S1 Air Filter casing WARNING
Discussion
It is remiss of me not to have posted this one before, and thanks to Glenrobbo for reminding me on an earlier post regarding the S1 air filter.
I would urge
ALL S1 owners to check this issue, it is almost certain to apply to all of us.
The plastic airbox is used on several Ford models of the period. It had to be mounted differently on the TVR S1 and it appears that a problem arose. The airbox isnt terribly well mounted in view of the weight of the injector head and air flow meter valve on the top. To stiffen it up steel plates were rivetted inside each of the two parts of the airbox. These are aluminium 'pop' rivets. 4 on each plate.
The airbox is much more exposed on the TVR S and the outside of the airbox gets wet and corrosion of the rivets is inevitable. After 25 years that corrosion will be significant in any of our cars. At the very least the steel 'pip' will have fallen out which will allow a little air through, more likely the rivet will have split or dropped out.
This isnt too much of a problem on the intake side of the air box as air still has to pass through the filter. However on the downstream side of the air box the situation is much more serious. Any air leaks lead to air being drawn in unfiltered, and this is air from under the car which wont be clean. The slightest amount of dust getting into the very delicate air flow meter is bad news and will rapidly upset the mixture.
In addition, any bits of rivets or larger dust which get to the air flow valve itself will score the very finely machined edges and cause the air valve to either leak or jam.
This is precisely what proved to be wrong with mine,
and caused the symptoms which proved so difficult to find.
My car ran fine on a wide open throttle but would NOT run correctly on a small throttle opening, whether trickling in traffic of on a trailing throttle. No amount of adjustment of mixture sorted it.
What I eventually found was:
firstly: the air meter valve had dirt on the top face, changing it's weight which caused the valve to be over 1mm lower than it should be. The effect of this is that the air meter has to rise a little more before air flows through it, but while it is rising it is opening up the injection meter, so the mixture briefly goes very rich. If you have seen how little the injection meter travels you will appreciate that any change in the air meter valve position will have a significant effect.
secondly, something had clearly gone through the air meter and caused a little damage to the very fine edge which was just causing a very slight contact. But as the air meter is only moved up by suction this slight contact was causing it to stick then free off at small throttle openings. That causes sudden changes in mixture. It would stick and free going up (as air demand increased) and when going down. So at small openings the valve was not moving freely in accordance with air demand, the engine would be starved of air then the valve would come free and move too much, then drop down again etc.
All because some pop rivets to a strengthening plate on the downstream side of the airbox had corroded!
Now here is the real word of wisdom, the real EUREKA moment for me!
IF THE MIXTURE IS WRONG THERE MUST BE A REASON FOR IT.
DONT PLAY WITH THE MIXTURE CONTROL ON THE TOP OF THE INJECTOR UNTIL YOU KNOW WHAT THAT REASON IS.
If you adjust the injection meter to try and deal with this symptom it doesnt just change the fuel injection metering, it also effects the air metering. If that air metering is the problem it will merely make the problem more difficult to find and the fuel side of the mixture is now out as well!
Believe me it is a bugger to reset if you have reset the fuel side and then find both are now out! Even when you have got the air meter clean and positioned correctly the mixture cannot be reset correctly without use of a gas analyser and it will take some time to get the adjustment back right.
THINK FIRST BEFORE ADJUSTING THE MIXTURE. So before you take advice to adjust the mixture STOP and THINK.
Experience of course is something you get after you need it most.
Now get out there, take that air box off and change those rivets!!
I would urge
ALL S1 owners to check this issue, it is almost certain to apply to all of us.The plastic airbox is used on several Ford models of the period. It had to be mounted differently on the TVR S1 and it appears that a problem arose. The airbox isnt terribly well mounted in view of the weight of the injector head and air flow meter valve on the top. To stiffen it up steel plates were rivetted inside each of the two parts of the airbox. These are aluminium 'pop' rivets. 4 on each plate.
The airbox is much more exposed on the TVR S and the outside of the airbox gets wet and corrosion of the rivets is inevitable. After 25 years that corrosion will be significant in any of our cars. At the very least the steel 'pip' will have fallen out which will allow a little air through, more likely the rivet will have split or dropped out.
This isnt too much of a problem on the intake side of the air box as air still has to pass through the filter. However on the downstream side of the air box the situation is much more serious. Any air leaks lead to air being drawn in unfiltered, and this is air from under the car which wont be clean. The slightest amount of dust getting into the very delicate air flow meter is bad news and will rapidly upset the mixture.
In addition, any bits of rivets or larger dust which get to the air flow valve itself will score the very finely machined edges and cause the air valve to either leak or jam.
This is precisely what proved to be wrong with mine,
and caused the symptoms which proved so difficult to find.My car ran fine on a wide open throttle but would NOT run correctly on a small throttle opening, whether trickling in traffic of on a trailing throttle. No amount of adjustment of mixture sorted it.
What I eventually found was:
firstly: the air meter valve had dirt on the top face, changing it's weight which caused the valve to be over 1mm lower than it should be. The effect of this is that the air meter has to rise a little more before air flows through it, but while it is rising it is opening up the injection meter, so the mixture briefly goes very rich. If you have seen how little the injection meter travels you will appreciate that any change in the air meter valve position will have a significant effect.
secondly, something had clearly gone through the air meter and caused a little damage to the very fine edge which was just causing a very slight contact. But as the air meter is only moved up by suction this slight contact was causing it to stick then free off at small throttle openings. That causes sudden changes in mixture. It would stick and free going up (as air demand increased) and when going down. So at small openings the valve was not moving freely in accordance with air demand, the engine would be starved of air then the valve would come free and move too much, then drop down again etc.
All because some pop rivets to a strengthening plate on the downstream side of the airbox had corroded!
Now here is the real word of wisdom, the real EUREKA moment for me!
IF THE MIXTURE IS WRONG THERE MUST BE A REASON FOR IT.
DONT PLAY WITH THE MIXTURE CONTROL ON THE TOP OF THE INJECTOR UNTIL YOU KNOW WHAT THAT REASON IS.
If you adjust the injection meter to try and deal with this symptom it doesnt just change the fuel injection metering, it also effects the air metering. If that air metering is the problem it will merely make the problem more difficult to find and the fuel side of the mixture is now out as well!
Believe me it is a bugger to reset if you have reset the fuel side and then find both are now out! Even when you have got the air meter clean and positioned correctly the mixture cannot be reset correctly without use of a gas analyser and it will take some time to get the adjustment back right.
THINK FIRST BEFORE ADJUSTING THE MIXTURE. So before you take advice to adjust the mixture STOP and THINK.
Experience of course is something you get after you need it most.
Now get out there, take that air box off and change those rivets!!
Great advice as always Richard, i must admit the symptoms really do sound (along with the split in the air flow meter cap) alot like what my 'S' was going through..
I will double check mine when i pop the new 'k&n air filter' in, any sizes/sources for the rivets to replace? maybe a stronger variation that wont rust?
I will double check mine when i pop the new 'k&n air filter' in, any sizes/sources for the rivets to replace? maybe a stronger variation that wont rust?
Edited by greyhulk on Tuesday 19th January 19:13
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