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Discussion Starter #1
Hi folks,

Been on and off this forum lots over the past 5 years and it has often saved my sanity when 'her' Spider decides to come over all Italian! Seen lots of comments about flat spots etc, often down to MAF issues. Her car has been modified at some point in the past, the air cleaner system has been replaced with a short pipe from the throttle body to the MAF, then a cone filter. Overall inlet tract length is therefore much shorter than OE. The car has always had a bit of a flat spot, but has generally been fine to drive, but recently it failed MOT due to high O2 readings (Lambda). I replaced the Lambda probe and MAF sensor (both OE Bosch items) and the car passed MOT - just. Looking at the emission test results, the car is still running lean, and the flat spot is, if anything, worse with the new sensors. I can't imagine the intake mods will have affected the mixture, (it should be a closed loop control system), so wondered if any else had suffered similar issues with lean running??

I am trying to collect all the various bits needed to reinstate the OE intake system to hopefully rule that out as a cause.

Any suggestions welcome!!:thinking::thinking::thinking:
 

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Have you changed the cone filter, is it dirty or do you have a washable one? It might be worth trying both the ECU and Throttle reset proceedures. Details on here, just do a search. Otherwise if you have multiscan diagnosis, see if that throws up any faults.
Personally the Cone filters look great but I stick with the OE system.
 

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Hi folks,

Been on and off this forum lots over the past 5 years and it has often saved my sanity when 'her' Spider decides to come over all Italian! Seen lots of comments about flat spots etc, often down to MAF issues. Her car has been modified at some point in the past, the air cleaner system has been replaced with a short pipe from the throttle body to the MAF, then a cone filter. Overall inlet tract length is therefore much shorter than OE. The car has always had a bit of a flat spot, but has generally been fine to drive, but recently it failed MOT due to high O2 readings (Lambda). I replaced the Lambda probe and MAF sensor (both OE Bosch items) and the car passed MOT - just. Looking at the emission test results, the car is still running lean, and the flat spot is, if anything, worse with the new sensors. I can't imagine the intake mods will have affected the mixture, (it should be a closed loop control system), so wondered if any else had suffered similar issues with lean running??

I am trying to collect all the various bits needed to reinstate the OE intake system to hopefully rule that out as a cause.

Any suggestions welcome!!:thinking::thinking::thinking:
Just my two pennies worth. However, I could never understand why it is that people claim such startling improvements by changing the air inlet system.

My understanding of "Mass Flow" is: to measure it accurately, one has to remove any turbulence and linearise it, as it passes over the sensor. Systems I have worked with have three elements; 1) a heated resistive element - central, 2) an "up-stream" temperature dependent element and, 3) a "down-stream" temperature dependent element. Up - stream is closest to the system intake. Not all systems have three elements, but the one's I am familiar do. The three elements are axially aligned, centrally within the air flow. As air flows through the system, the "Up - Stream element is cooled by the air flow and the "Down - Stream" element is heated by the air flow; being warmed by the air as it passes over the "Heated Resistive Element". Both up and down stream elements are equidistant to the central heated element.

Electronics refer this differential change between the resistive values of the "Up and Down Stream" temperature dependent resistors, to an "Embedded map" within the Process control system. Paramount to the accuracy of the system is the removal of turbulence and the linearising of the flow to enable accurate measurement. To do this, normally a very long manifold is required to reduce turbulence and then a tubular "Grid" reduces any minor turbulences to a minimum. Thus great accuracy can be achieved, particularly in systems which are measuring environmental discharges and compliance is legally required to be within specific levels.

In principle, I can't see why this should be any different w.r.t. MAF's used within engine manifolds and I can understand why flat spots occur. Any turbulence within the MAF, at any point in an engine's rev range can lead to either an over-rich mixture resulting in poorer performance, contaminating the Lambada Probes, or lean burning; raising cylinder temperatures and risking burning valves out.

To at least restore the inlet manifold to original at least gives you a bench mark to work with.
 

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Discussion Starter #4
Have you changed the cone filter, is it dirty or do you have a washable one? It might be worth trying both the ECU and Throttle reset proceedures. Details on here, just do a search. Otherwise if you have multiscan diagnosis, see if that throws up any faults.
Personally the Cone filters look great but I stick with the OE system.
It's a foam filter, tried washing and re-oiling but no noticable difference. I agree that the OE system must be the best option - at least it will rule out one possibility! Tracking down all the parts is proving interesting!
 

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Discussion Starter #5
Just my two pennies worth. However, I could never understand why it is that people claim such startling improvements by changing the air inlet system.

My understanding of "Mass Flow" is: to measure it accurately, one has to remove any turbulence and linearise it, as it passes over the sensor. Systems I have worked with have three elements; 1) a heated resistive element - central, 2) an "up-stream" temperature dependent element and, 3) a "down-stream" temperature dependent element. Up - stream is closest to the system intake. Not all systems have three elements, but the one's I am familiar do. The three elements are axially aligned, centrally within the air flow. As air flows through the system, the "Up - Stream element is cooled by the air flow and the "Down - Stream" element is heated by the air flow; being warmed by the air as it passes over the "Heated Resistive Element". Both up and down stream elements are equidistant to the central heated element.

Electronics refer this differential change between the resistive values of the "Up and Down Stream" temperature dependent resistors, to an "Embedded map" within the Process control system. Paramount to the accuracy of the system is the removal of turbulence and the linearising of the flow to enable accurate measurement. To do this, normally a very long manifold is required to reduce turbulence and then a tubular "Grid" reduces any minor turbulences to a minimum. Thus great accuracy can be achieved, particularly in systems which are measuring environmental discharges and compliance is legally required to be within specific levels.

In principle, I can't see why this should be any different w.r.t. MAF's used within engine manifolds and I can understand why flat spots occur. Any turbulence within the MAF, at any point in an engine's rev range can lead to either an over-rich mixture resulting in poorer performance, contaminating the Lambada Probes, or lean burning; raising cylinder temperatures and risking burning valves out.

To at least restore the inlet manifold to original at least gives you a bench mark to work with.
My understanding is that the Alfa system (on the Phase 2 at least) has only one point of measurement - a combined hot film flow sensor, and a temperature sensor mounted in the MAF sensor body. The hot film flow sensor is heated to a pre-determined temp, and subsequently cooled by the flow of inlet air. The amount the element is cooled is compared to the reference measurement provided by the temp sensor, and the mass of incoming air worked out by the ECU. Using this data along with throttle position, engine speed etc., the correct amount of fuel can be injected. Post combustion, the lambda probe measures the amount of oxygen remaining in the exhaust gasses, (an indication of the correct fuel/air ratio) and this data is added to the incoming air mass data to try and ensure the correct stoichiometric ratio, an important issue on cars with catalytic converters where too much unburnt fuel can damage the converter.

Its a great system in theory, if a little crude by today's standards, and fairly simple...which is why I am puzzled by the lean running I am experiencing!
 

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My understanding is that the Alfa system (on the Phase 2 at least) has only one point of measurement - a combined hot film flow sensor, and a temperature sensor mounted in the MAF sensor body. The hot film flow sensor is heated to a pre-determined temp, and subsequently cooled by the flow of inlet air. The amount the element is cooled is compared to the reference measurement provided by the temp sensor, and the mass of incoming air worked out by the ECU. Using this data along with throttle position, engine speed etc., the correct amount of fuel can be injected. Post combustion, the lambda probe measures the amount of oxygen remaining in the exhaust gasses, (an indication of the correct fuel/air ratio) and this data is added to the incoming air mass data to try and ensure the correct stoichiometric ratio, an important issue on cars with catalytic converters where too much unburnt fuel can damage the converter.

Its a great system in theory, if a little crude by today's standards, and fairly simple...which is why I am puzzled by the lean running I am experiencing!
Broadly speaking, the principles are the same. In the system you describe however, the degree of cooling is referenced against an embedded value of the element, whereas the one I described, the two temperature dependent components are selected (matched) and accuracy is thus much greater. How well the Alfa one works is very much dependent upon manufacture tolerances. There may even be a "Cold Junction" element within the E.C.U. to take into account the ambient temperature of the air. I.E., is the car being used in the Arctic or the Sahara. With the system I described, it doesn't matter. With the one you describe, it does.
However, what is crucial to the function of both methods is the linearity of the air flow over the sensor. The "Tubular Grid" I described is probably not an accurate enough description. It is a "Tubular Capillary Grid" about 150 mm long, which divides the air flow up such that any turbulence is greatly reduced to no more than the maximum diameter of any one capillary. This produces a uniform pressure front across the width of the orifice. The pressure rate changes due to mass air flow changes but it is a uniform rate of change, across the whole of the orifice.
All the MAF's I have seen, have a plastic grid across the face and it is largely assumed this is to protect the engine from debris. But the other function is to try to eliminate turbulence, but only when used in conjunction with the long ductwork. The Alfa manifold, along with every other manufacturers manifolds ( to my knowledge) is long as this greatly reduces turbulence and an element of "Ram Air" further improves the "Smoothing" effect. Modulation of the throttle also produces turbulence so this is also reduced by the long duct work and the element of Ram Air. Air flow systems and venturi are complex design areas. If the air flow pressure is greater at the edges of the MAF body than it is at the centre, where the flow is sampled, then the ECU will choose a fuel - air ratio (along with the other parameters) lower than the optimum, and you will get a lean burn mixture. Conversely, if the pressure is lower at the edges of the MAF than the center, where the air flow is sampled, you will get a rich mixture, resulting in sooting/caking of the Lambda Probes and as you rightly say, damage to the CAT.
It is surprising how air flow pressure can vary greatly across small areas such as throttle bodies/inlet manifolds and the mixture ratios we are considering are also very small. but the difference it can make to the overall performance of an engine is huge. Air flow inertia, just as oil flow inertia is an important factor so a lot goes into the design of such systems.
I cannot stress enough the need to go back to basics. Alfa is not my flavour of the month right now. But with regard to the original inlet manifold, I don't think they got it wrong. Probably because they didn't design it.
 

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Discussion Starter #8
Which inlet bits do you need? Dan
Hi mate,

I've managed to get hold of the filter housing, Inlet elbow & Resonator; with Mounting bracket on the way. I need the 'half-moon' securing clamps which hold the MAF housing to the filter housing...probably other bits as well which I will no doubt discover when I go to fit it all together!!
 

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Probably not a sensor issue if you have changed them. MAF's are pretty crude technology and not that bothered about the marginal fluid dynamic changes from modded intakes. Look for a vacuum leak or more likely a fueling issue so fuel filter or injectors. Try a good concentrated dose of injector cleaner.
 

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Discussion Starter #12
I have found some of the half moon brackets you were after. I also have the front pipe/snorkle bit.
Sorry mate, busy at work this weekend...I'd forgotten about the cold air feed at the bottom of the air filter box!! Sounds like you have what I need..what's the damage and how would you like paying?

Thanks for digging them out!:thumbup:
 

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The square end is the inlet and fits into the bumper or front cross member. The conical rubber piece fits between it and the filter housing. Came off a 2001 CF3 TS. You could check on Eper for part numbers and I can check if the parts have the same number.
 

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Discussion Starter #17
OK, so I am officially an idiot! Just checked the wife's car again and discovered that the cold air feed pipe is still on the car..the only piece missing is the conical rubber joint!! Amazing how it all clicks into place when you actually use your http://www.alfaowner.com/Forum/images/smilies/censored.gif:paperbag: eyes!!

Dan, I'll, take you up on the parts you have for the aforementioned £20..hopefully this will enable me to put the inlet system back the way Alfa intended. Please let me know how you would like paying..I can do Paypal if you use it??

Cheers
 
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