Ford >86 6.9 IDI, 87-94 7.3 IDI, 94.5 7.3 IDI Turbo
>86 6.9 IDI
87-94 7.3 IDI
How the fuel injection system works
These engines use what is called a hydraulic injection system. Fuel is delivered to the injection pump from the tank(s) by a mechanical lift pump. The injection pump contains a governor which contols the amount of fuel delivered to the injectors. The accelerator linkage basically changes the minimum governed engine speed (RPM). If the engine speed decreases for a given throttle setting, the governor increases the amount of fuel to maintain the desired RPM. The injection pump also contains a transfer pump which increases the fuel pressure inside the hydraulic head to 60-120 PSI. Excess fuel passes through a bleed into the governer housing where it is used to lubricate and cool the mechanical portion of the injection pump before returning to the fuel tank.
The injection pump hydraulic head not only distributes the fuel to each injector, but also opens the injectors. It does this by pressurizing the fuel in the injector lines. From the transfer pump the fuel is sent to a plunger-type intensifier pump which increases the fuel pressure further and sends it through the shaft and distributor rotor to each individual injector line, depending on shaft position.
When the fuel pressure in the injectors gets above 1400 psi (new injectors typically open at 1700 psi), it overcomes the spring inside the injector and the valve (pintel) rises off its seat allowing the pressurized fuel to spray from the nozzel. As the fuel is injected into the cylinder, the fuel pressure drops and the internal spring re-seates the pintel.
Air inside the fuel lines compresses and this is what causes so many performance and no-start problems. Hydraulic pressure can't build, so the injector won't open.
Changing the fuel filter
When ever I replace a fuel filter on a diesel, I try to do it with the engine already warmed up to aid in starting and to ensure that oil is distributed throughout the engine. If the Fuel filter header can be removed from the bracket, I do this because it reduces the amount of fuel spilled on the engine. Changine the filter is just like changing an oil filter--you lube the new gasket(s) with clean engine oil and hand-tighten only. Before installing the filter on the header, I refill it to make starting easier. Use clean diesel fuel, but if you don't have any on hand, you can save the fuel dumped from the old filter in a clean container and strain it before putting it back into the new filter. If I don't have enough fuel to fill the filter, I top it off with some ATF. Since the engine has been warmed up, it will start, but it is going to stall. Sometimes you can keep it running long enough by "feathering" the accelerator pedal to purge the air from the system. But if it stalls, disable the glow plug system (to keep from burning out the plugs) by disconnecting the relay ignition wire, run a jumper from any positive battery source to the cold start solenoid
and try to purge the air by cranking the engine. Only allow the engine to crank for 30 seconds or starter damage can occur. Sometimes it may be necessary to loosen some injector lines and hook up a battery charger if excessive air has gotten into the system. As you crank the engine, if it sounds like it is trying to start, tighten the injector lines.
There are basic things that need to be checked: power to the glow plugs; fuel delviery to the injection pump; air, exhaust and fuel return restriction; battery condition and starter draw/speed; compression; fuel quality/contamination or air intrusion; and fuel delivery to the injectors. With the exception of the glow plug circuit and batteries/starter system, these things are also going to affect performance as well.
Unfortunatly, tests for the fuel system assumes the engine will start.
Starter and Batteries
The first thing you should check for on a no- or hard-start concern is the batteries. Clean the terminals and check each battery individually (one negitive cable disconnected). They both should pass a 15 second load test of half the rated cold cranking amps (voltage drop no lower than 9.6 volts). Starter draw should be no higher than 500 amps with both batteries connected and engine RMP should be no lower than 200 RPM.
If the cranking speed is too low, the engine won't produce enough compression to ignite the fuel.
Glow plug circuit
Check each of the glow plug resistance from its terminal to ground with an ohmmeter--the glow plugs should be less than 2 ohms when cold. Another way to test the glow plugs is with a test light (not a LED/circuit tester). Connect the alligator clip to the positive battery terminal and touch the probe to each (unplugged) glow plug terminal. The test lamp will light brightly if the glow plug is good.
Even one open glow plug can shorten the controller on time sufficiently to affect starting.
Next connect the glow plug harness and check for voltage at the relay "hot" terminal with the key off, then check for a voltage drop at the glow plug terminals (86 and earlier) or at the controller/relay "hot" terminal (87 and up) with the relay energized.
If the voltage is low or drops below 10 volts with the relay energized, check for loose connections at the glow plug relay, starter relay or engine harness connector, or bad fuse link(s). Also check for voltage at each glow plug terminal with the relay energized. Glow plug circuit diagrams:
Injection pump solenoids
The only other electrical check is to make sure that there is power reaching the injection pump fuel solenoid and the cold timing advance/high idle solenoids. If the engine is cold and the high idle solenoid activates with the key on, it's good. If you have no high idle, check for voltage at both terminals of the cold start switch just behind the thermostat housing.
The cold advance solenoid also aids in purging air from the injection pump.
Next check for fuel delivery through the fuel filter. On 6.9 engines this is checked at the 3/16" hose barb on the fuel filter outlet elbow, and on 7.3 at the fuel filter orifice/return line fitting or restricted filter sensor port. If checking either at the filter return line fitting, plug the return hose. Fuel pressure here should be 1 psi minimum at idle. Lift pump pressure is taken at the fuel filter bleed schrader port and should be 2 psi minimum at idle. Fuel volume is taken at the same point and should be at least one pint in 30 seconds at idle. Inspect the fuel taken during the volume test for signs of water or contamination.
If the engine won't start, these specs may be lower as idle speed is 675 RPM and cranking speed will be less.
Fuel supply and return line restriction is normally tested with the engine at 3300 RPM. For supply restriction a vacuum gauge is tee'd into the lift pump inlet hose and should read less than 6 in/Hg at 3300 RPM. For a return line restriction a pressure gauge is tee'd into the hose running from the rear of the engine. This should read less than 2 psi at 3300 RPM. But a return line restriction can also be detected by installing a clear hose in place of the return line hose at the fuel filter. Watch the flow of fuel while cranking and if it flows towards the filter, inspect the fuel return circuit. Installing a clear line at the filter return can also be used to detect air intrusion into the fuel supply system if this is suspected, although at this point the symptom would most likely be a stall after starting followed by a hard start, in which case by changing the location of the clear line you can pin point the area of the air leak. If air is getting into the injection pump, this would cause hard start concern. A clear line can be installed at the injection pump outlet to detect this.
If the concern were a rough idle, the clear lines can be used to detect aeration of the fuel. Install the lines and start the engine. Run the engine at 3000 RMP for 2 minutes, then watch the clear lines for signs of air. Some bubbles less than 1/16" is normal, but if the bubbles are larger, constant, or if the fuel appears to foam, there is air being pulled into the supply system.
To check the transfer pump pressure inside the injection pump, a special adapter which replaces the transfer pump cover lock screw and attaches to a 160 psi gauge (the cover lock block has to be in place). Transfer pump pressure is taken at 3300 RPM and should be 90-110 psi for 6.9; 90-120 psi for 7.3.
If the engine won't start, all other checks are normal, and there is no air inside the injection pump, chances are the transfer pump is not producing enough pressure to start the engine. This can be checked by opening one or more injector lines while cranking. If no fuel is reaching the injectors, suspect an internal injection pump problem.
To perform a compression test on this engine, you need to have a diesel compression gauge and a glow plug adapter. Remove all the glow plugs to check any cylinder. Crank the engine at least five revolutions and the same number of revolutions for each cylinder. It would probably be a good idea to have a battery charger hooked up during the test. Ford lists no compression specs for these engine, only stating the lowest cylinder should be no more than 25% lower than the highest cylinder, with a low to high comparison chart showing a range of 195 to 440 PSI. In reality the compression should be at least 350 psi.
Timing these engines depends on what equipment you have. Luminosity probe timing gauges depend on fuel cetane level, engine and ambient temperature and can read as much as 10 degrees retarded from the actual injection time.
To detect a missfire, you could slowly loosen each injector line to see if the way the engine is running changes, but an easier method is to disconnect the glow plugs and measure their resistance with the engine running (the glow plugs have to be in good condition). As the engine gets hot, glow plug resistance increases. A cylinder that isn't firing will be colder than one that is. After starting, glow plug resistance usually rises to 15-20 ohms on a operating cylinder, but stays below 10 ohms on a weak one--even lower if the cylinder is dead. If you own an infrared temperature gun, you can detect the missfiring cylinder by measuring exhaust port temp. If the miss cannot be isolated to any cylinder(s), then there may be an injection pump or fuel quality problem.
6.9/7.3 IDI/7.3 Turbo IDI tips
White smoke: Caused by unburned fuel passing through the engine. Some white smoke is normal on cold start-ups.
Excessive white smoke could be an indication of inoperative glow plugs, loose injectors, low compression from worn rings or bent connecting rods, or coolant leak into the cylinders. Black smoke: Caused by excessive fuel for the amount of air drawn into the cylinders. Some black smoke on hard accel or at higher altitudes is normal.
Excessive black smoke could result from restricted intake or exhaust, inoperative leaking or weak turbo (if equiped), intake manifold gasket leaks (turbo), leaking or worn injectors, fuel return or supply restriction, advanced injecion pump timing or defective injection pump. Blue or blue/white smoke: Caused by insufficient fuel or oil consumption. Normal when engine is cold or idling for extended periods.
Excessive smoke could be caused by air in the fuel, contaminated fuel, loose or plugged injectors, thermostat stuck open, oil consumption, plugged crankcase depression regulator valve, retarded injection pump timing, or defective injection pump.
Glow Plug system update, 6.9
There have been many glow plug system changes and redesign over the production run of the IDI engines. In fact, 83 trucks have two different wiring schematics. The old, screwed-in-the-head controller/sensor was undependable and frequently failed, and usually would seize in the head.
Reciently Ford has suggested that the old-style system be replaced with the new, intergrated system. The good news is, you can buy the integrated controller and a set of glow plugs for about the same price as you would pay for a replacement screw-in controller (from Ford). The bad news is you have to replace the glow plug harness.
You need the following parts to perform the update:
You can either leave the original controller in the engine, or remove it and install a pipe plug with teflon thread sealer.
Now the update gets a little tricky. You can either choose to use the original glow plug feed wires to supply voltage to the new controller by removing them from the glow plug power relay output terminal and installing them on the relay battery terminal, or you can overlay this circuit with a 6 foot 6 gauge starter or ground cable with two parallel 6 inch 14 gauge fuse links soldered to the end that attaches to the relay battery terminal (see below). I recommend the second because it by-passes any resistance problem areas in the original chassis harness and connector. Whichever way is acceptable as long as the old power relay is being used as a junction block. Remove the relay coil energize and ground wires. On trucks with a 6 pin chassis-to-engine harness connector and a "wait" light relay (early 83), unplug the wait light relay (under the dash below the diesel warning light module) and jumper pin 5 (BK/PK--from light) to pin 2 (O--to controller).
Remove the connector hardshell from the chassis and new engine harness and connect the ignition switch feed (R/LG) to the controller ignition wire (R/LG), the wait relay wire (O) to the wait light control wire (BK/PK) and the wires from the glow plug power relay (Y) to the controller power wires (Y)--unless you have over-layed the circuit as described below--and tape back any unused wires and connectors.
The fuel heater and temp sender wires are on a seperate harness.
On trucks with an 8 pin chassis-to-engine harness connector and "wait" light powered by the glow plug power relay ("wait" light on whenever glow plugs have power; late 83-87), install the wait light power wire (B) on the power relay terminal opposite from the one being used as a junction for the controller battery feed. Install a jumper from the battery feed terminal to the relay coil energizing terminal. Remove the wait light control wire (BK/PK) from the engine connector and run a wire from it to the power relay ground terminal (this will cause the "wait light to be illuminated only when the controller grounds the power relay). A Bosch-type ISO relay can also be used. Otherwise the "wait" light wire can be installed on the glow plug feed terminal of the controller and the light will come on every time the controller cycles.
If the fuel heater is supplied from another harness, remove the fuel heater wire (DB) from the engine connector and tape it and the fuel heater connector back. If the heater is powered through the same connector, you need to remove the wire from the engine connector and reinstall it in the hole which had the BK/PK wire in it.
Plug the engine and chassis harnesses together and check for proper operation. 87 6.9 and/or 7.3 loss of voltage to glow plug controller:
Usually as these trucks get older, the wires from the starter relay to the glow plug controller build up resisitance--usually at the engine harness connector--and melt the terminal at the controller, the harness connector or one or both fuse links at the starter relay. The best repair I have found is to overlay a new circuit, by-passing the trouble area of the engine harness connector. You need a 6 foot long 6 gauge starter or ground cable (ring terminals at both ends) and 12 inches of 14 gauge fuse link wire and some 1/2" diameter heat shrink tubing. Cut the end off the two yellow wires at the glow plug controller and remove the double wire or single cable at the starter relay and tape back the ends. About 4 inches from one end of the 6 gauge cable, cut the cable and stip back the insulation approximatly 3/4". Cut the fuse link wire in half, strip all 4 ends. Double up the two fuse links side by side and solder them between the two pieces of cable. Insulate the solder splices with the heat shrink. Install the cable at the starter relay and glow plug controller, routing it along the original harness and secure with plastic wire ties or electricians tape.
Stall after starting (especially after hot-soak/cool-down) then hard start
Air intrusion into the fuel supply system. Usually, the source of the fuel leak can be determined by the time from when the engine starts to when it stalls. On 6.9 engines with a firewall-mounted water separator, the engine will start and run for upto a couple of minutes before any air which may be in the separator reaches the injection pump. The 6.9 water separator is prone to leaks, both fuel and air. The best cure for this is to replace the OEM seperator with an aftermarket one (much cheaper--$30-$60 vs. $180), or remove it and its hoses and connect the line from the tank to the one running to the lift pump. Since it's not recommended to operate a diesel engine without a water separator, replace the fuel filter with the 7.3 type filter/water separator assembly. You can either purchase the header and sedimate bowl from Ford or a wrecking yard and install a new 7.3 filter. Another option is the Racor fuel filter/water separator kit. This kit contains a filter which fits on the original header and has a water sedimate bowl which screws onto the bottom (@ $35). The filter can also be purchased separately (@ $20), and you would want to keep a spare on hand as the replacement filter would not be available at your local parts store.
The 7.3 filter/water separator can develop fuel/air leaks at the fuel heater and restriced filter sensor or the filter drain (all three are servicable) and water in fuel sensor o-ring. The air bleed Schrader valve can leak on either filter.
The next common area for air leaks on both the 6.9 and 7.3 engines is at the injector return cap o-rings and hoses. This will cause the engine to stall after about 30 seconds of running if the air is able to travel into the fuel filter. On 6.9 engines the return line from the filter should be long enough to loop about four inches above the filter.
The 6.9 can be modified to have a check valve at the fuel filter return to prevent air from entering the filter. A 7.3 Econoline filter outlet fitting (E8TZ-9C402-A) can be installed in place of the original outlet fitting. An early 3/16" 7.3 filter return orifice with a "flapper" valve can be installed into the port ment for the E-van's restricted filter sensor.
On 7.3 engine the filter return orifice contains a check valve. This check valve is usually a rubber flap inside the fitting, and if this fails air is drawn into the filter as the fuel cools and contracts. This can be detected by removing the fitting and trying to blow through it from the hose barb end. If you are able to blow through it from this direction, it needs to be replaced. Seal the threads on the orifice with Loctite 515 Gasket Eliminator or PST. There are two different flapper valve orifices--3/16" and 1/4"--and the correct one needs to be used with the coresponding hose size or leaks may occur. Starting in 92 a 1/4" filter orifice was introduced without a flapper valve using a spring and plastic check ball. The spring-and-ball and flapper orifices are not interchangable; they have different headers. Also, the correct size return lines hose needs to be matched to the injector caps and the proper clamps used--not worm-gear, this will distort the hose; either OEM spring clamps or fuel injection system screw-and-band type. When replacing injector return o-rings on one injector, you should replace all on that cylinder head as they tend to leak after they have been disturbed. Use silicone dielectric grease to aid in reassembly and some times it helps to install a third o-ring between the return cap and injector line nut to keep the cap in place.
On the fuel supply lines at the filter inlet, filter outlet and injection pump inlet, there are seals which can allow air to enter the fuel system if they become deteriorated or dried out, even if there are no visible signs of fuel leakage. If there is a leak on the line between the filter and injection pump, the engine will seem to try to start, then become hard to start. Note that there are seals of the same type on the injection pump return line at the injection pump and at the return line collector fitting on the rear of the engine (some applications).
Less common areas for air leaks are the injection pump outlet check valve and the fuel lift pump, but both have been know to happen. Using clear hose on various sections of the fuel suppy and return systems can usually pinpoint the area of the air leak. Install the clear hose at the suspect areas, start the engine to purge any air, then allow to cool. Watch these hoses for large air bubbles or pockets when starting the engine to determine the origin of the air leak. Also allow the engine to come up to operating temperature to look for air leaks which may occur when the system is hot. These may migrate into the filter and cause a hard start concern.
Engine stalls at stops or when deprsessing clutch
Stalls returning to idle after snapping throttle open. Injection pump problem caused by poor quality or contaminated fuel. Check for presence of water in the fuel--removal of the injection pump governer cover may be necessary to find contamination, but is not advisable unless you have experience. Check idle speed setting and injection pump timing, as well as cold timing advance--timing should advance at least 2 degrees with 12 volts applied to the rear solenoid terminal. Adding Stanadyne's All Season Diesel Fuel Conditioner may cure this problem, but if it persists, or if there is no cold advance, replace the injection pump. Recommend that the Stanadyne All Season Fuel Conditioner be used periodically to prolong injection pump life.
Injection Pump replacement tips:
Diesel transmission controls--VRV and FIPL sensor adjustment Vacuum Regulator Valve--C-6 Remove the throttle cable and return spring. Reinstall the return spring to hold the throttle bellcrank at wide open throttle (engine off). Remove the vacuum modulator hoses from the VRV; install a vacuum gauge on the lower (output) port and a vacuum pump on the upper (input) port. Apply vacuum and maintain 20 in/HG on the gauge; cycle the bellcrank from WOT to idle position 5 times. A gauge block for the throttle lever can be improvised using the 13mm head of an 8mm bolt. Insert the head of the bolt between the flat boss on the right side of the injection pump and the throttle travel screw. The vacuum gauge should read 6-8 in/HG. If it does not, loosen the VRV screws and adjust the VRV so the gauge reads 7 in/HG. If this reading cannot be achieved, replace the VRV and restart this procedure. After adjusting the VRV, remove the spring, apply and maintain 20 in/HG of vacuum to the VRV and cycle the throttle 5 times. The vacuum gauge should read at least 13 in/HG at idle position. If it does not, replace the VRV and repeat this procedure.
Fuel Injection Pump Lever sensor--E4OD The screws holding the FIPL sensor bracket to the injection pump are epoxied, but enough adjustment may be achieved by loosening the screws holding the FIPL sensor to its bracket.
The FIPL should be adjusted using a scan tool. Remove the throttle cable and return spring, reinstall the spring so that the throttle is held to WOT. Enter and retrieve KOEO and Continuous trouble codes. After both fast and slow codes have been retrieved, turn on the scan tool speaker and press and release the OverDrive Cancel switch. Continue to press and release the ODC switch until the scan tool begins to beep repeatedly. A gauge block for the throttle lever can be improvised using the 13mm head of an 8mm bolt. Insert the head of the bolt between the flat boss on the right side of the injection pump and the throttle travel screw. The beeping should become a steady tone. If it doesn't, loosen the FIPL sensor (T-15 torx screws) and adjust to get a steady tone; a faster beeping occurs when the the FIPL is set too low.
If a scan tool is not available, connect an ohm meter to the top and center FIPL terminals and adjust to 1800 ohms +/- 50 ohms. You can check the adjustment of the FIPL by back-probing the center wire of the FIPL sensor connector with a digital volt meter. The voltage should read 1.0-1.1 volts at idle, 1.6-1.9 at 30 MPH, and 2.0-2.5 at 55 MPH.
If these readings can't be achieved, replace the FIPL sensor and re-start this procedure. It may be necessary to remove the epoxy from the bracket screws (T-27 torx screws) to adjust a new FIPL sensor.
Tis information was from http://www.intellidog.com/dieselmann/idi.htm