My favorite old ford is dying. I have a 1990 F250 Lariat with a 351 Winsor EFI. It has just over 450K miles on it. One day it ran great the next it acted like three cylinders were dead and had no power. What I have done so far. Replaced MAP Sensor, Replaced Distributor, Replaced Cap, rotor, wires and plugs. replaced O2 Sensor, All of these had had over 250k on them anyway. The EGR system has been caped off years ago. I replaced the temperature control sensor. Then I did a test start. It started and ran great. But, I did not have the two big air hoses on that go from the air filter box directly to the ejector induction system. Not sure of the proper name for this fuel system just EFI system. . So I turned it off and put the big air hoses on from the filter box to the intake. Now it will not start. So, I took the hoses off. Still will not start. Air filter is new. It gets fuel. Compression showed all cylinders just over 120 PSI except #4 and #8 the back two. They are at about 90 psi. I cracked open the fuel return line. Did not squirt fuel when turning the motor over.. But it is not supposed to. So now I am stumped.
Any help is appreciated.