Alfa Romeo Forums banner

1 - 20 of 24 Posts

·
Registered
Joined
·
320 Posts
Discussion Starter #1
Added an AFR gauge to my GTV6.
On driving its between 15.2 and 16. On full throttle about 14.2-14.5
What would be the optimal values?

Fuel pressure is between 2 and 2.5 bar
 

·
Push hard and live
Joined
·
10,180 Posts
Assuming the gauge is accurate, driving between 14-14.5, acceleration +/- 12.5.
 
  • Like
Reactions: cda951

·
Registered
Joined
·
320 Posts
Discussion Starter #3
So I am far too lean. This is adjusted by the screw in the housing of the air flow meter, right?
 

·
Premium Member
Joined
·
2,950 Posts
Where is your sensor located?

I'd also start looking for air leaks in your intake hoses post AFM.
 

·
Registered
Joined
·
320 Posts
Discussion Starter #6
Left collector.
All hoses new and silicone

Except the large AFM hose, that one was looking good.
Will inspect it with.brake cleaner and see if rpm rises. 2-2.5 bar fuel pressure is ok?
 

·
Premium Member
Joined
·
2,950 Posts
The AFM is a very simple device. I would do a good search for fugitive air before I'd start playing with the AFM.
 

·
Registered
Joined
·
874 Posts
Hpsimotorsports.com for a good set of new vacuum hoses. Fix those air leaks and your lean readings should come done and engine running better.
 
  • Like
Reactions: chairmankaga

·
Registered
Joined
·
874 Posts
My milano with the vacuum hose kit
7CD747D6-72BF-4B81-83E5-9947B9B18C0A.jpeg
 

·
Registered
Joined
·
874 Posts
Don’t forget the hose to brake booster too can cause air leaks and rough running engine.
 
  • Like
Reactions: horsewidower

·
Registered
Joined
·
1,111 Posts
Fuel pressure sounds about right 36 / 37 psi (2.5 bar) with engine off (jam the AFM door open and turn the key to "on"). 15 - 16 AFR at light throttle cruise is not a problem. 14s at acceleration sounds lean. 12s are appropriate at acceleration.
 

·
Registered
Joined
·
320 Posts
Discussion Starter #13
Had not yet the chance to do the brake cleaner test.
But fitted a vaccuum gauge.
Have between 0,7 and 0 bar. (Vaccuum for fuel pressure regulator)
Afr on idle is between 15.5 and 16

Vaccuum in distributor advance is less. Is this normal?
 

·
Premium Member
Joined
·
374 Posts
On the face of it, your readings indicate a lean mixture across the board.

But, before you dive into the fuel injection system, does your AFR/wideband sensor setup require free air calibration and was this done according to the instructions?

Also, have you checked for exhaust leaks? This would allow extra air/oxygen into the exhaust stream and make the readings seem to be lean.

If that is all OK, I would agree with the others about checking for intake/vacuum leaks, but I will point out that vacuum leaks mostly affect idle and low RPM AFRs, and have a diminishing effect with increased load/RPM.

If no vacuum leaks are found, and you are sure fuel pressure and volume are good, I would then move onto the airflow meter and experiment with small adjustments. Be sure to mark your starting point if you start messing with spring tension!
 

·
Registered
Joined
·
320 Posts
Discussion Starter #15
Brake cleaner test turned up nothing.
Lambda is a bosch adv which needs no calibration.
Cold car is about 13-13,5
Wot up to 5500 rpm is 14.2 ...
Will search for air in the exhaust next week.
Seems like I am 2 AFR too high in all conditions

As my fuel pump always starts running when I turn ignition, maybe there is something wrong with the afm flap.
Moves freely around, but i will inspect it lore closely and soak it in carb cleaner.

Anything else that could get wrong with the afm?
 

·
Premium Member
Joined
·
374 Posts
As my fuel pump always starts running when I turn ignition, maybe there is something wrong with the afm flap.
Moves freely around, but i will inspect it lore closely and soak it in carb cleaner.

Anything else that could get wrong with the afm?
No, I suspect that your fuel pump circuit is not wired correctly. While the starter is cranking, the fuel pump portion of the double relay gets its coil input power from pin 4 of the ECU, as the engine does not provide enough airflow while cranking to close the microswitch within the AFM. Once the engine fires, the AFM microswitch closes and maintains the power to terminal 86 of the fuel pump relay coil.

In any case, it is not likely that any of the above has to do with your seemingly lean running condition, so you should maintain focus on that for now.
 

·
Registered
Joined
·
320 Posts
Discussion Starter #17
So no vaccuum leaks.
A minor leak in the exhaust but a while past the lambda sensor. Also tightened the lambda sensor a bit more. AFR did not change.

Any other option than the CO screw?
 

·
Registered
Joined
·
2,908 Posts
Check you spark plug colours: are they dark brown, its OK. If they are black and fouled there is too much fuel, if they are grey or white you have too lean fuel. Check plugs at idle and you can drive at speed turn off engine pull out plugs and check colour under that condition. If they are grey you should be careful, however if they are black its quite normal and you can relax. Also a shop can check your CO which should be 3-5% not leaner however the adjusting screw at the AFM is only idle dont help to adjust that for CO at driving or load.
 

·
Registered
Joined
·
513 Posts
While a default for the O2 sensor is to run rich (for example if you run with no sensor), a malfunctioning sensor can cause lean running. You might have one or more bad injectors. Fuel filter clean? Finally you might be just fine and have a poorly calibrated wideband AF meter. What did the plugs look like, you should pull alll. If that’s all good, Suspect that you still might have an air leak.
 

·
Registered
Joined
·
320 Posts
Discussion Starter #20
Have not checked plugs yet. But I now know that my AFR reading is correct. Had i in the shop today. On idle CO is 0,12%.HC is 1670, Lambda show 1,7 ( which would be worse than AFR 16?)
Fuel filter and pump are new, fuel pressure fine.
Yesterday evening I blew compressed air into the hose of the aux air valve i let to Plenum (like it's described in the manual) did also turn up nothing. I just can hear air going down to the AFM flap.
Sprayed connections and plenum hoses with soap spray, no bubbles. I also don't hear any sucking sound on running engine.
Any more tests?
At wot afr drops from.15,8 to 14,5 so I guess fuel volume is enough, otherwise it couldn't get better? Any sensors fooling ECU? But they would make the mixture richer, like the thermal probe?
 
1 - 20 of 24 Posts
Top