I have a 1993 Volvo 850 GLT with 140k. For the last couple weeks I've been trying to find the reason as to why it wouldn't stay running. What it does is it cranks starts idle rough at about 500RPM for about 5 secs then dies. The first step we took was using the OBD to see any codes would come up. We ran through every system and only received one code from the A6 the ignition system code: 3-1-4. We looked up the code and it had said the car had a faulty RPM Sensor (Crankshaft Sensor) so immediately we go to the parts store and bought a new one. We installed the new sensor and still got the same code from the ecu even though we had replaced and cleared the code from the ecu. So we purchased a new ECU installed it got the same result and same code. I've read online that if there was a fault RPM Sensor then we would be getting no spark to the spark plugs. So I purchased and installed new plugs and tested all 5 cylinders and each plug sparked up just fine. While I was at it I did a compression test on all 5 cylinders and got 180 for all 5. So then I moved on to check the fuel system. The first thing I checked was the fuel pressure and I got a constant 45nm. So then I had thought maybe bad gas. I added two bottle of octane booster and 5 more gallons of fresh gas still getting the same result. Also i forgot to mention that when it cranks and runs for a sec if I touch the gas the car dies quicker. So I purchased some starter fluid to see if I could get the car running any longer on starter fluid and it did. I turned it over sprayed a constant mist of starter fluid into the throttle body and the car idled for about 10-15sec. My main thought at this point was fuel delivery so I replaced the fuel filter still got same result. Then I checked the fuel pump relay but bypassing it with a hot wire and still got them same result. So then I checked the fuel injectors and when I pulled the out the front of them were cover in this black gunk as if the car had been running without an air filter. I check the air filter housing and sure enough no air filter was present so I bought one and installed it. I cleaned the gunk off the end of each of the ends of the injector and reinstalled them. After that I turned it on to see if it made a difference and the car ran for itself for about 15secs. I wanted to right aways just replace all 5 injectors but at the cost of $60.00 a piece I want to say it's something else because it highly unlikely that all 5 injectors would go bad at the same time. All the parts I've replaced so far are the RPM Sensor, plugs, fuel filter, battery, air filter, ECU, fuel relay and keep on getting the same result. I want suggestions on what else it could be before I pay a large sum of money to replace all the injectors and that not be the problem. Does anyone have any ideas what it could be?

 

Are you still getting the crank sensor code ??

Due to the "gunk" and missing air filter I would buy a can of MAF cleaner and clean off the Mass Air Flow Sensor.
I'd also pull and clean the Idle Air Control valve/motor.
Also pull the hose and clean in place the throttle body and plate. NOT with carb cleaner!
I would also buy a pressurized can of Seafoam to spray into the intake while it's running any way you can get it to so as to clean up some of the crap in the throttle body and intake and the bottoms of the injectors.

At this point I would NOT replace an injector. Like you said unlikely five died at the same time and dirty can be cleaned.

Were you able to check the fuel pressure while it was running for the brief 15 seconds to see if your pressure dropped ?? Static pressure might be higher than when the system is trying to use it. Might be dropping below what's required to operate.

 

I am still getting the crank sensor code and I wasn't able to get the fuel pressure reading while it was running but I will try too