Does my '91 4.9 have a mass air flow sensor? I have a haynes manual which does not have anything about it.

 

If it is stock, it does not have a mass air flow sensor. It should have a MAP (manifold absolute pressure) sensor instead, mounted just above the HVAC stuff on the passenger side of the engine compartment.

 

Thank you, I do find that in the manual. I guess it performs a similar function? Can it be cleaned or does it have to be replaced.

 

I don't think the MAP sensor can be cleaned. What makes you think it is failing? You can test it with a six cylinder tachometer or a multimeter that can measure frequency to make sure it is sending the correct output frequency to the computer.

 

I had a problem a few years back with missing, rough acceleration and lurching. I changed egr, plugs & wires, tps, and everything else with no improvement. I finally took it to a shop where they changed the MAP sensor which solved the problem. I now am having the same problem. It smells as if it is running really rich but I am not getting any "check engine" light. I'm shooting in the dark.

 

I would test it before replacing it because they are kind of pricey. I would also check the fuel pressure and the fuel pressure regulator to make sure the pressure isn't sky high or that the regulator diaphragm hasn't ruptured, which would allow fuel past the regulator straight to the manifold.

 

I changed out the regulator several months back but didnt check the pressure. I need to get some guages but, will do that. I let you know.