GregKneupper Posted August 12, 2009 Share Posted August 12, 2009 I have a 1997 7.3 here with 175000 miles on it that the customer states dies at times and will not restart. Then it does start it runs real rough and shakes then smoothes out. Sounds like a fuel pressure issue. The only codes in it are a p0344 and and p0470. I do not work on these to much and was not around when they were being built. When i do a fuel pressure test at idle it fluctuates between 50 and 56 psi which I figures was normal due to the mechanical pump. But under wot the fuel pressure jumps around from 0 to 70 psi and the gauge flickers so fast you can barely read it. I have done an inlet restriction test and only have 2 inches of restriction. The fuel pump is not leaking any fuel. Is this reading normal or should it stay at a relatively steady reading under wot. If not then what else should I be checking. I also have not duplicated this concern but the fuel pressure reading is really bothering me. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted August 12, 2009 Share Posted August 12, 2009 The P0344 can be a false code from extended cranking, so I wouldn't put a lot of faith in that one, and the EBP code won't be of much help either. You're on the right track, check FP and quality for a start. The FP regulators are a high maintenance item on these trucks and it need to come apart and be cleaned occasionally. Regarding FP: Use a long hose and don't bleed the air out of it to dampen the pulsations so that you can get a real reading. Massive fluctuations are normal otherwise that will ruin the accuracy of your gauge! Have you checked a fuel sample for clarity and quality? Breeze this thread, as there's good pics and info here: (and the fucking search engine actually worked for once!) http://www.forddoctorsdts.com/forums/ubbthreads.php?ubb=showflat&Number=23909&page=1 Good Luck! Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted August 13, 2009 Author Share Posted August 13, 2009 The fuel pressure regulator and the water seperator were replaced about a year ago at another dealer the customer has told us. It does look new so I would assume that there is nothing wrong with the regulator. The hose I am using is about 5 feet long. Is that long enough? The pulses on the thing are wicked in my opinion. Of course as soon as you let it return to idle it goes right back to fluctuating between 50 and 56 psi no problem. As for the fuel it is clean and appears to be of good quality. I have nothing else to compare it to at this time. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted August 13, 2009 Share Posted August 13, 2009 The pulsing is normal, remove your hose and swing it around to get all of the fluid out of it. It needs to be filled with air to dampen the pulsations. I'd hang a known good CMP for S&G and check the harness very well for rubs. Wiggle and tug on everything and see if it quits. Intermittents are the worst..... Quote Link to comment Share on other sites More sharing options...
Brad Clayton Posted August 13, 2009 Share Posted August 13, 2009 Has this thing been chipped by chance? You can look at the back of the PCM over near the park brake and see if someone piggybacked a plug in module into the back of the "brain box". I have seen aftermarket crap shut the PCM down at times. Also if you have someone drive it or give it back to the owner to drive, have them verify that the glow plug lamp comes on when it won't restart. This can give you an indication if the 5 volt ref is being pulled low by a bad sensor. This of course if you don't come up with a problem in the fuel area. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted August 13, 2009 Author Share Posted August 13, 2009 I doubt that this truck has been chipped. It is always possible but I do not feel that is has been. I will drain my fuel pressure tester hose and see if that helps the problem with the fuel pulses. It is possible that this thing may just have a bad cam sensor in it. I have been burned by them before. It does have the old black colored one in it. I would just like to duplicate the concern and get this thing fixed for this guy. If I cannot duplicate it by tommorow evening I may just see if he wants to try a cam sensor in it and see how it goes. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted August 13, 2009 Author Share Posted August 13, 2009 Bruce, thanks for the pointer on the fuel hose. Worked like a champ. Now that I can get a better fuel pressure reading the fuel pressure is about 40 psi wot which is a little low. So I decided to pull the fuel filter and this thing has what looks like gray latex paint coating the filter. I have never seen anything like this before. It is very smooth and there are no large particles or chunks in it. It looks like someone just dipped it in a gallon of paint. Kind of smells like it to. I took another fuel sample and I do not see any traces of this stuff in the fuel. Anyone have any idea what this stuff could be? I am going to put another fuel filter in it and see if the fuel pressure comes up to normal. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted August 14, 2009 Share Posted August 14, 2009 40PSI won't cause a stalling or low power issue. Those engines pull well even with FP in the 20's or teens. I've driven them with FP in the single digits or zero and could not tell a huge difference. Could the junk be fuel tank lining? Quote Link to comment Share on other sites More sharing options...
eastendpowerstroke Posted August 14, 2009 Share Posted August 14, 2009 Quote: this thing has what looks like gray latex paint coating the filte your tank coating is delamanating, this may be the first time you've seen this but it won't be the last time. Quote Link to comment Share on other sites More sharing options...
GregKneupper Posted August 14, 2009 Author Share Posted August 14, 2009 I though about that but I did not think that this was an issue on these older trucks. We do not have alot of issues like that around here and I was told that a delaminating tanks will show silver flakes in the filter. But I guess it is always a possibility. I replaced the fuel filter and now the fuel pressure is perfect. I do not know for sure if this is the only problem but the fuel pressure is much better looking. It will only go down to 35 wot and fluctate a few pounds which is in spec. It does not bounce around near as bad as it was and it now looks like I would expect it to. Quote Link to comment Share on other sites More sharing options...
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