Check engine code P0191..

The 0191 code refers to LOW rail pressure. Yes, the dealers are doing a re-flash or clearing of the code, and, YES they believe it to be erroneous nonsense. I had it a couple times too, and both times the dealer cleared it. I have since installed a rail pressure gauge, keeping an eye on the pressure, and YES the rail pressure does drop significantly now and then, so now I know that it is not an erroneous nemisis but is in fact a REAL code with a real reason behind it. The computer is right about no/low pressure when it sets off the code. My truck is stock, no rail mod, but there is definately a pressure problem, I think it is the relief valve, possibly sticking open? My dealer DID replace the relief valve BOTH times that I had the truck in to them, so they must also think it is a valve issue too. My paperwork from them only indicates them clearing the code with a no trouble found. I marked the valves, that's how I know they were changed. I even asked them directly about changing the 2 valves and they lied straight up and told me they changed nothing. I am now carrying a rail press mod kit just in case the valve sticks open completely when I am out somewhere and broke down as a result with no rail pressure at all. So far I have noticed that the drop CAN be duplicated - if you go some distance like 3-4 miles, say in 4th gear at about 3K maybe right about a posted speed limit that is better driving in the high revs in 4th, and then shift up to 5th without hitting your skinny pedal by much, it will throw the code. Seems to be about changing fuel pressure after a duration of feed? I hope that description works to get the idea. Must have something to do with it at least because that is when you can get the pressure to drop off very noticably and throw the code.

CD

Installing the cap would just be a band aid to the real problem. Yes it would prove that it IS the valve, but then what? Run with high pressure all the time? The relief valve DOES serve a purpose in preventing possible down line pressure problems to the rail itself. There seem to be 2 schools of thought to this code - one, that the valve itself is a piece of junk and something better needs to evolve from DC, and two, that the computer has a programming glitch regarding when the valve is brought into play in a timely manner to safe operation to relieve the fuel pressure when it is operationally necessary.

I am keeping an eye on the pressure drops and recording them, it may well be that this kind of information will in the overall provide something usefull in information or some clue as to the proper direction of correction. I can install the rail kit at anytime, but since I have a new truck with a warranty I would like to stay out of the warranty gray zone for a while longer. Every time I am into the dealer having this code cleared/flashed/whatever is more evidence of their failure to address the issue with any REAL fix - which ultimately should be the goal here. At some point in time they either will find a good solution or I will install the kit, but only after the nuisance factor has taken it's toll. Why get into having your warranty voided for a mod when in fact you could turn this around into them telling you to install the kit to get you out of their face? And of course this will also be put in writing by DC before I go there.

Look at it this way - GM is using a similar rail system that is twice the size of ours with a really good relief system and those guys are not having this problem- why not put DC into a position to admit this design is poor (at best) and then go on to solve the problem with a better system - maybe a recall? This failure could actually become MORE dramatic a problem, possiby a road safety concern with the valve itself, or could become just as big a problem or greater a problem with putting in the plug - which direction would then be better? Got me, that's why I am procrastinating installing the valve and being done with it.

I am expecting the aftermarket to develope something better as they always seem to come to the rescue downline. The momentary drop in pressure and the code stuff is small in comparison to the long-range implications, of which should be shouldered by DC. It certainly is not going away any time soon, more and more people are having the problem, ultimately something will give.

CD