from a poor earth at this terminal would cause the current pulses from the injectors firing to induce interference into the knock sensor and crank sensor signal lines and could cause major problems given the sensitivity of the knock sensor circuit...

ME05A which goes to pin 2 of the ECU is listed as the earth return for the coil packs (via switching transistors inside the ECU) so a poor earth here would limit the primary current of the coil packs causing a weak spark, and depending on what else inside the ECU shared pin 2 for its earth connection, the coil primary current would induce switching spikes into that circuitry as well.

So a poor/intermittent earth connection at either (or both!) of those two terminals has the potential to account for all the symptoms I'm seeing including low supply voltage as measured inside the ECU...

So how does this fit in with the dramatic worsening of engine running when I swapped the fuel pressure regulator over and had the fuel rail out, and the massive improvement when swapping the coil pack ?

Easy - normally when I take the inlet manifold out I don't bother to unbolt those two earth wires as is usually suggested, there is just enough movement to unbolt the plastic guide that holds the wiring and pull it forward to clear the manifold. However THIS time I decided to unbolt those two wires to give a bit more freedom of movement of the wiring loom, and thats when the performance went down the toilet. So I had disturbed those earth connections when usually I leave them alone!

When I replaced the coil pack and the performance came back to normal I didn't unbolt those earth wires however I'm sure I probably bumped them or pushed on them a bit while taking the spark plug leads off and on.

My conclusion now is that one or both of those earth points is bad! It could be either between the terminal and the engine, or it could be corrosion in the crimp between the wire and the terminal. (or a bit of both) I think I have the right size terminal so this weekend I'll replace the terminals with new ones and see what happens!!

If its not those two terminals I'm sure its still somewhere in the wiring loom across the top of the engine because the loom did get tugged around in all directions when I was trying to get the pressure regulator out, it might be at the plug/socket to the left of the manifold near the pressure regulator vacuum line that most of that wiring goes through to reach the ECU, I have used contact cleaner on that connector before but haven't checked it any further than that.

Something else I'd also like to check is the earth connection from the battery to the engine, does anyone know where on the engine it bolts on ?

[addo]

It's usually on the gearbox top somewhere. Follow the wires from your clamp.

[RichardW]

Simon

When I had to do the +ve on mine last year, I fitted one of the quick release ones from Halfords: Clamps I've still got the -ve one as no need to fit it yet.... Just measured the cable hole - with the screws done up it is an elipse 5mm high and 10mm wide which should easily clamp down on the lead - there is only just enough room to get the +ve in with the screws right out, but it makes a good connection (a lot better than the old one!). Certainly looks from service.citroen that engine earth is to top of 'box.

[Mandrake]

Thanks Richard. In typical Halfords fashion the website picture for those quick release clamps shows nothing useful about what they actually look like!

They are listed in stock at my nearest Halfords so I'll go and get a pair or at least have a look at them to see if they will do the job. 5mm x 10mm sounds about right to fit the two wires side by side. Turns out I don't have the right size eye terminals for those earth connections on top of the engine either so I'll need to get some of those at the same time, assuming they have them.

Here's what the clamp I currently have looks like, as you can see from the pen beside it the hole is huge and no way would it clamp on the two medium size negative wires without a lot of packing, even if I folded them double I think it would still be loose!



It would fit the 4 wires on the positive terminal ok, but not the two wires on the negative...

[addo]

You could also replace the ground cable with new heavy gauge that's pre-terminated in an eye for the gearbox end.

[CitroJim]

Earth is to a bolt on the top of the gearbox. Bolt and crinkle washer...

Check the other main earth to the bodyshell on the plate on the NS Inner wing too...