Warm starting problem
 

Hi out there,
I have a 1990 420 SEL that takes several revolutions for the car to start after it has reached normal operating temperature. It runs fine once it starts no rough idle and the fuel pump and filter have been replaced. Any thoughts?

thanks

KE-Jet or LH=Jet injection? Not sure about the LH-Jet, but a leaking accumulator or bad check valve on the fuel pump will allow the residual pressure in the fuel main to drop too far and it will vapor lock hot. Need a fuel pressure guage to check, it should hold 2 bar or so indefinitely for the KE-Jet, some pressure (20 psi?) for the LH-Jet.

Peter

Yes, if the pressure drops due to a leak somewhere, the car will have warm start problem.

Another item that can cause this problem is the coolant temperature sensor also called fuel injection temperature sensor (atleast on my 87 260E). This sensor informs the computer about the engine's temp and the computer adjusts the air/fuel ratio accordingly. On my 260E, this is the last sensor (closest to the windshield) on the air intake side. It has two terminals. You should have a high resistance (2.5K to 3.5K) when cold (20 deg-C) and a low resistance (250 - 350 ohm) when the engine temp is 80 deg-c. The exact numbers may be different on your car BUT the resistance should reduce by approx a factor of 8 to 10 when the engine temp changes from 20 to 80 deg-C.