Hello everyone, after driving 26000 km after my engine rebuilt 16 month ago, I have an unexplained running rich situation. I say unexplained because there are no vacuum leaks, evap valve is new, I just changed the following during that last two month : coils, plugs(iridium), injectors, MAF, water temp sensor, both O2s, cleaning of the cats, TB assembly, removed and cleaned the air intake plenum (filled with oil), fuel pressure valve, fuel filter, fuel pump (tank is very clean). Basically every week I moved forward by elimination. I hate throwing parts like that but since OBD readings are normal I didn’t know better... at this point I really don’t know what to investigate anymore. LTFT is around -20% and sometimes the car shakes at idle. Or worse : shakes when accelerating... Thank you in advance for your ideas on what to check next!!!!! All the best to you all

 

That's not really consistent. It's either one or the other.

And you should have 2 readings for most, Left and Right bank.

How are you reading your OBD info?
Any chance you can read them live?
I am pretty good at OBD interpretation / trouble shooting, but I will need more detailed info.

 

Thank you for answering! I’ll take pictures and share...

 

 

It's in french but I'm sure you can guess what value is what... STFT is "calage carburant a court terme" and LTFT is "Long terme"

 

"temperature liquide de refroidissement" is water temp. "température d'air" is air temp. FYI : the car was warm 3 hours ago. Here I just turned it on to take the values and temp gauge was half way cold...

 

I know you have 26k kilometers on it but, how many kilometers have you put on it since this issue started?

 

I’d say about 4/5k. It grew progressively. It started to be problematic recently. Every time I changed one of the things listed above I thought I nailed it and drove.

 

See how bank 1 STFT jumps. That’s why I posted several pictures of page 1

 

Clean the throttle bore and plate. Replace the MAF sensor with the old one. Maybe need a new temperature sensor (in the cross pipe). Your water temperature readings are telling the ECU to enrich due to cold . . . MAF? Temp sensor? Thermostat? Coolant mixture?

 

Check for all. I have 3 MAFs, TB was cleaned just a week ago and is super tidy. Water temp sensor is 2 weeks old and gives the same data as the one I replaced...

 

But one thing I haven’t explored is the coolant mixture... never thought of that. What do you advise please?

 

Let me get this correct before jumping to any conclusions:
1. Is the date fresh after a hard reset of the battery, or accumulated over a certain mileage?
2. Do you have any other codes than the P0172?

What I should do, is to collect some live OBD data, after a hard reset, starting with a cold engine, then along the way while driving:
1. throttle position (specially lowest)
2. coolant temperature
3. MAF reading at idle, in N and D
4. MAF reading in P at 2500rpm
5. MAF reading in D at 1500rpm
6. LTFT for bank 1 & 2 at idle, and at various rpm's (you will see the LTFT fluctuate if moving the accelerator, but you will recognize there are some different "levels", which represent the various fuel maps the car is running in. Driving the highway at constant, various speeds will work the best to collect the info.
7. STFT for bank 1 & 2 at idle, and at various rpm's (same as above. Remember that the final trim is the short and long term combined. In your case, where long term are negative, and short are positive, it might give you a trend of where its going).
8. Check for updated fault codes after the testing.

I am not sure what OBD scanner you are using, but I have good results of live data with a simple ELM327 and Torque pro on my phone, just by a good setup and then looking while driving (2 man job ....).

 

I agree with Eric (fortunately, he didn't answer in mandarin). I was concerned with the coolant temperature -- but yours likely at startup -- which Eric points out. Should run fifty - fifty water to coolant (coolant choice as suggested in Drivers' manual - most likely red stuff) and after stabilizing, should be very close to 212*F or 100*C, not 134*F.

Final thought: your injectors may be very dirty (spitting instead of spraying): maybe a can of a really good fuel system cleaner . . .

 

Hahaha yes sorry for the French language... I’ll do that test step by step and report. Thanks so much for looking into my little problem!!!!

 

In these cars it tages ages to move long term fuel trims. From hard reset all of the trims are way off. And as trims normally are they are not same all the rpm range. They are load point specific. So different throttle and rpm points are different values.

 

I do not agree; I disconnect the battery on my car if I don't drive, so I always start from zero.
The LTFT's for the various load-maps settle rather quickly, then don't move much.
Remember, on a well functioning car, the LTFT's are within -3 to +3, that's not far from the zero after a hard reset.

That's correct, and just a part of the rather complex 3D-world fuel maps / tuning is.
However, we can blur out some Facebook-like nonsense reply, based on an rather unknown situation of the PO, or we can try to get some structure in the information, then go from there.
Considering the fact that PO has changed most of the components to new, it can't be that hard to see a trend in the info he is going to collect (or so I hope).

The 2things I am wondering about till now:
- The very large difference between the LTFT (-7 & -15) and STFT (~ +20), but I have no idea if this is momentary or structural,
- The difference between bank 1 and bank 2 (indicating there must (also) be a non-shared component involved)

 

The last operation I did (last week end) was to remove the intake plenum and check all for a leak even if my smoke test showed nothing. Besides the usual oil in there everything was absolutely clean and all gaskets are perfectly fat and soft... about injectors: I have 3 sets. The original ones and two refurbished ones from different sellers. With all 3 I have the same results... I’ll add all breather hoses were changed when the engine was rebuilt last year. As well as all other hoses for that matter. The rebuilt was 15K€ so no expense spared as that car is a daily driver. Not a Sunday car: I have my series 1 for that purpose. I’m waiting for a new air filter before performing the test as it’s over 6 month old and I go daily on dusty construction sites... it might be dirty.

 

See how clean the valley is... overall condition is consistent: when the car was rebuilt 100% of the engine bay was empty.

 

Rich means something (possibly more than one thing) may be misleading the PCM:

e.g.
1. MAF says X air but is wrong (i.e. too much so PCM adds too much fuel)
and/or
2. IAT is wrong (I'm doubtful it can be wrong enough but hey this is just blue sky thinking) so again PCM adds too much fuel
and/or
3. injectors are bad (such as leaky / wrong parts) and let in more fuel than the PCM expects
etc

Basically you need to think why the PCM starts with too much fuel and has to use trims to cope with that mistake.