Why are my fuel injectors not firing?
 

i have a 1991 190E 2.6 automatic....Continued from an earlier thread about camshaft timing, i found out my real problem is the fuel injectors so i made this thread in case somebody knows what could be the problem.

I rebuild my engine and now when i crank it, it wont start. I have spark, and i think my timing is right but i found out my fuel injectors are dry and then took one out and while cranking it does not even spray. I hear the fuel pump buzzing for a few seconds while i turn it on so i do get fuel to the distributor, but not any to the injectors. Any suggestions?

Have you verified fuel pressure? Are they clicking? (use mechanics stethescope). Do you have a schematic? Since you have a spark I will guess the CPS is good.

i dont have a stetheoscope and i do not hear them clicking. How do i check fuel pressure? I disconnected my fuel pressure regulator and fuel was coming out of it.. which is the exit side .. but it does not reach the injectors as they are dry... as if they are not getting a signal to inject. The cold start injector however is wet.. What could be causing the injectors to not work?

Without a schematic I can only give you general advice. First, to confirm that fuel is the problem you can spray some starting fluid into the intake and it should run for a second or two. That confirms that you really have the spark.

As far as the injectors, they are switched by the ECU. The ECU either switches on the low side or the high side. So one end of the injector is connected to the ECU (or a resistor) and the other side is connected to +12 or GND (or a resistor) depending on the schematic. So basically it is a long way of saying make sure your wires are all connected correctly. When the engine is cranking you should see some voltage across the injector (with a meter). It will be a pulsing voltage. If no voltage then there is some electrical problem. Unfortunately I cannot give you any really helpful advice on that car but hopefully someone else can.

Injectors not firing
 

Did you do anything to your pressure reg. ? This engine if I am correct has mechaical fuel injectors which will not actuate if the pressure is not adequate. Check fuel presure at the big mac (fuel distributor)

If they are mechanical then please ignore everything I said!! I didn't think there were mechanical systems still in '91.