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I don't know why nobody else has mentioned this yet. There is a strainer filter at the fuel inlet inside the tank. The strainer can get clogged and won't flow any fuel. You can remove the fuel line at tank side fitting of the LP and blow air really hard into the fuel line. This will temporarily unclog the strainer.
 

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Discussion Starter #42
I've been wondering about what's the inside of the tank looks like condition wise...I'm still considering replacing the lift pump. What should the flow look like out of the bleeder valve? Should it be a forceful stream or just kinda run out?.

Are there any other suggestions on what could be causing my problem?

One other thing that I did notice is that the truck seems to top out about 60-65mph and then feel like that's all she's got.
 

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R.I.P. Sam
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I don't know why nobody else has mentioned this yet. There is a strainer filter at the fuel inlet inside the tank. The strainer can get clogged and won't flow any fuel. You can remove the fuel line at tank side fitting of the LP and blow air really hard into the fuel line. This will temporarily unclog the strainer.
Never seen one, is it something people pull out to syphon?
 

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OK so. I replaced the return line plug. I test drove it. It did much better for the first hour then the problem came back. So here is a list of what I know.

1. The lift pump flow and sound are fluctuating. When its noisy as hell the flow is pretty good not gushing but I would assume OK, but when the sound calms down so does the flow, down to a gentle trickle out of the water outlet.

2.I'm getting no fuel from the air valve on top of the filter housing.

New OPS. New lift pump relay. Full tank of fuel. Diesel clean additive ran through previous tank.

Symptoms- mild sporatic bucking or jerking.

When on flat land power is OK but when on incline truck downshifts bogs with pedal to the floor and dies. 3 or more attempts to get started, once idling I check fuel flow out of water valve and nothing not a drop. I let it idle for a couple more seconds and get diesel out of valve.

PLEASE HELP IM STUMPED!
Sounds like the lift pump is dying slowly
 

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Mad (Sean) Max
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Yup sounds like a dying lift pump. Electric lift pumps making any real noticeable sound are an indicator that they are on their way out.
 

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Let's take the Truck!
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OK so. I replaced the return line plug. I test drove it. It did much better for the first hour then the problem came back. So here is a list of what I know.

1. The lift pump flow and sound are fluctuating. When its noisy as hell the flow is pretty good not gushing but I would assume OK, but when the sound calms down so does the flow, down to a gentle trickle out of the water outlet.

2.I'm getting no fuel from the air valve on top of the filter housing.

New OPS. New lift pump relay. Full tank of fuel. Diesel clean additive ran through previous tank.

Symptoms- mild sporatic bucking or jerking.

When on flat land power is OK but when on incline truck downshifts bogs with pedal to the floor and dies. 3 or more attempts to get started, once idling I check fuel flow out of water valve and nothing not a drop. I let it idle for a couple more seconds and get diesel out of valve.

PLEASE HELP IM STUMPED!
1.You have a new lift pump on hand install it and see what results are.
2. I believe your lift pump runs off the ops circuit like 94&95 6.5 diesel so the ops will burn out because amp draw so ops lp circuit with a separate relay modification is necessary if so. LP "relay" only powers during cranking until oil pressure builds then ops take over task.
So... You replace the ops, did you buy ACDelco part or other? Some off brands bwd, other store brands are junk out of the box might as well put it in a pipe and try to smoke it.
You have a ffm? Sorry i didnt read everything but they need to be clean also a screen at bottom.
3. I strongly suggest you check your diesel fuel cap and drop the tank to inspect or replace the strainer (ACDelco ts1012 if needed) and dont blow air. You have a fp gauge? LP may struggle to death if restricted. Try breathing through a red coffee straw and get back to us.
 

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Discussion Starter #48
The only OPS in town was a Borg warner but they put a lifetime defect warranty on it soooo I will hold them to that.

ffm? Fuel flow meter? Sorry kinda rusty on my acronyms.

I will be replacing the fuel pump today and will post the results. What's the easiest way to prime it afterwards because I know it's bad for them to work dry?
 

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Let's take the Truck!
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The bwd needs to be replaced with acdelco.

If you have the FFM at the rear of the intake click here http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/224943-need-part-buy-parts-cure-fuel-leak-2.html

If you have the model 80 box excuse my ignorance of 93 6.2 :HiHi:

Fuel cap info
http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/42338-reference-material-fuel-cap-4.html#post676819

heres some sock action
http://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/637953-our-1995-chevy-suburban-3.html#post6620705

Far as priming the line maybe mighty vac. The LP is designed to allow fuel to be sucked through forward even if its inoperable. Someone else may have a killer tactic.



After frequenting the boards for awhile, you’ll notice there seems to be a few things that come around, and around, and around again. One of those things is the Lift Pump, official title: Fuel Lift Pump. So, what is a lift pump, and why does it lift fuel? The lift pump is an in-line fuel pump mounted on the frame rail under the driver’s seat. This is a small electric pump that “helps” bring fuel out of the tank and up to the injection pump. This is to help prevent the expensive injection pump from having to “suck” it’s own fuel all the way up from the tank, which it can do, but can cause damage to itself and it's driver module - more on that in another section*.

Now, that’s pretty straight forward isn’t it? So, why so much fuss about a lift pump anyway? Only because it causes so many issues* when it’s not working.

Will my truck run without the lift pump? Yes it will. How well? Well, to some it will be very noticeable when it’s not working. Some may not even notice.

If I don’t notice that my lift pump isn’t working, I’m okay right? Not exactly. That means that your expensive injection pump is doing all the work in the fuel system. This is NOT a desirable thing. Plus you are setting yourself up for problems*.

How can I tell if my lift pump is working? Do the famous “lift pump test.” How do you accomplish this highly scientific experiment you ask? Very simple. Pop the hood - you’re half way there. Find on the front top of the engine the thermostat housing. You should see a little T-handle valve standing proud there in front of you. (If you have a van, you’ll have a schrader valve down deep behind the oil fill) That T-valve is calling your name saying “turn me.” Pay attention, ‘cause there’s a hose on the end of the T-valve. That hose should have diesel fuel come out of it when the engine is idling and you open the T-valve. When you open the T-valve and the engine is idling, and no fuel comes out, you’ll hear your engine cough, sputter, and die within 30 seconds. If it doesn’t cough, sputter and die with the T-valve open and no fuel coming out, something is plugged up in your fuel system between the fuel filter cannister and the t-valve, perhaps even inside the fuel filter cannister.

If the engine does die, it has emptied the fuel cannister and run out of fuel, so you will need to close the T-valve, then troubleshoot and repair the lift pump system, as follows in the text below.

Now, if you get a continuous stream of fuel out the hose, then close the T-valve and open the plastic air-bleed valve on the top of the metal filter cap - if fuel spurts out there, then congratulations! You are the proud owner of a working lift pump. Not everyone is as blessed as you are at this moment. If you're not, keep reading.

To those not as blessed, pickup reading here. You must determine why you have no fuel supply coming to your injection pump. There are two main culprits to the demise of a lift pump. Either it’s out to lunch, or it’s in the morgue. See, one means it still might work, the other means it’s dead. How do you tell? Check to see if it has power.

First, find the lift pump under the truck. With the engine idling along, pull the plug for the lift pump. You can either use a test light, or a meter to see if you have voltage at the pins. Make sure you get a good connection, otherwise you may condemn the wrong thing. Sometimes it is difficult to get a probe to meet up with the pins inside the plug, so make double sure you’ve got it.

If you have voltage, *chances* are you have a dead lift pump. Not always, but could be a dead lift pump. You may have voltage present under a "no load" condition. This means that voltage may be present when the lift pump is not attached to the circuit, but once the lift pump is connected, the load exceeds the amount of power the circuit can provide because the OPS contacts are creating a high resistance. For more information on this see this thread on electricity and how it can affect your voltage readings with loads and no-load situations.

Now, if you don’t have voltage, you’ll have to verify upstream from there why there is no voltage present. What is upstream? The infamous OPS (Oil Pressure Switch), or fuse.

What does the OPS have to do with the lift pump? Doesn’t sound right does it to have oil pressure tied to fuel does it? Well, some think that it is a fail safe that in case your engine ever lost oil pressure, it would shut off the lift pump so that engine would stall. Guess what? If you read a little bit ahead of this paragraph, you’ll find 'dat ain’t so'. The real reason why this circuit even exists is because of an accident. In case you should be in a wreck, the last thing you would need is to have your lift pump going to town pumping out that precious, expensive, fuel all over the accident scene. After all, should you be bleeding and having a thumpin’ head - the last thing you’ll be thinking is “Hey, I just paid $2.50 a gallon for that, somebody get a shop-vac!”

Why would the OPS not allow my lift pump to work? Well, from time to time, or shall we say in the corporate world, from dime to dime, some decisions get made. Some for the good, and some for the good of the keepers of the money. The OPS has a set of contacts inside to power the lift pump. This set of contacts are not heavy enough to carry the pathetic amount of current to the lift pump. Sad, I know, but true. So, what ends up happening is your lift pump works fine, but the OPS gets smoked, and then it quits. You think the pump is bad, but it’s not.

Can I just eliminate the OPS? Well, be careful, it is a safety device in some people’s eyes, and to the rest of us, a pain in the rump. Eyes, rump, pick your part. Anyway. If you just “jump past” the OPS, then your pump will run all the time. Not just all the time, but ALL THE TIME. Christmas and Easter included. It will stop when your batteries are dead. Because, while you are grocery shopping, that pump is running. While you are down for a long winter’s nap, it’s pumping. Doesn’t matter if the key is on or off, it’s pumping.

You can make up another circuit and repower it some other way, but be careful how you do it. Some methods have kept the truck running after the ignition is shut off and keys in pocket.

Back to our little friend the lift pump.

The lift pump may fail in a variety of different ways. It may fail “open” meaning that the coil driving the pump no longer has continuity. It may fail mechanically where it is just frozen and nothing moves. It may even (not as often) fail to pump. This means, it makes noise, but doesn’t actually pump.

Does the lift pump make noise? Yes it does. The model year of your truck will determine if your lift pump is powered during the Wait To Start period. That’s the time where that light is on before actually starting your engine. '96-up OBD2 models pre-run the lift pump during WTS and during START, '94-'95 OBD1 models pre-run the lift pump only during START.

The lift pump is characterized by a kind of “purring” noise heard beneath the truck. That noise is quickly drowned out by the engine, once started. When you shut your engine off, you will hear that pump run briefly, maybe only a quick second or two. If you shut your engine off when cold, you will hear the pump run much longer, sometimes up to 30 seconds or more.

A loud clacking noise would indicate no fuel from the tank, or the lift pump is failing or failed - it will run without pumping fuel when the one-way valve(s) fail.

A faint purring or vibration when touching the lp body indicates it is running, but the internal valve-shuttle armature is stuck due to mechanical failure.

So what kind of problems will it cause if the lift pump isn’t working? Many. It will cause all sorts of fuel related issues*. It can be some of the following:
°Stumbling
°Hard Starting
°Lack of Power
°DTC (Diagnostic Trouble Codes) on the Computer
°Stalling

There are be other* issues too, but these seem to be a very (un)popular list.

Where do I get one of these? Some of our site vendors, or any of the popular auto parts stores, or the dealership. More often than not, the auto parts store is a good bet for Ineeditrightnow.

Diesel Place tip: Ask for the version for the '93 6.5TD truck - it is a direct-fit HD replacement that will supply increased fuel pressure and volume to the Inj Pump, which is a good improvement for the '94-up EFI trucks.
FYI: don't mention that you have a '94-up truck, or you will just confuse the parts guy\gal - just describe your truck and drivetrain as a '93.
The ACDelco or Delphi lift pumps are the best replacement, which you can get from O'Reilley's or NAPA , and some of the site vendors, such as Heath Diesel.
Also FYI: the parts-guy\gal may call it a fuel pump.

Are they difficult to change? No - loosen the tubing-fitting nuts on either end, remove and reinstall. Now, if it were only really that easy. Let’s get real here, no camera out-takes…. You’ll end up getting a Diesel bath. You see, depending upon how much fuel is in your tank, there will be fuel that wants to come out of the fuel line. Be ready, because your chances of a date after changing that lift pump dwindle a bunch, unless they are really into the smell of a Diesel cologne. J

After the successful fuel lift system repair you will need to refill the fuel filter cannister - after opening the air-bleed valve, which is the plastic nut on the very top of the metal cap, power up the lift pump, then close the air bleed when the bubbles stop and fuel begins spurting out - if you still get no fuel, you likely have a stopped-up fuel filter - no need to tell you what to do in that event, right?
FYI: after successful fuel flow out the air-bleed, the engine may take a while to restart and run as the Inj Pump begins to draw fuel from the filter, fills internally, then starts pump-up to 1900psi injection pressures.

This is at least enough to get you started on your lift pump journey. If you have any specific question, feel free to post them by starting another thread. We’ll be glad to help you out.
 

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Ex- 6BT Square Body Man
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I'm having one hell of a time getting it to not leak. The new hose outer diameter is bigger making it impossible to get a clamp on it. I cut 1" off of another return hose but now the clamps I bought are to big. Heading back to the parts store to try again.
I have seen people use mini zip ties to hold the lines on also.

Another option is Tygon hose from a chain saw or lawnmower shop.
 

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R.I.P. Sam
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32,078 Posts
Most parts stores don't sell the correct sized hose, so I don't agree with a lotta suggestions for improvisation. The correct newer hose is thicker, but its internally barbed so the clamps arn't needed.
From my experience, trying to find small hose clamps at a part store is near impossible as well. They probably have it listed under something specific, and have no :idea: where to look.

This is the made in Germany stuff, with sizes on it, in a roll, not the precut junk. It is the same stuff for VW TDI's and Mercedes, so that is probably something to look under at a local part store. 3 5mm Diesel Fuel Injector Return Line Hose Made IN Germany 1 Meter Ships Fast | eBay

$(KGrHqQOKk!E1u+duTnMBNr7,-swoQ~~_12.JPG

$(KGrHqMOKm4E1T6VTMClBNkqSyusDQ~~_12.JPG
 

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I have seen people use mini zip ties to hold the lines on also.

Another option is Tygon hose from a chain saw or lawnmower shop.
I used something similar to replace rotten injector return lines. I went a size smaller and let the hose sit in the sun to warm up so it would stretch a little more and used needle nose pliers to pre-stretch the ends. It was a PITA to get installed, but it did not leak in the 6 or so months that it was on there. Also required careful use of a razor blade to remove. I would have kept it longer, but I have a set of new delphi injectors and new return hose to install with my rebuilt IP.

Also, I had good luck using a small 12V compressor on the return line to pressurize the tank slightly and prime every thing to the IP. If you use too much pressure you could rupture a line somewhere.
 

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Most parts stores don't sell the correct sized hose, so I don't agree with a lotta suggestions for improvisation. The correct newer hose is thicker, but its internally barbed so the clamps arn't needed.
From my experience, trying to find small hose clamps at a part store is near impossible as well. They probably have it listed under something specific, and have no :idea: where to look.

This is the made in Germany stuff, with sizes on it, in a roll, not the precut junk. It is the same stuff for VW TDI's and Mercedes, so that is probably something to look under at a local part store. 3 5mm Diesel Fuel Injector Return Line Hose Made IN Germany 1 Meter Ships Fast | eBay

I work at Autozone and found those pesky clamps one day while cruising the aisles, couldn't believe we had them. I have used and would recommend the self sealing German hose though.
 

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Let's take the Truck!
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Although those dorman pinch clamps Look Ok I can vouch that they are near useless. The small ears that you grab with pliers quickly straighten out or break off rendering them useless. They quickly loose their spring. Better off buying 1/4 pinch clamps in the plumbing dept. when youre in a "Pinch" Better yet buy the correct hose and end plug / clamp kit Delphi makes a nice kit for around $25. Before I knew any better I bought those dormans and quickly threw them in the trash where they belong. More beneficial to spend your $7 on cheeseburgers imo.


I would buy a Delphi kit which many vendors seem to sell in a repackaged offering by looking at pictures or this from badger in Wisconsin. Hmm his kit says that the end caps included DO Not require clamps which I never noticed. I have a spare delphi kit on hand and just ordered one of these to check it out. http://pages.ebay.com/motors/link/?nav=item.view&id=281585255949&alt=web

From the ebay KRServices (Badger Diesel) listing:
"This is a return line kit for any 6.2 or 6.5L turbo or non turbo GM diesel engine. This kit includes more than enough line to do the full job with 8" of line per injector rather than the 3" that the competition offers having only enough to barely do half the job. Thats 266% more line! This kit includes 64 inches of line and 2 caps for the end injectors. Neither of these items require those troublesome clamps put on by the factory because they are made out of a special material that seals onto the injector. This is not the cheap chineese stuff that I see listed on here for a similar price and can be identified by the yellow stripe on the side of the line, this comes directly from Germany. If you put the cheap stuff on it will become brittle and crack in only a few months. I am able to offer this at a low price because of low overhead and factory direct ordering, not cheap material cost. If you have any questions feel free to ask.

If you have any problems with this line in the first year due to manufacturers error I will send you another kit or refund your money if you prefer that! I fully stand behind my products and wouldn't waste my time and reputation if it were junk"
 

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Let's take the Truck!
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I actually traded my 79 gasser for the 84 6.2 because I just couldn't keep away from these old diesels :HiHi:
Yes and about time btw:HiHi:
 

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R.I.P. Sam
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32,078 Posts
I work at Autozone and found those pesky clamps one day while cruising the aisles, couldn't believe we had them. I have used and would recommend the self sealing German hose though.
Awesome Floyd, I have asked at a few parts stores, nothing as such carried. Unfortunatly its Dorman, quality will be iffy. They look cheap, JC added his experience. :(

No one should hold working at AutoZone against you, your still OK. :HiHi:
 
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