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Faulty air mass meter?[740-760/1986] posted by Paul Stasko on
Wednesday, 22 April 1998, at 3:12 p.m.
Have a 1986 760 Turbo with 275,000 miles. Yesterday the engine suddenly started running rich. Sluggish uneven acceleration and some visible black smoke. Later in my travels it ran fine. Last segment of about 40 miles was pretty consistent with low power, some black smoke. This AM I pulled the plugs and they were fouled like too much gas. In thirty miles of use today, ran fine, then the same thing happened again. I supect the air mass meter since I had similiar problem at 100,00 miles and after several trips to the dealer, they replaced the air mass meter and the problem was solved. My question is, is there some way to test the air mass meter to see if it is bad? Could it be something else? Any advice will be appreciated.
Re: Faulty air mass meter?[740-760/1986] posted by Steve Seekins on
Wednesday, 22 April 1998, at 4:20 p.m.
Paul - if the problem is intermittant, then it is more likely an electrical connection than the Air mass meter itself. First unplug the AMM and clean the plug connections. Then apply dielectric grease to the female terminals and plug it back in. Do the same to all other electric connectors under the hood EXCEPT the O2 Sensor lead. Also, remove and clean the ground leads that are fastened to the intake manifold. Carefully inspect all underhood wiring for signs of the dreaded insulation deterioration that leaves bare wires for shorting and grounding.
Another possible source of rich running is a problem with the engine temp sensor - can be hard to troubleshoot because they are intermittant sometimes. If wiring OK and everything else checks out, consider trying to test it with an ohm meter. Best to take it out of the block and use a beaker of water and a thermometer on the stove, and graph the resistance vs temp. Compare it to the values given in the manual. Note that it is a thermister of the NTC (negative temp coeficient) type meaning that resistance goes DOWN as temp goes UP.
Be sure to check and make sure that the thermostatic flap in the air cleaner box is fully closing when the engine is warm. If it is stuck open due to a failed thermostat element, the constant flow of hot air can fry the AMM.
PS - any relation to Sharon Stasko in Newport, RI??
Steve Seekins,
Sunday, 26 April 1998, at 7:38 p.m.
Steve
I cleaned the electrical connections as you suggested. Drove about 300 miles since with no problem. Perhaps that's all it was. Thanks for the advice.
P. S. Don't know a Sharon in Newport.
Paul
Re: Faulty air mass meter?[740-760/1986] posted by Dan K. on
Thursday, 23 April 1998, at 10:30 p.m.
Nine times out of ten when I see this problem the tailpipe is sooty black. If you can catch it putting out black smoke while idling, tap on the fuel pressure regulator and see if it straigtens out. If the pressure regulator is plugging up, you will get too much fuel into the cylinders. If REALLY plugged, no fuel will be coming out the return line; tapping on regulator may start the flow.
Whatever you find, don't consider the repair done without a good oil change, as you probably have some fuel washdown into the crankcase.