Cummins ISC 8.3 Stalls and heals overnight. Fuel pump? ECM?

[lbw6303]

I’ve been searching the Forum for circumstances/symptoms similar to what happened to my 2004 Monaco Diplomat WRT stalling out (40ft Pusher With Cummins ISC 8.3 & 66K miles. Tow a 2005 Silverado). I’ve not seen the exact symptoms on this forum so far, so I will describe my situation as briefly/concisely as I can:

We were traveling back to Fl in Oct 2019 from Mn. We travel about 300 miles per day. Always top off fuel in the AM to be able to drive all day to next stop. Result, we get to evening destination with about ½ or less in fuel tank. Diesel kleen about every other fill.
First several days were uneventful. We stopped in Clarksville,Tn for the night and left for Montgomery, Al the next day. Re-fueled in Clarksville. Drove thru Nashville & Birmingham (250 mi) just south of Birmingham, the rig started to act sluggish and then finally stopped cold. Engine ran smooth up to that point. No stuttering, or misfiring, just started “dogging it” and stalled. Coasted to side of I65 and stopped. Tried restarting – No Joy. Called Good Sam for help. No help. Used Onstar in my Toad. Got info on a Mobile Mech. He suspects fuel filters/bad fuel. Can’t change them because of I65 traffic. Runs a computer diagnostic. No fuel pump pressure. Time for a tow. Deposited for the Night in a Camping world parking lot. Next day another mobile Mech comes. Wants to check fuel filters. Spins engine, pumps working fine. Change filters, Engine cranks right up and is running smooth.

Conclusion: bad fuel/plugged filter(s). Keep going.

Late start, so fuel up and drive 50 miles to Campground in Montgomery. Runs just fine. Good power.
Next day. No need to refuel. Strike out on 300 mile trip to Perry, Fl KOA. Lots of hills until the last 50 miles. Running fine. Get within 4 miles of KOA, in town, Stalls again. Coast to side of road. Find a local Truck mechanic. Locate 2 more filters. Still thinking I’ve got contaminated fuel. Open filters. Water separator looks like it’s low/not full. Are you out of fuel? Nope the tank says half and a flashlight proves it, but the Lift pump feels like it’s cavitating. Unit won’t start. Is it the fill tube in the tank? Is it sucking air somehow? Overnight. Next AM bought a 5 gal gas can and put 15 gals of fuel in the tank. Tried to start the engine. Starts right up and runs fine. Should have tried to start it B4 adding fuel. Probably would have started.

Conclusion: Probably not fuel, but somehow we’re sucking air into the system. Bad/failed fill tube in tank? Do I have the equivalent of a 50 Gal tank instead of 100 gal?

200 miles from home. Let’s go for it, but will top off fuel at halfway point. Did so. Engine running fine. It’s about noon in St Pete, Fl and temps are near season record high in 80’s. We’re in Stop/go traffic on US19. Within 6 miles of storage garage. Stalls again. Coast into turn lane coincidentally one for a local KOA. Won’t crank back up. Get a tow into their parking lot and leave it for the night. Next day drive back over. Engine starts right up and runs smooth. Will wait one more day and come back at 6AM when low traffic and make a run for it – 6 miles. Did so. Uneventful. Ran smooth.

Conclusion(s):
1) Probably never did have bad fuel. Filters were probably OK. Don’t know how/if air getting in and causing main pump to starve.
2) The computer probably put the engine into sluggish mode to save it from damage??
3) It’s probably not the “lift pump”, because it only runs at start up. Then the primary pump takes over. Although I’ve seen analysis that suggests that it could be where/how air could be getting into the system.
4) The primary pump may be weakening and after a long day, it warms up to the point that it gets sluggish/weak??? Because the fuel is re-circulating, is it also warming up causing the pump to overheat when we get below ½ tank?
5) The computer (ECM) could be failing (electrical component over heating). I’ve seen other analysis here that suggests it could be related to ignition switch, or bad ground causing too low a voltage for the computer causing it to malfunction or run degraded. The unit won’t start up right away, but seems to be just fine after it has set/cooled for a few hours (8-12)? I believe that I always got a “Check engine” light upon re-start, but it always cleared in less than 30 seconds.
6) I’ve seen the writeups about FASS fixes that install a pump near the tank to push fuel toward the primary rather than make it Suck fuel all that distance through two filters (I have two filters). This is tempting, but concerned that it will mask the real problem for a while til whatever it is finally fails “Hard” and strands me again.

So those are my symptoms. Intermittent failures that seemingly heal themselves temporarily can be brutal. I don’t want to just throw parts at the problem. I haven’t yet talked to Cummins, but will soon. I’m interested in your experiences. Hope I’ve explained adequately for good understanding. All instruments appear to be normal all day long – Engine temp, oil press, boost, etc.

[mackwrench]

I'd be suspect of the fuel line from tank to primary filter.
Sounds like it's running out of fuel more than sucking air into system.

If secondary filter was low, then my thoughts are fuel restriction in lines between that filter and tank.

Unless it has nylon fuel lines, You, or your next mechanic, could cut into the primary filter to check for black fuel line pieces. Biofuel can eat away the inner liner on "fabric" looking fuel lines...

But not for one second do i think you need a ECM... you'd have a bunch of diagnostic codes if anything more than fuel supply was an issue.

Me? I'd remove fuel filters, then using a air hose see if when I blow air into tank that I get a good stream of fuel at the filter head. (Use a rag around a air blower to "pressure" the tank)....

Can you see fuel lines at primary filter? Are they a brown or black plastic nylon type? Or aeroquip flex hose.... that'll help determine if you have a line restriction issue as the nylon type rarely fails.

[lbw6303]

Thanks for the quick reply.
Each time the fuel filters were replaced, the mechanic poured the fuel out of the old filter and noted that it was "clean and green" one small black particle out of the water sep the first time. the guy who ran the first computer diag may have seen some codes, but he didn't write them down nor explain them to me if he did. Only that he noted virtually no fuel pressure, suggesting my pump had failed, but it "healed" over night and ran fine for about 350 miles until the 2nd stall.Have not done a "readout" of the ECM since the very first stall. I will, but that's all I have for now.
Does the fuel run through the lift pump when the primary pump takes over, or is it bypassed. I've seen one thread where someone suggested that the lift pump screen was plugged/affected and causing the primary to have to work too hard. If it is bypassed during normal operation, that wouldn't seem to matter. I've also seen a thread where the guy tightened 3 bolts holding the lift pump in place and suggested that air was getting into the system because of that.
lbw6303

[mackwrench]

Any debris in lift pump would have to get by both filters to be there.... not likely.

Loose lift pump diaphragm cover screws usually have fuel leak.

All fuel runs through electric lift pump, weather it's running or not.

Pouring fuel from filter may or may not show any reason for restriction. The black particle you seen could be a bad sign.
Only by cutting the filter open will show if it's really restricted.

Since you don't have a continuous CEL on, I'd discount anything electrical controlled.

A diesel that's experiencing a fuel restriction may run somewhat ok, maybe even great at times, but a engine that's sucks air into system will not come and go like you described.

[lbw6303]

thanks for that analysis.

If I understand correctly, you are thinking in terms of fuel supply restriction somehow between the tank and the filter(s). Could a plugged vent line cause such a restriction? one post I read mentioned mud daubers getting in the vent line, which in my case comes out the top of the tank and wraps down to protrude out just under the chassis. Could that cause this kind of restriction?

I'm trying to understand the failure behavior. How does the pump behave when it seemingly runs starved for 2-300 miles. does it heat up? Does the ECM somehow sense the starvation, or a temp rise in the pump and put it into a degraded mode to protect the pump/engine? How can I explain the seeming cool down after a few hours that allows it to crank back up and run for, in one case almost 300 miles and another almost 200 miles. No misfiring, stuttering, sputtering. Just runs normal until it seems to go sluggish/lose some power and then just stall/shut down. not even a check engine light until it actually dies.

Sorry for all the questions, cause you've been very helpful. I'm going to go talk to cummins soon, but I'm trying to get to the best explanation of symptoms and failure modes that I can in order to help them with a diagnosis.
Needless to say, I don't want to venture very far with this rig until I'm 99% sure that I've gotten to the root cause of this failure.

lbw6303

[Ray,IN]

Originally Posted by mackwrench

Any debris in lift pump would have to get by both filters to be there.... not likely.

Loose lift pump diaphragm cover screws usually have fuel leak.

All fuel runs through electric lift pump, weather it's running or not.

Pouring fuel from filter may or may not show any reason for restriction. The black particle you seen could be a bad sign.
Only by cutting the filter open will show if it's really restricted.

Since you don't have a continuous CEL on, I'd discount anything electrical controlled.

A diesel that's experiencing a fuel restriction may run somewhat ok, maybe even great at times, but a engine that's sucks air into system will not come and go like you described.

The only inline fuel pump with adequate volume capacity for continual use(GPM) are those such as FASS and AirDog, and other brands I cannot now name.
Afterthought; this website will explain to ibw6303 what is happening: https://www.turbodieselregister.com/...estion.250314/

[Reka]

When it dies loosen fuel cap and see if you get an pfft sound of air rushing into tank, your symptons sound very much like a vent problem

[Reka]

As the tank is becoming a vacuum as fuel is being used engine will become sluggish and eventually die as fuel pump can't pull against the vacuum would take awhile but will shutdown and as it cools overnight vacuum is gone

[twinboat]

You say you looked at the fuel level with a flashlight after it shut down.
If you did that thru the fill cap, and it still didn't start, plugged vents are not your problem.

If your fuel filters are coming off empty or low, air has to be getting in somewhere. Ever try sucking beer out of a bottle ?

There could be the slightest leak in the line or pickup tube that lets a bit more air in as the fuel level drops.

[1st-tt2018]

Another thing to check is a weak fuel line, it may have failed internally and the pump may be collapsing the fuel line as it heats up, restircting flow until it starves the engine...

[imnprsd]

THIS WILL MAKE YOU FEEL BETTER... if it works!

I feel your pain with the odd-ball symptoms you experienced.

I too thought I got bad fuel, and then I was replacing fuel filters at 5,000 miles...

Eventually my engine would not start on a few cold mornings; and/or when my left my fuel tank with less than 3/8 of a tank. Just like you! At one point it would start and keep running when I removed my fuel filler caps; and for a while I thought my fuel tank was not venting right. (ALL NOT TRUE!) Twice, I thought I needed to call a tow truck, but I finally got the engine started and kept it running when the engine warmed up.

You will be surprised at how easily we fixed this problem. We also have a Cummins-ISC-350HP (CAPS) engine, and it did not cost us aything!!! ==>All we had to do is tighten 3 lift pump manifold bolts!

I can't believe more people don't check this first! And I am surprised other members on this forum who know about this problem have not told you to first check your lift pump bolts.

Ours took 3/4 to a full turn.

Others people have told me that 80% of the time you are probably loosing negative fuel pressure (vacuum) by air leaking through the lift pump gasket... BECAUSE YOUR 3-LIFT PUMP BOLTS ARE LOOSE!

==> In fact, to everyone reading this thread, you-all should check and tighten your lift pump bolts if you have more than 50,000 miles on your engine!!! This is good preventative maintenance!!!

*** Don't tighten these bolts too tight! You don't want to break a bolt or more likely strip one.

Note: Pre-2002 Cummins engines have been known to have fuel leaking from the Lift Pump Gasket... due to ULSD fuels affecting he material they used prior to 2002. Therefore, you pre-2002 Cummins ISC owners may not find you can fix your fuel "suction" problem by just tightening the 3 Lift Pump bolts. In these situations you may need to replace the gasket. Consequently, you also need to make sure you get the right gasket for your engine serial number.

HOW TO ACCESS THE TOP OF YOUR ENGINE

I have a Winnebago with a Freightliner chassis (8.3L-CAPS Injection) and I had to access the top of my engine by removing the bedroom floor between the bed and the closet.

In your RV, I do not know if you can access the top of your lift pump... on the passenger side of your engine... by another method. The Lift Pump sits above your ECM and towards the front of your rv. ...under that 4" air tube.

See picture below on what 3-Lift Pump Bolts look like in my 8.3L Cummins-ISC. (I think they were 7/16".)

After these same horrific experiences, I then researched this whole "Lift Pump Thing" and decided to install a FASS electric "Titanium Series" Lift Pump to safeguard my CAPS system. Here's the link you can read about on how I did that.

http://www.irv2.com/forums/f123/cumm...mp-458337.html

Let us know how things turn out!

[lbw6303]

Several good inputs above --- Thanks to all of you:

1) vacuum in tank from blocked vent line -- after the 2nd stall, Within 30 minutes I opened the fuel tank to check fuel level because it appeared my fuel gauge might be faulty. No apparent vacuum build up. I do plan to run a flexible snake up into the vent tube just to be sure.
2) I've seen the write-up by imnprsd about lift pump bolts and plan to check them as well. I've also seen his write up about FAS pump installation and if I do finally conclude that I have a failed supply line either in the tank or in the "inaccessible" (nigh impossible to inspect or replace) line coming from the top of the tank to the rear by the engine or to the filters, I anticipate going the FAS installation route to push fuel rather than suck it to the filter(s).
3) But none of this seems adequate to explain how the system appears to "heal" itself after a few hours of just sitting (6-8-10 hrs??). After the first stall, when the computer test said no fuel pressure in the afternoon of the stall, The Mobile mechanic who came the next AM, first loosened the water sep filter and had me crank the starter --- the pump is pushing fuel. He changes the filters and we crank right up and drove for 2 different days. The 2nd stall in Perry FL, even after changing both filters, the engine wouldn't start. The next AM it did. 3rd/final stall -- same thing. Didn't touch the filters, just waited for it to cool off. So i'm skeptical that the root cause is in the fuel supply side, even though I'll check further there (lift pump bolts etc).
4) I'm really wanting to understand better how the Primary pump actually works So that I can declare it Good, or replace it. It seems like it must be a multi-stage pump that sucks/pulls fuel in from the tank and then transitions internally somehow to push/pressurize the fuel out to the injectors. I'm wanting to better understand the failure modes & symptoms for that pump. Further, I' need to understand the role of the ECM in the shutdown process. What is it watching on the pump or the engine that might cause it to take action to degrade engine performance and/or to shut it or the pump down(presumably to protect the engine and/or the pump). I know I need a Code read out and will get one. for now I'm just trying to understand the function and interaction btwn fuel pump(s) and ECM.
5) because nothing so far helps me understand why the pump appears to fail, but after sitting for a few hours, it works and the engine starts, runs smoothly and does so for as many as 300 miles before it just stops again. that just seems like it could be "temperature-related. Could it be that the "suction stage" of the primary pump is failing/marginal/overheating and perhaps thus starving the injector/pressure stage (to the extent that the ECM says "enough" -- time to degrade/shut down??
6) I'm a retired Aerospace engineer (electronics). I've had to chase intermittent electronics failures that showed up at high/low temps but then "healed" at nominal temps (I realize that could be causing me to over analyze this and miss the obvious - to the guy with a hammer, everything looks like a nail!!, So I'm wanting to learn more here. Thanks for the indulgence and the help.
lbw6303

[imnprsd]

Everything you said, describes all the "craziness" I went through. ...And I too did not think all my pain and heartache would come down to 3 loose lift pump bolts. BUT IT DID!!!

I eventually decided ambient temperature and engine temperature was key to understanding why air was getting sucked through the lift pump gasket. In my case, it sounds like cold air temperature affected my negative fuel pressure (vacuum), but I suppose it could just as easily be warm air. Thermal expansion is how would describe it.

So go out there and DODGE A BULLET! And prove it to your self first, so you can tell us what you found?

[imnprsd]

1) The CAPS pump costs ~$3,500 for the part to replace and $3500 - $5000 to install due to the difficulty of the R&R process. My Freightliner chassis is the worst when it comes to being easy to work on the CAPS pump. Your Spartan Chassis may be better. Also, I have a basement AC on the passenger side of my coach so I don't have side engine access like some RVs do after they lift up the compartment grill. (I do not know what you have?)

2) When you CAPS pump goes it can throw a huge electrical "spike" back to the ECM; that overcomes the ECM Suppressor Diode (aka protection diode) and many mechanics tell me that 8x out of 10 they also replace the ECM when they replace a CAPS pump.

So while we both own one of the best, every built Cummins engines (ISC), you need to know your CAPS injection pump, which was not designed to run on ULSD fuels, and was built to very tight tolerances, will prematurely fail if it does not receive enough lubrication and cooling from the fuel. This is one reason most of us use an additive. You like PS-Diesel. I like Howe's. It's all good for a CAPS system.

==> You might want to read more about fuel in this thread: "Fresh Diesel vs Bio Diesel" http://www.irv2.com/forums/f59/fresh...el-458351.html

Note: Everything I have written about has been a journey, so feel free to read the fist post and then go to the last posts where I try to provide a summary.

Back to the subject at hand:

In 2015, my CAPS and ECM failed and Cummins charged me $9,500 for the complete job. (And that did not include the towing bill.)

...And so, protecting my CAPS pump from another failure maybe the the #1 reason I went to a FASS fuel pump. However, after I installed the FASS "TS" Pump I really like the extra 2 fuel filters; and the "fuel polishing" that I think eliminated my algae concerns. Not to mention a better sounding engine at idle and no more "bucking" up a hill.

Whatever is going on, my engine now runs smoother; and yes... positive 15-18PSI of fuel pressure is always better then -5PSI of vacuum pressure.

And now that I have a FASS Fuel Pump I know my CAPS low pressure gear pump will never be starved of fuel in the future! I also have every reason to believe my CAPS injection pump will last a lifetime now that's it's receiving positive fuel pressure and I'm not worried about bio-fuels like I use to be. In fact, all studies show, bio-fuels have MORE LUBRICITY than #2 USLD fuel. So if anything, I would like you to know you don't have to be concerned about bio-fuel wrecking your CAPS pump. (If you read that thread about "Fresh Diesel vs Bio-Diesel" then you know this now.)

Would I buy an older RV with a CAPS injection pump again? YOU BET! I would not only get a better value and lower price; I now know a CAPS pump will run forever if you install a FASS or AirDog Lift pump... and I would do that immediately if I was a new owner.

Note: If you don't drive your RV very much, and/or this is your last year of ownership, then you might not want to upgrade to a FASS pump. Just know this: In my opinion all CAPS pumps are running on borrowed time if they don't have one of these little jewels!

3) Only the older mechanics, who use to repair CAPS injection pumps, know how to repair these things. (Unless you are in farm country where a lot of older ISC-CAPS engine are still in service.)

For example: The accumulator (that rectangular looking aluminium block that sits on top of your CAPS pump) might get replaced if you had an algae problem. (My accumulator was replaced by the previous owner back in 2009 with only 40,000 miles on it, but back then he was fighting an algae problem.)

And then there is the STATOR that controls the fuel metering to the fuel distributor might be another part you can replace. (And still can. But first I would say good luck finding a mechanic who can properly diagnose a CAPS problem.) Note: There is an Engine code for the Stator and you need to check for this. It's a $150 part and not hard to replace.

Here's a thread about my CAPS fault codes, but you need to know these were the codes after my CAPS pump blew-up. Still you probably have a few "low pressure" codes logged. Just remember to ask your mechanic to look at the HISTORY so you can see how many time your EMC logged "low pressure" as a fault.

Note: What about your engine light. Did it ever come on? Mine did a few times, but it will not always come on. Or your ECM will rest it and you will never see the engine light flash on the dash. However, your ECM will still log this time. These are "Soft Codes" and are worth looking at.

http://www.irv2.com/forums/f101/2003...-a-364681.html

Note: And don't worry about your 10-micron fuel screen inside the CAPS pump. This will only get clogged if you have serious algae concerns.

...I remember at one point I was thinking a clogged CAPS screen filter might be my problem, and when I talked to 10+ mechanics, including those on Cummins Quick Serve... who never knew there was a 10-micron fuel screen in the CAPS pump... I thought I might have have just found my problem.. but no cigar! And after I examined my screen (in my broken fuel CAPS pump) it was clean.

3) Yes, the ECM will log several engine codes to help with the diagnosis, but because very few mechanics have ever taken apart a CAPS pump, more often or not they will just try to sell you on the replacement of one.

Think of it like this: At one time your car mechanic knew how to overhaul an Alternator; but now all he knows how to do is replace the Alternator with a re-manufactured unit.

Same goes for CAPS. In fact, I had so little confidence in the Cummins-Colburg, OR team that I felt forced to buy a complete CAPS pump, because I did not trust their ability to properly fix my failed CAPS pump. So don't think your Cummins Shop is more qualified to repair a CAPS Injection System over Joe's Garage. In fact, I would argue just the opposite.

To repair or replace a CAPS pump you two things: A) You need to find a mechanic 50-70 year of age who use to repair CAPS pumps; and B) You need to find a shop with a younger mechanic who can get inside your engine bay to do the R&R.

The problem most people face is that the right shop is the one you towed your RV to.

4) CAPS pumps are failing (in part) due to ULSD fuels they were not designed to run on, but the real reason for CAPS premature failure has more so due to fuel starvation... in my opinion.

I.e., every time your engine stalls out you are loosing negative fuel pressure (vacuum in the fuel line)... to the point there is not enough fuel for the low pressure gear pump to work.

This is also true when you engine bucks when climbing a hill or under acceleration. And not enough fuel means not enough lubrication and cooling. So these CAPS pumps are failing due to heat... and constant low fuel (vacuum) pressure... that is caused by leaking air getting sucked in where your lift pump gasket mates with the lift pump fuel manifold. And this is why many people find they can just tighten the 3-lift pump bolts and all is well again!

5) What else drops negative (vacuum) fuel pressure below the minimum -5PSI?

* Fuel levels in the tank below 50%. In the Dodge-Cummins world this is known as the "1/2 Tank Problem."

* Loose Lift Pump bolts

* Poor Tank Venting caused by bad fuel caps or even sand-dabbers building nests on top of your fuel tank vent.(although I don't have that one confirmed... other members have claimed this is possible.)

* Rotting out fuel lines??? This is something to watch for, but all I have heard is that you will see black specs in your fuel filter if you cut it open.

Here's the rub: A fuel line under vacuum pressure will lose pressure if the fuel line starts to suck air in through it's pours. This will cause your CAPS inlet fuel pressure to drop blow -5PSI and you will see all the symptoms you described. And fuel lines are the last on the list of things to replace when you can't find a vacuum fuel problem in an older RV.

Other solution: You can install a FASS Fuel Pump. One smart person (I think it was TR4) said: "Any amount of positive fuel pressure you can deliver to your CAPS pump is better than negative (vacuum) fuel pressure."

6) Cummins specs -5PSI as the minimum pressure the CAPS pump needs to operate properly. So you can bet, when you engine will not start or just quits, your fuel pressure will be less than this.. and your CAPS fuel pump is dying a slow death due to lack of lubrication and cooling.

Note: -5PSI is a common reading for vacuum pumps. So don't let that number through you if you are use to seeing +15-+18 PSI on a fuel pressure gauge.

IMPORTANT: You can measure your fuel pressure very easily in your engine bay, and I recommend every one do this: All you need to look at is the top of your fuel filter mount. And if you have a 10mm port on top of your filter mount then you can add the following parts to measure your Vacuum Pressure.

Note: This 10mm allen-plug would be on top of your secondary filter if you have 2 fuel filters in your engine. Cost (<$30).

Here's the parts you can order on amazon:

M10 x 1.0 Male to 1/8-27 NPT Female ($5): https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Oil Filled Vacuum Pressure Gauge - 1/8" NPT ($11):

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
or
https://www.amazon.com/1-1-Filled-Va...ustrial&sr=1-2

Note: Some people might prefer a gauge you look at from "on top" vs. "on the side." These are available too. Plus most gauges have 1/4" NPT threads. I went with 1/8" NPT and a smaller Fuel Pressure Gauge. You might do something different, but given how easy it is, and how low cost it is to add a fuel pressure gauge on top of your fuel filter mount, I think everyone should do this... or install a remote electric fuel gauge if you want to go the "whole 9-yards!"

Here's the Scan tool I have used. (Thanks to another IRV2 member recommendation.)

Scan Tool ($119): https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

So my recommendation for you to diagnose your fuel delivery concerns in the future is to buy these items. After you tighten those 3-lift pump bolts!