Date: Mon, 18 Apr 2005 04:04:17 +0100 From: Pooh Bear <rabbitsfriendsandrelationsnospamail.com> Subject: Re: C900 Check Engine Air Mass Meter Disaster - HELP
Al wrote: > I have a 1987 T16 Aero. It isn't boosting fully, and my specialist blamed > lack of fuel on the Bosch mass air meter (Part Number 0 280 212 0050) > > I got a spare "working" one off ebay, and tried it today. Immediate check > engine light and lumpy running, no go at all when the accelerator depressed, > like the cars being held back. > > I immediately re-fitted the original, but have exactly the same symptoms! > > Is there a way of re-setting the system, would I be right in suspecting the > engine management system has switched to an emergency setting. > > Whilst my specialist blamed the original part, it did at least run fairly > well, even if I wasn't getting all the boost I wanted. It now exhibits all > the faults of the newer part I bought. Would a reset prior to using the > newer part be worthwhile? > > A new part is getting on for £200, which is frankly beyond my budget for a > month or so, your help would be much appreciated as this is my only > transport currently and I don't fancy the train! Here's some advice found on google quickly... " Air Mass Meter Diagnosis. Simple Functional Diagnosis of AMM. [Editor] The classic test of AMM failure is to disconnect it; if the car runs better, then the AMM is at fault. But here are the OEM tests per the OEM manual for Bosch 2.4 (the-016 AMM): Check the ground point of the AMM: ignition off; disconnect AMM connect ohmmeter between ground and terminal 1 should be 0 ohms if not 0 ohms, check the ground point on the intake manifold Check signal from AMM: clean off sensor connector, removing any corrosion -start engine connect voltmeter between ground and back of terminal 3 on back of connector should read approx 2.3 volts. if not approx. 2.3 volts, substitute another AMM Testing AMMs and Calibration. This is a response from Python Injection (rebuilders of AMMs) to a question about testing AMMs. From: Joe Evert, Director of Engineering, Python Injection Subject: Re: Technical Question about AMM The reason the OEM doesn't give a test procedure for calibrating the air mass meter is two fold. First of all BOSCH Hot Wire Air Mass sensors are not linear devices like a throttle position sensor. The output does not change the same amount for a given air change. To make it short, most linear sensors will give you say... 1 volt for 100cfm air flow, 2 volts for 200cfm air flow, 3 volts for 300cfm airflow etc. This is a linear device. Bosch hot wire sensors are not like this. They change a great deal at low air flows but once the air flow increases past a certain point, say 50% of what the engine can draw, they change very little. This makes the sensor very accurate at low to moderate air flows and good enough at high air flows. Just a small amount of inaccuracy at low RPM and the vehicle will run terrible. If the voltage for a given air flow is off by 100 milli volts at low RPM the car will barely run. At high RPM A 100 milli volt deviation will not even be noticed. Because of this it makes it next to impossible for the technician to accurately diagnose the air mass in the field. We use a calibrated flow bench that measures the exact CFM air flow to then compare the voltage to. This is not practical in the field because temperature, altitude, humidity and the mechanical condition of the engine will affect how much air the engine is drawing in. So just to say that the Air mass should have xx.xx volts at idle would be completely false since all these parameters must be accounted for. Also even if a range is given just a small amount of deviation in the output causes poor performance. So what are you to do? For on-vehicle diagnoses the best way is just unplug it at idle; if the vehicle runs better it is most likely bad. This is because if the air flow sensor is off voltage at high RPM it will also be off at idle. Also if you are experiencing repeated failures you probably have a defective air box thermostat. This little thermostatic bulb is located in the air filter box and controls the hot air into the engine. When this fails it fails in hot air mode and routes hot air from around the manifold into the air intake. This will destroy the air mass meter in no time. " http://www.volvoclub.org.uk/faq/EngineFuelinjection.html Graham
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