I HAVE A CM 870 HERE WITH A ROUGH IDLE. I REMOVED METERING ACTUATORS AND DID THE BLOCK OFF TEST AND FOUND #5 INJECTOR WAS BAD. REPLACED IT AND IT RUNS BETTER BUT STILL A ROUGH IDLE. I CONNECTED FUEL PRESSURE TEST HGUAGE TO PORT ON FRONT OF GEAR PUMP AND I HAVE 210PSI AT LOW IDLE. IF I AM CORRECT I BELIEVE I SHOULD HAVE 230 TO 270. I HAVE ISOLATED FUEL LINES OUT AND WENT DIRECTLY FROM A BUCKET OF FUEL TO THE LIFT PUMP AND STILL NO CHANGE IN PRESSURE. IF I REMOVE THE ELECTRICAL CONNECTOR FROM ONE OF THE TIMING ACTUATORS THE PRESSURE MIGHT RIGHT 5 TO 10 PSI. I AM LEANING TOWARD THE GEAR PUMP BUT IM NOT SURE. ANY HELP WOULD BE GREATLY APPRECIATED.
Do a bank cutout. Cut the front three and then the back three. If the engine runs better on the front or back bank then you have isolated it to either those three injectors or the actuators running those three injectors. I did the bubble test and after swapping in injectors (used from another engine) I had no bubbles. Took all 6 to an injector shop and had three blowing air and one wouldnt fire on the stand. Dont rule out bad injectors because your not blowing bubbles.
Another thing you can do is get a laser temp gun and check your exhaust manifold ports. If you have a bad injector you should see a temperature difference in the exhaust manifold port.
What do u think about the low fuel pressure?