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Spider 2.0 TS (Ph2) Flat Spot/Poor Pick up

1K views 19 replies 5 participants last post by  spankdanny 
#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:
 
#2 ·
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.
 
#3 ·
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.
 
#5 ·
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!
 
#8 ·
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!!
 
#10 ·
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.
 
#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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