High Short Term Fuel Trim on 1.6 THP

[X8R]

Hi gentlemen and gentleladies

I am puzzled again with my Citroen DS3 1.6T with the infamous EPCDT engine and I am hopping the brains trust and the THP gurus will shed some light

The engine doesn't seem to run 100% right. While it seems to cruise OK, it does not like sudden throttle openings. It occasionally misfires on wide open throttle after a long downhill with the throttle closed. Shuddering and stuttering at that moment.

I did run some basic diagnostics and I found something a little strange. The short term fuel trims at 3,000 rpm and no load show +20% fuel being added. At idle, it sems to hover around 0.
Long term fuel sits at 4%. See files attached.

What do you think it is happening?
- Faulty PCV?
- Buggered O2 sensor?
- Carbon buildup?

Misfire count seems to go up in Cyl1 when going WOT right after a long downwill coasting - ocassionally setting the EML light on. Swapping coils and plugs makes no difference. Plugs seem healthy too.
I did a manual carbon clean myself with pick and solvents. It's not 100% clean but decent.

Thanks folks!

 

[dmccurtayne]

The engine will run richer with carbon build up and you would have super knock codes. I would be leaning towards pcv is there any vacuum when the oil cap is removed with engine running. Try introducing a bit of fuel at idle ie carby cleaner and see if the trims s/t go negative that way you rule out o2 sensor. Also road test with fuel pressure pid up to make sure your low or high pressure pumps are not stuffed which is very common on these.

 

[ozVTR]

Swap #1 fuel injector with any other (swap with #4 if you are not sure of the cylinder numbering). Cylinder numbering right to left on these engines? See if misfire moves.
Data a bit contradictory. LTFT/STFT OK under load but STFT 15% at idle (I assume first graph is idle?). Vacuum leak? But it's not extremely bad. Borderline for investigation.
Try injector first.
P037 DTC? What is the downstream sensor saying? Voltage steady? Pending/temporary fault?

 

[X8R]

The engine will run richer with carbon build up and you would have super knock codes. I would be leaning towards pcv is there any vacuum when the oil cap is removed with engine running. Try introducing a bit of fuel at idle ie carby cleaner and see if the trims s/t go negative that way you rule out o2 sensor. Also road test with fuel pressure pid up to make sure your low or high pressure pumps are not stuffed which is very common on these.

I appreciate the answer, DMC!
There's definitely vacuum on the oil fill cap at idle but I also understand there is a correct amount of vacuum but I can't remember the value.
I'll need to check if my O2 is working, throwing a bit of carb cleaner is a good idea.
Fuel pressure from the HPFP seems OK at WOT. It may not be during the transition from coasting to full throttle, however!

Swap #1 fuel injector with any other (swap with #4 if you are not sure of the cylinder numbering). Cylinder numbering right to left on these engines? See if misfire moves.
Data a bit contradictory. LTFT/STFT OK under load but STFT 15% at idle (I assume first graph is idle?). Vacuum leak? But it's not extremely bad. Borderline for investigation.
Try injector first.
P037 DTC? What is the downstream sensor saying? Voltage steady? Pending/temporary fault?

Thanks ozVTR!
I really don't know which cylinder is which but I suspect Cyl 1 is next to the timing chain? It may be an injector problem, you are right.
The graph I posted (1st photo/figure on the left) is Short Term Fuel at 3000 rpm and no load (showing +20%). Weirdly enough, at idle however is around 0%.
The code it was throwing was P1337 (misfire cyl1?)

 

[dmccurtayne]

Well if you unplug a coil you will quickly find what’s what but it’s flywheel side btw.

 

[seasink]

P1337 in the Citroen book is:
Misfire in cylinder 1 sufficient to damage the catalyst with low fuel.

Cyl 1 is as dmcc mentions, flywheel end. The French numbering system.

 

[ozVTR]

I really don't know which cylinder is which but I suspect Cyl 1 is next to the timing chain? It may be an injector problem, you are right.
The graph I posted (1st photo/figure on the left) is Short Term Fuel at 3000 rpm and no load (showing +20%). Weirdly enough, at idle however is around 0%.
The code it was throwing was P1337 (misfire cyl1?)

That's why I said swap #1 and #4. They are at either end of the block, you don't need to know the cylinder numbering then.

0% at idle, then no vacuum leak.

Ah, OK, the misfire was logged at 71Kph and 4440RPM when (as) the throttle was closed and the engine ECU has gone into coasting lean mode. On the surface it looks like the injector has cut off the fuel altogether but the engine ECU was expecting combustion on that cylinder.

20% under no load might be exaggerating the the size of the problem. 20% of a small amount (of fuel) is still a small amount! I am not saying there isn't a problem I'm just saying the fuel trims while the engine is under load in real-world conditions are more important. LTFT in freeze frame data only shows 3.9%. Again, I'm not saying there isn't a problem, I'm just saying that if it's the injector, it's malfunctioning under specific conditions or it's performance is borderline. One problem with GDI engines is that the injectors must do their job much faster than port injection injectors. So at low RPM (idle) GDI injectors are not working as hard.

Fuel rail pressure is 11MPa at the time of the incident. I don't know what it should be, however, I would have thought low fuel rail pressure would bring on a warning?

OH, by the way. I have a TU3JP engine in my 2003 C3 and LEXIA will not show the fuel trims. It will show and log the out put voltage of the O2 sensors but that is not the same as fuel trims!! I had to buy a $30 scanner to get that. So in this case your aftermarket OBDII scanner is better than a LEXIA! I do not know if I am doing something wrong or if other (later) versions will divulge this information on later vehicles? Also, I have not tried Peugeot Planet. The LEXIA/PP gurus might correct me there.

Its possible there is a problem with the cylinder (#1). Compression or valves but I think this might cause a rich mixture situation as the fuel will not burn properly. Yours is a lean mixture situation. The plug on the far right looks a little different to the other three. If that came out of the flywheel end (right hand looking at the engine from the front) that would be the #1 cylinder.

I am not familiar with GDI engines but I can't imagine swapping the injectors would be fun?

 

[seasink]

Injectors are on a rail underneath the plastic-ware on the back of this engine. Definitely not an easy swap. In this pic you can just see the rail (brown) at the fuel pressure sensor between injectors 2 and 3.

 

[X8R]

Ah, OK, the misfire was logged at 71Kph and 4440RPM when (as) the throttle was closed and the engine ECU has gone into coasting lean mode. On the surface it looks like the injector has cut off the fuel altogether but the engine ECU was expecting combustion on that cylinder.

Fuel rail pressure is 11MPa at the time of the incident. I don't know what it should be, however, I would have thought low fuel rail pressure would bring on a warning?

Its possible there is a problem with the cylinder (#1). Compression or valves but I think this might cause a rich mixture situation as the fuel will not burn properly. Yours is a lean mixture situation. The plug on the far right looks a little different to the other three. If that came out of the flywheel end (right hand looking at the engine from the front) that would be the #1 cylinder.

I am not familiar with GDI engines but I can't imagine swapping the injectors would be fun?

Hi ozVTR and Seasink

I confirm the trouble cylinder is the one closer to the flywheel (passenger side). The spark plug on the right is slightly darker that the rest too as you've pointed out. I took the car to "Real Automotive" shop in Huntingdale, Victoria. Teddy, the shop manager, seems to know what he is talking about. They are exclusively a mini specialist and works on many R56's with the same engine. He has also worked at a Peugeot dealership in the past and he is very familiar with these infamous EP6 engines.

Some notes below:
- Teddy could reproduce the misfire and confirmed the trouble cylinder
- He put a new sparkplug and coil with no change in behaviour
- Cold and Hot compression test was OK and consistent across all cylinders
- Leak down test was also OK and consistent across the board/ Carbon buildup on the valves is minimal at this point despite they look black (not shinny).
- He mentioned all spark plugs show that the car is running rich (or burning oil?) There's also a significant amount of soot in the rear bumper
- He ran out of ideas of what to do and only charged me for a basic diagnostic despite having the car for a week
- The car seems to have power otherwise and quite an stable idle compared to other cars with this engine
- He didn't want to swap injectors at this stage because we were guessing but I may have to do that when I do some other maintenance around that part of the engine as you Seasink mention.

He is suspecting the car may have a faulty ECU or corrupt software, but it is just a guess at this point. ozVTR I can read between the lines you are saying that too?

The overall running rich condition as seen in the the sparkplugs colour is making me wonder. I am suspecting the car was remapped at some point or even it is still remapped and something is tripping that cylinder. The injector may be a potential culprit along with the ECU?

 

[ozVTR]

I am NOT an expert in these engine so you must temper my comments with prudence.
Judging by your original comments the misfire only represents a very small amount of the time. So that explains the relatively small difference in presentation between the spark plugs.
Having said that the plugs don't really look to exhibit signs of a rich mixture. Over all they look pretty good. Again you say the average performance is good and idle is above average. You would be the one to ascertain if the engine was burning oil or fuel consumption was high. Is it?

For an engine to work it needs air, compression, ignition and fuel. Well the air bit is a no-brainer. You (er, Teddy) confirmed the compression on the cylinders was OK. The coilpack and plugs were also checked OK. That only leaves fuel. I would assume the fuel rail pressure monitor would tell you if there was a fuel pressure issue? Was the fuel rail pressure checked? I doubt that is the problem, but it should have been checked anyway. Teddy confirmed the engine ECU diagnosis was correct and "confirmed the trouble cylinder". So, by deduction (or elimination), the problem is fueling of one of the cylinders. Anything "outside" the engine would tend to effect ALL cylinders.

It is astronomically unlikely to to be software related, it's just the way the ECU's are built. Yes, It could be a faulty injector driver and that is part of the engine ECU. Again, swapping injectors would confirm that. However, you really don't want the fault to be in the engine ECU!

I can see from a labour point of view that swapping fuel injectors just for fault finding is a duplication of effort. It's a lot of time wasted if it's not that, and if it IS one of the injectors, then you have to do it all again to replace the injector. Dammed if you do, dammed if you don't!

Sorry but you are going to have to make the call to swap the injectors around (as I see it).
That's all I have, again I'm not an expert on this particular engine but at it's core it is a petrol powered internal combustion engine and so should behave as such.

 

[X8R]

Hi ozVTR

Thanks for the input and I agree I may need to swap the injector to confirm it. Fuel pressure is OK and HPFP seems to be doing a good job. In addition, problems with fuel pressure should give random misfires in all cylinders, not just in one.

Note there have been documented cases of trouble with MED 17.4 ECU's losing control on one injector. Despite my car is a 2011 build model it is exactly what seems to be happening and I found interesting. Extracted section below:

SOURCE: https://www.etuners.gr/peugeot-citroen-thp-engine-maintenance-servicing-101

"Electronic control unit
In general, the engine control unit does not cause problems or produce faults by itself. However, there have been many reported cases of generation 1 ECUs (produced up to 2008) losing control of one injector. The engine starts misfiring and rattling when that happens, without any hardware problem. In case something like this happens, the first step is to get the latest ECU firmware update from the manufacturer and see if that solves the problem. In most cases it is just a hardware fault of the injector driver and the ECU needs to be replaced."

 

[jaahn]

Hi
Just my two cents worth. If the ECU is faulty then the diagnostic output from it may be suspect also. Depends on whatever is failing ??
I have had some experience with a diesel ECU failure that progressively got worse. In the end the experienced technician with quality scanner was stumped as the scans did not make sense and suggested the ECU could be faulty. We swapped mine as same part number and it burst into life and settled into running properly again. So the owner bought a used ECU and job finished after quite a lot of wasted time !
Lucky the technician did not charge for the wasted time spent on it.
Jaahn

 

[dimistyle]

I guess the next stop is you're friendly Peugeot dealer to update SW with latest and greatest. And hopefully they confirm you have an older ECU.

The SW can only be updated by a dealer.

 

[ozVTR]

Hi ozVTR

Thanks for the input and I agree I may need to swap the injector to confirm it. Fuel pressure is OK and HPFP seems to be doing a good job. In addition, problems with fuel pressure should give random misfires in all cylinders, not just in one.

Note there have been documented cases of trouble with MED 17.4 ECU's losing control on one injector. Despite my car is a 2011 build model it is exactly what seems to be happening and I found interesting. Extracted section below:

SOURCE: https://www.etuners.gr/peugeot-citroen-thp-engine-maintenance-servicing-101

"Electronic control unit
In general, the engine control unit does not cause problems or produce faults by itself. However, there have been many reported cases of generation 1 ECUs (produced up to 2008) losing control of one injector. The engine starts misfiring and rattling when that happens, without any hardware problem. In case something like this happens, the first step is to get the latest ECU firmware update from the manufacturer and see if that solves the problem. In most cases it is just a hardware fault of the injector driver and the ECU needs to be replaced."

Hmm that's interesting.
They do a lot with software these days. While I rag on programmers for being lazy, I find it amazing the amount of work they can extract out of ECU's. Having said that, the programmers obviously botched that one.
However, they do mention the injector driver failing. Again, you don't want it to be that.
You have to explore all avenues I guess, swapping injectors would be a pain in the a$$ and you don't want it to be a hardware failure in the ECU!

Just mentioned fuel pressure as a matter of course. I don't think it's that but I have seen crazy $h!t happen. It's possible the other 3 injectors work OK at low fuel pressure and #1 doesn't? Again, I don't think it's that (for the reasons you mentioned) but you need to cover all bases.

 

[dmccurtayne]

1 if the oil cap is hard to get off replace the rocker cover
2 if the software has not been updated and the auto adaptives have not been reset correctly you are basically flying blind because as engines age things change and new maps for want of a better term are needed.
3 lexia/ pp2000 can show fuel trims you need to use diag tool and use the eobd software that is in there.
4 checking the cylinder filling percentage can help you see if your head cleaning was successful.
Diagnosis is a process and as soon as people say things like fuel pressure seems ok this is a red flag it must be close to the reference pressure.