Peugeot 607 – one bank rich, bad starting, misfires

Hello,
I have 2005 Peugeot 607 3.0 V6 XFV. A few months ago, my car started to behave weirdy. At first, check engine popped up. However, the diagnostic device showed only very generic codes:

P0172 System too rich (Bank 1)
P2192 System too rich at higher load (Bank 1)

Then, starting, especially in cold conditions, became very rough (i recorded it on included video) and misfires started to occur (I can smell unburnt fuel coming from the exhaust). But the engine runs smooth after minute or two, but Bank 1 is still very rich (long term fuel trim is currently -25 %).

So far i:
-Replaced ignition coils and spark plugs
-Swapped fuel injectors between banks to see whether the problem moves to another bank (it did not)
-Replaced O2 sensors
-Checked fuel pressure and compression (ok)
-Replaced air filter
-Checked catalytic converter whether it is plugged or not (it is not)

I’m honestly running out of ideas, so if anyone has an idea or advice, I would be very appreciate.

Thank you for your help in advance.

The video with car behaviour (607 one bank rich, misfires - YouTube)

Based on the codes and what you have replaced, I’d guess you have and air leak on the bank 1 side of the intake manifold. I am not familiar with the specifics of the engine so I don’t know how seperated the sides of the manifold are. Normally a leak would affect both banks. If there are 2 mass airflow sensors…one for each bank…both codes point to a bad bank 1 MAF.

An exhaust leak at the manifold or pipes would be very specific to bank 1 and would certainly cause the P0172. Check that.

This site mostly has USA participants so we are not familiar with the 607 but an engine is still an engine! Post back with what you find and we will keep trying to help.

Seems like unmetered air is getting to the O2 sensor. Could be an intake or vacuum system leak, but unless these symptoms started immediately after some engine compartment work, on an 05, my guess is the exhaust system has rusted and a leak has poked through. A simple driveway test is to park on a level, dry spot, then look under the car soon after a cold start. Best tp do this in the AM when it is cooler. It’s normal to see some water dripping from the end of the tailpipe in that situation, but you may also see some water dripping from the middle exhaust section. If so, you’ve probably found the culprit.

Does this vehicle have two banks with two oxygen sensors before the catalytic converter? I know 6 cylinder Fords in the USA do that. 3 cylinders exhaust to one sensor only. I assume yours must be like that since it has 6 cylinders.

How does this usually work? Do all the injectors always inject the same amout of fuel? I assume it wouldn’t have a separate mixture control for bank 1 versus bank 2. So wouldn’t a vaccum leak on bank 2 cause bank 2 to run lean, so the mixture would go more rich on both banks, which would cause bank 1 which doesn’t have the vacuum leak to then become too rich?

The P2192 (high load too rich bank 1) just doesn’t make sense with a vacuum leak. When you go to full throttle vacuum leak problems go away. Maybe P2192 always happens first along with P0172 (bank 1 always too rich).

Could there be an electrical wiring problem related to the bank 1 oxygen sensor? What if you disconnect the bank 1 oxygen sensor completely, so the car can’t use it at all? See if this causes the rough starting issue to go away. Can you measure the Voltages on the oxygen sensors themselves? Higher Voltage put out by the sensor means the mixture is rich, because less exhaust oxygen, so the greater the difference in oxygen in the exhaust compared to outside, so more Voltage produced by the sensor.

An intake or exhaust leak ahead of the upstream oxygen sensor would cause lean codes, not rich codes

We would be seeing P0171, not P0172

personally, I’d want to see the fuel trims for both banks, not just the one that’s coding

It’s been my experience that often the bank that did NOT code is nearly as bad, just not quite bad enough to code

So there may be a problem that’s affecting the entire engine, not just one single bank

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Have you checked to see if the injectors on the rich running side are pulsing on the off chance that they may be held open all the time and not ever closing?

I mention this because of a Volvo I saw once in which all 6 injectors were staying open and never closing.
Running very rough, acrid too rich smell, black smoke out the tail pipe, etc.

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Thank you for all your replies.

The engine has two separate banks, each one has its own catalytic converter with a pair of O2 sensors. So I guess that each bank has its own fuel measurement system. But there is only one MAF sensor, so I guess that the problem with it would cause problems on both banks. So i don’t know, whether the intake leak would affect both banks, or only one. Actually, when i go full throttle, the problems even get worse; the car starts to misfire a lot and the check engine light start to flash (that happenes when the computer detects a misfire). I already tried to disconnect oxygen sensor, unfortunately with no effect.

Long term fuel trim on bank 2 is currently 2 %, it changes, but it’s always around 0.

Today, i checked the codes again and another popped up.
P2099 Post Catalyst Fuel Trim System Too Rich bank 2.
I checked the voltage on O2 sensors and noticed, that pre-catalyst O2 sensor on bank 2 has corresponging voltage as post-catalyst. I’m not sure, but doesn’t that mean a not functional catalyst? As far as I’m concerned, the post-cat O2 is present only to check whether the catalyst converter is functional, it does not affect the fuel trim. Pre-cat O2 sensor on bank 1 has the right voltage, but the post-cat shows a very low (around 0.1 V), which propably indicates rich condition. I have no idea if this can also affect one bank, the car seems to have an independent fuel controls. I checked the injectors and they seem to be operating corretly, I even tried swapping them between banks and nothing happened. Accoring to a car behaviour, I think that the problems occur mostly when the car is on load (going uphill, idle).

I’m thinking about some wiring problems or ECU related issue. And I will also check the manifold intake.

Agree… that thought came to me after the post. The site I checked for the P0172 code did list intake and exhaust leaks as a possible issue. See below.

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The car has 2 catalytic converters, correct?

And the bank 1 downstream oxygen sensor is fluctuating just as fast as the bank 1 upstream sensor? . . . that would indicate the bank 1 catalyst isn’t doing much at this time

How did you determine the catalyst wasn’t plugged?

Backpressure gauge?

You’re correct about the downstream sensors . . . they merely monitor the catalyst’s condition

What about the bank 2 fuel trims?

Are they fine, or are they also very negative, like bank 1?

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Have you checked the PCV system, the crankcase vent that goes in to the intake? Engine gasses normally don’t contain oxygen, unless you have a bad oil pan seal and it’s sucking in air, so this is routed to the intake after the MAF as it doesn’t affect the mixture. If you have a disconnected PVC hose or a non sealed engine it will suck non MAF metered air in to the system and cause a lot of problems. The PCV system wouldn’t be routed to just one of the banks would it? Can you check? You can try disconnecting the PCV hose and plugging the inlet to the air intake for testing.

I think that’s right. The computer varies the mixture from lean to rich all the time during normal operation to allow the catalyst to function properly. The lean periods somehow charge the catalyst with oxygen so it can do its job. The other method of making the catalyst function properly is to pump clean air in to the exhaust to give the catalyst enough oxygen. I wouldn’t worry about the catalyst right now as it probably can’t function with the mixture so messed up. Just don’t drive the car more than needed for testing to prevent damage to the catalyst.

The down stream oxygen sensor is confusing to me since I thought that more rich means less oxygen which means more sensor Voltage. But low sensor Voltage would indicate excess oxygen in the post catalyst exhaust, indicating that the cataylist isn’t using the oxygen to do its job hence the catalyst failure code. So why do they call it rich in the P code? I don’t know.

The important thing is that the Voltages measured at the oxygen sensors match what is shown on the scan tool.

I beleve mechanics do smoke tests on vehicles to find vacuum leaks. You may want to have this done to your car.

If you’re bored you could disconnect the 3 fuel injectors on one side so it only runs on 3 cylinders and see what that does. Then try it on the other side. If it runs properly one way then you know you have a problem with the other bank.

Concur w/ @db4690 above, the -25% fuel trim means the computer needs to inject 25% less fuel to meet the O2 sensor’s requirements, than it would otherwise inject based on the MAF and other sensors. That pretty much rules out an exhaust leak as the cause, b/c if there were an exhaust leak the fuel trim would be positive rather than negative. If the fuel trim problem only appears on one of the banks, couldn’t be the MAF b/c MAF most likely is shared between both banks. Most likely causes are

  • O2 sensors on faulty bank
  • Fuel injectors sticking open on faulty bank
  • ECM problem

Some ECM’s use the post-cat O2 sensor only for sensing cat function; but I believe other ECMs use the post-cat O2 sensor for setting fuel/air mixture as well. You’d have to consult your car’s service data to know which applies. Average voltage on O2 sensor pre vs post cat is not how cat function determined by ECM. The voltage vs time signal’s are compared.

I think if I had this problem first thing I’d do is disconnect then reconnect ECM. May be a slightly corroded connection on the ECM connector.

This is how the emission system looks like.
IMG-20220704-151515

The car has two catalytic convertes. I have unmounted bank 1 catalyst and I friend of mine checked it. I guess it was some kind of pressure test, since he told me that it’s definitely not clogged. Bank 2 fuel trims are ok, around 0 %. Latest long term value is 2 %.

I guess I’ll have to check the ECM. O2 sensors should be fine, they are basically new. And I don’t know whether the bad O2 sensor can cause hard and rough starting. And since I already swapped the fuel injectots between banks, I guess they are ok, the problem did not move to other bank.

The banks have mutual MAF sensor, so I think a problem would appear at both banks.

I presume this car has a returnless fuel system, meaning there is no fuel pressure regulator in the engine bay . . . ?

What happens if you disconnect all 3 injectors on one bank? Does it run correctly even though it is only 3 cylinders?

Your original post indicated a LTFT of -25% bank 1 (presumably). What is it now? What are the current diagnostic codes? Suggest you do a reset in other words. Just in case whatever problems there are have changed.

You’ve done quite a bit of useful testing yourself. Be aware however that problems like this often end up requiring a fuel rail pressure test, noid test (injector pulses), fuel contamination test (e.g. water), and a compression test before the nature of the problem is discovered. Your idea to next look at the ECM connector seems sound.

If we went back to diagnostics 101, if a car owner reports (cranks ok, but poor cold starts, misfires), first ideas would be too lean rather than too rich. If you are certain it isn’t too lean, then battery/alternator, compression, EGR , fuel pressure, or fuel contamination.

O2 sensors don’t do anything for the first few minutes after a cold start. So the starting problems tend to say the O2 sensors unlikely culprits.

Air has to move through the engine easily and exhaust gasses out the tailpipe for it to work correctly. No chance of engine air starvation, right? Check the area where the air comes in, from there to the air cleaner, make sure no rodent nests or other debris accumulation. Good, strong flow of exhaust gasses out the tailpipe, right? You have 2 cats, but just one tailpipe, right?

hmmmm … My own experiences over the years with difficult to diagnose cranks ok but poor starting, misfires … fuel system or fuel pressure for the most part, vacuum system (or intake manifold) leaks causing “too lean”, ignition system after that, but never any ignition system problems on vehicle with electronic injection.

Feeling overwhelmed? Nothing saying you can’t ask a shop to do the diagnosis, then you can do the repair yourself if you like. Sometimes this is useful if only to get another set of unbiased eyes on the problem. Could be something obvious you just aren’t seeing b/c you think such a possibility is so unlikely. One poster here had set of difficult to diagnose problems, replaced this & that, no help, asked for a shop diagnosis, shop said problematic timing belt. Poster replaced belt and installed a new water pump, engine ran like a champ. (hmmm … come to think of it, with one bank out of sorts, the other ok, the cam timing mark alignment on the bad bank seems worth checking.)

Is it actually safe to run engine on only one bank? If it is, I might try it.

It it still -25 %. Which is quite strange, since the number does not change. The codes are still the same, system too rich (bank 1) and system too rich on higher load (bank 1). Nothing changed.

Yes, two catalysts and one tailpipe. I might actually look for help in a shop. The reason why I’m trying to diagnose the problems myself… the car is quite old and I don’t really want to spent fortune on it. I guess I’m going to check my ECM or send it to diagnostic.

Remove the spark plugs from bank 1 and see if they have equal carbon soot or if there is one problem cylinder.

I don’t see why it isn’t. No fuel is being injected so there is no unburnt fuel going in to the catalytic converter. The entire bank is disabled so there won’t be oxygen going past the oxygen sensor that will cause the working cylinders on that oxygen sensor to go extra rich. I think doing this would be more safe than running it in its current condition with unburnt fuel going out the exhaust.