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Discussion Starter #1
1999 gmc suburban heavy half, 6.5 200k kms on it, 4x4

Not really sure how to diagnose, but i think its my lift pump, so im just gonna start from the begining of my troubles. Had weeping fuel lines, and replaced them, but in diagnosing the lines i ran the lift pump of lubrication (got a code) dont remember the code, but it said somthing about fuel pump lubrication, kept sucking air, after the lines were replaced every time id bump the key into run mode id hear the pump under the drivers door sounding a little like a clicking sound, but itd fire up and idle for an hour if needed.

I moved to a new shop today and loaded the burban full of shelving and tools and set forth to the new shop, got down the street and it died when i turned on the radio. Now every time i bump the key i get minimal pressure out of the fuel filter valve, and no clicking under the drivers door, which leads me to believe the LP went on me. No biggie if it did, but i dont want to go chasing an issue that im not 100% on the cause of said issue. Im new to diesels, and unsure where to start with diagnosing.
 

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As far as I know, there is no code for a faulty lift pump.

Check first to see if the lift pump is connected to the lift pump wiring connector.

If you can find this: http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/698297-help-fuel-pressure-drops-after-several-mins-5psi-0psi-shutdowns-2.html#post6910025, apply 12v and open the water in fuel drain by the thermostat. Make sure to have a container to capture fuel. If you get a steady stream of fuel the lift pump is working.

If the lift pump works, then there is a problem with the lift pump relay or another electrical short.
 

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1995 GMC Suburban
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Well, you can take a chance and replace the LP and go from there.

Also, check the batteries.
If LP goes, cranking takes longer, batteries gave up.
 

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Discussion Starter #4
Ill have to try that out, but i believe itd still be hooked up under the truck, i havent messed with it, but ill try it, what would the lubrication code be? Ill go down and see if there are any previous codes stored so i can tell you exactly what the code was.
 

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Ill have to try that out, but i believe itd still be hooked up under the truck, i havent messed with it, but ill try it, what would the lubrication code be? Ill go down and see if there are any previous codes stored so i can tell you exactly what the code was.
There is NO code for the Lift Pump failure.

If you suspect there are codes, get a scanner and read the codes and post it here for us.
 

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A lot of things in this truck does not code, even for a 99.

For it to code, there should be a sensor of some sort.
There is no sensor in the Lift Pump or PMD.

A lot of codes are to warn about Injector Pump conditions or boost condition.
 

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Discussion Starter #7
Im gonna replace the LP tommorrow evening, and if i still have the same conditions, how would i go about checking the injector pump? And whats the likely hood of it being just a clogged filter?
 

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Well, i went out and bought a lift pump, probably gonna install tmrw, but i now have a clacking sound coming from under the drivers door again, it was there yesterday when i cold started, and when it died i didnt have any clacking, batt was too dead to turn over, and was wearing good clothes so i didnt check pressure, but i scanned the codes to see if any had stored, and had no previous codes. So i cant actually tell you exactly what code it was.
 

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Im gonna replace the LP tommorrow evening, and if i still have the same conditions, how would i go about checking the injector pump? And whats the likely hood of it being just a clogged filter?
There are lots of other things to rule out before you condemn the IP.
A properly cared for IP will last you 250,000+ miles... Change the fuel filter, Clean out the screen Manager inside of the bottom, center of the Fuel Filter manager.
When your down in there, inspect the bottom and if it is full of crud the best thing to do is to pull the whole thing out and clean it.

If you have any doubts about the screen manager you can replace it.

Stanadyne #29244
 
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Actually.. On OBD2 models, the Lift Pump is monitored, at least its voltage (amp) is..

Intermittent P0231 code


P0230- Fuel Pump Relay Control Circuit
P0231- Fuel Pump Secondary Circuit Low
P0232- Fuel Pump Secondary Circuit High

More info on
P0230
P0231
P0232


As I understand it.. The PCM notes the LP voltage (amperage draw) during Startup Mode, and uses that reading to monitor the LP performance for the duration of that ignition cycle.. Thats why alot of LP failures dont SET DTCS, during STARTUP MODE, its noting the skewed voltage reading of an already struggling and/or damaged liftpump..





The IP is the last of a long list of possible suspects.. Dont be so quick to convict without all the FACTS. Rush to judgement often compounds the pain and suffering of a costly misdiagnosis..


Good Luck..
 

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Im gonna replace the LP tommorrow evening, and if i still have the same conditions, how would i go about checking the injector pump? And whats the likely hood of it being just a clogged filter?


Sound like maybe the Lp is crapping out or a wiring issue along with a fuel flow problem maybe filter / sock. I would test the Lp correctly. You have to start testing though cant just put parts in and hope. Fairly common people install new parts and things "seem" to be better but usually doesnt last too long. Dont waste your time and money replacing the ip. Wouldn't even glance at it even if people are standing around pointing their fingers at it.
 
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Discussion Starter #13
Im gonna go ahead and install the LP anyway due to it not sounding too healthy, and its 81 dollars, if no change i can get my hands on a number of parts, the gfs dad is parting a 96, so injection pump, and pmd are 2 things im most likely gonna pick up from him anyway. Also gonna price an OPS just so i know its new and not faulty.
 

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Discussion Starter #15
So i went down to the truck, whichsat on the charger all night, turned the key and heard the clacking under the drivers door again, wait to start went out and it fired up, and ran for a few mins, i shut it down, im gonna say LP is pooched, gonna replace it anyway, and do some tests around fuel system, but i believe thats whats gonna be my issue, as the pump didnt click or clack when i tried restarting it when it died tues evening.
 

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Weak LP is intermittent.
 
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Agreed, sounds like lift pump or fuel supply problem. IF the LP is noisey for extended periods before it grows ever more silent as LP developes positive head pressure, it may be damaged..

Healthy LP should have a rapid muffled thumping briefly until some system pressure is established and quickly grow ever more quiet if not completely silent as max head pressure is obtained.
A lift pump should get quieter as max static pressure (engine off) is reached.

A liftpump should not continue to run indefinitely when max static (engine off) LP pressure is reached. The fuel pressure should overcome a healthy solenoid lift pumps normal operation, preventing it from pumping...

Definitely should NOT be able to hear the LP with the engine running, even if laying under the vehicle. If so its likely hammered.

If its a sharp tone like rimming a drum head, hammer on anvil like, the lift pump is probably damaged from dry t'humping to much......

Often with liftpumps that struggle to draw fuel through clogged strainer or other fuel restriction (kinked hose or crushed line for ex), or subjected to a microscopic breach (airleak) in the supply (suction) line that only opens up like a zipper during..... wait for it.. sudden demands aka increases in fuel FLOW. Fuel flow thats created by sudden LP demand to pre-prime aka pressurize the fuel system and in doing so
increases atmospheric pressure trying to suddenly equalize the low pressure zone created by the demand.... As the liftpump goes intermittent or NOT performing up to minimal specs be it from low voltage or other problems, the ever binge drinkin' DS4 pump is left to fend for itself during high flow demands and will further unzip your cash when your least expecting it..

Proper procedure when replacing LP is to drop, clean, and thoroughy inspect the fuel tank and fuel sender. After testing the fuel sender for possible air leaks, be sure to replace the fuel strainer. Should you decide to replace the sender, again be sure to purchase ACDELCO TS1012 strainer also as ALL aftermarket diesel senders are shipped with a gasoline sock, aka diesel chokers, especially in cold weather.
With tank removed, thoroughly INSPECT the fuel lines and fuel sender connections for any signs of corrosion, deterioration or structural degradation. Repair and/or place as necessary..

THE LP SUCTION LINE MUST REMAIN POSITIVELY SEALED AND LARGELY UNOBSTRUCTED AT ALL TIMES... Slightest breach will cause severe driveabilitry problems.. greatly effects DS4's performance..


Deleting the OEM strainer is not advised, inadvertantly lose access to the bottom of the fuel tank and the last few gallons of fuel/water are cut off, inaccessable without the strainers wicking ability..
As natural condensation collects in the fuel tank, the water coelesces and collects at the BOTTOM of the tank thats cut off without the OEM strainer, providing the PERFECT breeding grounds for microorganisms and fungus colonies to thrive in..

Supposed to drain @ 1 liter of fuel from the WIF every other tank of fuel, or at least monthly. Set it aside for a day or two to inspect for water or other 'sediments' once its settled. Cold or hot and humid climates, more so. The 'system' was designed to constantly strain off any 'water' collected in the tank at a snails pace of 1 gallon of water per 1000 miles, or @ every other tank of fuel.. So long as you drain the WIF regularly, you may not see any significant WIF if detectable at all.. However, not draining the WIF regularly will shorten the life of th FFM elements, and restrict the IP when it goes on a sudden binge, aerating the fuel as the fuel crosses the snotty FFM element as its being subjected to sudden pressure loss if not a vacuum. Having a WIF lamp doesnt mean you only drain the WIF whenever the light comes on as so many do.


Hope this helps... Good Luck..
 

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You may just have an ignition switch problem. Which is fairly common, so when it dies, see if anything else is not working, like lights or the radio, etc...If there is no PCM power it cannot start, and the LP also needs ignition power for the priming mode where you hear the clacking.
 

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Discussion Starter #20
But i do greatly appreciate this forum, best one ive been on without bashing of stupid questions or flaming users, good work dieselplace.com !
 
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