Lambda issues?

[ozvtr]

I believe the 2 lambda sensors and the the purge valve share a power feed wire so maybe its possible that a fault with 1 of these can throw up all 3 fault codes?

Only if it's the common power supply. A fault with one will show up as a fault with one. Or it will blow the fuse...and you are back to a power supply problem.

I was wondering if the upstream sensor was faulty too as I've read even a heater circuit fault can cause the ecu to over fuel the engine.

Possibly. The sensor diagram shows the heater is indirectly connected to an amplifier virtual reference ground.

I can't see any fuel trims with the scan tool I have but it says
O2 sensor 1 -0.012mA
Bank 1 sensor 2 0.455v

I have seen some scan tools give out O2 sensor readings as milliamps, I don't know why...not helpful.
0.455V is the output bias point. I.E. the point about which the voltage "swings". For a downstream sensor this shouldn't swing too much, but it should not remain static. So either the engine is not running, the engine is not warmed up or the sensor is faulty.

I've just measured the heater circuit resistance on the pre cat sensor and it's reading about 04.5 then another time it read 06. something.

That looks OK, as we suspected.

I checked the pins on the plug coming from the wiring loom and all the pins showed about 3v power and when I checked for ground they all showed about 9v. Im a little confused by this but maybe its normal.

I wouldn't bother with anything other than pin4. It should be supply voltage (between 12 and 14 Volts). The heater ground will be modulated by the engine ECU and may or may not show resistance to ground (not voltage). The other pins are amplifier inputs and so could be anything. So there is not much to be gained there.

[Andy207cc]

Thanks for that detailed break down, I'm not sure where to check next though, should I take a punt on the upstream sensor and change that even though the heater resistance appears to check out ok. Is it worth checking for power at the 2 wired plug on the evap purge valve (very awkward to access)?
I do have a spare ecu but don't think it will be much use as I believe they need to be coded to the key or something as its from another 207.

[wheeler]

As it is the spare ecu is not much good without the matching BSI & key.
Either that or have it cloned from the original ECU. This cant be done with diagbox.

[ozvtr]

I'm not sure where to check next though, should I take a punt on the upstream sensor and change that even though the heater resistance appears to check out ok.

You don't have much left. It won't hurt anything except your wallet. Although, I would still check the powers and grounds first.

Is it worth checking for power at the 2 wired plug on the evap purge valve (very awkward to access)?

IMHO, no. As Wheeler said, the heaters and evap are going to be on the same circuit, so if you have power at the heaters then, most likely, you'll have power at the valve. The valve could be stuck open but statistically speaking, I doubt that. You would be looking at lotto winning odds for that and other things happening at the same time.

[Andy207cc]

So after testing the O2 sensor plugs with the ignition on, the results are as follows...

Pre cat sensor (5/6pin).... pin2 (power) 2.5v
pin3 (ground?) .574ohms
Post cat (4pin) ..... pin 4 (power) 0.4v
pin 3 (ground) 0.04 ohms

These power supply readings seem low but I'm no expert, the ground on the pre cat sensor seemed a high reading too but I'm not sure if this is normal and the ecu deals with it?
Now I'm thinking the ecu could be at fault?

[ozvtr]

As I said the engine ECU should modulate (turn on and off) the ground to the heater. This is to reduce over all power consumption and reduce the risk of the heater burning out. So your "funny" ground readings seem OK. Without putting an oscilloscope on it the ohm meter reading will look a bit strange.

There is no power supply to the sensor element so don't bother probing any pins except pins 3 and 4. The reading won't make any sense.

However the #4 pin 0.4 volts is not good. This is supplied from the BSM and should be battery voltage with the ignition on but the engine not running. Without a circuit diagram, you'll need to chase the wire back to the BSM electrical connector and test the voltage there too.
I'm beginning to suspect power supply problems.

[Andy207cc]

Does anyone please have a wiring diagram based around the fuse box as I don't have 12v at fuse 10 which feeds the O2 sensors.

[ozvtr]

You are now looking at an internal BSM issue. My bet is a faulty solder joint on that fuse holder, as otherwise you would have other faults.
Most of the power distribution (in the BSM) comes straight from battery positive and is then fused on each sub-circuit. It may go through an isolating relay, but I'll get to that in a moment.
The question is; do you have the skills to repair the BSM? If you do, then tracking down the problem...shouldn't be a problem.
If you don't, then it looks like the BSM needs to be replaced.
Anyone could pull the BSM out and then open it up "to have a look". As I said any damage should be apparent. A burnt out track or bad solder joint. I don't think it would be a relay failure, as a relay would (typically) run multiple sub-circuits and you only seem to be having trouble with one thing.

[Andy207cc]

Thanks for the reply, further investigation found that power was evident at the fuse when the engine was running.
This brings me back to where I was before and the latest is that I ha e no power coming from the ecu at pin 17 which is the feed wire for the o2 sensors and evap valve which are causing my eml light to come on and I assume the rough running.
I have tried a known good replacement ecu to no avail.
I am at a complete loss with where to look?!

[Andy207cc]

I can only think that it may be possible that a component or wire within the circuit is causing the ecu to not send power to the circuit?
Does anyone think this sounds feasible?

[ozvtr]

Ok this is turning into a bit of a round about.

While the loss of the heater circuit and purge valve will cause the check engine light to come, it really won't effect the performance of the engine.

I think the fault in the power circuit is close to or at the BSM. Perhaps the connector on the BSM that goes to the two suspect circuits. The fault is common to both the 2 heater circuits and the purge valve so the fault is closer to the source than further away. Remember the BSM supplies positive and the engine ECU supplies a ground. You have no positive supply at the devices but you do have positive at the fuse.

The major problem is the rough idle and the sooty spark plugs. And yet we have no DTC for rich mixture. We DO have a DTC for "aging catylist", probably because the converter cant handle the rich mixture??

I'm not that familiar with the prince engine, but my guess is the upstream O2 sensor. If the O2 sensor was telling the truth, the ECU should compensate for, or warn of, a rich mixture. But that's only going on the info from your scanner...which isn't a lot.

The prince engine has the crazy variable valve lift system instead of a classic throttle body and "butterfly" valve (but it DOES have a throttle body as a back up). But, again NO DTC's for the valve lift or the camshaft timing solenoids (or your scanner cant read them).

So there isn't much to go on.

[Andy207cc]

What you're saying makes alot of sense. I need to check the wiring between the fuse box and the ecu so if anyone can supply a wiring diagram that includes this that would be great.
If I can get to the bottom of why the eml is on, then if that doesn't resolve the rough running I will treat that as another issue.

[Andy207cc]

I'm wondering if I've been looking at this from the wrong angle. As ozvtr previously stated these fault codes relating to the circuit which includes the o2 heater sensors and evap purge valve shouldn't be affecting the running of the engine at least not to the point of rough idle that I am experiencing.
Last night I was checking live data and fault codes again when I noticed 3 new ones ...p1336, p1337 and p1339. These apparently relate to misfires in at least 2 of the cylinders. After further investigation on the internet I found a page which described these fault codes in detail for the 207 and stated that they can be responsible for deactivating the purge valve circuit and the rich mixture regulation or something along those lines, basically the circuit which I can't find power on.
I've tried disconnecting the coil packs individually but it's impossible to tell if any are at fault as I'm guessing the misfire is intermittent and every pack I disconnect does affect the engine idle to some extent.
Does this theory seem feasible? Should I be looking for a more basic fault with the ignition system, maybe coil packs or maf sensor?
Its hard to say what's causing what and its strange to me I'm not getting more DTCs to point me in another direction.

[Andy207cc]

Update...

Have cut the 12v feed wire for the O2 heater cicuits and evap purge valve from the ecu and installed a fused 12v supply from the battery.
This seems to have solved the issue as now the engine idles smoothly and the eml has stayed off.
A look on live data shows that the fuel system is running in closed loop with no fault and is taking information from both O2 sensors.

Fingers crossed this has fixed the issue.

[ozvtr]

Normally The purge valve is closed and applying power opens it. It allows petrol vapors from the purge canister to be burnt in the engine.
It usually bypasses any air volume metering devices. The engine ECU controls when the purge valve opens, which is usually when the engine is at high revs, low load and not at idle. The purge valve is closed most of the time.
If the purge valve is open at idle it acts like a vacuum leak and disrupts the air/fuel ratio because, as I said, it bypasses the metering devices. The oxy sensor sees that as a lean mixture and the engine ECU richens up the mixture.
However, as I said, the purge valve is usually closed and requires power to open. So if it had no power it should have remained closed.
The valve needs to remain closed when the engine is not running otherwise the vapors from the fuel tank will vent to the atmosphere through the inlet manifold.
I'm fixated on the purge valve because, out of the the valve and the heaters, the valve is the is the only thing that could effect the performance of the engine. But the symptoms don't fit the theory.
I also said that I'm not that familiar with the Prince engine, so I could be barking up the wrong tree.
Could there be something else in that circuit that the engine ECU needs to run correctly? Was the purge valve stuck and now it's working? I don't know.
Good luck, I hope you have found the fault.