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Discussion Starter #1
Hi, I have a 97 with a 6.5, my truck seems to run fine until I put the throttle all the way to the floor, then it acts like it is missing on a few clyinders or have a lack of fuel, if I put the throttle 3/4 of the way it runs fine and seems to have alot of power, it only does this at full throttle, I put a new fuel filter in and about 5000 miles ago I put in a new lift pump, any suggestion on what could be causing this problem? I have been told it could be in my cat. converter, can I remove the converter and put in a straight pipe? what effect will this have on my truck?


Thanks Blaine
 

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Blaine,


Look at fuel filt change again I picked up some bad fuel within 5K of a filt change I had same problem, a partially clogged one can limit supply to IP and power/top end, mine only showed up when pulling a 5800 lb trailer. There also could be a problem with the lift pump, on front of engine just left of thermostats is a tee handle brass valve; this is the drain for the fuel filt bowl, connect a gauge to the drain line and open the valve while running should be 4-6 psi while at idle, run line/gauge into cab and observe while driving under load should be variable 3-4 psi on lift pump/bowl, make sure gage line does not get pinched it will fault the reading I ran mine out back of hood under wiper and thru open window.


If those check out okay then you can look to the cat








Edited by: Turbine Doc
 

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Discussion Starter #3
Turbine Doc


I checked the fuel pressure, in idle the pressure was about 4 psi, crusing at 55 mph it read about 3 1/2, when I gave it full throttle it slowly went down to 2 1/2 (from 55 to 60 mph with loss of power) then it dropped very fast to about 1 to 1 1/2 psi around 70 mph. Loss of power appears to happen around 50 to 60 mph, then again around 70 mph, between 0 to 50 mph and 60 to 70 mph it seems to run fine, I just put a new fuel filter in and it also has a new lift pump.


Thanks Blaine
 

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Blaine,


How long ago on the new filt, I still suspect it as you say fuel press is dropping off to 1 psi that is too low, mine drops to no less than 2 but comes back up to 3-4 at that speed once I stop the acceleration demand and hit cruise speed, If you picked up some bad fuel and you aren't running a pre-filt you could be partially blocked when it happened to me I couldn't understand it either, my filt was only 5K old so I thought it to be new also, truck ran like a raped ape empty on way to trailer dealers.


When I hooked up my new 5600lb, 9T rated GN trailer, the truck fell flat on its face; at 45 mph truck started bucking and stalling, I could only do 25 up a hill, running without the trailer all was back to normal. I called RATDOC for his .02 he said right away bad filt, I had my doubts but changed it anyway, sure enough that fixed it, next pull of that trailer it was loaded with a tractor and implements. 18,700 GVR tow up to 75mph never below 50 on long grade. Change filt and see what gauges say then, if no difference save filt as a used but good spare.


If you still suspect the cat, disconnect the cat inlet flange separate the joint about 1/2" or so, and see if it helps letting the flange leak. won't be too noisy; the turbo knocks down most of the loud noise.
 

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Discussion Starter #5
Turbine Doc


I just replaced the filter about 150 miles ago, I had a local auto parts store read the codes on the computer, and it came back with one code, "P0236-Turbo Charger boost sensor A circuit range/performance" any idea on what this would mean? could this be causing my problem?


Thanks Blaine
 

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Allrighty then; P0236 turbocharger boost performance, something we can work on. Per my 98 manual that code is set via low or hi boost 20kPa delta from desired by PCM, I suspect a bad turbo wastegate solenoid, vac leak, bad vac pump, bad boost sensor, or worst case problem in turbo/wastegate or PCM. Bad WG solenoid is also supposed to set a code 1656.


1) check all vac connections for broken loose fittings


2) put vac gage on vac pump main line, main vac at pump should be 22" +


3) put tee/gauge in line to WG actuator supply read vac while driving, this is a normally open solenoid, and is pulsed open/closed as PCM demands WG closure, should be 18"+ vac to WG act. when PCM commands boost sol to close WG. at full closure should be = to vac reading on main line of vac pump assuming it's good.





Start with those and we can go some more, it still puzzles me though why your fuel lift press is going down to 1 psi, still could be that fuel filt if you got some bad fuel.
 

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Discussion Starter #7
Turbine Doc


I picked up a new gauge today to measure fuel and vac., so I will check the fuel pressure again and the vac. pressure but it might not be until sunday, me and my wife are taking off for a few days. I want to thank you for all your help and I will let you know on sunday or monday what the pressure readings are.


Thanks Blaine
 

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Turbine Doc


for some reason my truck seems to be running fine now, my fuel pressure still goes down to 1 1/2 and my vac. seems ok, if it happens again I will retest and let you know, thanks for all your help, I really appreciated it


Thanks Blaine
 
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