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Discussion Starter #62 (Edited)
Fuel Systems Learning Curve

Issues with the fuel system can be summed up - bad OPS, questionable lift pump and primary LP relay, worn out seals and hoses.

The fuel system issues were a pain to drive around with for so long but it helped me to learn more about what to look for.

Symptoms:
- Normal start when cold or sitting over 4 hours or so
- No check engine light or error codes
- Hard starting after hot
- Fish biting, stumbling and hesitation under WOT or load
- Engine dies randomly
- No white smoke
- Sometimes black smoke under WOT with fish biting
- No air bubbles in the fuel lines

The Fix:
- Fuel tank sending unit replacement as tubes were rusted and fuel float sensor was shot (wild gauge below 1/4 tank)
- In tank fuel sock replacement
- Rebuild the FFM
+ Remove all the buildup in the FFM
+ Replace the fuel strainer in the FFM
+ Replace both o-rings
+ Replace all the lines into and out of the FFM as they were shot
- Replace the failing OPS
- Replace the questionable lift pump with a higher capacity
- Replace the questionable fuel pump relay in the under-hood electrical center

Why all the parts?
1. Primary goal to increase reliability as I may be heading out of state for work, needing a worry free truck
2. Discovered many of the parts had been recently replaced by PO with low quality parts
3. Discovered many of the parts needed to be replaced as they were worn out or broken

Things Learned:
- Because of a plugged in-tank sock, and low quality OPS & LP, it caused primary fuel system to fail in delivery of fuel necessary for feeding IP fuel demand
- After replacing the sock and sending unit, fish-biting\stumbling continued

- Truck basically passed the lift pump test at idle & at operating temp
+ When checking the lift pump at idle, it was always running
- After the truck had ran for while under load, the symptoms would appear
+ Basically the FFM would be de-fueled as the OPS and LP were not able to provide sufficent fuel to the FFM & IP (is and has been my working opinion)
+ Seems to be a heat & running under load (vs. idling) that causes the OPS to stop working
+ When checking the lift pump after running under load, the lift pump does not stay on and runs sporadically (tested by putting hand on the pump and feeling for normal running vibration)
- When truck was running poorly or shut off, could prove de-fueling of the FFM each time by opening the FFM; a hiss was heard each time, indicating a vacuum
- If I didn't open the FFM after de-fueling, the truck was hard to start or would not start at all
- Using a piece of wire to jump the fuel pump relay in the under-hood electrical center is the best way to keep the lift pump running with a failing OPS
+ Replacing the lift pump, OPS (with an AC Delco) and doing the OPS relay modification corrected all the issues

Other Things Learned:
- My working opinion that the stock design of the electrical system supporting the OPS & LP in 94/95 trucks contributes to premature electrical failure of the OPS & LP. Failure of these contributes to stress and premature failure of the IP over time.
- The OPS relay mod is a must for increased IP life on 94/95 trucks
- Good OPS seems to deliver better oil pressure to the dash gauge
- Healthy primary fuel system makes the truck run better and sound different
- Taking the fuel screen out of the FFM can be a challenge without fancy tools
- A low budget way to get the screen out can be done with (2) zip ties :HiHi:
 

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Discussion Starter #63
Might be cheaper to replace the whole FFM, rather than just the fuel heater.
Yep this is true. I'm contacting guys I know that have replaced their FFMs with something else to see if they want to do some horse-trading or something for a reasonable price as money can be scarce these days.

That being said, I'm glad I stockpiled some parts for a later time before my job was gone. I just didn't make it to this one. :HiHi:
 

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Discussion Starter #64 (Edited)
USB to ALDL (OBD1) Cable Construction

On the to do list is the USB to ALDL cable for OBD1 communication with tools like GMTDScan and others.

Last year I thought about building my own and looked into how to do it. I wanted a setup like the DIY by neel2008 based on the FT232. The FT232 is a great platform for high quality interface from legacy serial connections to modern USB. Genuine FT232 are the only way to correctly communicate with Cisco and old embedded manufacturing tools.

Previous experiences with knockoffs and counterfeit devices lead to months of troubleshooting and frustration at work and I knew I wanted a dependable connection. I had my mind on a little more simplified setup then the great one by neel2008.

Then last week the owner of the FT232 design released a software update that turned many counterfeit devices into paperweights. (Link to this issue here) This move brought the USB to OBD1 cable back to the forefront. Work began on it again to have a simplified setup based on genuine parts for a few dollars more with the added peace of mind.

The results are great as I have completed testing with GMTDScan Basic today. :thumb:
 

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Discussion Starter #65
Just Made My Day!!!!

Sometimes people can still blow you away with an act of kindness! Today someone did something really nice that I won't forget! Thanks so much being so kind!
:clap: :bounce: :bow: :thumb: :coolnana:

Hope you all have had a great day and hope you have an opportunity to be kind to someone around you or even a stranger! :bounce: :thumb:

Happy Halloween!
 

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Yep this is true. I'm contacting guys I know that have replaced their FFMs with something else to see if they want to do some horse-trading or something for a reasonable price as money can be scarce these days.

That being said, I'm glad I stockpiled some parts for a later time before my job was gone. I just didn't make it to this one. :HiHi:
I yanked my ffm from my 94. I have it sitting in unknown condition. Truck has 120, 000 miles so im guessing original stuff. Is there a way to test the heater in it? I dont need it.
 

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Discussion Starter #67
Maybe do a continuity test then an Ohm test. Does any one know how many Ohms a healthy heater should have?
 

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Can you apply 12V to it and see if it gets hot? Don't do it too long without a load to absorb the heat.

Sixto
97 C2500 burb 187K miles
 

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Ill give that a shot. Since its 55 outside I suppose it should heat but ill have to bring it in the house for the first test.
 

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Discussion Starter #71 (Edited)
Can you apply 12V to it and see if it gets hot? Don't do it too long without a load to absorb the heat.

Sixto
97 C2500 burb 187K miles
Ill give that a shot. Since its 55 outside I suppose it should heat but ill have to bring it in the house for the first test.
According to the shop manual, to test the heater, it needs to be 46F or lower. If testing in the FFM, it needs to have fluid in it (no dry testing?) or if testing just the heater, submerge in ice water.

Mine works but with sparks because the wire is shorting out in the FFM and the RTV "patch" I did in the summer was removed when USLD was leaking from the FFM :thumbsdow

Now the FFM seals are fixed, and will have to keep the heater unplugged as my wife dosen't like sparks in the engines of her trucks. :HiHi:
 

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Discussion Starter #72
Happy Friday! Links to links

Hello, happy Friday to everyone! Hope you 6.2s & 6.5s are running strong!

Have been off on a tangent, researching Suburban 1500 vs 2500. Compared to the pickup trucks, Suburbans really do have their own options.

More about the 1500 vs 2500 here at http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/672585-1500-2500-suburban.html

During the research, I came across a lot of PDF manuals for our trucks and Burbs here at PDF of Square Schematics & GM Training Manuals - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Today the front brakes let me know they are toast. Tell me what you think about brake & rotors here http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/674890-whats-your-experience-front-brakes.html
 

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Discussion Starter #73
Last weekend was awesome when some one gave me an expensive tool for nothing and this weekend premium brake rotors for cheap!

Again I am blown away!
 

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Discussion Starter #74 (Edited)
Progress!

It's been awhile... found a job and now its time to get the Burb back on the road. :coolnana:

Where we left off is the front brakes were shredded due to bad calipers with stuck pins & pads and an overall neglected brake system.

Much time and careful spending we were able to gather all the parts together for the repair. This weekend it all came together finally...

Info for now, pictures when I can dig them out of the camera in a day or two..

Front brakes have been completely redone and the truck is back on the road. To recap cost, part numbers and materials: :coffee:

Parts & Materials
- (2) EBC rotors UPR7191 - both $68.54
- EBC Ultimax2 pads UD370 - $47.98
- (2) AC Delco Pro Durastop Remanufactured Calipers 18FR741 & 18FR742 - both $46.84
- (2) Raybestos Hydraulic Hoses BH38662 & BH38663 - both $12.80
- (2) National wheel seals 4740 - both $5.25
- (2) Cotter pins - both $0.06
- Permatex Anti-Seize Lubricant 80078 - $7.49
- Permatex Silicone Lubricant 22058 - $5.47
- Super Tech DOT 3 Brake Fluid, 1 Gallon 001050305 - $14.67
- Valvoline Multipurpose Grease VV614 (NLGI 2\GM 1051344) - $3.47
- Brake
- (3) Super Tech Non-Chlorinated Brake Cleaner 001048578 - $2.97 each
Total parts and material cost: $221.48

Tools
- Penetrating lubricant
- Rags & paper towels
- Gloves
- 14 mm lug nut wrench or socket
- Jack
- Jack stands
- GM panel removal tool to take out the splash guards
- 3/8 hex for calipers pins
- Small & large flat screwdriver
- Needle nosed pliers for cotter pin & hydraulic line clip removal
- Channel Lock pliers for seating the wheel bearings
- C-clamp or brake caliper piston tool
- Hammer and wood block for driving the inner wheel seals flush into the rotors after repacking the inner wheel bearings
- Brake bleeder kit with 3/8 I.D. hose
- 150 & 120 grit sand paper
- Wire brush & wire wheel
- Oil pan to catch brake fluid
- 9/16 line wrench for hydraulic brake hard line
- 16 & 17mm wrenches for hydraulic brake flex line
- 10mm wrench for brake bleeder screws on the calipers
- 11mm socket and ratchet for banjo bolt
- 13mm socket\ratchet and wrench to remove the hydraulic brake line support and wheel speed sensor
- Torque wrench
- Torch

Notes in general order of operation:
- Get info from videos like the ones below; Know what you are getting into before you're in it up to your eyes
- Acquire and check all parts first BEFORE starting ~ Somehow ended up with two of the same side calipers and the wrong size wheel seals
* Suburbans are weird when it comes to brakes, suspension and drive line parts ~ VIN on my Burb says its 1500, but the door badges say 2500 - Brake part options are 7200 lbs, 8200 lbs (rare), 8600 lbs or more :think: :Insane: :uhoh2: :duh:
~ My 1500 VIN\2500 badges, 9" rear 3.42 semi-floating axle Burb used all 8600 lbs. (2500) brake parts :think: :Insane: :uhoh2: :duh:
~ Local parts store computers tell service clerks all the parts for a 2500 Suburban use 7200 lbs. (1500) parts! Had to bring originals and compare, then cross check with Rock Auto and other sources :think: :Insane: :uhoh2: :duh:
~ Final authority on parts for your GM truck\Suburban is AC Delco parts check by VIN here at ACDelco Parts ; Wish I would have found this site sooner
- Hit the ends of the hydraulic hose hardware with penetrating lubricant a couple of times the day before they are replaced
- If replacing rotors, check the new rotors for leftover casting sand and clean each one before starting
- Work on one side at a time to completion as it is easy to mix up parts
- After the wheel is off, remove the splash guards to avoid destroying them during the hydraulic brake line replacement
- Apply anti seize and silicone lube to the pads and pins BEFORE starting the removal of old parts
- Load the brake calipers with brake pads BEFORE starting the removal of old parts - this will keep the grease and grime off the new stuff
- If replacing the rotors or turning them, now is a good time to complete this task, before messing with the calipers & hydraulic hoses
- If reusing your wheel bearings, completely clean them and thoroughly inspect them for damage as bad ones will void the warranty on your new expensive rotors, calipers and brake pads if they fail
- Pack\repack your wheel bearings with NLGI spec 2 grease (see Eric the Car Guy's video on how to do this below)
- Wheel seals and cotter pins are cheap, replace with new
- Good and cheap source for cotter pins and copper crush washers is Harbor Freight if you don't have $14 or more to buy a set of "genuine" new parts at the auto store
- Fill the brake fluid reservoir and replace the cap BEFORE opening the brake lines to slow fluid loss and prevent running the master cylinder dry
- Having a 9/16 line wrench is a must for replacement of hydraulic hoses
- Using the 9/16 line wrench with the 16 or 17mm wrench will make removal of the flexible hydraulic much easier
- Break the hydraulic lines loose BEFORE removing the hydraulic line clips
- Break the banjo bolts free BEFORE unbolting the calipers
- Reuse the banjo bolts as the ones provided with the rebuilt calipers did not fit :think:
- If reusing the banjo bolt, check for stuck copper crush washers and remove before reusing
- If reusing the banjo bolt, check that the hole is clear
- Copper crush washers can be reused by heating them with a torch until glowing (annealing)
- (2) copper crush washers are required for each caliper to connect\seal the flex hose and banjo bolt to the caliper
- Replacing the hydraulic flex hoses can take some time, check the fluid reservoir before and during replacement
- When connecting the hydraulic flex hose to the hard line, turning the nut on the hard line offered quite a bit of resistance as this is a pressure fitting ~ This was normal for both sides and may feel like it is cross threading as it did not turn easily by hand
- When the hydraulic system is back together, gravity bleed the caliper by opening the bleed screw ~ this will make bleeding easier
- After the hydraulic system is back together, check for leaks with a bright light by having a helper press on the brakes with the engine off ~ Don't be surprised if the connection between the hard line and flex line leaks; Had to tighten these more than what is comfortable with regular bolts and nuts
- For my setup with EBC components, they recommend easy braking for the first 1000 miles to bed the pads and rotors

During this segment of my project, learned that I'm not a fast brake person... for me, slow and steady won the race as it took me over 4 hrs to complete both front wheels. The notes above come direct from my blunders, so maybe you will have a quicker turnaround. :HiHi: Then again this is the brake system and getting it right is more important than getting it done quick especially when lives depend on it. :bounce:

In the end the brakes are much more responsive and no more grinding :thumb:

Helpful wheel bearing document and video links below

Eric The Car Guy

- Replacing Rotors with Tapered Roller Bearings https://www.youtube.com/watch?v=ccsbu2hT0MI

- How to Spot and Service a Stuck Rear Caliper https://www.youtube.com/watch?v=urK2EsZn4pQ

- How To Replace Brake Hoses https://www.youtube.com/watch?v=iE9LM1ppR6g
 

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Discussion Starter #75 (Edited)
Brakes are great, but the SES light would come on during trips to and from work. GMTDScan tells me DTC 35 & 36. Did complete troubleshooting on the whole fuel and engine electrical system. Everything points to a bad PMD right down to the strange smell of the PMD itself.

The SES and DTC errors got more and more frequent until last Friday night the truck died on the way home. Got it off the road safely, restarted it, got to the house and parked it. Monday morning, it started up, ran for about 10 seconds and the engine died. It will crank but no start. :bawl:

My Stanadyne 39405 is toast :bawl:

If there is something to learn, its to get the PMD out from under the hood ASAP. When we bought the Burb last year the PO had it on an extension cable mounted to a large heat sink, under the hood near the ABS module. It was moved to the bumper but the damage was already done.

A new D Tech is on the way with a # 5 resistor. :thumb:

In the mean time, all the interior door handles broke and you had to pull the door open from the outside handle. :HiHi: Replaced both front door handles and will finish up the backs tomorrow, weather permitting.

After that if nothing else goes, need to get: (no particular order)

- Set of tires (suggestions?)
- Fix AC (leak somewhere as it will not hold refrigerant)
- Get the headlight relay kit to take stress off the difficult to replace multifunction control lever on the steering column
- Clean up the aging headlight lenses
- Replace the windshield wiper arms as they are not stock (got 2 14" wipers currently :think:)
- Find out why no fluid to the windshield thought he pump runs :think:
- Transmission fluid and filter change (not a flush)
- Oil cooler lines
- Rebuild the front suspension\bushings (Energy Suspension & Moog Problem Solvers?)
- Shock absorbers
- Replace the speakers
- Battery cable upgrade
- Glow plug cable upgrade
- Look into a possible power steering leak
- Fabricate the mount & install a primary fuel filter between the fuel tank and FFM
- OPS extension tube
- Seal the inside of the fuel tank stopping the corrosion found last year when replacing the fuel sender and diesel sock
- Find & install a K47 air intake\filter
- Replace the brittle insulation under the hood
- Check the rear brakes
- Install CB radio
- Install inverter
- Replace both mirrors (outer shells are shredded & the glass is foggy)
- Fix the front door retainer springs
 

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Wanted to give you a big THANK YOU, because I used your thread and pictures to go off of for dropping my fuel tank and deleting my fuel sock this past weekend. Your instructions made it that much easier. If I had to do it again, I could do it in half the time now.

Also installed an inline WIX filter before the lift pump. This is temporary until I can gather up the rest of the parts for my FTB system deleting the stock FFM altogether and go 3/8" braided -AN lines all the way from tank to IP.
 

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Discussion Starter #78
Wanted to give you a big THANK YOU, because I used your thread and pictures to go off of for dropping my fuel tank and deleting my fuel sock this past weekend. Your instructions made it that much easier. If I had to do it again, I could do it in half the time now.

Also installed an inline WIX filter before the lift pump. This is temporary until I can gather up the rest of the parts for my FTB system deleting the stock FFM altogether and go 3/8" braided -AN lines all the way from tank to IP.

No prob, glad it helped! :thumb:
 

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Discussion Starter #79 (Edited)
39405 you say? I know some folks who would like to inspect that toosted PMD, myself included if you dont mind?
Curious, if your IP has the updated harness (grey connector) or not?
Anyway.. Gladly pay S&H to 67401, LMK..

PUMP MOUNTED DRIVER (PMD) AND PUMP WIRING HARNESS FOR DS PUMP MODELS
Heavy, the autopsy on the 39405 is underway. Enlisted the help electrical engineer friends to help with this one. Hopefully will get some interesting info in a week or two.

The PMD extension cable has a grey connector, like the one in the picture of the Stanadyne technical PDF.
 

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Discussion Starter #80 (Edited)
New PMD arrived today and went in without a hitch. However the SES light is always on with fresh DTC 36 errors all day long :shake:

The new D Tech PMD shipped with a # 9 resistor installed. Tried the # 5 resistor with no effect on the SES... :thumbsdow

Looked over a few post, and it seems this is a common issue with various "fixes".

Any definitive solutions to squash this bug for good or did I get a bad PMD?

Should I get another Stanadyne 39405?
 

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