Mixture Setting
Discussion
On my 1992 V8S I have been trying to solve my idle problem and one thing I have noticed is that the plugs are always black and sooty. I was told that the allen key adjuster on the hot wire airflow meter adjusts the mixture. I have screwed this in a couple of turns (in stages) and I now have a better idle and the plugs are the right sort of colour.
Does anyone know how to set the mixture correctly and am I adjusting the right thing?
>>> Edited by bobv8s on Saturday 18th May 17:31
Does anyone know how to set the mixture correctly and am I adjusting the right thing?
>>> Edited by bobv8s on Saturday 18th May 17:31
Bob
First question is your system a hot wire system with the stepper motor or an early flap vavle type? that only uses the allen key thingy, because below is a description for the setting on a hot wire system. If you do not have this then I think it is all done on the allen key bypass vavle thingy. Anyway here goes:-
The allen key thingy is set approx 2 1/2 turns out (factory base setting), that is to say; from all the way in (clockwise) then screw it out 2 1/2 turns out (anti clockwise), this puts it in the right area for the ECU, utilising the stepper motor, to then set idle correctly.
If you squeeze the hose (completely with a hose clamp if you have one) that goes to the stepper motor housing, the allen key setting should give a tick over of 400/500 rpm (this should be around 2 1/2 turns again) but is considered to be a more accurate setting of the allen key thingy. When you let go of the hose now, the stepper motor will then (should) be working and the idle should be around the 900/1000 rpm mark, if it doesn't come up to this speed then the stepper motor is suspect.
BTW I get a lot of sooting if rumbling around town and it hasn't has a good blast
.
I hope this helps (and makes sense!)
Harry
First question is your system a hot wire system with the stepper motor or an early flap vavle type? that only uses the allen key thingy, because below is a description for the setting on a hot wire system. If you do not have this then I think it is all done on the allen key bypass vavle thingy. Anyway here goes:-
The allen key thingy is set approx 2 1/2 turns out (factory base setting), that is to say; from all the way in (clockwise) then screw it out 2 1/2 turns out (anti clockwise), this puts it in the right area for the ECU, utilising the stepper motor, to then set idle correctly.
If you squeeze the hose (completely with a hose clamp if you have one) that goes to the stepper motor housing, the allen key setting should give a tick over of 400/500 rpm (this should be around 2 1/2 turns again) but is considered to be a more accurate setting of the allen key thingy. When you let go of the hose now, the stepper motor will then (should) be working and the idle should be around the 900/1000 rpm mark, if it doesn't come up to this speed then the stepper motor is suspect.
BTW I get a lot of sooting if rumbling around town and it hasn't has a good blast
. I hope this helps (and makes sense!)
Harry
Just re-read your thread and see it is a hot wire system, so ignore the first sentence. Whether this will clear a permanent over rich mixture I'm not so sure, but it will certainly set the tick over to the correct position. Is yours pre cat? as I only really understand the close loop systems with cats and lambda sensors, for the right mixture and to stop poisoning of the cats! How pre cats do this I don't know, apart from them being open loop? anyone else?
Harry
Harry
Harry: Thanks for the info. There are infact two allen key adjusters. The one on the Plenum does indeed adjust the base idle as described in Steve Heaths book on page 65. But there is a second on the hot wire unit itself and it is this one that seems to adjust the mixture but no mention is made in the book. Mine is a not cat machine.
Bob
>> Edited by bobv8s on Sunday 19th May 11:48
Bob
>> Edited by bobv8s on Sunday 19th May 11:48
quote:
Does anyone know how to set the mixture correctly and am I adjusting the right thing?
You may be affecting the fuelling, you may be compensating for a problem at tickover, you may even be correcting the problem. But the fuel injection system is pretty complex (well, Mark Adams says its simple but I disagree) and trying to put it right by guesswork without really knowing what you're doing or what the problem is, sounds to me like a 'brave' approach. If you
it up so it runs lean under power, would you notice? Before you trash the engine, I mean? This sort of job really is best left to the experts. Presumably you have it serviced by TVR specialists, and no doubt they can sort this for you safely and easily. Personally, I wouldn't fiddle with it.
Bob
Been looking around and found this
www.rpiv8.com/carbs-2.htm#setting-up
Yes it does mention the setting of this adjuster to set the CO for non cat models. As Peter says, I think if you have any doubts about this then I'd get it set by a garage, too lean and you will do damage unless you have a accurate CO meter.
Out of interest had a look at the cat version for mine, I measured the voltage for the air flow meter as describe on mine was spot on at 1.63v so the info does seem to be accurate.
Harry
Been looking around and found this
www.rpiv8.com/carbs-2.htm#setting-up
Yes it does mention the setting of this adjuster to set the CO for non cat models. As Peter says, I think if you have any doubts about this then I'd get it set by a garage, too lean and you will do damage unless you have a accurate CO meter.
Out of interest had a look at the cat version for mine, I measured the voltage for the air flow meter as describe on mine was spot on at 1.63v so the info does seem to be accurate.
Harry
quote:
Harry: Thanks for the info. There are infact two allen key adjusters. The one on the Plenum does indeed adjust the base idle as described in Steve Heaths book on page 65. But there is a second on the hot wire unit itself and it is this one that seems to adjust the mixture but no mention is made in the book. Mine is a not cat machine.
There is a very definite reason why that is not mentioned: twiddling it without the appropriate anlaysers etc can be detrimental to your wealth. It is normally set at the factory and left well alone. The ECU programming assumes that it is set around a standard meter and if this is changed, it also screws up the ECU programming. It can be used to fine tune for emmisssions but it is equally possible to lean the micture too much and cause pre-detonation which can cause considerable damage to the engine. It is something to leave well alone. If the emiisions are too high it is usually symptomatic of a problem elsewhere in the system.
Steve
www.tvrbooks.co.uk
Steve
Many thanks for the info. I will put it back as it was. My problem is that the idle is hunting up and down. Raven have looked at it and said that when the temp gets to 90+ the ECU gives an error code 48. They tried changing stepper motor and ECU but nothing seems to help. It will idle fine cold then when it warms up it idles at 1100 and drops to 600 every 5 to 10 secs. Raven thought it may be a bad wire but where do you start?
Bob
Many thanks for the info. I will put it back as it was. My problem is that the idle is hunting up and down. Raven have looked at it and said that when the temp gets to 90+ the ECU gives an error code 48. They tried changing stepper motor and ECU but nothing seems to help. It will idle fine cold then when it warms up it idles at 1100 and drops to 600 every 5 to 10 secs. Raven thought it may be a bad wire but where do you start?
Bob
quote:
Steve
Many thanks for the info. I will put it back as it was. My problem is that the idle is hunting up and down. Raven have looked at it and said that when the temp gets to 90+ the ECU gives an error code 48. They tried changing stepper motor and ECU but nothing seems to help. It will idle fine cold then when it warms up it idles at 1100 and drops to 600 every 5 to 10 secs. Raven thought it may be a bad wire but where do you start?
Bob
Well as you know, code 48 is basically the stepper motor running out of travel which suggests to me there may be a problem with an air leak, incorrect base idle adjustment or gunge round the throttle butterfly. Nothing here points to an air metering problem, although if you *do* have an air leak you could be hiding the symptoms by frigging the MAF sensor so the ECU overfuels. If Raven think this is a problem with the ECU or stepper motor then perhaps they know something I don't. I would start by cleaning the stepper motor (again), cleaning the throttle butterfly, checking the base idle and checking for air leaks.
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