91 740 Turbo - Out of the blue I start it up and it idles like it is running on 3 cylinders. This is a constant miss all throughout the rpm range.

Main fuel pump, relay and filter are new, I can hear the in-tank pump running. Fuel pressure regulator has vacuum with a dry hose. No black smoke is present.

We have good spark at all cylinders, noid lights tell me all injectors are firing or at least are getting power.

What is interesting is that the car will not start or run with the wire to injector 3 or 4 disconnected. With the wire on injectors 1 or 2 disconnected, there is no change in the way the car runs.

I'm thinking maybe a bad injector(s)or plug(s)but I am interested in other opinions before digging into it.

Suggestions are solicited and welcomed!

Thanks in advance,
Curt

So, if one and two change nothing, and three or four make it dead, then you are basically running on two cylinders...which would be oh-my-gosh rough. But...I'm suspecting more of a "share" thing...as if one and two are at 50% instead of 100% and that is why it feels like three cylinders. The first thing I would check is the intake gasket...I'd spray carb cleaner on the gasket, particularly around one and two...and see if I got a response. If no, I'd next pull the plugs on one and two to see if they were white (lean) or black (rich) and go from there. Lean means injectors give no fuel; rich means injectors stuck open (seldom), weak spark (which you've ruled out) or blown diaphram in the fuel pressure regulator, which is, of course, closest to which two cylinders? one and two.

Let us know...



And so you know, but don't worry overmuch since this is SUPER rare; I've had it happen twice in 16 years...the fuel pressure regulator died and forced fuel into where there should be air...air compresses, fuel does not, and it literally burned a trail right through the headgasket between one and two.

Chris

...and if I unplug the spark plug wires 3 or 4 the car will die. If I disconnect plug wires 1 or 2 there is no change in the way the car runs. We smell gas also.

You can swap injectors between 1,2 and 3,4 to find out if it is in the injectors themselves or something else. That would be a start.