Performance issue with your new injection pump?

More often then not, when a customer contacts us regarding a performance issue with a new pump, the problem can be traced to a fuel supply issue, and not a fuel delivery issue. 

If you are running an old stock pump, and it performs well, but then dies for some reason and you opt to replace it with a new pump, there is the chance that on occasion someone will experience a disappointing first run with the new pump.  This can be due to a couple of things, and while assumptions are generally being made about the situation, you should consider a few factors.

First, it is helpful to consider the failure of the prior pump.  If it died suddenly, or blew a lot of blue smoke, then these types of failures are usually the injection pump becoming broken or worn.  If it died very slowly, lost performance, or just wouldn't start any more, we have to assume that the decision to replace it was based on validation of adequate voltage, cranking speed, glow plug operation, and fuel pressure. Now that the new injection pump is in, and either the old symptoms are still present, or a new symptom such as low power is in play, we have to consider other things.

Second, assuming that the new pump has the engine running, has it been timed properly?  A lot of people will time a pump by ear and call it good.  However, when troubleshooting, it is always best to KNOW what is right, rather then guess.  Proper troubleshooting usually involves removing the possible cause of a problem by validating the various tests.  Moose Diesel has a timing meter rental available.

It is our experience that the biggest source of performance disappointment out of the box, is the vehicle fuel supply system.  Not everyone understands the basics of hydraulics and the flow of a liquid through a system, and so troubleshooting these problems can  be vexing to some. 

Most of the trucks that these pumps are going on, are quite frankly, old, and in many cases, neglected.  Specifically, the fuel tank(s).  A common scenario, is that a truck with a stock injection pump has been drawing fuel through the fuel system of the vehicle and has never demanded more than the maximum amount of fuel that injection pump can provide for the engine. 

Consider the intake screen or "sock" that many fuel tank pickup tubes have on the ends of them.  These live on the bottom of the tank, or very close to it, and are of a common design for a manufactures product line.  In other words, a fuel tank pickup, and the fuel lines which carry the fuel to the engine, may be sized for the largest engine that that manufacturer produces.  This sizing is going to be based on full throttle operation, producing the rated power under load, plus some additional overhead, designed to compensate for aeration of the fuel, returning excess fuel to the tank used for cooling, or other purposes. 

As an example, a 170hp 6.9 diesel which gets 18MPG is going to demand a lot less fuel then a 7.5L gas engine which gets 8MPG, however the fuel tank lines and sock are going to be the same.  Let's for the sake of conversation, say that the 7.5 L gas engine, uses twice the number of gallons per hour then the diesel.  Now, if we apply that logic to the fuel pickup sock, we could in theory clog half of it, and still get the same amount of needed fuel through it to produce that 170hp.

The reality is that in most cases, SOME of it IS clogged.  After all, that tank has been accumulating dirt for 30+ years.  Let's for the sake of discussion say that half of it IS clogged.  Now if the 60cc pump the truck came with, is replaced with a 100cc pump, and the horsepower of the engine is now closer to 300, rather then 170, what can we assume will be the effect if the fuel tank is not able to deliver that amount of fuel?  Well, that new 100cc Moose pump, is only going to act like a 60cc pump.  Only worse.  Because it is designed to use a much greater volume of fuel all the time, and not just at full throttle.  Much of that fuel gets returned to the tank, but if it can't GET to the pump, then performance will be greatly impacted.

There is a direct correlation between fuel PRESSURE and fuel VOLUME.  And you cannot change one, without affecting the other.  More often then not, a technician will check for fuel pressure as a primary means of evaluating a fuel system.  However, fuel volume cannot be adequately tested, unless the engine is close to its rated maximum horsepower.  This means in order to use fuel pressure as a valid test, you have to duplicate the fuel volume.  This cannot be done in a driveway, and because often fuel problems are a function of vehicle motion and demand duration, fuel pressure cannot really be evaluated without driving the vehicle and creating real world situations.  

If you contact us for tech support, and performance is the issue, the first conversation that is going to come up is fuel pressure testing under load.  There is incredible resistance to this by most technicians.  Most people just want to change parts without any scientific validation, which can be a huge waste of time.  Being able to measure fuel pressure IN-CAB during an actual drive is the only way to rule out the vehicle fuel system as the source of a performance problem.  Some people will still say "but I dropped the tank, cleaned it out, put a new lift pump on, and a new fuel filter.  Everything is NEW!"  But yet, with the same conviction, they cannot state what the fuel pressure is.  They still assume that everything is as it should be.  We've often seen cases where when everything is new, it is cause for even more concern, because now there are possible routing issues, pinched or kinked hose, a clog due to pipe tape being used incorrectly or any number of reasons.  

The point is this.  Unless you KNOW what your fuel feed pressure is under load, you have no idea what is going on with your fuel injection system.  Moose Diesel offers products that can help eliminate this problem.  We sell a complete high end pressure monitoring kit for the ultimate solution as well as a more basic fuel pressure gauges which you can T into the feed line between the filter and the pump with your own ingenuity.  

We don't want anyone to experience a performance issue with their pump.  Moose Diesel is well known for excellent technical support via email, and we will work with you to resolve the issue when you buy one of our products.  However, we hope and expect that you will be willing to do the necessary tests to validate the parts that are supposed to work with the new pump, as a way to function as a team to get your truck running  the way you want it to.