Bad MAP Sensor???
 

My 1973 450 SL has a nasty black soot problem and bad gas mileage. (9 Mpg) I was reading another post about MAP sensor resistance. I was hoping someone could confirm the correct ohm values for the 4 pins coming out of the sensor. Mine has 92 ohms on the outer two pins with the connector out and 88 ohms with the connector in. The inner pair is open circuit without the connector and 340 ohms with the connector plugged in. This does not sound correct.

Can someone help????

Thanks,
Mark

Mark:

Resistance between the two outer plugs (across MAP) should be about 90 ohm. This is terminal 7 to terminal 15.

Between the two inner connectors (#s 8 and 10) resistance should be about 350 ohms.

There should be infinite reistance between any pin and the case.

Test with plug disconnected.

The only real test is, of course, to replace it with a known good one and see if the problem goes away.

However, I would check the air temp sensor first -- the one in the air filter housing horn up front. If it is disconnected, most of these old beasts run VERY rich (black smoke, fouled plugs, etc),

Also, check the wiring to the temp sensor in the intake manifold -- if that one is bad or the wires or loose, it is running in startup mode all the time -- very rich.

Also check cold start valve for leaks, and for vacuum leaks all round -- this is brake booster, vac line for distributor, vac for locks and climate control, etc.

And replace the hose from the manifold to the MAP -- if it is hard and cracked, it will leak and cause the EFI to dump in extra fuel.

A bad throttle position sensor can cause trouble, too!

The MAP is the most expensive part, naturally.

Peter

Don't know if this will help - will post anyway:

http://db.mercedes.cx/mb/199906/30/0018.html