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Discussion Starter #1
Hey All,

I'll tell you my symptoms and then my suspicion.

I have a 1999 GMC Suburban K1500 F code. Lately when driving to work in the morning it will not want to rev past around 2000-2200 RPM and it feels like it is breaking up. If you accelerate in P or N it will rev up all the way to redline, but still break up around 2000-2500 RPM. After the short drive to work I sometimes go out for lunch and it runs tip top. I have associated the behavior with it being cold as it only seems to happen when it has sat overnight.

I have been searching for a couple weeks but can't find anybody with the exact symptoms I have. Some people have similar symptoms but have a bad IP (I hope that's not it).

I discovered a few days ago that if I cycle the key twice so that the lift pump is running for awhile, the symptom is very reduced or gone all together.

I think I must have an air leak somewhere and it's probably losing pressure over night so there are air bubbles causing my issue.

Let me know if anybody else has any theories

Thanks,

Donny
 

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Hey All,

I'll tell you my symptoms and then my suspicion.

I have a 1999 GMC Suburban K1500 F code. Lately when driving to work in the morning it will not want to rev past around 2000-2200 RPM and it feels like it is breaking up. If you accelerate in P or N it will rev up all the way to redline, but still break up around 2000-2500 RPM. After the short drive to work I sometimes go out for lunch and it runs tip top. I have associated the behavior with it being cold as it only seems to happen when it has sat overnight.

I have been searching for a couple weeks but can't find anybody with the exact symptoms I have. Some people have similar symptoms but have a bad IP (I hope that's not it).

I discovered a few days ago that if I cycle the key twice so that the lift pump is running for awhile, the symptom is very reduced or gone all together.

I think I must have an air leak somewhere and it's probably losing pressure over night so there are air bubbles causing my issue.

Let me know if anybody else has any theories

Thanks,

Donny
Dirty Fuel Filter, dirty Screen Manager down inside of the FFM.

Dirty Air Filter.

Weak Lift Pump.
 

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Discussion Starter #3
Dirty Fuel Filter, dirty Screen Manager down inside of the FFM.

Dirty Air Filter.

Weak Lift Pump.
Changed the fuel filter, only had about 10k on it but I did resurrect the truck from sitting for a few years so it likely needed to be changed more frequently as a result.

Air filter was done just a few weeks ago (maybe 1k if that) so I'm good on that.

The problem seems dramatically reduced after a fuel filter, and I can get it up to speed in a reasonable time.

The lift pump does seem a bit weak when I did the t-valve test. I have rubber hose on either side of it, would it be more beneficial to go with an aftermarket fuel pump like a walbro?
 

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Changed the fuel filter, only had about 10k on it but I did resurrect the truck from sitting for a few years so it likely needed to be changed more frequently as a result.

Air filter was done just a few weeks ago (maybe 1k if that) so I'm good on that.

The problem seems dramatically reduced after a fuel filter, and I can get it up to speed in a reasonable time.

The lift pump does seem a bit weak when I did the t-valve test. I have rubber hose on either side of it, would it be more beneficial to go with an aftermarket fuel pump like a walbro?
You can upgrade to an aftermarket lift pump like Walbro or Airdog but it's really overkill..

Your stock lift pump does just fine and it's not bad on the wallet.
AC Delco: EP1000/BGV00100 (1999 model year Lift Pump).
 

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Follow your gut, and permanitely install a fuel pressure gage between the FFM and IP asap. Check for DTCs but dont get overly concerned if you find some.

Stock form, an upgraded liftpump is totally unnecessary. I would suggest using an ACDelco 158.


I suspect your liftpump is worn and/or damaged, and has opened an elusive 'air-port' that assaults the sensors errr damaging PMD as the fuel supply system must re-prime during cold start up and is then forced to self purge leaving the Optical Sensor kicking and screaming bloody murder the entire time..

End result is often the same. Rough Starts, Hard Starts, No Starts, Smokey Starts, etc etc etc and dont be surprised if theres a spooky DTC or two or three present or not.. One should expect even more frightening DTCs if excessive cranking is employed, 17, 18, 19, 29, 34, 35, 36, just to name a few 'common dtcs' routinely found following fuel supply system repairs and/or maint that requires 'Bleeding Air From The Fuel Supply System' especially when the 'crank engine' to prime method is employed. Excessive engine cranking should be avoided at all cost..

And finding a DTC is not an indication the part(s) and/or systems identified are defective. DTCs simply indicate a fault occurred within said part(s) and/or operating systems. A prime example is running out of fuel. Most often while replenshing and restoring fuel flow, several Optical Sensor and/or engine timing components DTCs often result. Once restored, the DTCs should be cleared to avoid left over DTC(s) possibly complicating and/or influencing future driveability issues

A quality low pressure fuel pressure gage can help monitor the 'systems' performance during NORMAL operations, and when not in use. Contrary to popular misbelief, air leaks and fuel leaks are NOT synonymous. FACT IS, many 'air-ports' dont even exhibit wet spots and routinely appear dusty and bone dry to the naked eye. If it was only that easy, I wouldnt need to further explain it as I do.

The lift pump has 2 one way check valves that work in unison to pump fuel to the IP. Be it age and/or damage, the check valves can begin to leak (may aerate) fuel DURING OPERATION, and when not in use. Provided an absolutely sealed fuel supply system, gravity and atmospheric effects cant act upon (fuel cant drain back to lowest fuel level) the 'lifted' or 'suspended' fuel when not in use..

I say again. As long as the fuel supply system remains absolutely sealed when not in use, air necessary to displace the fuel cant enter the fuel supply system. Thats how inop, worn and/or defective lift pumps manage to go undetected for so long, or not.

Once the fuel supppy system and/or lift pump starts to break down, it exposes the entire fuel supply system to atmospheric assaullts further exacerbated by the DS4's quite capabilities of drawing fuel, although not intended too 'self serve', it will certainly try to suck (creates significant vacuum) when the unmonitored fuel supply system pressure and/or flow fails to keep up with DS4 demands. Much like electrical current, vacuum signals seek out the path of least resistance. Open the WIF drain to check the lift pump inadvertantly provides the vacuum signal a new path of least resistance. Once the IP has sucked the WIF drain line and FFM housing dry, engine may exhibit a fishbite or two before it stalls as if the ignition was turned OFF with no fuss.

FACT IS Air molecules can easily squeeze past tight spots that liquid fuel can not, even when subjected to low (normal operating) system pressure...

Being positively sealed and absolutely sealed are not the same thing... One can be positively sealed (maintains low operating pressure without leaking a drop) but not absolutely sealed and vulnerable to atmosphere assaults when the low fuel supply system normal operating characteristics are turned on its head..

I'll elaborate little more about my own observed fuel pressure readings later and how unchecked fuel deficiencies and/or fuel restrictions (dirty fuel filter/element for ex) can quickly amplify and/or magnify atmospheric assaults..

For now, heres my base line numbers taken at the IP unless stated otherwise.
Actual fuel pressure varies significantly with ambient temps...
10-12psi static pressure, engine off.
8-11psi dynamic pressure, engine idling.
6-9psi, cruising 65 mph
4-7psi, when the DS4 senses significant engine loads eg bucking strong headwinds, racing up steep grades, hauling or towing heavy.
And try as I might, not even close to the 3psi minimum necessary to ward off atmosphere attacts but I suspect that will progressively drop as the element becomes ever more restrictive over time.

Once exposed to atmosphere, and fuel supply system pressure and/or flow restored eg new lift pump installed, any newly formed air-ports dont just disappear or fix themselves. Finding and eliminating air-ports requires a pro-active approach or ya better carry few spare PMDs until it surfaces on its own eg starts to seap and/or leak fuel.

The low pressure fuel supply system is NOT monitored by the PCM(s) and assumed good by PCM and diagnostic charts. Unfortunitely many professionals and DIYrs assume so too and routinely elect to skip all those underhood visual/physical inspections and most 'Important Preliminary Checks'. Like tires and brakes, the fuel supply system requires periodic maint, inspections, and repairs every few years if not at least once a decade..

Fact is whenever the liftpump is found faulty or defective and replaced, the fuel tank is supposed to be dropped, cleaned and inspected. The fuel sender is supposed to be removed, cleaned, inspected, and tested before replacing the fuel strainer. The fuel hoses, fuel lines and/or connections are supposed to be cleaned, inspected (repair or replace as necessary) and all critical seals and/or o-rings replaced; however, its almost never done (skipped too) given the lift pumps convenient location, outside the fuel tank unlike our gasoline counterparts..
Be it OBD1 or 2 models, its also reccommended that the OPS be replaced at the same time. Logic is that by the time the lift pump is discovered, the OPS has likely been damaged in the process..

Most folks are unaware that the OPS problematic and perceived 'flaw' was intentionally designed to fail when the lift pumps 12vt current load began to exceed 5 amps, thats nearly twice the nominal 3 amps necessary for a healthy and unrestricted lift pump. The liftpump circuit and PCM learned memory circuit share B+ power, so the OPS acts as an non serviceable inline fuse for the liftpump so the PCM memory isnt inadvertantly wiped out everytime a faulty lift pump attempts to blows the ECMB 20 amp fuse.. Thats why you should always check voltage (amp draw) as well as pressure and flow before and/or after lift pump replacement to assure your not placing the new liftpump back in harms way....

How many new lift pumps has it been since the tank(s) were dropped and/or fuel supply system properly serviced much less treated to a thoroughly inspection.

FWIW My recently fully restored (Jan '16) OEM fuel supply system still maintains 3-4 psi after several days of inactivity, indicating my old IP and new lift pump are healthy and the fuel supply system remains positively sealed.

The lift pump's check valves will likely begin to relax with age allowing the system pressure to drop to zero soon after shutdown however the fuel remains 'suspended' assuming the fuel supply system remains absolutely sealed.

If the fuel pressure falls off rapidly after turning the ignition OFF, indicates a problem... A slow bleed down to zero within a half hour or so is indicative of a worn or damaged liftpump.

If the system was NOT designed nor intended to maintain some pressure when not in use, there would be no need for the repeated warnings in the (diesel) FSM to carefully release system pressure before servicing the fuel supply system. read the system is normally lightly pressurized.

I currently have 3 fuel supply system monitoring stations employed.
Station #1 is located post FFM, pre IP. Currently using 0-15psi pressure gage but have a spendy combo vac/pressure gage w/pointer thats waiting for next round of simulations and/or road testing. For example- FFM pressure differentials and the effects of clogged FFM element on otherwise fully operational fuel supply system when the DS4 is demanding mo' fuel.

Station #2 is located post lift pump, pre FFM.. 0-15psi gage used to measure liftpump pressure and health unabated and provides for differential readings to monitor element as it becomes ever more restrictive.

Station #3 is located post sender, pre lift pump. Now employing a vacuum restriction monitor (replaced the spendy combo vac/pressure gage) to keep an active eye on the fuel strainer condition..

Ive been conducting numerous road test and experiments damn near every weekend since x-mas while closely monitoring many facets. Preliminary and conclusive findings to be fully disclosed at a later date. Currently trying to learn, comprehend, and understand the live scan data logs necessary to further connect the dots between fuel supply deficiencies and repeated PMD failures since noone wants to subject there vehicles to such torture or willing to try new PMDs in order to see if c-times are a product of damaged (fatigued) PMDs and/or damaged fuel solenoid.. Stay tuned for that report.
 

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Discussion Starter #6
I seafoamed the FFM twice. While siphoning, my aquamarine coloured diesel (due to 2 stroke oil) was a very dirty yellow. I sucked up a bunch of rust particles out of the bowl. (And a couple larger chunks)

The first seafoam was like night and day performance wise, it really woke the sucker up. The second seafoam was because I was still having a small issue in the morning... But I think that was from the other issue that cropped up....

I went on a trip on Saturday and got a P0236 (I think) code. I suspect I've had the issue that tripped the code all along, just not enough fuel to warrant that much boost!

I had a buddy over on Sunday and we cobbled together a TurboMaster with the stiffest spring I could find at TSC. Naturally it was waaaay too flimsy and couldn't hold a lick of boost in.

I picked up a storm door or front door stop apparatus with a nice chrome (nickle probably) spring on it that was really tough. I mutilated it to get the spring and was happy with the result.

I have my homemade TM cranked up pretty good I expect as it accelerates 0-100km in about 10.5 seconds, if I cranked it up too far, it would give me an overboost code right? I've floored it going up hills to try and trip a code to make sure I'm still good. It's not really making any turbo noise on the highway cruising only when accelerating.

I have never been able to make the ole' burb accelerate under light throttle, you really needed to get it close to the mat before it would start moving from a constant speed. Now if you move the pedal a 1/2" while going a constant speed you start picking up more!

I expect my issue was a compound one. With cleaner injectors and a reasonable amount of boost, my issue was non existent this morning, and it was our coldest morning in a long time (11-13* over night). I expect the cold advance timing was changing enough to cause a stumble when it didn't find boost when it expected it.

On a side note:

My glow time is always around 6 seconds regardless of temperature, and always does the afterglow cycling. Is that normal?
 

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I seafoamed the FFM twice. While siphoning, my aquamarine coloured diesel (due to 2 stroke oil) was a very dirty yellow. I sucked up a bunch of rust particles out of the bowl. (And a couple larger chunks)
Be sure to clean and inspect the small screen manager down inside of the bottom of the FFM. That is a last ditch screen that gets forgotten about.



I have my homemade TM cranked up pretty good I expect as it accelerates 0-100km in about 10.5 seconds, if I cranked it up too far, it would give me an overboost code right? I've floored it going up hills to try and trip a code to make sure I'm still good. It's not really making any turbo noise on the highway cruising only when accelerating.
When you reach approx. 12psi. of boost, the PCM is programmed to light up the CEL and set an over boost code and put the engine into limp mode to protect things.
If you are using a Manual wastegate controller (turbomaster) then you must have a Boost gauge to monitor things..


The GM-X Turbo does not make a lot of noise, so what you described is normal.







My glow time is always around 6 seconds regardless of temperature, and always does the afterglow cycling. Is that normal?
That is normal..
You can also do the manual glow plug override mod to help extend glows a bit.
http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/340695-how-glow-plug-override.html
 

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Discussion Starter #8
Do I have to use a boost gauge that's $60-$100? Or can I buy an $8 0-100 PSI gauge for a pump? From what I understand it should read 0 at idle anyway. That'll be next weekend's project I think. I would like to see what kind of boost I'm making.
 

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Do I have to use a boost gauge that's $60-$100? Or can I buy an $8 0-100 PSI gauge for a pump? From what I understand it should read 0 at idle anyway. That'll be next weekend's project I think. I would like to see what kind of boost I'm making.
As long as you get an accurate,working Boost gauge it don't matter...
 
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