Engine Miss -- 1973 280sel 4.5
 

Hello again,

Recap: Engine missing on four cylinders. Replaced plugs,wires,cap,rotor & trigger points. Compression, dwell & timing all good.

Update: While idling: (1) Fuel pressure only 18psi -turning adjustment screw on fuel regulator has no effect. (2) Mixture adjustment screw on ECU - turning it through entire range has no effect on engine. (3) Low vacuum - 19Hgi @ distributor vacuum advance, 10Hgi @ door lock vacuum line, 5Hgi @ MAP sensor.

I hope this info can enable those more experienced than I to point me in the right direction. Thanks -Mike

Check the ground wires, also you may want to double check the trigger points (from the points to the ECU).

Fuel pressure should be 30psi, you will need to determine the cause of your low pressure. (Pump, regulator, electrical fault??)

I'll check in with you tomorrow!:)

If you have 19 inches HG at the distributor and 5 inches HG at the manifold pressure sensor on the firewall it sounds like you have a pretty bif vac leak. What condition is the line to the sensor? It runs from the back side of the left head up to the sensor. On my 4.5 the line was the original braided line and appeared to be good, that is until I removed it a looked closely. The line was severely cracked all along it's length. I couldn't find an original replacement so I used 5/16 fuel injector line. It fits good on the barb at the sensor but loose at the fitting on the head. I had to use a small hose clamp...it is a tight fit but doable. Check out that line.

Checking In

Have you discovered the cause of your low fuel pressure issue? As well, have you had the opportunity to double check the trigger point action to the ECU?

The trigger points are sending the signals to the ECU. I have not yet figured out why the fuel pressure is low. Could subpar fuel pressure cause 4 cylinders to work, but not the other 4?

No, not electrically. You do need to address the low fuel pressure issue and the 4 cylinders dropping out, which order is entirely up to you. I think I would address the low pressure issue to start then move to the injector problem.