View Full Version : Motorway cruising AFR's
Cruising: Normal driving, light throttle and cruising you should aim for around 14:1 again. 14.7:1 is where most factory cars are tuned to, but this is a compromise on
torque in order to obtain better fuel efficiency. 13.5:1 would be acceptable, much richer than that and you are wasting fuel. Much
richer than 12.5:1 and you are not going to be doing your piston rings and bores any favours either. At about 15:1 or leaner the engine will start to feel "flat" (a lack of
torque). At about 16:1 or leaner it will generally not run at all, or be very hesitant.
Taken from the articles section!
Now I know 'compromise' is the optimum word here, but I have noticed that motorway driving 'part throttle' - 5th gear - around 3.5/4rpm I'm boarding low 16-17 on the gauge.
Should I be concerned?
And I'm wondering if I want a little more fuel for this scenario is it just a case of adjusting the acc pump?
Im the same mate, so will be keeping an eye on the replies :)
Your lucky to get it that lean lol, that must be with a small amount of boost at that rpm? Does it hesitate when applying more throttle?
This could also be due to a small air leakin the exhaust or sensor location. The furthur down the exhaust the leaner the readings seem to be at idle/part throttle
No doesn't hesitate, and with a little more throttle afr's improve! - I tend to actually just back off then it levels back to 14's
Boost is marginal and if any really!
And the sensor is in the downpipe- say 10" MAX from the turbo!
I've adjusted the acc pump again and was hoping to give it a test run, but for one reason or another I can't at the minute:disagree:
I'm heading to Andys RR so I just didn't wanna drive it for 3hrs without asking the question:agree:
Just to add also, it drives well and feels 'stable' if that's the right word:wasntme::scratch:
An afr of around 16 is pretty much ideal for motorway cruising, so assuming you're not getting any jerking from the engine (ie, if it were too lean), I'd leave well alone.
If it drives fine forget about it and enjoy the fuel economy..my tungy is the same and returns 35+ mpg on a run. Id only alter it if it were hesitating or misfiring.
Cheers guys:agree::agree:
Matt Cole
16-04-2013, 13:15
An afr of around 16 is pretty much ideal for motorway cruising, so assuming you're not getting any jerking from the engine (ie, if it were too lean), I'd leave well alone.
:agree: Just to add, theres very little engine load so could be your carb is working well.
Your lucky to get it that lean lol, that must be with a small amount of boost at that rpm? Does it hesitate when applying more throttle?
This could also be due to a small air leakin the exhaust or sensor location. The furthur down the exhaust the leaner the readings seem to be at idle/part throttle
:mad::mad: turns out I do have a leak somewhere, been road testing the car today to try and get it ready for Andys RR on Saturday.
I can pretty much hear it, and have lost a few PSI on the turbo's boost:disagree:
It's got progressively worse because on idle the afr's have decreased from normal 14-1 reducing to 15 or occassionally as low as 16's and pulling away its now got a flat spot:disagree:
Will try and look at it tmrw, but feel a late night coming on to be ready for RR as my Nans been rushed into hospital today, so will obviously go and see her first after work!
Despite all that, it's been an awesome day upping the boost and giving it the beans:D
Morning,
I'm really pushed for time today, so was wondering if anyone could point me in the right direction as to try and sort this air leak.
Just speaking to a guy from work and he's mentioned that because of the afr's (15's/16's) that it is likely the leak is on the inlet side?
I had thought it was from the turbo or possible the manifold, but havent had a chance to get a good look.
Basic symtons are: idle afr's 15's or 16's (although ticks over 'normally'!)
loss of boost pressure (around 4psi drop)
flat spot pulling away from stationary?
will add more as i think of it and will get back on line when possible - any help really appreciated:agree::agree:
Dave Reed
19-04-2013, 10:18
Since you've built it have you tightened the inlet and exhaust manifold nuts? If you haven't this would be the first place I'd be checking.. Then whilst your there check the turbo flange bolts and down pipe..
If its blowing you should be able to hear a ticking noise.. Or if you want to test the inlet side get a can if easy start and have a spray around, if the idle raises then you have a leak..
Hope that helps
Since you've built it have you tightened the inlet and exhaust manifold nuts? If you haven't this would be the first place I'd be checking.. Then whilst your there check the turbo flange bolts and down pipe..
If its blowing you should be able to hear a ticking noise.. Or if you want to test the inlet side get a can if easy start and have a spray around, if the idle raises then you have a leak..
Hope that helps
Does help Dave:agree: just really pushed for time today:disagree:
Did have a spray around the carb last night, but didnt notice anything, will absolutely check the above:agree:
Thank you again:agree:
Emkay, got it stripped down:
Turbo looks fine
Down pipe looks fine
Tightened the manifold nuts (barely half a turn!!)
Sprayed carb cleaner around the carb and mainfolds whilst running, no change.
So will get it all back together and fingers crossed!
Can anyone point me in any other direction??
Romil Davda
19-04-2013, 20:21
Check all vacuum pipes. aei unit to carb, actuator to carb, any boost gauges you got fitted, also check jubilee clips from turbo to IC and IC to carb/plus DV if fitted.
When the car is running, put your hand around the turbo manifold and see if you got a leak here.
Check all vacuum pipes. aei unit to carb, actuator to carb, any boost gauges you got fitted, also check jubilee clips from turbo to IC and IC to carb/plus DV if fitted.
When the car is running, put your hand around the turbo manifold and see if you got a leak here.
On it:agree:
Once I've got it back together:disagree:
Stu just txt me your number so if I really get stuck I'll buzz you:agree:
Thank you:agree::agree:
Check all vacuum pipes. aei unit to carb, actuator to carb, any boost gauges you got fitted, also check jubilee clips from turbo to IC and IC to carb/plus DV if fitted.
When the car is running, put your hand around the turbo manifold and see if you got a leak here.
Sorted:agree::agree:
See you in the morning mate:agree:
Im the same mate, so will be keeping an eye on the replies :)
Morning:)
Just so you know really Jonny:agree:
After the 300 odd mile trip to the RR, constant revs on the motorway around 3500k - i wasnt totally happy with the fueling (16's/17's still)
Changed my main jet from 120 to 125 and its a different drive completely - before the larger jet i didnt really realise but the car was 'flat' - with the new 125 main im seeing comfortable 15's (even 16's at real low revs @ 2k) and the car is alot more responsive.
May be worth a try yourself and see how it feels to drive:agree:
Morning:)
Just so you know really Jonny:agree:
After the 300 odd mile trip to the RR, constant revs on the motorway around 3500k - i wasnt totally happy with the fueling (16's/17's still)
Changed my main jet from 120 to 125 and its a different drive completely - before the larger jet i didnt really realise but the car was 'flat' - with the new 125 main im seeing comfortable 15's (even 16's at real low revs @ 2k) and the car is alot more responsive.
May be worth a try yourself and see how it feels to drive:agree:
Cheers Alex,
Mine does appear to be slightly different to yours now, as steady crusing im sat at mid/high 14s.
Mine tended to drop to 16s only for second when i had been using part throttle then slowly increasing throttle with little or no boost for an extended period of time.
As soon as i lift off even slightly, all is back to normal. WOT is fine too.
So not sure, feels nice to drive tho as well :scratch:
Glad you got yours sorted :)
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