OPS? fuel sender sock? stalling, im stumped

[bluemirage188]

First off, i've searched a fair bit on numerous sites. I dont know if i am in a different situation or have overlooked something.

1997 k3500 6.5lTD, open exhaust for the time being, other than that, stock.

less than a year old fuel tank/sender, hard fuel lines up to the LP, fuel injection line for the return and feed up tot he filter manager/IP. New LP/OPS less than a year ago. filter is good, visually inspected, and tank sock i checked a few weeks ago and looked brand new to me. water drain has a constant flow when running, and fuel shoots out of the filter purge easily. Truck had a PMD replaced prior to my ownership (stanadyne), and I have not yet taken the plunge on that (because of the cost).

So my issue is, from cold, it starts with a little extended cranking (always has) and will run great for some time, usually 30min to an hour of driving. Then i get a stall, or an almost stall. sometimes it works through it. When i re-start it, it seems like i have to let the LP run a few cycles before she wants to start, also having very extended cranking time. My fuel system is all relatively new, and seems to work great for the first part of a drive.

Now i know everyone is itching to say, relocate and buy a new PMD, and to be honest i think at this point even though i dont think that is what it is, it would be ruled out if i did get a new one.

Could it be as simple as something clogged in a line, or the sock clogged? maybe a clogged injector line? clogged injector? i am at a loss for new ideas here. I'm pretty mechanical and can fix just about anything, but this has me stumped. HELP?!?!?!!!

[racer55]

Have a look at the center of the filter manager,there should be a last ditch screen there that has been known to plug.If you can only see what looks like a spring,then the screen probably got stuck in a filter and tossed.

There are also screens in the IP inlet fitting that can get clogged but would be more of a constant problem.

A diagnostic aid that I would do is replace the IP fuel return hose with a piece of clear diesel rated fuel line.Watch the return line with the engine idling and look for bubbles.
Bubbles in the return line indicate air entry in the fuel system between the fuel in the tank and the LP most often-I know your parts are new but china isn't known for quality and most parts come from there now no matter the brand name.

[bluemirage188]

Have a look at the center of the filter manager,there should be a last ditch screen there that has been known to plug.If you can only see what looks like a spring,then the screen probably got stuck in a filter and tossed.

There are also screens in the IP inlet fitting that can get clogged but would be more of a constant problem.

A diagnostic aid that I would do is replace the IP fuel return hose with a piece of clear diesel rated fuel line.Watch the return line with the engine idling and look for bubbles.
Bubbles in the return line indicate air entry in the fuel system between the fuel in the tank and the LP most often-I know your parts are new but china isn't known for quality and most parts come from there now no matter the brand name.

I dont think i have a screen in the middle of the manager riser. or at least not that i have noticed. I did have the manager out when i did the OPS, and i cleaned it out really good (there was alot of rust ect. from the old rotted lines in the bottom of the FM). Maybe i blew that screen out? I will take a look tonight, as for the IP fitting, im assuming that you follow the line from the filter manager and the fitting with the screen is the one that the hose connecting the two is attached to? Ill check that.

Is there a permanent line that you would use on the return line? right now i have rubber fuel line connecting the hard line out of the IP to the hard fuel line i have on the frame rail. I can put in a clear line and just run it to the tank and watch it too.

Thanks alot for the suggestions!

[racer55]

The return line from the IP joins up with the injector return lines in front of the IP so you would have to keep that connection-just replace the black line with clear.

BTW:do a google search for filter manager screen or search stanadyne part number 29244
to get a picture of what it should look like.

[Burning Oil]

http://www.youtube.com/watch?v=CGRBW...Sef3_ReVqw9v0=

I would also check your tank sock and throw it in the trash. Add a 30micron filter pre LP.
Aftermarket socks are not correct for the diesel anyway.

[arveetek]

I just spent 3 months chasing a similar problem. I, too, had replaced the sending unit/pickup assembly not long ago. Turns out the 'sock' on the pickup tube is a different design and will not allow diesel fuel to flow very well. My sock was collapsing after driving a few miles.

I still had my old sending unit, so I put the OEM sock back on, which is a very different design from the aftermarket version, and all has been well since then.

In this pic, the sock on the left is the aftermarket version with an extra plastic mesh inside the sock. The one on the right is the OEM version, that is shaped more like a cylinder and is more of a screen than a filter.





Even though the aftermarket sock passed visual inspection two times before, it wasn't until I dropped the tank for the third time that I actually tried blowing through the sock to check for obstruction, and could barely pass any air through it. The OEM sock with over 200K miles had no obstruction, so I put it back on. Has been running great since.

Casey

[bluemirage188]

After tinkering with the fuel system a bit, i now have completely new lines to and from the IP, and excelent fuel flow without air. It drives great, untill maybe 10min of driving steady. If i go for a quick mile or two drive, no issue. If i go for a little longer, it stalls, and progressively gets hard and harder to start, and goes less and less further each time I attempt to start it.

Now im thinking PMD, have i ruled everything else out? i think so, just hate to pony up 300$ for the kit if i dont need it. Its not my everyday driver, its my farm work truck, so we definitely need it, but money is tight as you could imagine.

Thanks Guys for any input!

[racer55]

Sounds typical for a stanadyne PMD failure,progressively shorter run time with trouble starting hot.

If no one in your area has a known working PMD to try/borrow for diagnosis,then getting a kit with a new PMD is in order.

You may also want to look at the IP inlet screens for evidence of them being plugged but it doesn't sound like the problem.

I have had very good luck with an ebay vendor named "angelofishes".

Be sure to get a resistor when you order the kit with PMD,6' extension harness and heatsink no matter who you buy from.

Also the "tested good" PMD's advertised are sketchy when diagnosing problems because they are often as bad as what you have,so when figuring out a problem NEW is best.

[Burning Oil]

If I can help you with a PMD or kit let me know. I have them in stock for $275 or $304 both are full kits. Just click on my link www.pmdcable.com

[racer55]

If I can help you with a PMD or kit let me know. I have them in stock for $275 or $304 both are full kits. Just click on my link www.pmdcable.com

Excellent pricing and dealing with a site vendor is always a plus.

[kaar5kel]

Hello. I'm new here...Been looking over hundreds of posts the past few days to a week here and on other forums. I am an old school Big truck Mech(before computers). Just bought my first personal Diesel. Dont know anything of it's history except that it had a ton of new parts in it. Mine is a 1995 C2500, 6.5 TD -Fcode.,, Manual Conv. lock, 4" sized up to 5"welded SS exh. Temp guage, 8lbs boost w guage, Air cleaner, relocated PMD, New OPS, TCC, LP, remaned stanadyne IP, new sump, Hard lines, filter, and a Rebuilt 4L80e Trans w/ Kit. like new 04' DuraMax 8lug alum wheels, class 3 hidden tow, Clean for its age w/ 230k on it. So bought it blind, at night, needed a truck to get home ASAP as my 90 GMC decide to drop a tranny in NC (I live in SC). So, 1400.00 on CL. I thought it was a work in progress..Probably had that much in new parts in it..And it was a diesel to tinker on. As I looked over I see alot done, but, half asssed, (spliced , wires, weak grounds, old hoses and SOME new lines, ect..) Ran perfect and it drove right though. I Drove it 70-75 miles in NC to get a bit comfortable to drive 200+ miles home, Changed oil/filter/cleaner/Rad cap, and looked it over fairly well..... 5 miles from home, Bucking, sputtering, popping.....anything over 1500 rpm's, So...I think, fuel guage is bouncing, maybe out of fuel?, maybe Water, ????.. I Filled up, still had about half tank. Addded FPPF, and Valvoline Water remover for diesels(love my Valvoline, 30 years and no engine failures...knock on wood)...But, she was Still bucking, popping sputtering..only above 1500 rpm...So I used the checklist here(thanks Guys), go trough all of it, Double checked everything, or so I thought........My issue was solved, at least so far, by finding a loose hose clamp on the line that feeds the filter bowl. I felt around, and grabbed lines and clamps and gave them the twist test..to see if loose. Well, the one at the bowl, nice and tight, the one on the line from LP, Not so much...So i tighten all loose lines, go to Autozone to test fuel Pressure, 3.5-4lbs @ Key on, 2lbs idle, couldn't test @ higher rpm as they wouldn't let me leave with it for road test, and didnt have long enough hose to run to windshield to see when operating. But, after tightening all hoses, and clamps........No more, I guess what you youngins call, fishbiting.. Runs smooth and clean now. I will obviously run all new hoses, clamps, and clean it all up, But 5 days of thrashing and testing..It was a hose that was loose cusing air @ the Filter. Since then, 40+ miles, a few WOT, and some 60mph + runs and, no issues, no skips, pops or stumbles, but, i will keep you all up to date...So the reason for my two cents is, I see alot of forums, including this one (no offense) that say, PMD,IP, OPS, and what not, as first reaction, but, when I was talking to an old timer, even older than me, said nope, look for air/fuel issues, always look for air first, then fuel, then electric, then, sensors, then, others. He said in his 50 years of Mech, 35 years of rebuilding IP's, and heavy equipment expert. he says almost 40-50% diagnosis of IP failures and about 30% of failed PMD diag. wrongly, and are very common, too common, especially @ dealers and Mech shops, as a poor lift pump, or air in system can and will set codes off on these trucks(he owns 2). He has rebuilt one IP, and replaced only 1 Pmd on his 2. each over 150k. He says, his have been, Air leaks, fuel issues, OPS, and electrical, usually grounds...Sorry for the long story, but, Hope this helps someone else as it has me. Sometimes...them old guys, have a story to tell....now, so does this old guy.. FREE FIX other than a headache and a handfull of Advil and about 8-10- hours of testing everthing...

[racer55]

Hello. I'm new here...Been looking over hundreds of posts the past few days to a week here and on other forums. I am an old school Big truck Mech(before computers). Just bought my first personal Diesel. Dont know anything of it's history except that it had a ton of new parts in it. Mine is a 1995 C2500, 6.5 TD -Fcode.,, Manual Conv. lock, 4" sized up to 5"welded SS exh. Temp guage, 8lbs boost w guage, Air cleaner, relocated PMD, New OPS, TCC, LP, remaned stanadyne IP, new sump, Hard lines, filter, and a Rebuilt 4L80e Trans w/ Kit. like new 04' DuraMax 8lug alum wheels, class 3 hidden tow, Clean for its age w/ 230k on it. So bought it blind, at night, needed a truck to get home ASAP as my 90 GMC decide to drop a tranny in NC (I live in SC). So, 1400.00 on CL. I thought it was a work in progress..Probably had that much in new parts in it..And it was a diesel to tinker on. As I looked over I see alot done, but, half asssed, (spliced , wires, weak grounds, old hoses and SOME new lines, ect..) Ran perfect and it drove right though. I Drove it 70-75 miles in NC to get a bit comfortable to drive 200+ miles home, Changed oil/filter/cleaner/Rad cap, and looked it over fairly well..... 5 miles from home, Bucking, sputtering, popping.....anything over 1500 rpm's, So...I think, fuel guage is bouncing, maybe out of fuel?, maybe Water, ????.. I Filled up, still had about half tank. Addded FPPF, and Valvoline Water remover for diesels(love my Valvoline, 30 years and no engine failures...knock on wood)...But, she was Still bucking, popping sputtering..only above 1500 rpm...So I used the checklist here(thanks Guys), go trough all of it, Double checked everything, or so I thought........My issue was solved, at least so far, by finding a loose hose clamp on the line that feeds the filter bowl. I felt around, and grabbed lines and clamps and gave them the twist test..to see if loose. Well, the one at the bowl, nice and tight, the one on the line from LP, Not so much...So i tighten all loose lines, go to Autozone to test fuel Pressure, 3.5-4lbs @ Key on, 2lbs idle, couldn't test @ higher rpm as they wouldn't let me leave with it for road test, and didnt have long enough hose to run to windshield to see when operating. But, after tightening all hoses, and clamps........No more, I guess what you youngins call, fishbiting.. Runs smooth and clean now. I will obviously run all new hoses, clamps, and clean it all up, But 5 days of thrashing and testing..It was a hose that was loose cusing air @ the Filter. Since then, 40+ miles, a few WOT, and some 60mph + runs and, no issues, no skips, pops or stumbles, but, i will keep you all up to date...So the reason for my two cents is, I see alot of forums, including this one (no offense) that say, PMD,IP, OPS, and what not, as first reaction, but, when I was talking to an old timer, even older than me, said nope, look for air/fuel issues, always look for air first, then fuel, then electric, then, sensors, then, others. He said in his 50 years of Mech, 35 years of rebuilding IP's, and heavy equipment expert. he says almost 40-50% diagnosis of IP failures and about 30% of failed PMD diag. wrongly, and are very common, too common, especially @ dealers and Mech shops, as a poor lift pump, or air in system can and will set codes off on these trucks(he owns 2). He has rebuilt one IP, and replaced only 1 Pmd on his 2. each over 150k. He says, his have been, Air leaks, fuel issues, OPS, and electrical, usually grounds...Sorry for the long story, but, Hope this helps someone else as it has me. Sometimes...them old guys, have a story to tell....now, so does this old guy.. FREE FIX other than a headache and a handfull of Advil and about 8-10- hours of testing everthing...

Something like post #2 of this very thread?

[mrwilecoyote]

Grounds are also very important and if your gauges are bouncing all over, I would not ignore those.

[Snowbound98]

Check the fuel cap. Something as stupid and simple as a non venting fuel tank will cause low power, hard starting warm, and drive ability problems. Easy check. After driving for your 10-20 min range and it starts to act up, pull over shut it off and go open your fuel cap. Do you hear it suck louder than normal? I had a fuel tank implode on me while taking a long trip on highway. Couldn't see it from under the truck because of the cover on the tank but when I dropped the tank( cause I checked everything else I could think of) I pulled he sending unit and the lines were bent. I bought new sending unit and it wouldn't fit into the tank. A little thought and some engineering I was able to pressurize the tank to about 10 PSI and it popped back out. Installed tank and ripped off o-ring around fuel cap and never had another issue. But all that was on a 92 C3500 6.5. Non computer controlled. If you have computer you should have a vent and purge solenoid on your tank that allows a small range of vacuum and pressure on tank but it's controlled. But I do see a lot of these vent solenoids fail and that could be your issue too. Just my 2 cents.

[JTodd]

I am going through something similar. What is the definitive explanation of when the LP runs and when it does not? I have checked it with a multimeter with the engine running, and it is working, but sometimes I have my doubts. What I do know is that the FFM is not filling with the pace the engine uses it. I just changed the LP to an ACDelco unit and while at it changed the FFM last ditch screen. I have a fuel tank sock on the way, but am trying to determine what exactly is the problem.

When I turn the key initially to 'run' I can hear the LP. Does it run enough to build pressure and stop? Does it run for a set duration? With engine running, does it run constantly?

[mrwilecoyote]

About 40 seconds IIRC. Maybe less but yes a set amount of time. Are you sucking air somewhere ? That is often overlooked. A clear piece of fuel line between the FFM and IP will tell the tell. That is called Sightglassing.

[Diesel 4 blood]

I just noticed on my 94 6.5 that the lp isn't turning on when I turn the key on but as soon as I start cranking it starts pumping is there another relay besides the one under the hood for the lp

[racer55]

I just noticed on my 94 6.5 that the lp isn't turning on when I turn the key on but as soon as I start cranking it starts pumping is there another relay besides the one under the hood for the lp

That is the normal condition for a 94,the LP prime only happens when the key is in the start position and the OPS takes over once the engine is running-OPS relay mod is a must in my opinion for long term reliability,google it.

For 96+ the ECM controls the prime and running LP functions with the OPS as a backup power supply.

[Snowbound98]

To test without starting I used to trick mine. On level ground block the wheels put gear selector in drive and turn the key like your starting it. It won't crank because the neutral safety switch but it would turn the LP on. My truck ran for months with no power to the LP. I wasn't thinking when I installed an autometer electric oil pressure gauge. Thought I didn't need the factory unit anymore. Ended up putting in a relay for it. What a difference that 6psi LP makes.

[mrwilecoyote]

Yeah, the DS4 can pull it's own fuel and under light driving conditions can often run for months unnoticed. Mine was dead for awhile me thinks and I didn't realize it until I went to prime a new fuel filter. However that taxes the transfer pump in the IP and it has been theorized by some that might be why PMD's fail mounted to the inj pump because of lack of sufficient fuel flow to keep it cool. Alot of people are running around with dead LP's and don't even notice it.
I truly belive any diesel should have a fuel pressure gauge. I will personally never own a diesel without one.