PSD Hard/No start diagnostics - Diesel Truck Forum -
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post #1 of 1 (permalink) Old 11-03-2006, 03:19 PM Thread Starter
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PSD Hard/No start diagnostics

This applies to all PSD powered trucks and vans from 1994 to 2007, some later Ford models have slightly different Glow Plug (GP) systems.

No PSD engine will start in cool to cold weather if even one GP is not working properly. The more GPs that are not working, the harder it will be to start. Also, the GP system is VERY sensitive to proper voltage. Loose connections (anywhere, even at the batteries), low battery voltage, or a bad GP relay can all cause low voltage to the GPs - this also applies to the 6.9L/7.3L IDI engines.

A minimum of 625 PSI of oil pressure is needed by the injectors for them to inject fuel during cranking. The Injection Control Pressure (ICP) is controlled by the Injection Pressure Regulator (IPR) solenoid or valve as it is sometimes called. The IPR valve needs 12V (battery voltage) with the key in the “RUN” or “START” position, or you will not start the vehicle.

If the Powertrain Control Module (PCM) does not get a signal from the Camshaft Position Sensor (CPS or alternatively CMP) the PCM will not attempt to fire the injectors as it does not think the engine is turning over.

All voltage checks MUST be done with everything connected, and are relative to good clean BATTERY GROUND (AT the battery post - NOT the cable or clamp).

Troubleshooting steps:
1) Check the battery voltage, if it is 12.6Vdc or less, check and clean the terminals as needed, if the voltage is still low, change them and try again. If during cranking the voltage falls below 9.6Vdc, the engine will not start.
2) Are you getting fuel to the injectors (are they firing)? Smoke = yes, no smoke = maybe not. You need to check for fuel pressure in the fuel lines.
3) Do you have battery voltage at BOTH larger terminals on the GP relay with the Wait to Start light “ON”? If the voltage is NOT equal on BOTH terminals, or within 0.5V (1/2 volt), the GP relay is bad.
4) Does the IPR valve have full battery voltage with the key in the “RUN” position and the connector plugged into the valve? To check this you can CAREFULLY insert a small needle into the back of the IPR connector’s RED wire, under the seal on the wire insulation. DO NOT puncture the wire insulation.
5) Does the PCM think you are cranking the engine over? If the CPS is not working, the computer will not try to inject fuel. On most pre’02 vehicles, if the “TACH” indicates RPM, the CPS is working. You also need a minimum of 200 RPM of engine speed to start the engine, so a bad starter can cause a no start condition in addition to weak batteries.
6) Do you have oil pressure? If the oil pump cannot supply oil to the High Pressure Oil Pump (HPOP), the injectors cannot fire. This could be due to low oil level in the pan, or less commonly, a bad oil pump or oil pump relief valve.
7) Do you have enough Injection Control Pressure (ICP)? If you have low ICP, below 625 PSI and the IPR valve has power, it could be that an injector “o-ring” has failed completely (all PSDs), the “STC” fitting failed (6.0L), or the HPOP is not getting oil from the engine oil pump (reservoir is empty - all PSDs). It is almost unheard of for the HPOP to fail to the point where the engine will not even start.
8) Older 7.3L PSDs can have the injectors “stick” when the oil is cold to the point that they will either start hard, misfire cold, or not start at all (generally after the misfire and hard start cold have been long-term problems). This can be fixed w/o injector removal, the injector coils need to be re-shimmed. Basically it is a tune-up for a non-EGR equipped PSD. There is ABSOLUTELY no reason to replace the injectors for this concern, especially not “all 8”.
9) The Injector Drive Module (IDM) controls the injectors directly, if it fails (pre ‘98s) the injectors will not get proper voltage so they cannot fire. If ALL the wiring is OK, and everything else checks out, swap an IDM off a running engine and try it. That is about the only real test for a bad IDM.

'93 F-250 HD, 7.3L IDI, 5spd - FARM TRUCK
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