Rough Running

[NASFD35]

My truck is acting-up and I’m hoping someone can help me.
Under normal driving (not towing anything) the truck is fine. When I accelerate (e.g. on a highway entrance ramp or pulling a load up a hill), the truck acts like it’s starving for fuel. A feeling similar to a gas motor that has a “miss” or only 7 out of 8 spark plugs working.
I’ve changed my fuel filter with no relief. I have 2 remotes PMD’s one located in the bumper and one located off of the intake. I switched units and I’m having the identical problem. This is a 1995 TD. I also check the air filter, which is good.
Thoughts on what this could be? Or what I should check? Wastegate possibly?

[racer55]

Fuel starvation from an aftermarket sending unit sock or air intrusion would be a good guess.

Replace the IP fuel return line with diesel rated clear tubing and watch for bubbles when the engine idles.

Bubbles indicate air intrusion between the fuel level in the tank and the LP.

Also check for excess vacuum when yo remove the filler cap-the caps are vented for air entry as fuel is used and plugged vents cause similar symptoms,also if the cap was ever switched out for a gasser cap.

[NASFD35]

Ok….so I didn’t get much info on my first attempt, so I’ll try again with some new info.
The problem seems to be getting worse. I pulled our camper and after about an hour of driving the truck wouldn’t get above 35 mph, was sputtering like before, and was blowing white smoke. The wind blew smoke back into the cab and it was diesel fuel. If I turned the truck off for a few minute it would run for another 5-10 mile before the problem got real bad again.
I checked the turbo, and the blades spin freely.

Racer
There is no excessive vacuum from the tank…problem is still there when I drove with the cap loose.
I have not tried to replace the fuel return line as I’m not sure how to do it.

[Robyn]

This sounds like a failing Injection pump.
The fact that it gets somewhat beeter after sitting for a bit makes this seem even more likely.


The one subject I dont see discussed was, When Was The FUEL FILTER last changed ???????

A plugged filter can cause this sort of issue.


Let us know

Missy

[Warren96]

The fuel return line under question is located above the injection pump in front of the engine and is 6 or 8" long, its easy to replace temporarily with a piece of clear tubing, which will provide you with an indication of the fuels quality.Just don't leave it on very long because most plastics are not diesel rated and will turn to "mush" in a short time.

[oceanguy]

I would suggest a visual inspection of the fuel lines from the tank forward. I just had a very similar situation that progressed real fast. Felt like a fuel filter clogging issue and replacement seemed to fix it temporarily - then hesitation and low power returned. Pulled the plunger from the fuel shut-off solenoid and again seemed to work at first drive. Ended up being fuel lines near tank had corrosion and were visibly wet from fuel. If I had the clear fuel line to view, it would have saved me diag time but so it goes. Please post your solution when found. It helped me with finding my problem.:cool:

[NASFD35]

Robyn....The fuel filter was changed a few weeks ago….the problem has gotten worse since changing it. And yes, it does get better after it sits, but it also gets worse the longer you drive it. Could be a clog getting worse….could be an electrical component heating up or shorting out….

Warren96...Thanks for the info on the return hose…now I know which one hose we’re talking about.

Oceanguy....The fuel lines are all new. I replaced them about 6 months ago. I'll still do a visual just to be sure though.

I spoke with a diesel mechanic that’s known for his experience with the 6.5 TD. His suggestion was to put a fuel pressure gauge in as close to the injector pump as possible, drive the truck, and watch for a drop. Also suggested putting in a vacuum gauge in between the tank and lift pump as a way to check to see if the sock on the sending unit it clogged. I also have a wire harness for the lift pump that I plan on connecting to the battery to see it the sensors are failing.
Along with the sucking air/clear hose trick listed above, this seems like a good path to start with as a means to rule everything out before I go after the injector pump.
Thoughts?

[NASFD35]

Raise your hand if you said “air in the fuel line”!!! John…..tell them what they won!!!! :D
I placed a fuel pressure/vacuum gauge in the line just before the filter canister. I also put a clear section of hose in as suggested. I used the jumper wire for the lift pump and I started out with 7psi, but when I started the truck it went to 15 inches of vacuum. I was also able to see air bubble through the clear hose. I turned the truck off, used the jumper wire to bleed the air out off the filter canister, plugged the truck harness in and had the same results.
So, now my problem is 2 fold….where is the air coming from and where's the blockage....:confused:

[DmaxMaverick]

The (normal) restriction is the filter, but irrelevant. Once you get the air under control, the pressure should normalize. Air compresses, which allows the pressure to rise, but as soon a flow starts, it goes away. The pump doesn't like air, and won't make dynamic pressure unless it's gone.

[racer55]

Already mentioned that air in the lines tends to come from somewhere between the fuel level in the tank and lift pump-otherwise you would notice a fuel leak from pressurized fuel rather than where it is under suction.

Holes in the sending unit dip tube to anywhere along the metal lines or failed O-rings at joints can be the cause.

[NASFD35]

So….I fixed the problem. I used a 5 gal fuel and a hose to check each fitting from the lift pump back to the tank. Everything checked out. Pulled the sending unit out of the tank and the sock seemed to be clogged with what looked like rust particles. Cleaned the sock, put everything together, and took the truck for a ride and it ran like a scalded dog.
Now to figure out why the fuel gauge isn’t working…..

[rapidoxidationman]

Were you able to clean out the tank while the sending unit was out?

I'd be concerned with the remaining rust in the tank causing the same problem sometime down the road...

[DmaxMaverick]

If you are, in fact, seeing rust in the tank, cleaning it, or the sock, is only a band aid. Next stop is a leaky tank. Either find the source and fix it, or the tank will rust through. Tanks are expensive, but only a little more than a tankful of fuel and the towing bill from somewhere in Egypt.

[greatwhite]

Rust in the tank?

Time for a replacement.

The "sock" should have had a valve type arrangement in it that will go into bypass when/if the mesh is clogged up. If it's not there, someone has installed a non OEM "sock". That should also be changed while it's apart.

Tanks can be cleaned, but once rust has gained a foot hold it will only continue until the tank is trashed. Not to mention; if rust particles do manage to make it past the filter the IP is a goner in short order....:eek:

I only wish we could get poly tanks for these or better yet; extended range poly tanks....

[NASFD35]

If you are, in fact, seeing rust in the tank, cleaning it, or the sock, is only a band aid. Next stop is a leaky tank. Either find the source and fix it, or the tank will rust through. Tanks are expensive, but only a little more than a tankful of fuel and the towing bill from somewhere in Egypt.
I had the tank out of the truck for about 2 years, so that’s where the rust is coming from. The truck was going to the recycling yard, but I needed to put it back on the road. I didn’t see anything inside when I put the truck back together. When I take it back out I’m going to clean it and coat the tank. The question is, what do you clean the inside with?


Were you able to clean out the tank while the sending unit was out?

I'd be concerned with the remaining rust in the tank causing the same problem sometime down the road...
I’m concerned about an issue further down the road as well. I didn’t have the opportunity to clean the tank when I fixed it this time because of the amount to fuel left in the tank. I plan on running the tank down and cleaning it.

[NASFD35]

I only wish we could get poly tanks for these or better yet; extended range poly tanks....

http://www.autopartswarehouse.com/sku/Chevrolet/K1500/MTS/Fuel_Tank/1995/Silverado/8_Cyl_6-dot-5L/MTS2025.html

[NASFD35]

So, after cleaning the sock inside of the tank it seems like the problem is coming back. so I have a few questions.
(1) I'm thinking abour ordering a tank. Is there a difference between the Gas Tank and Fuel Tank?
(2) If I decide to clean out the tank, what should I use to clean it? And should I use something from Eastman.com to coat the inside of the tank?

[Warren96]

The inside of the tank is dirty from your fuel supplier.Take the almost empty tank off and look inside.One dirty load of fuel will keep plugging the sock.When i took my 15 year old tank off to replace it , mine was shiny and clean inside, it had a hole in it at the seam. It had rusted from the OUTSIDE in.

[NASFD35]

Ok….so it’s time to revive this thread….
After cleaning the sock the first time, the truck ran like a top. Now the problem is starting again. I really believe the problem is cause by debris in the tank or dirty fuel vs. rust inside of the tank. I opened the tank, looked inside and I don’t see the first hint of rust. The sock seems to be clogged again, so I went looking for another sock. NAPA didn’t have a stock part, but they think they could match one if they have the dimensions for the original.
I’m thinking about taking the sock off and putting an inline filter between the tank and the lift pump….
Thought?

[DmaxMaverick]

Removing the sock still doesn't solve the problem. You need to remove the tank and clean it. Fill with fresh, clean fuel. The sock shouldn't need replacement, and it seems to being doing well what it was designed to do. Unless it's damaged, just clean it and use again.

[NASFD35]

This last attempt at cleaning the sock wanted as productive as last time. It corrected the problem, but only slightly…

[phantom309]

Where you getting your fuel? I,m not sure what your temps are like,. but #2 fuel in chilly weather can cause grief,.

You are dropping the tank to clean the sock,. In my opinion you have air entering the fuel system,.and you disturb the connection/crack/hole etc,.

Pulling off the sock and adding an inline filter would make life much easier for you if you have a debris problem,.an inline filter would take longer to clog up,.

best fix is to have the tank boiled out at a rad shop,..

The smoking and poor performance certainly could point to bad IP,.

Nick

[racer55]

Where you getting your fuel? I,m not sure what your temps are like,. but #2 fuel in chilly weather can cause grief,.

You are dropping the tank to clean the sock,. In my opinion you have air entering the fuel system,.and you disturb the connection/crack/hole etc,.

Pulling off the sock and adding an inline filter would make life much easier for you if you have a debris problem,.an inline filter would take longer to clog up,.

best fix is to have the tank boiled out at a rad shop,..

The smoking and poor performance certainly could point to bad IP,.

Nick

We are not supoosed to encourage folks with the wrong sock or a collapsing sock to remove it and add an inline screen pre LP at this forum-even though it has been reported to be easier to maintain and takes care of the symptoms involved.

I and DmaxMaverick have gone around this pole several times before.

A clean tank with clean fuel is paramount.

[phantom309]

We are not supoosed to encourage folks with the wrong sock or a collapsing sock to remove it and add an inline screen pre LP at this forum-even though it has been reported to be easier to maintain and takes care of the symptoms involved.

I and DmaxMaverick have gone around this pole several times before.

A clean tank with clean fuel is paramount.

If my opinion encourages someone,. it's because they have made their mind up already,..

[racer55]

If my opinion encourages someone,. it's because they have made their mind up already,..

I like that quote enough to to steal it,err borrow indefinately.

[DmaxMaverick]

We are not supoosed to encourage folks with the wrong sock or a collapsing sock to remove it and add an inline screen pre LP at this forum-even though it has been reported to be easier to maintain and takes care of the symptoms involved.

I and DmaxMaverick have gone around this pole several times before.

A clean tank with clean fuel is paramount.

Not correct. I only discourage removing the sock, if it's being done as a "corrective" action. There's nothing wrong with replacing the sock with an inline filter, but it does leave the system more vulnerable to failure due to some other types of contamination. The problem I see, as in this situation, is it does NOTHING to address the original problem. If the sock is plugging, and plugs again after cleaning, something is wrong with the fuel. I've never heard of, or seen, a "failed" fuel inlet sock. Plugging isn't failing. If it's plugging, it's doing its designed function, exactly. A 30 micron (or even much greater) filter will quickly foul, if there's enough crud in the fuel to plug an OEM sock as quickly as is here. The only advantage is accessibility, but it still doesn't address the reason for doing it in the first place. If fuel or tank quality is an issue, it doesn't really matter what else you do. The problem is still there, and will cause other (more serious) issues, eventually. The tank, lift pump, lines, and fuel is the cheap end of the system.

[racer55]

I don't believe that a paper type inline filter is the way to go,I would much prefer that folks use an inline screen that is more inline with the sock/strainer style orifices.

I agree that the tank must be clean,but there is oft documented cases where the aftermarket sending units are being sent with the wrong strainer/sock that will collapse when the viscosity of the fuel thickens in colder temps-they don't have the proper size orifices nor do they have the structural stiiffness to stay expanded in the same conditions that a stock strainer will.

In those cases I do advocate re using the stock strainer on the aftermarket sending unit or installing an inline screen.

We have expressed our opinions more than once and I am tired of fighting about a prictical soloution to a problem created outside of detroit.

[phantom309]

a nice raycor filter with sediment bowl would be the best.

Nobody is fighting,. it,s just taking Dmax a while to broaden his thinking,.

[DmaxMaverick]

a nice raycor filter with sediment bowl would be the best.

Nobody is fighting,. it,s just taking Dmax a while to broaden his thinking,.

No "broadening". Take everything in context. My "thinking" is backed by extensive experience, and not just with my own equipment.

[NASFD35]

Well, the last 8 posts were enlightening…..Many comment made answered a few questions. Let me start by adding some of the things I’ve done.
(1) Everything from the lift pump back (with the exception of the tank) is brand new. Which makes me wonder if the sock on the aftermarket sending unit is part of the problem.
(2) When I cleaned the sock the second time, it wasn’t nearly as dirty the second time. I really think there WAS debris in the tank, but upon inspection last time I didn’t see anything in the tank.
(3) Last time I took the sending unit out, I emptied the tank. I ran all of the fuel through a coffee filter (the only fine thing I could think of) coming out if the tank and going back in.
(4) The original problem (which still exists) is bucking problem…like it’s running out of fuel. I used a pressure gauge all the way back to the tank….that’s where the gauge was reading a loss. All of the fitting and seals are in place; and connections are tight. In the absence of pressure and liquid, air is easily pulled into the system by the vacuum caused by the injector pump.
With all of that said, why would a screen be better than a paper filter? I would have though a paper filter would catch more particulates than a screen.

[DmaxMaverick]

"Better" is a relative term. They perform different functions. The original design and purpose is not to "filter" the fuel, and the lift pumps don't suffer from not having the fuel filtered. They die of other reasons long before contamination becomes an issue.

To begin with, any aftermarket fuel intake screen that is of a less quality or diminished performance does not "meet or exceed OEM specifications", therefore, is a defective product, marketed by less than honest suppliers. I do not include any part that may fall into this category in discussion, other than to discourage their use. An OEM quality screen, or nearly any part for that matter, will perform as designed with acceptable quality (in most cases--there are exceptions). If your screen isn't up to at least OEM quality and/or performance, it is defective, and does not meet or exceed OEM spec's. Either reuse your serviceable original screen, or replace it with a suitable part.

Now, the function of the screen isn't to "filter" the fuel to any reasonable degree. It will decrease the velocity of the fuel where it first enters the system from the tank, by increasing the intake area by more than a dozen times. This does a couple things. It greatly reduces opportunity for debris to block the intake, and helps prevent a vortex, which can, in itself, cause air to be introduced into the system. The filtering of the fuel is managed by the fuel manager. This design is used in millions of systems, and is considered highly reliable. If it were a flawed design, every manufacturer of similar equipment wouldn't be using it.

As I said, there's nothing wrong with adding an inline filter ahead of the lift pump. This increases the filtering efficiency of the system, but adds an additional point of failure (reduced overall reliability) and another maintenance item. If there is enough debris in your fuel tank to plug the intake sock, an inline filter, even a relatively large one, may require replacement several times before the sock would have blocked enough fuel to cause a significant issue. If the debris is large pieces, the tiny intake tube end may be plugged by only 1 piece of debris.

[NASFD35]

Thank you for the explanation and valid points. At a minimum, I would place an inline filter into the system for the sole purpose of ensuring that I’ve diagnosed the problem correctly. I’m trying to avoid swapping numerous parts on an “I think”.

[racer55]

Again it is better to use a screen pre LP and a filter post LP.

Also filters work better under pressure than they do under suction-screens work the same both ways.

Although 1 drawback of a screen if it is metal rather than nylon or some other synthetic,is that in cold temps they can effectively freeze quickly if moisture is present in the fuel.

[NASFD35]

Ok...so now that we're talking screen issues....I did a search on E-bay.
I have a sending unit like this (http://www.ebay.com/itm/Dorman-Fuel-Tank-Sending-Unit-Chevy-GMC-6-5L-Diesel-Each-692-097-/331088880411?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AGMC&hash=item4d166f631b&vxp=mtr).
I found one like this (http://www.ebay.com/itm/Chevy-GMC-C-K-1500-2500-3500-Pickup-Truck-V8-Gas-Tank-Fuel-Sending-Unit-Diesel-/310751019955?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AGMC&hash=item485a3443b3&vxp=mtr). Which one is right? I would think the second one would be better....
Thoughts?

[DmaxMaverick]

Ok...so now that we're talking screen issues....I did a search on E-bay.
I have a sending unit like this (http://www.ebay.com/itm/Dorman-Fuel-Tank-Sending-Unit-Chevy-GMC-6-5L-Diesel-Each-692-097-/331088880411?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AGMC&hash=item4d166f631b&vxp=mtr).
I found one like this (http://www.ebay.com/itm/Chevy-GMC-C-K-1500-2500-3500-Pickup-Truck-V8-Gas-Tank-Fuel-Sending-Unit-Diesel-/310751019955?pt=Motors_Car_Truck_Parts_Accessories&fits=Make%3AGMC&hash=item485a3443b3&vxp=mtr). Which one is right? I would think the second one would be better....
Thoughts?

The first one is junk, and the second is only slightly better than junk. Neither of them are OEM, or acceptable replacements for OEM.

[NASFD35]

The first one is junk, and the second is only slightly better than junk. Neither of them are OEM, or acceptable replacements for OEM.
Ok....but before I spend 300.00 on a sending unit from GM, I'm like to find a strainer like the one in the second like.....just to confirm that i'm on the right track.

[DmaxMaverick]

On the right track to what end? If the sock, any sock, is plugging quickly, the problem isn't the sock. Replace it with whatever you want, it still doesn't address the original issue. If you're still trying to burn up your old, dirty fuel, or continue using a deteriorating fuel tank, the sock style will only buy time between "repairs".


......Neither of them are OEM, or acceptable replacements for OEM.

It's more than just appearance. While the first sock is the most common one of discussion (of poor aftermarket design), the second is not "better". Yes, it is more rigid and less likely to collapse, BUT it has only a fraction of the surface area, and appears to be a much finer screen. Either of them would likely fail in about the same period of time. Anything less than OEM is just that. Less. I hate to sound like a broken record, but none of this addresses the original source problem.

[NASFD35]

(2) When I cleaned the sock the second time, it wasn’t nearly as dirty the second time. I really think there WAS debris in the tank, but upon inspection last time I didn’t see anything in the tank.
(3) Last time I took the sending unit out, I emptied the tank. I ran all of the fuel through a coffee filter (the only fine thing I could think of) coming out if the tank and going back in.
I'm wondering if the sock collapsing is the issue.....that track.
As stated above, the tank has been drained....and filtered....twice.
The inside of the tank has been visually inspected....no rust or debris at the bottom of the tank.
I still drive the truck to work. I'm going through about 1 tank a week, so old and dirty fuel can be ruled out.
I'm not trying to buy time in between reapirs; instead i'm trying to determine the exact cause of the problem. If that means taking the truck apart, switching the sock for a 20 part before I spend 300 on a GM part, and potentially having to take the truck apart again, then that's what I intend to do.

[phantom309]

I am heartly sick of all the attention given to the bloody socks in the tank,. what a lot of band width,.
pul the sock run the truck,. if the performance is god its the sock if its not good,.

In my opinion now you have a problem thats commonly called "fishbiting",. where it coughs momentarily or :bucks: as some folks describe it,.

read this,. chase poor wiring,. remove the filter harness,. try a third pmd,.

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=32849

my money is on pmd,. or what robyn said,.. try the 2000 rpm steady hold see what happens.

[NASFD35]

I guess it's safe to say that the sock was the problem. New tank has been ordered..

[racer55]

Looks like an aftermarket strainer.

[greatwhite]

http://www.autopartswarehouse.com/sku/Chevrolet/K1500/MTS/Fuel_Tank/1995/Silverado/8_Cyl_6-dot-5L/MTS2025.html

Haven't been around a while.

Nice find.

:)

Too bad it's the small tank. No good for me....:(