1988 240 runs only after clamping fuel return hose

mitrue · Post by **mitrue** » 24 Jan 2006, 17:27

My 240 will idle only if I clamp the return hose after the fuel pressure regulator. I just replaced the fuel pressure regulator and still I must clamp the line in order for it to idle. If I remove the clamp it dies immediately. With out clamping the line, it will start erratically by constantly pushing, then releasing the gas pedal, but it has no power, will not idle and is undrivable. The fuel pressure is 70lbs/psi, ignition and valve timing are good. It has been a great car with no problems, it ran fine one day, the next it didn't, it wasn't a gradual happening. The fuel pump(s) are audible for a few seconds after it stalls, but unlike my 760T, I do not hear them at startup. I don't know how old the fuel filter is and will change that next. Any suggestions are greatly appreciated.

Guest · Post by **Guest** » 24 Jan 2006, 18:07

by clamping the return line you are increasing the pressure and making the car more rich. If your fuel pressure is correct unclamped I would suspect that your temperature sender is bad and it is telling the computer that it is like 200 degrees F. The computer acts on this and leans the car out. Temperature sensor are reverse coificient thermistors which means that when cold they have high reistance and when warm the resistance lowers. Measure your coolant temperature sensor (you have two one for the gage and one for the ecu) when cold with an ohmeter. Resistance should be quite high (from memory like 273K ohms) I found one last week that measured 41 ohms on a Ford F150. Truck would barely idle and you could not move truck at all. Replaced coolant temp sensor and everything is fine again. Measure sensor and see if this is it. Of course it could be something else that I havent thought of. Let us know what you find.

mitrue · Post by **mitrue** » 24 Jan 2006, 18:25

Thank you very much for your information and efforts. I wiil check that. With the clamp removed, I just removed the air flow sensor connection and the car ran much better, it idled and responded to me giving it gas, it is probably driveable. The second that I reconnected it, the car died. Could the temp sensor affect the air flow sensor via the CPU or do they work enitrely independent of each other? With these results that I have, would you replace the air flow sensor?

Guest · Post by **Guest** » 25 Jan 2006, 15:28

check the coolant temp sensor first when you disconnect the maf you put the car into limp home mode and I am thinking the computer may disregard the coolant temp sensor. I think it does ign and inj pulse based soley on throttle position if coolant temp sensor for ecu is good replace maf

mitrue · Post by **mitrue** » 28 Jan 2006, 17:49

I replaced the MAF sensor and it works beautifully. Thank you for the help.