Tulmaster wrote:
Hello everyone.
Sorry for the long wait but I did not have anything positive to report for quite sometime. I will attempt to make this long story as short as possible. First to recap, I like many have experienced engine shut down under load with a P0093 code. The conditions before shut down, engine temp and how much of a load varied from time to time depending on what I had done for repairs in an attempt to solve the problem. As an example it suffered engine shut down after slight warm up 3 miles or less for quite sometime, until I performed repeated heavy acceleration on a steep 2 mile hill (often referred to as an Italian tuneup).
After doing this many times I found the problem seemed to take longer and longer before presenting itself, sometimes as much as 100 miles (of course I was always mindful of keeping a light foot and not doing any extra acceleration on hills).
I can safely say that I have replaced every possible sensor in an effort to find the cause of this condition. I have taken the Jeep to the dealer twice where they had worked on it for hours and hours, and to a well reputed diesel only repair center to have a load put on the injection pump to test out put pressure and volume (While still on the car) with no positive results.
I purchased the GDE Eco tune and the installer tool which eliminated the engine dying and instead sent it into a limp mode. I might add that the limp mode was barely noticeable with a light foot and my top speed on the flats was raised to about 70 mph and I could then climb a 6% grade at 50mph. However it continued going into limp mode after about 5 seconds of applied load.
In the several years I have worked on this problem I have researched the engine as best as I could and learned a good deal about the inner works of the fuel system. I have received a lot of good advice and suggestions. For the most part the suggestions were based on what solved a particular, or similar problem by the person making the suggestion. Replace the injectors or the fuel injection pump or some other expensive part, but without giving a reason as to why it was causing the problem to justify such an expense.
On some of the repairs I made I did see signs which would have directed me to the cause of the problem, however at the time I did not understand what I was seeing. Now I do and my intent is to give you some idea of what is happening, why it is happening and how to determine what the cause might be.
My research has led me to determine that the programing in the ECM is set to kill the engine if the flow to the common rail is not great enough to maintain the fuel pressure that the ECM is asking for. In other words the ECM takes input from the throttle position sensor (TPS) as well as other locations and tells the injection pump it wants a pressure that can be as high as 24k psi + and if after a couple of seconds it does not see that pressure it will kill the engine. The conditions could be heavy load up a hill, or gently pulling out onto a highway or anything in between such as running out of fuel or a restricted fuel filter, so long as the rail pressure is less than what the ECM is asking for.
In my case I was at about 80k miles when my problem first presented itself and for more than a year I only drove it for testing purposes until the Italian Tune and my purchase of the GDE tune allowed me the decent use of my jeep once more. I waited until I hit 90K and performed a Timing Belt swap (there is a great how to DIY video on youtube) and removed the injection pump to send out for repair and bench testing. End result being I sent it to Industrial Injection Service in Utah who indicated there was sufficient rust inside the pump that they could not test it and of course I ordered a Bosch remanufactured pump. Once installed, lines bled of air and running, I have put over 1k miles on it without failure at all. So now we all know what the root cause of my problem was, fuel by passing parts and unable to maintain flow at high pressure, and I will now attempt to go through the steps on how those of you with a similar problem can determine as best as possible what the cause is.
One should keep in mind that on the Jeep 2.8 the P0093, depending on what book or code reader you reference, means a “Large fuel leak” or “Positive fuel pressure deviation”. This is just engineering speak for “Less fuel pressure than the ECM is asking for”. The code is caused by the difference of the fuel pressure between what the ECM is asking for and the actual fuel pressure read by the fuel pressure sensor. Under load if means the pump is not able to maintain enough flow to supply the engine needs AND maintain high pressure requested by the ECM. Many code readers may indicate this as a large fuel leak, but is actually a lower flow of fuel being pumped by injection pump than what is needed to keep the pressure up high. This can be caused by many things including a restricted fuel filter or air in the fuel line.
So step one, Since you will be working with the fuel lines and constantly needing to prime the system I would suggest an inline fuel pump, electric. Nappa has a couple, one at 3psi and another at 14 psi (which I used) I think they are made by Carter and cost about $50. They have similar on ebay, and you can bolt this to one of the fuel filter mounting bolts running a wire to ground and touching the hot lead to battery when you are priming. I think I listed the part number in and earlier post, but if needed I will hunt it up and post it again. I do recommend the 14 psi pump as it will maintain about 8 psi positive pressure with engine running and many CP3 pumps come with a lift pump suppling 12 - 30 psi depending on the application.
With the electric lift pump installed place clear fuel line at all points, using about 6" - 12" from the main fuel line to the electric fuel pump to the inlet of the fuel filter and down to a manual switching valve to direct fuel to an open air bleed hose that you can place in a container to bleed the air out of the system. When all the air is out, close the valve and drain the bleed hose. Double clamp the hose at all points with small screw down hose clamps to ensure no air can get around the hose ends. Keep in mind that there will almost always be some small amount of air in the fuel lines and the system is designed to purge this air and run fine. It is large amounts of air that are unwanted.
Once you have determined that air is not the problem and that plenty of fuel is reaching the injection pump, if it still fails by dying under the same conditions, simply look at the fuel lines to see if air is the problem. A new fuel filter should eliminate any possibility that the filter is restricted and the clear fuel lines will also expose if the filter head might be defective.
Now we all know that water is the worst enemy of the injection pump, but how does one look for a bad pump especially when you have taken it to the dealer and other places to do on the car testing and they say everything is working fine? Well here are three locations to check for rust in the injection pump itself.
1st. Pull the inlet fuel line from the injection pump.
2nd. Pull the return fuel line from the injection pump.
Using an item such as a pipe cleaning swab (something that will not be leaving any of itself behind) push into the steel fuel pipes and inspect for rust debris. If found you can remove the banjo bolts and steel fuel lines for better visual inspection by removing the alternator. If you find rust on the pipe cleaner any rust, the probability is high that the pump is toast.
3rd. If you recall from and earlier update, I had replaced the fuel pressure solenoid and had to remove the fuel rail. While doing so I mentioned I found a red slim on the inside of the rail. I now know that this was microscopic particles of rust. You should be able to check for this rusty slime by removing the fuel line from the injection pump where it meets the fuel rail and again using a probe such as the pipe cleaner, probe inside the rail bending the cleaner slightly so that it will touch the bottom wall of the rail. Again if there are signs of rust then this would justify pulling the injection pump for inspection and testing.
I should mention that if rust is found in the rail, there is always the possibility that the injectors have been contaminated also. I believe that the rail forms kind of a settlement bowl due to all the outlet lines being high, so the tips were not plugged by the contamination. My advice is clean the rail and test the pump and wait on the injectors if it has otherwise started and ran fine.
After verifying my pump was bad due to rust contamination I again pulled my fuel rail again for inspection just to be sure. Removing the fuel pressure solenoid and then using the same sensor I re installed it with no noticeable problems as yet. The Jeep manual indicates to replace it should it be removed.
Well that is all I can think of at the moment and I hope I was not too confusing. Should I remember something I missed or there are specific questions I will post follow ups, but other wise I thing this thread has run it’s course with a final resolution to my problem.
I also found a flaw and solution to the fuel filter in this vehicle that has not been addressed before to my knowledge and I also have $15 cure for the $125 Thermostat, both of which I will start new threads on, so you can check back later for that.
Mark
Good stuff, interesting and very helpful - FYI:
Diesel fuel is a light oil - very difficult for rust to get a toehold in Diesel fuel
- exception can be water in fuel, resulted from fuel fill at less-than-reputable stations
- water in fuel breeds bacteria
- bacteria in fuel turns greenish\yellowish clear Diesel fuel to brownish not so clearish with nasty odor
- bacteria in fuel results in red-brownish slime thru-out fuel system, tank to injectors
- bacteria slime can result in rust
- rust is not slimy
- bacteria slime is very difficult to cleanout, requires complete disassembly for chemical flush from tank to injectors
- various brands of Diesel fuel additive have various levels of bacteriacide
- any infested case should immediately result in fueling at better stations with minimum of additive treatment and several new fuel filters, which clog-up with the slime
- worst-case will require fueling at better stations, or adding increased bacteriacide-specific additive with repeated flush-out
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4/11)..Bus gone to Scarp 8/23/11 
