KKersey Posted June 15, 2007 Share Posted June 15, 2007 I have a 97 f-250 with 36000 miles on it which misses hot and lacks power after about 10 miles of driving with 12000 pound trailer. My question is on the fuel system pressure, it starts out at about 55psi then the guage fluctuates rapidly. When it is fluctuating it starts out with an average of 55psi then drops to 20psi average. No air in fuel system, 2inhg on suction side. No oil aeration, no codes, passes cyl.contributiion test, substituted IDM, switch box will not pinpoint cyl. while miss is occuring, however if you kill 6 it smoothes out engine. No noticeable valvetrain issues. Lift pump was replaced and fuel pressure was pretty stable at 60psi for about 10 miles and now it acts like the old one. Regulator has also been changed. Best I can remember the guage fluctuations are normal but I dont think the drop is ok since the spec is 40-70 psi. I also installed a spacer on the standpipe to be sure it is fully open. Return fuel seems limited when ran into a container, about 1pint per minute.Any ideas or fuel system info that I have missed welcome. Quote Link to comment Share on other sites More sharing options...
Bruce Amacker Posted June 18, 2007 Share Posted June 18, 2007 I have a 97 f-250 with 36000 miles on it which misses hot and lacks power after about 10 miles of driving with 12000 pound trailer. Is this misfire a dead hole, or general roughness? My question is on the fuel system pressure, it starts out at about 55psi then the gauge fluctuates rapidly. This is normal for the old mechanical pump. If you're using a Snap-on style gauge with a bleeder, don't bleed the air from the hose, or use it to check volume. The pulsations from the pump will ruin the accuracy of your gauge. When it is fluctuating it starts out with an average of 55psi then drops to 20psi average. No air in fuel system, 2inhg on suction side. No oil aeration, no codes, passes cyl.contributiion test, Try running the CCT test 2-3 times in a row when it's hot, and idling in gear. This will tend to make a weak cylinder set a code quicker. substituted IDM, switch box will not pinpoint cyl. while miss is occurring, however if you kill 6 it smooths out engine. The firing order is 1-2-7-3-4-5-6-8, which means #6's companion is #7. I'd be looking harder at that cylinder. Use an infrared gun on the manifold, and Windex, or a spray bottle of water on the exhaust manifold to see if it's running colder. No noticeable valvetrain issues. Lift pump was replaced and fuel pressure was pretty stable at 60psi for about 10 miles and now it acts like the old one. Regulator has also been changed. Fuel pressure regulator was changed with a new one, right? These Gen 1 regulators had a lot of issues with debris in them. I might suggest disassembly and inspection for debris. If it has rubber chunkies in it, it's o-ring time. I also see them with aluminum shavings from bad pumps. Best I can remember the gauge fluctuations are normal but I don't think the drop is ok since the spec is 40-70 psi. Yes, the drop is not normal, but these trucks run pretty well on low fuel pressure. Does it have dual tanks with a switching valve? I have had starvation problems in the past from a problem here. I use an old 6.9/7.3 mechanical pump hooked to the suction tube at the engine and activated by hand to verify good flow from the tank area. You should be able to access the twin disconnects on the left side of the block pretty easily for a test. I also installed a spacer on the standpipe to be sure it is fully open. Return fuel seems limited when ran into a container, about 1pint per minute.Any ideas or fuel system info that I have missed welcome. How does this truck run unloaded? What is MFDES at a hot idle? It should be under 12mg. If it is in the 14-16 range, it is starving for fuel from low pressure or bad injectors. Have you tried any Stanadyne Performance Formula, PM-17-A, or F8AZ-9C077-AA additive in it? I'd put a half pint in the filter housing and the rest in the tank and drive it. If the problem changes, it's either bad injectors or bad fuel. I had one years ago that was a nightmare, and turned out to be a loose injector that would aerate the fuel only after a hard run with a trailer. The problem would not occur without a trailer or unloaded. Good Luck! Quote Link to comment Share on other sites More sharing options...
KKersey Posted June 27, 2007 Author Share Posted June 27, 2007 Bruce Thanks for the reply. It turned out to be a cam sensor. Sounds simple in retrospect but I never saw one with those symptoms and got going down the wrong path with fuel pressure. Quote Link to comment Share on other sites More sharing options...
KKersey Posted June 27, 2007 Author Share Posted June 27, 2007 Bruce One question. Can you explain the windex or water method to check manifold temp? I have an inferred temp gun I use but have not heard of using windex or water. Quote Link to comment Share on other sites More sharing options...
Jim Warman Posted June 27, 2007 Share Posted June 27, 2007 Squirt the exhaust manifold next to the head and see how long it takes for stuff to evaoprate.... Quote Link to comment Share on other sites More sharing options...
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