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Old 12-17-2010, 12:09 AM   #21 (permalink)
Stax
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I got this code randomly when my ip ground was loose. Along with stalling, surging, and random hard starting.

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Old 10-24-2011, 03:33 PM   #22 (permalink)
sdherington
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I am getting this code (251) and also 370. SES light stays on but I can reset it through my computer. I do have my PMD behind the LP. New injectors, filter, LP, rebuilt Turbo, and new TCS. My problem started occuring after I changed the Tstat from aftermarket 180 to factory 195. I did the fuel flow test and filter test. Now on the ground wire, are you talking about the small wire coming out of the harness on the IP (that is almost impossible to get too) or is there another ground somewhere else?
Mine sputters a little then sets the codes. I do know that if the lift pump does't work there is a code for it.

I purchased this truck in 97 when it had <6k miles.
Dad bought it from me and drove it everyday until he had a stroke. It was sitting for about 4 years. Did go out and start it every once in a while to keep the batteries up and seals soft. Now I am trying to get it road worthy again. Yea it doesn't get great fuel milage with 4.10's in the rear but I can drive allot for 1000.00 car payments.

96 GMC C2500 Sierra HD with Tow package.
145k miles

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Old 10-24-2011, 06:32 PM   #23 (permalink)
racer55
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Do you use any 2 stroke oil in the fuel a lubricity additive?

Normal 2 stroke/cycle oil is often dyed heavily and that can stain the optical sensor and cause the code.

marine 0 ash oil is a preferred quality of 2 cycle oil for this reason.

Like mentioned earlier you may have an IP with a bad OS.

Also the ground on top of the IP for the PMD harness is a place that needs good clean contact but the 3 grounds on the rear intake stud can cause similar problems if they get broken or corroded.

Make sure every ground in the engine bay is clean and functional.
Both ends of the battery grounds,the rear intake mounted grounds and the engine to body and engine to frame grounds all need to be spotless and conductive.

On a related issue the power wire to the underhood relay center should be maintained along with the connection points for the fuses and relays.
If the ECM only receives a limited power supply all of it's calibration will be affected.

I would venture to say that the P0251 and the P0370 are related,you more than likely have a faulty OS or wiring in it's circuit.

If you do have the PMD relocated to behind the LP I hope that you used the proper gauge cable for the extension,resistance of wire is affected by distance.
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Old 10-24-2011, 07:16 PM   #24 (permalink)
sdherington
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Thanks Racer55
Yes I do use 2 stroke oil. 1 bottle every 3rd tank. I will start using the ashless. I have it for my RC planes.
I hope the gauge of the wire is correct. I got it from one of the vendors on here.
I will check all the grounds first.
I would assume that the OS is an encoder for the swash plate position?
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Old 10-24-2011, 07:40 PM   #25 (permalink)
racer55
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The reason I asked about the oil is from your comment of using the power service and had an improvement.
Dye clouding the OS can make you condemn the OS when you caused the problem yourself,and end up replacing a good IP only to have the problem re-appear.

Also I am not aware of any code for a faulty LP.

The IP has more than 1 ground also,1 on the fuel solenoid at the back of the IP inside the ring of fuel lines(seldom a problem) and the one mentioned that should be under an OS screw on top of the IP.
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Last edited by racer55; 10-24-2011 at 07:41 PM.
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Old 10-24-2011, 09:14 PM   #26 (permalink)
sdherington
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Thanks again.
The tank is almost empty now so I will run it out then fill it with just diesel for a few. I hope I haven't ruined the OS but I may have. On another note does anybody in the Dallas area have a way to set the timing if I have to change the IP? I may have to go to the dealer but that is a pain in the butt.
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Old 10-24-2011, 09:23 PM   #27 (permalink)
racer55
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The top of the 6.5 page has the tool and help thread:
https://www.dieselplace.com/forum/showthread.php?t=25950

PM the members in your area and ask for help.
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Old 10-27-2011, 06:54 AM   #28 (permalink)
sdherington
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If the OS has been clouded, wouldn't the code be set instantly? I can reset it and idle for a while with no problem. I have driven for a couple of hours with no problems. It seems to be intermitent. Checking all the grounds today. Thanks again
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Old 10-27-2011, 11:19 AM   #29 (permalink)
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As with most OS related faults or fuel system issues, "check for air leaks" should be near the top of the troubleshooting list.. I am not talking 'bout just sniffin around for a fuel leak neither, which may or may not be present with an air leak. If it was only that easy.

You can try the clear hose method first, but note its not always 100%. Air leaks dont always conveniently show up as a steady stream of air bubbles out the return line. More often than not, depends on the location of the source, tiny air bubbles can collect in the top of the fuel manager and slowly displace the fuel until a a large, more significant blast of air is passed onto the IP which then immediately encounters and disrupts the numerous OS pulses, triggering a fault and/or engine stall...

I found the best way to positively eliminate an air leak from the list of possible causes is to do a pressure test of the entire fuel system however, DO NOT PRESSURIZE THE FUEL TANK.
Remove the supply and return lines from the fuel sender (tank). Use a bolt to plug the return line, then temporarily install a valve stem (eg bicycle inner tube) into the supply line. Then using a bicycle hand pump with built in pressure gauge or equivelant, slowly pressurize the system to no more than 25 psi. Then observe the gauge for several minutes. If the pressure wont build up or quickly bleeds off, you have a definite air leak,, somewhere. The beauty of this test is it makes locating any air leaks (if any) much easier as it often forces fuel to leak (you'll see it) from the source and/or starts to hiss (you'll hear it) as the pressure escapes. Once you've fix the leak(s), conduct the test again until the pressure holds.
If the pressure holds relatively steady for several minutes, short of an internal IP air leak, you can positively eliminate it from the list of potential suspects.


If you think an air leak cant be the problem, simply stop reading now.
Since the inception of the electronic 6.5TD, "air leaks" have directly contributed to hundreds of thousands, if not millions of unnecessary IP and/or PMD replacements. Thats not my opinion, thats the expert testimony of "Stan" (name changed to protect ID), my stanadyne man! Stan claimed 80% of the IP's his facilty is asked to test, test good. Note however, because of GM's and other service centers warranty policies, few service centers ever reinstall the old IP once removed due to possible future warranty issues, if not a conflict of financial self interest. And why would they say "hey, we screw'd up"? They already have the unsuspecting customers on the hook for the $1600+ IP replacement, and to admit they R&R'd the old IP unnecessarily would imply they misdiagnosed the IP and/or skip'd and/or missed something that should have been checked off the list long before they were so quick to diagnose a faulty IP which for most establishments is a most PROFITTABLE repair!
Another contributor is the age and/or condition of the rubber fuel lines, o-rings, ect ect. Rubber components, much like tires, deteriorate over time and as such require intermediate maint if not replacement at least once a decade to avoid having a $5.00 rotten hose or a lose hoseclamp leaves you walking and unnecessarily cost you serious bucks and/or months of headaches..
Lets just say that after 4 new reman IPs, 3 new PCM's, a new CPS, a new timing chain and gear set, and $2500.00 spent over the course of 40 days, my truck was no better off than it was on day 1! What really got my crawl, *** my GM long Block engine was practically brand new and still covered under full factory warranty and because I refused to "authorize" a "brand new GM IP" (+$800.00 to my ever increasing bill, claiming my original and all the reman IP's weren't communicating with all the new PCM's) or any other totally unrelated (to my stalling complaint) repairs, they claimed "I became uncooperative" after 39 days of getting the run around. They literally push'd my truck out into the parking lot so I could take it elsewhere read they still didn't have a f'n CLUE what was wrong with it!
All that BS, for what was later found to be to an inop LP (due to a faulty OPS) that exposed a hidden air leak under the fuel manager. I guess because they had installed the new LP and replaced all the fuel hoses (dry rotted) just 8 months prior, they skip'd over all them checks too.. Funny thing, my old reman IP (didn't have 25,000 miles on it) and original PCM was the only things no longer covered under some type of GM warranty ***..

Which brings me to this lil nugget I later learned from Stan and although I am reluctant to discuss it because I cant provide any proof to support it, I think it should be stated for the record.. According to Stan, theres a little know safety feature built in to the PCM, intended to prevent fuel starvation ie possibly damaging these most expensive electronic IP's. So it seems GM/Stanadyne engineers went to great lengths to protect these costly IP's, unfortunitely few ever got the memo..
We all know of the various PCM limp modes, but few if any know of the "Time Out" feature. I discussed this feature several years ago with a resident diesel expert who claimed to be prevy to the PCM's internal emissions programming, he was supposed to check into this and get back to me.. Needless to say, I am still waiting...
I call it 'time out' because that best describes it. Dont bother trying to find any reference to it in any factory authorized service manual. Trust me its not there but I know for a fact that it is noted in one of Stanadynes service bulletins, I've seen it.
In effect, any time the PCM feels threatened, becomes confussed, gets overwhelmed, or simply thinks your running out of fuel, the PCM can call a "time out" ie PCM turns itself off effectively killing the engine and will not reset for aprox 30 seconds no matter how much you try and crank on it. This "Time Out" feature acts much like a faulty PMD, ie engine inexplicably shuts off. With a raise of hands, how many here have replaced the PMD with one of those $500.00 FSD kit or home made equivilent, only to have the same problem(s) reoccur soon afterwards? If your hand is raised, you may have been put in "Time Out" and not know it.
Let me be crystal clear, I am NOT trying to take anything away from the need or neccessity of a FSD kit, but the PMD, much like these IP's, have been subject to undue if not unjust criticism over the years, resulting in their less than stellar reputations..
It chaps my *** everytime I read about a "stall incident w/ or w/o DTC's," and the first thing most often served up is the PMD without any mention of further troubleshooting.
If I had a $1.00 for everytime "check for (or) air leaks" is stated as "possible" if not "most likely" cause of, or routinely referred to throughout the factory service manuals, it would pay for one or two monthly mortgage payments, yes its that many times... Yet it is often the last thing to be checked or even suggested in most parts.
Anyhow, if the condition still exist when the PCM resets, it may immediately take another time out. Note that, much like a PMD, the PCM may not set any DTC's when electing to take a time out. Thus explains why the "diesel mechanic" claimed my new PCM's weren't communicating with the new reman IP's. Although I was allowed to briefly glance at the "classified" stanadyne service bulletin, he would not let me make or have a copy of it claiming "proprietary info" so you can either take my word for it or not... There Ive said it.


Good Luck.

Last edited by HeavyChevy95; 10-27-2011 at 11:30 AM.
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Old 10-27-2011, 12:17 PM   #30 (permalink)
sdherington
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Another tool in the arsenal.

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