7.3L diesel stalling
I have a 1991 Ford 7.3L diesel that starts with no trouble, while warming it up the rpm goes between 500 to 1100 and stalls. After that it is hard to start and will stall out when driving it warm or cold. I’ve had the injector pump replaced, and it helped but still have the same problem.
Basic Diesel Engine Troubleshooting
The generic steps below can help solve many diesel engine starting problems.
1. Remove and fully charge both batteries, disconnecting the negative battery cable first. Diesels require strong batteries, particularly in winter.
2. Clean battery terminals and cables–apply dielectric grease.
3. Check all underhood and underdash fuses with a test light or multimeter:
. Test Light. Turn ignition switch to ON (Position II), connect alligator clip to vehicle ground, and touch the probe to each test point on the fuse. The test light must come on at each test point on the fuse; otherwise, the fuse is bad.
. Multimeter. Set multimeter to DCV, turn ignition switch to ON (Position II), touch the black test lead to ground, and touch the red test lead, in turn, to each test point on the fuse. The meter should record 12+ volts. Voltage must be recorded at each test point on the fuse; otherwise, the fuse is bad.
These methods allow you to accurately and quickly check all underhood and underdash fuses in several minutes, even in dark, cramped locations. They eliminate the possibility of removing and replacing the fuse in the wrong slot. Should a fuse test bad, use the fuse puller, provided in the underdash fuse/relay box, to remove it.
4. Check for Diagnostic Trouble Codes. Attach code reader or scan tool to the Data Link Connector (under the dash), turn ignition switch to ON (Position II), and read codes.
5. Ensure engine oil is full and that the oil and filter have been recently changed. This can affect fuel pressure.
6. Verify oil pressure on Ford PSDs with a known good mechanical gauge. Oil pressure may be too low. The cutoff will shut the engine down when the oil pressure is too low. PSDs use the Hydraulic Electronic Unit Injection (HEUI) System, so it completely relies on the oil level and condition of the oil to fire the injectors. Running the oil level low or too long can cause unusual problems.
As the name implies, the HEUI injection system uses hydraulic energy to actuate unit injectors. A PSD has two oil pumps–a low pressure lubrication pump, located near or in the front engine cover below the water pump, and a high pressure hydraulic pump, located at the front of the engine V, underneath the fuel filter assembly. If the problem persists, focus on the High Pressure Oil Pump. If the Injector Control Pressure (ICP) is lower than expected (engine cranking), it is usually caused by low injection oil pressure or regulator (IPR) valve. High pressure oil is used to pressurize and inject fuel into the cylinders–each injector is essentially its own injection pump. The IPR is a by-pass valve that controls the high oil pressure, depending on demand. The ICP Sensor monitors the oil pressure in the LH head. Check for oil in the upper reservoir–it should be within one inch of the top (add as necessary). Verify that the correct oil is being used and that it has not thinned out. For no-start concerns, check ICP Sensor readings with a scan tool or pressure gauge.
7. Check glow plugs, which are used to heat the fuel:
. Testing. Use an ohm meter to check for continuity, which will tell you if the glow plug is shot, has continuity, or is worn. Ohm out each plug through the harness. Good glow plugs will have a resistance between 0.6 and 2 ohms. If you get infinite resistance on any plug, it is either bad or the connector under the valve cover is loose.
. Removal and installation. With the engine “stone cold,” disconnect batteries, remove valve cover, disconnect glow plug connector, remove glow plug with a 10 mm deep socket, install new glow plug (torque to 13 ft.-lbs.), and reattach connector. After finishing the remaining 3 glow plugs on that bank, clean valve cover, install new gasket, and reinstall valve cover (torque to 97 in.-lbs.). Do the same thing for the other bank of glow plugs and reconnect batteries. Not a difficult job–should take several hours.
8. Check glow plug relay (GPR). Ensure the engine is cold, so that the PCM will tell the GPR to turn on. If the engine is hot, you won’t have as much time to check. Locate the GPR, which is often behind the fuel filter on top of the engine, slightly toward the passenger side of the valley on PSDs. There may be two relays there. If so, the rear relay is the GPR. It should have two fairly large wires (Yellow and Brown) connected to one of the large posts. With multitmeter set to DC volts, or 15V range if not autoranging, clip the positive (Red) lead to the output terminal (with yellow and brown wires connected), and the negative (Black) lead to ground. Turn the ignition switch to ON. If the GPR is good, it should click, and you should see 11 volts or so on the meter; then, depending on temperature, it will click off up to 2 minutes later. Do this a couple of times, to ensure it consistently makes the connection. If there is no voltage with this test, confirm by retesting as follows. Remove the two small wires from the smaller two of the four GPR terminals. With jumper wires, apply voltage from the battery across the two small terminals. If the voltmeter now reads voltage on the output terminal, the GPR is good and the problem is in the PCM circuit that tells the GPR to activate.
9. Check block heater, which is used to heat the engine.
10. Check fuel injectors. Take the valve cover off and look at each injector’s exhaust, while the engine is running. Each time an injector fires, you should see oil exhausting from it. If you see oil coming out, then the injector is good. When replacing a bad injector, cut fuel, remove the glow plug, and crank the engine to get any fuel and oil out of the cylinder. If you don’t, you could hydro-lock and bend a rod.
11. Purge fuel filter or fuel separator of water. Do this at least monthly–daily, if necessary. Water can be a big problem with diesels, particularly in the winter. Replace fuel filter every 15,000 miles.
12. Use full-synthetic diesel heavy duty engine oil (HDEO). Installing a by-pass oil filter makes using top-quality synthetics very cost-effective, when integrated with a used oil analysis (UOA) program. All engines run better on synthetics, particularly turbo diesels. Besides significantly improved engine life, turbo life, performance, and gas mileage, synthetics promote easier starting, by allowing increased cranking speed. This last factor is particularly important in cold weather. Synthetics are also easier on batteries and starter motors. Excellent choices are:
Mobil Delvac 1 5W-40
Mobil 1 Turbo Diesel Truck 5W-40
Delo 400 LE Synthetic SAE 5W-40
Amsoil 5W-40: http://www.amsoil.com/storefront/deo.aspx
13. Check turbo–it may be coking up or turbine blades may be bent. Only use full-synthetic diesel HDEO with a turbo.
14. Check/replace air filter. Diesels require lots of air–restricted air filters can bend turbine blades. Check every 5,000 miles, replacing it as needed.
15. Assess fuel quality. In cold weather, many diesel owners have problems with the new ultra low sulfur diesel fuel (ULSD). The problem comes from the refining process used to attain the ultra low sulfur ratio. It affects the naturally occurring wax and can cause the fuel to gel more readily in cold temperatures. Gelled fuel clogs the fuel filter and starves the engine, causing it to stop. Adding diesel fuel additive often helps. Diesel fuel additives, such as Amsoil’s, and ultraclean kerosene added to the fuel help prevent this problem.
