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Just As We Figure It Out, Manufacturer Changes ItPosted 12/11/2007By Bob Mordorski
Good Example: Ford Diesel Engine
Just when we start to figure something out, the manufacturers change it on us ... why is that? Many technicians have become familiar with the 7.3L powerstroke diesel. They are comfortable diagnosing and repairing them, but just when we figured we had a good handle on them, along comes the 6.0L powerstroke diesel. Anyone who has had the displeasure of working on a 6.0L knows how difficult they are to fix, not only because of the physical packaging of the engine but because of the complex design of the engine and operating system. The 6.0L has been around for about four years but within the past six months or so, the calls have really started coming in, due to the early model vehicles going out of warranty. One call I took recently seemed fairly straightforward but proved to be quite a challenge. The truck would start OK but soon started running very poorly. Then it would stall and only start after it sat for several minutes. The company that owned the truck had been filling it from a bulk fuel storage tank, so my first thought was to diagnose the fuel system. It's always good to check the fuel quality, check for water contamination or off-road fuel. Also, we wanted to keep an eye on the fuel pressure to make sure the fuel pump was supplying adequate fuel to the engine. After getting the correct fittings to hook up a fuel pressure gauge to the truck, the pressure always seemed to hold steady at about 50 psi and stayed steady even when the truck would quit running. For good measure, the fuel tank was flushed, and the fuel filters were changed. The engine oil was changed, in case of any contamination. The problem, however, did not change. At this point the fuel supply appeared to be good so the next plan of action was to monitor the basics on the scanner. One challenge was that the truck would not set any codes to help pinpoint the problem. The basic things needed for these vehicles to start and run are good crankshaft and camshaft position sensor signals, engine oil supply, at least 500 to 600 psi of injection control pressure (ICP), fuel pulse width from 500 microseconds to 2.0 milliseconds, and the fuel injection control module (FICM) needs to be powered and able to operate the injectors. On the scanner, the readings we were watching were the rpm, cam/crank sync, ICP psi, injection pressure regulator (IPR) percentage and fuel pulse width. Three readings not available in this case but worth monitoring are:
Something is bound to be incorrect on the scanner when the engine stalls and won't restart, right? Well, not in this case! If there is good fuel pressure along with good quality fuel, and the powertrain control module (PCM) shows all the correct information, then the truck should start. A lot of time had been invested in this truck. I had talked to the technician several times and everything appeared to be OK, so I had to start scratching my head and questioning what else we could be missing. Then the thought came to mind ... not only do we need good fuel pressure and clean fuel, but the fuel has to be steadily flowing and not aerated. Maybe that is what we had that we shouldn't have: aerated fuel. So we checked for air (or rather combustion gas) getting into the fuel system. To do this, we disabled the fuel system by disconnecting the fuel pump electrically and removing the FICM power relay. Next, we disconnected the fuel lines feeding each cylinder head from the secondary fuel filter housing and zip-tied a balloon to each line. While cranking the engine, the balloons should remain deflated. If they start expanding, that means there is at least one injector leaking on the side of the engine where the balloon is filling. We found leaks on both sides of the engine. At this point, we knew we were on to something. After discussing the problem with the owner of the truck, he decided that he just wanted all of the injectors replaced. After replacing all eight injectors and driving the truck for a while to bleed the air out of the system, the truck ran like a million bucks. And, as usual, now that we are just starting to get a little more comfortable with the 6.0L, it's being replaced by an all-new 6.4L diesel. It's totally different in design, and I'm sure it will present its own unique challenges!
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Copyright (c) 1996-2008. Automotive Service Association. All rights reserved.
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