Hello all from sleepy Adelaide. My first post. Mr Laurence the gold 1989 240GL had completely lost the plot and refused to start. I bought Mr Laurence from a good friend on Christmas eve 2024 to save him from U Pullit, a sad unworthy fate for a low mileage manual 240. The previous owner was Laurence Andris. Merry Christmas Mr Lawrence is not lost on me by the way.
Back to the problem at hand. I'm an old radio engineer who hates digital and am happy to get electrocuted on anything between DC and 24GHz. As long as it's analog. This volvo was not going to get the better of me. The refusal to start in any form was the evil white fuel relay. Resoldered. Now would start then die. Unplugged MAF. Started and idled. Ran crap with off idle bog down. Mind you I had to buy another EZK and ECU and fuel pressure reg to be sure to be sure. OK MAF is crap.
Pulled the MAF and set up the dining table as a MAF test bench. Concluded the MAF worked. Meaning it responded to wafts of air and seemed to the observer to be doing everything right. The Internet is wonderful. Thankyou to everyone who has gone to the trouble of poking and prodding these MAFs and reporting their results.
My conclusion. Seems a common fault that the 016 drifts low in output voltage over time. Read time in decades. My MAF was reading 1.24V at zero airflow horizontally mounted. Was that OK? Dunno. Bosch do not make crap MAFs. I pulled the cover off the MAF hoping to find out why it failed. Nope. Pristine 80's vintage thick film hybrid IC under perfectly clear silicone. It was beautiful. Bugger. My MAF was according to those who know indeed low in output volts so next line of attack was to see if I could pull or bias the output up a little. Inside the MAF was a pin that must have been part of the resistor bridge and was important to the LH2.2 series MAFs. Or part of the 2.4 calibration process. It read about 0.5V above the output pin. I tried using that pin as the new output but the result was way too rich at idle.
Next trial was to see if I could pull Vout by steering the "bridge pin" using a resistor to ground or 12 V. Bingo. Seems dragging that pin in any way to earth makes Vout go up. Took nothing. I used a 22K resistor to ground to pull up Vout by 80mV. Vout now 1.32V horizontal no wind. Fingers crossed. Installed and Woohoo. Started and ran perfectly. 80 bloody millivolts. What the heck? Anyway it seems these MAFs are adjustable using nothing more than a humble resistor and soldering iron. But you need to pull the cover and try a resistor across the two furthest apart pins within the innards.
It's all back together and running perfect. Bosch should have made their MAFs adjustable. They must have known.
Thanks all. MK
