Diesel Engine Troubleshooting

Ford 7.3L DI Slow or no-start

without comments

Begin with a walk-around the vehicle to determine that the tank is at least a third full, batteries are charged, battery terminals are clean and secure, and the radiator is topped off. Check the crankcase and high-pressure pump reservoir oil levels. Ford requires a 15W40 oil that meets SH, CG-4, and Mack E-0L specifications, and recommends that Motorcraft 15W40 “black-lid” be used because of its resistance to aeration. The oil level should come to within one inch of the top of the pump reservoir.

Question the operator to learn as much as possible about the problem and conditions that led up to it. Did it appear suddenly? After repairs to the engine? What parts were replaced? Does the malfunction occur at all engine temperatures or only during cold starts?

Mechanics differ about what checks to make first. But, however you sequence them, the main bases to touch with 7.3L are:

1. Replace the air filter and examine the exhaust system for restrictions. The exhaust butterfly valve, which should cycle closed on cold startups, may stick shut. The back-pressure regulator that controls this valve can also fail.

2. Retrieve active (current) and historical trouble codes. P1111 means that no codes are set and, as far as the ECM knows, things are normal.

3. Drain a sample of fuel from the filter while cranking. If water is present, drain the tank(s) and refill with clean fuel before proceeding. Inspect the water separator for oxidation damage and, if necessary, replace it.

4. Check the glow-plug relay, which is a high-mortality item and especially so in its original oval form. The newer round-case relay interchanges with the older unit. The red cable, connected via fusible links to the starter relay, should have battery voltage at all times. If voltage is not present, check the fusible links and connections for opens. The heavy 10-gauge brown wire going to glow plugs is hot when the relay is energized. One of the 18- gauge wires (usually red with a light green tracer) is the signal wire, energized by the lube-oil temperature sensor. This wire must have battery voltage for the relay to function. Depending upon the circuit, the “wait-tostart” lamp may signal when the glow plugs energize or merely count off seconds. Individual glow-plugs should have a resistance of about 0.1 to ground when cold and 2 or more after cylinder temperatures normalize.

5. Check fuel pressure while cranking for 15 seconds. If pressure is less than 50 psi, replace the fuel-filter element, remove any debris on the fuel screen and on the screen protecting the IPR deceleration orifice. See the “IPR” section for more information.

6. Check injector-oil pressure during cranking. A pressure of 500 psi must be present to enable the injectors. Expect to see 960–1180 psi at high idle and 2500+ psi during snap acceleration. If the computer senses that the IPR has malfunctioned, it holds idle oil pressure at a constant 725 psi. Trouble code 1280 means low IPR signal voltage, 1281 high signal voltage, and 1212 abnormally high (at least 1160 psi) oil pressure with engine off. See “Low oil pressure” below.

7. While cranking, check for the presence of an rpm signal. A failed CMP can hold oil pressure below the 500-psi injector-enabling threshold. Refer to “Camshaft position sensor” section below.

8. Check power at the injector solenoids with an appropriate scan tool. Zero pulse width on all injectors means a bad CMP sensor or IDM. Failure may trip trouble code 1298. The high power levels—10A at 115 VDC—put severe demands on the injector drive module. In addition, modules on Econoline 7.3L vans built before 4–11–96 have problems with water intrusion.

9. Finally, check for air in the circuit by inserting a length of transparent tubing in the return fuel line.

Written by Ed

February 14th, 2011 at 7:52 am

Posted in Electronic Systems

Tagged with

Leave a Reply

You might also likeclose