Rich long term fuel trims -24% bank 1, -20% bank 2. (Maserati Gransport 2006)

[Oxytorch]

Greetings.
Looking for a bit of guidance for my 2006 Gransport.

Using an obdii tool, long term fuel trims are showing quite rich both banks, but not bad enough to trigger CEL.
Since purchasing it in August last year, it has always had a mild hesitation at low rpm, most noticeable when taking off gently in first gear and particularly when engine cold. The other thing I noticed was somewhat rough idle, and in neutral trying to hold rpm at 1500 for example was difficult - it would randomly drop by 200 to 300 rpm with throttle held steady.
On one occasion last year a MAF related code was triggered. The sensor was cleaned and even though no more codes I replaced the MAF sensor anyway but it didn't make any difference. No other error codes are being reported. No misfires. No EVAP codes. Nothing.
Most recently, I have had the injectors cleaned and spray tested. All perfect. Also cleaned plenum chambers, throttle body, upper cylinder head clean - all looking like new. The engine is running more smoothly but still slight hesitation at low rpm and long term fuel trims are no better. New spark plugs also fitted. Air filter was replaced before purchase.

I'm now thinking of replacing the two front O2 sensors, as they are nearly 8 years old but only 23000 km on the odo.

I would appreciate any advice on where to proceed?

 

[alfatwo]

Welcome aboard Oxy....had a similar problem with my old 3200GT,although the car had only covered 24,000 mls the 02 sensors were over 13 years old and had gone out of calibration

Fitting new ones transformed the engine performance...

Dave

 

[ecarca]

Oxytorch, I love your problem

Please check this out:
http://www.sportsmaserati.com/showthread.php/12909-Help-needed-Misfires-and-other-CEL-s-Detailed-account-of-the-situation

There are troubling similarities: symptoms, mileage, etc. I also love to read that your injectors are cleaned (mine are not, or at least not professionally). The only thing is I have misfires and you don't.

Here is what I suggest: unplug the MAF. Start the car and try to see if the problem is there or not. Chances are it will be gone
If it is, then we are exactly on the same boat and can work this out together. I replaced my O2, drivability is better (I guess about the same improvement as when you cleaned the injectors) but not perfect. I think the thing is these small issues are actually amplifying the problem but are not its cause.

I tend to believe that it is a vacuum leak somewhere, that would be compatible with being gone if the MAF sensor is unplugged. I will try to diagnose my car this week-end, either smoking the lines with a cigar or carb cleaner spraying. Maybe you don't have misfires because your leak is smaller than mine...

Do you also have some kind of strange sound when that rpm hesitation happens? Like clunking, or a vibration, or equivalent?

Cheers

 

[Andyk]

A big warm welcome to the forum....Hope you get what you want from us.....

 

[CatmanV2]

Welcome Oxytorch. Interesting you appear to have described my car, although perhaps far more seriously. I have no issue with hunting idle, but I have noticed a slight roughness to idle and hesitation when cold. It's so minor I pretty much accepted it as normal, but now I think I'll drag out the ODBII and see if it's running rich as well.
Similarly, 12 year old O2 sensors, so could well be an issue.

C

 

[Oxytorch]

Thank you all for the warm welcome and advice so far. In response to ecarca, I disconnected the old MAF sensor and didn't notice a difference. This was after I had actually purchased a new sensor but before it was installed because I didn't have the right torx tool. Therefore I think the old MAF sensor was fine and in any case it now has a brand new one. I don't think it could be a vacuum leak because that would draw air in causing a lean fuel condition, which should cause positive long term fuel trim. Using obdii I watched the output of the front wideband O2 sensors while driving today. Most of the time the current was +/- 0.1 mA except on deceleration (throttle released) when it dips down to -2 mA or less (I think it was negative?) In any case, deceleration during released throttle does not contribute to fuel trims as far as I can tell - the short term fuel trims always drop to zero in this situation, so won't affect the long term fuel trim. I also tried to watch the short term fuel trims at different rpm and engine load but it was pretty hard to see a pattern - I logged the data but it'll need some sorting to make any sense of it.

I haven't noticed any strange sound when it's hesitating. I can hear a very faint rattling/grinding noise when turning corners or going around roundabouts in 2nd gear, which seems to be coming from the gear box or torque tube but I'm not sure. The indy couldn't hear it and it hasn't got any worse so I'm tending to ignore it now... It had a new clutch and torque tube fitted prior to purchase last year.

So at this stage I'm thinking about getting new front O2 sensors. This ebay seller in Latvia http://www.ebay.com.au/itm/161179358211?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649 has them for the best price I've seen US$134.50 each including free postage to Australia.

Cheers.

 

[ecarca]

I purchased my MAF and one of my O2 sensors from that guy. They arrived in China in about 10 days after posting. It might be faster to Australia, China Post is SLOW. It's a reliable seller, you can go ahead. Only the first time I placed order, he cancelled it because he had no stock but they're nice and the communication is great. When I purchased my MAF, I changed reference, they refunded me right away.

 

[Oxytorch]

Okay... CEL has come on.
Using standard OBDII
DTC: P2187 Bank 1 System too lean AT idle.

Also some pending DTCs:
P2178 Bank 1 System too rich OFF idle.
P2180 Bank 2 System too rich OFF idle.
P2189 Bank 2 System too lean AT idle.

Therefore, something is causing a situation of too lean AT idle but too rich OFF idle both banks?

Long term fuel trims at -25% and -24%.
While driving, short term fuel trims generally -5% to -9% with mild throttle. Generally +5% at idle.

I have ordered new front O2 (air/fuel) sensors. I hope that's the problem...

Googling the codes, other causes of too lean at idle include intake air leak, fuel pressure regulator, fuel pump, EVAP purge regulator valve fault (although I'd assume the last would trigger an EVAP fault code).

I think when I get the O2 sensors installed, I'll get the mechanic to do smoke test of intake and exhaust systems too.

 

[Oxytorch]

Waiting for my air fuel sensors to arrive, I decided to pull the spark plugs out to see if there are any clues as to what's going on in the cylinders. As mentioned earlier, high negative fuel trims both banks indicating that the air fuel sensors are detecting a rich condition and therefore reducing the injection time to compensate.
So I've attached photos of the plugs for anyone's opinion? These plugs have only seen about 2000 km of driving. There is some carbon deposit around the ring edge but not sure if this is normal or excessive. I don't think they look like lean burning plugs anyway, which I think usually display whitish deposit?
Cheers.
John

 

[Oxytorch]

Just googled how to read spark plugs and from what I can tell they look completely normal.
So if the new air fuel sensors don't fix things, I'll need to investigate the fuel pressure regulator I think.