Conestoga Diesel Injection


1321 Byerland church Rd.

Willow Street PA, 17584-9776

Hours: Monday through Friday 8:00AM to 5:00PM

Phone 717-806-5561  FAX 717-806-5572

Advice for the servicing of conventional PLN (Pump, Line and Nozzle) fuel injection systems.

During the service life of any diesel engine, eventually you reach a point where consideration must be given to the replacement of fuel injection components, primarily the injection pump and injectors.  

As injection pumps wear, the fuel delivery can drop off and the timing can become retarded.  This is due to a variety of factors, but the net result is that the engine can loose power.  Different pumps have different behaviors as they wear.  So do fuel injectors.  

As conventional injectors wear, their pop pressure can drop.  The pop pressure is the point at which the injector nozzle begins to deliver fuel into the engine's cylinder.  As the pop pressure drops, less line pressure is needed to begin fuel flow.  This has the affect of advancing the timing. 

 One can see then, that as a fuel system wears, the pump and injectors somewhat compliment each other as their mutual performance degrades.  This has the overall affect of keeping the engine timing somewhat in specification.  When an injection pump or an injector is rebuilt,  the original performance is restored.  What happens when a newly rebuilt set of injectors is mated to an old injection pump?  Or what is the result when a newly rebuilt pump is mated with old injectors?

Many engines do not have adjustable timing, or if they do, it is not possible to measure the timing accurately.  In agricultural applications,  this is common.  Many pumps are timed at TDC and are set using scribed marks.  In automotive or truck applications, a dynamic timing is often used and must be read with specialized equipment.  If you match up a new pump to old injectors, those injectors are going to potentially be flowing more fuel than before, and they will be opening faster.  This can cause an old and tired injector to fail.  It's pintle may travel farther than before and become stuck.  It can also cause carbon to become dislodged, resulting in an alteration to the spray pattern.  If the timing is not adjustable, it will be advanced, and the engine may run with more clatter or produce more black smoke.  When new injectors are used with an old pump,  the opposite may occur.  Timing may become retarded, resulting in lower power and less smoke.  The advance mechanism may be under additional stress, resulting in erratic or unusual behavior.

When fuel injection components are mismatched in this manner, even if none of the above is apparent, it is obvious that the fuel system will wear unevenly.  A machine which may have given a decade or more of trouble free service, may now be plagued with a new problem in only a few years.  The value of optimal performance, economy and trouble free operation will be subverted by timing that drifts with wear, and the balance normally in force in a fuel system will be uneven and lost.

Always consider a total rebuild of your PLN system when having an issue.  The money spent up front on a complete refresh, will pay dividends for many satisfying years to come!
Here we see a Ford IDI Van being timed with specialized equipment used to set the dynamic timing.  Ford and IH IDI engines require 8.5 degrees BTDC checked at 2000 RPM when using the pulse method.  The crankshaft probe has a 20 degree offset .  Luminosity timing can also be used, but that method relies very heavily on the quality of the injector in the cylinder being tested, as well as knowledge of the fuel cetane level.  The complexity and unreliability of the luminosity method has resulted in its disuse in most cases.  The pulse method is what is preferred.
The Farmall Super MD uses a static timing value, selected with this pointer and mark arrangement.  The marks are on the injection pump gear.  Static timing is more common than dynamic timing, and the actual value can be harder to determine, as diesel fuel cetane values come into play.