Help please ? 6.5 td lift pump problems
 

I have a 95 6.5 td k2500 suburban , now I have been having a ton of problems with this thing lately. I had replaced " with new " the injectors , the filter , injector pump " three times " , pmd , fuel pump relay, fly by wire throttle sensor, fuel tank , parts of the fuel lines that were rusted , crank shaft position sensor , .. Here are some things still clearly wrong with it.. The vacuum pump stopped working so I temporarily wired the waste gate shut cause around 70 mph it was bogging out , right now when key on I don't hear the lift pump prep , extremely hard to start it takes me about 10 15 minutes to start the truck, and when it does start a check engine like it on and rpm pulse and the motor sounds very very different , everyonce in a while during driving periods it will suddenly shut off for a spit second , it will run dead =" like I Jammed the breaks "run dead dead runnnn dead runnn dead dead dead , the more I hit the gas to try to get it to go and stop from dying it bogs out more to the point where it's gonna shut off and I have to pull over shut it off and restart it but still acts up , ops reads roughly just under 40 psi and I everyone in a while I have to tighten the batt cables on the batts because they come loose idk how. And also notice when it's acting up the volts gauge reads lower then normal but that's with all light on , both heaters on , and it doesn't over heat it runs about 180 / 190 ,,also I forgot to mention , when the truck is off and in gear besides neutral and park if I turn the key to start I hear the lift pump , but don't hear it when it's running, and when I open the waste valve the truck stays running and getting a decent amount of fuel coming out .. Dealerships can't find the problem and has several codes coming up all pertaining to the ip circuits , iv checked all wire plugs and did ground and lead and load tests on all the wires in the harness for shorts such.. Also idk if this is normal but when cranking it the speed gauge comes up to 10 mph and rpm come to about 3 / 500 please help me someone:scare2::argh::ouch:

It would help to have all the codes you are getting first of all because without them it is a shot in the dark. And then you did say you wired the waste gate closed and that may be an over boost problem but with out the codes we won't know that so get the codes and we can go from there.

Ok yea I'll get the codes, how do I contact you with the codes or will you keep an eye out for my message ? How does that work?

Keep an eye on your email inbox.

Ok thank you and codes are 17 , 18 , 35 , 36 , 54 , 73

Got all that money for new IP's, PMD kits, lift pumps, fuel tanks, fuel lines, etc, but wired the wastegate shut to "temporarily" fix busted vacuum pump? Surprised DTC 78 wasnt there also.. Was that problem ever properly repaired?
Of course the engine will bog (lack power) at 70mph when the turbo isnt working properly, and the PCM will default to "Backup Fuel" ie cuts BOOST (or so it thinks) and reduces/fix's FUEL when excessive boost is detected, only youve wired the WGV shut so your likely not seeing the "signs" excessive black smoke as you would under "normal" operating conditions when exposed to increased engine loads.. Rather, your more likely feeling the lack of power due to reduced/fixed fuel rates. Fix and/or restore the stock vacuum pump/ boost system asap..

As to the "Fishbiting, and the more you press the accelerator, the worse it gets..." paraphrasing of course.


Undiagnosed air leak most likely, possibly resulting from fuel restriction..



17, 18, 19, 35, 36, and other spooky DTCs can and are often result from air infiltration. In fact, those are the most COMMONLY found DTCs following a routine fuel filter element replacement and other fuel supply system repairs, anything that opens the sealed fuel system requiring "Bleeding Air From Fuel Supply System" (see attached). Note the last step of the procedure thats rarely ever done by pro's or DIYrs alike.

DTC 56 PCM Fuel Circuit Error :scare2: diagnostic aid states and I quote "Check to see if DTC 17 is also stored, if there is refer to that chart first, if not, replace PCM."
Note DTC 17's Diagnostic Aids (attached)......



Can we assume the fuel sender was also replaced with the new fuel tank?
Was the fuel strainer replaced and if so, was it replaced with the correct one?
Nearly all new aftermarket replacement 6.5L diesel fuel senders come pre-assembled with the WRONG (gasoline) fuel strainers that in cold weather operations, severely restrict fuel flow, which can quicly overheat (prematurely and permanitely damage) lift pumps and/or OPS.
If it doesnt look exactly like the fuel strainer w/ visable by-pass (see attached), one on the left being new replacement, guess what.... Probably going to have to PAY them to check and likely redo the common fork up..
If its all new, almost gauranteed its the WRONG strainer and is most likely RESTRICTING FUEL SUPPLY and prematurely damaging the lift pumps and/or OPS..


And before others tells you to delete the fuel strainer in lue of an in-line fuel flter. Just know that doing so may actually exacerbate the fuel restriction (starvation) problem, specially during cold weather operation.. A fuel heater was incorporated into the FFM housing for a reason, speaking of, does it even work?
Its also possible to have aerated fuel aka air leak although there isnt an external air leak present. I'll skip the science lesson and point you to this TSB 94-6R2- Suction / Vacuum Side Diesel Fuel Filters

Clogged pre lift pump fuel filter, restricted fuel strainer, same thing. Exposes the fuel to high vacuum releasing fumes, vapors (not liquid fuel) might as well be a knife being repeatedly jabbed in the Optical Sensors eye, PCM often freaks and may take a time out. OBD1 models are the worst, most sensitive to air, cloudy fuel, contaminated fuel, read anything that disrupts the OS most important PCM INPUTS, is a problem..



Theres a little known SAFETY FEATURE programmed into the PCM that got lost in the programming notes editing room floor. Optical Sensor provides the PCM with the most important signals. When OS signals are missed, the PCM is for all intensive purposes, "flying blind" on auto pilot aka "Backup Fuel". Depending on the frequency and/or severity of the condition, the PCM may take a short break to re-evalute the s'ituation...

Can I get a PMD anyone..

Fuel is the only form of lubrication of these most expensive injection pumps, as such GM took steps to protect these IPs, if even from ourselves.. Cant have inattentive operators trashing IPs everytime the run out of fuel or attempting to run on fumes... If that makes any sence, need more coffeee..


Excessive Cranking, Hard Start, No Start, are also driveability symptoms of AIR INFILTRATION. See attached "Intermittents," notice a reoccurring theme?




Needlessly throwing new parts at it presents another problem. 3rd recent replacement IP for example. We must assume it was properly installed and TDCO procedure was properly/successfully done, much like the rest of the work thats NOW IN QUESTION AGAIN... Surprised the stealership hasn't misdiagnosing a faulty PCM yet, if the tech(s) claim "PCM not communicating" grab your s'it and RUN FOREST RUN....
Hate to say it but you must start over again, assuming nothing. New yesterday, dont matter.. Good Luck..

I have not fixed the waste gate but will promptly, and the fuel filter heat is working, and iv had each ip taken to a specialist shop with equipment designed to bench test the ip's each of the two came back bad, as far as install was all done by two different dealerships. At one point before I bought the truck I saw the ecm was replaced " not the original " the truck was also fine up until I had to replace part of the fuel line on the frame rail , the rubber section going from the frame rail to filter " between the lift pump and filter " ever since then iv had problems with it not running right and stalling. And while replacement of that part the filter was flushed and changed. The truck then sat for about ten years and recently have been trying to get it fixed for my sons graduation gift cause has loves the truck and they are very hard , almost impossible for me to find. And I do once in a while see air in the clear line I put in on the return from the ip. But I don't see any leaks beside a oil leak by the oil filter , but I have cleaned and changed the filter and not sure where it's coming from, I don't know if that has anything to do with my problems though. And it's the original strainer I believe , but have notice the fuel gauge floats , I heard there is a plate that comes loose in the tank and bends the pick up shut , and that's why it floats. I'm not sure how true that is. And you have given me very useful information thank you.. A lot ton. But back to the truck as far as noticing a reoccurring theme , none that I or can induce. Tho I do know the battery cables kept coming loose till I replaced the bolts. Some times it starts in less then a second after glow and runs flawlessly , sometimes more then half it takes seer minutes of key on key off and quick blurps of the starter
I can get it to start fine, other wise it takes 5 or so straight minutes of cranking and it's guaranteed to run shitty with a light on surging and stalling, there are times where it will start and run fine but stall restart shitty or it will start shitty run it a bit shut it down restart and run flawlessly for several miles fine or times it will be that process and stall.

Yes coffee is very neededdded. I'm chasing this ghost and it's driving my crazy and running my wallet dry lol

I forgot the "Intermittent" Diagnostic Aids, here they are...
The trend I was referring to is nearly all have "CHECK: For air in the fuel supply to IP."


to be continued.

some more..

Just because you see no fuel leaks doesnt mean theres no air leaks.
If it were only that easy, fact is many air leaks dont exhibit wet spots.

Air can creep into the system when parked for extended periods (system unpressurized), an inop, weak, and/or faulty lift pump will often expose airleaks that otherwise wouldnt exist. However, once the fuel supply system (fuel pressure) is restored, those newly exposed air leaks usually dont just disappear. They often become the aforementioned creeps..

Whats tougher to find than an air head? an air head as a result of a fuel restriction eg clogged fuel strainer, fuel filter, anything that creates/exposes the fuel to an excessive vacuum. Thats why I dont advocate using "in-line" fuel filters pre lift pump in lue of OEM fuel strainer, and never use them together...


Want to give him a gift.. Start by downloading and give him these GM Training manuals. Very educational stuff, lots of diagnostic aids, and step by step troubleshooting guides.
GM 6.5 Liter V8 Turbo Diesel Engine

GM 6.5L Diesel Electronic Fuel Injection


Heres a most helpful diagnostic aid to "bleed air" and avoid excessive cranking..
Also use it to perform most "Fuel Supply System Checks."
Open underhood fuse/relay box, remove LPR.
Use the LPR as a model to fabricate a jumper from a paperclip (see attached).
Jumper installed, lift pump ON. Jumper removed, lift pump OFF..

Next time it doesnt start right away. Stop cranking. Bleed Air thoroughly from the FFM vent (not WIF drain) using jumper method (no cranking necessary). When primed, close bleeder vent, leave LP jumper installed, try starting the engine...

Thank you !! Also forgot to mention rarely when cold starting it has black smoke but typically it doesn't at all. But thank you very much for your inforamtion and help

Ok so I'm going to fix the waste gate, and since findin the leak will be hard the easiest thing to do is replace the entire fuel line the way it's suppose to be and make sure there is no debree, and see how that goes, I will kept your posted if you keep your eye on here , and he has been pretty good with help lokmong for information and helping with the truck haha he is trying at least but I will give him those sites thank you very much

Making any progress?

I am interested in any updates also.

A few weeks ago 1999 Suburban 6.5L left my wife stranded and had to tow it home. Cranking fast, no start. Strange thing was the shifter would not go into park, so I was dead sure that was the one and only problem. I have since fixed the shifter and now I am very experienced with bleeding the air out of the fuel to get it to start. I had replaced the fuel filter with Auto Zone brand (which now I am suspecting). I also replaced the lift pump with AC Delco EP309, even though the original pump passed tests. I temporarily connected a fuel pressure gauge and hooked it to the windshield wiper (not safe). 7 PSI when decelerating/braking. 6.5 to 5.5 PSI when cruising. The lowest I could get it was 3.5 PSI under heavier than normal acceleration. When parked and idle, fuel flow into a container is a little more than 1/2 pint in 15 seconds ok. The reason I replaced the lift pump is because there was some slight fuel wetness (no drip) at the fuel pump fittings. Yesterday I used compressed air and shop vac to push and pull fuel 20 times thru the return line with the fuel cap removed. So I can rule out a plugged return line. I have a piece of clear vinyl tubing at the return fitting of the injector pump. I think my next step is to pursue a more robust/permanent fuel pressure gauge so I can monitor properly on longer trips. Also I have an AC Delco fuel filter TP1256 to replace the newly installed Auto Zone fuel filter.

No more air in the fuel lines
 

New sending unit and all is well. No more problems with air in the fuel lines.

More info, someone might find this useful....
Before pumping out the tank for the second time, I had the fore-thought to first loosen the straps while the floor jack was under the tank. This way, the weight of the fuel helped to dislodge the tank from the black tar-like protective layer that holds it stuck to the frame. After dis-lodging, I pumped out the tank to drain as much fuel as I could. Removed the straps, the began lowering little by little until I could inspect the fuel lines going to the top of the tank. I could see the steel lines that are integral to the sending unit were wet and rather swollen with heavy rust flakes. even with the two-wrench method, I still ended up breaking the rotted steel lines. Got a new sending unit from Napa and re-installed everything and bled the fuel lines one last time and started it. Initially I kept a tally for how many trips in a row it would re-start without the need to bleed the lines, but now I have given up and I am now more than convinced and pleased that I have it properly fixed.

You can try Inlinetube.com for new lines.

On a 1995 and older 6.5 a dual lift pump relay upgrade is a good idea. It takes the load off the OPS and gives a prime feature for strarting.

Leroydiesel.com Sells a relay upgrade kit for a reasonable price. The onl;y thing I do not like about his kit, is that he uses mountable relays, instead of mountable relay sockets and replaceable relays. I believe you also have to request the prime feature.

If you make your own OPS relay upgrade. Do not do it like the pictures say. Do it like Leroy does his - No wire splicing - plug and play. plug into the wires going to the lift pump and run back to the relay. Then run wires from the relay, back to the lift pump. I believe Leroy uses 14 ga. instead of the tiny little OEM wiring

Everything you had just mentioned is adsactley what ive been dealing with for the past few weeks now, but everything but the PMD is brand new

A faulty ignition switch can cause random shutoffs, but usually the dash lights will also come on and off.

Heavychevy doesn't like this, but I tossed the fuel sock and haven't looked back. I thought it would suck air when the tank was low during driving conditions, but it has never done that.