Engine/Transmission (1994 - 1998) Power Loss

[illflem]

The solenoid very well could be suspect since it's about the only part of my fuel system that hasn't been replaced. Now that I have a new lead to go on I might just have to run the fuel tank down and buzz up and down Lost Trail Pass a few times. They're doing construction up there and it's down to one lane, one of my engine's favorite kind of places to die. Only problem is I've never been able to make it die when I want it to, it only does it when I don't want it to.



Anyone think a poor solenoid relay or connections could also cause the problem?

 

[BrentL]

Bill, I think I'm going to give the wiring-up the solenoid a shot before I change the over-flow valve. And if that doesn't work,

I'll look at the injectors. I've had some luck getting mine to act up

by running at 2500 to 2700 RPM's for an hour. I've had it do it

in less time when I have 25K behind me.

I have never had this truck act up except on the interstate (maybe those quality highways it doesn't like)! It never has given

me a problem in town no matter how much fuel, or how little was

in the tank.

 

[BrentL]

Thought I'd take a minute to pass on my latest findings:



This past weekend I had a great chance to test the solenoid theory. I tied the fuel shut-off valve wide open, hooked up 14K and headed down the Interstate. I had NO problems at all until the fuel level reached just below the half-tank mark during the return trip.

After this continued to happen a couple times, pulling over to the shoulder, dieing, restarting, and getting back on the Interstate, I resorted to hitting the ignition switch to attempt to revive the lazy solenoid (if this was the culprit) with no success. I am convinced now I should rule out the solenoid and look at something else.



Any suggestion on what to try first? Since the fuel level seems to have something to do with this, I was thinking a pin hole in the pick-up line, at least until I reread Bill's comment on his 3500 not starting when he had this problem. Now, I'm thinking maybe change the by-pass valve.

Bill, have you had any problems yet on the 2500 after replacing your by-pass valve?



Any other ideas?

 

[Andy Redmond]

Has anyone been able to monitor fuel psi while its acting up?

To me others have discussed isolating electrical vs fuel probs.



I've seen several fuel tank modules with this problem. Chafed pickup tube / coils



The "slides" allow it to move up and down slightly and chafe sometimes.



Several have disabled the slide effect on the module when they've been into the tank, while changing a sending unit etc.



J. Donnelly had some good photos of the module out of the tank on his arcticle of the Transfer Flow replacement tank (several issues ago).



I've even repaired a couple, but sufficent time hasn't expired to see if the fix was permanent. This vs a $400 fuel tank module allows one to be create and inventive.







Good luck

Andy

 

[Andy Redmond]

After reading all of the posts. . I'll add something that I should have stated in the original post.



The lift pump has several check valves in it, has this been changed?



The Cummins Shop manuals and the Cummins Troubleshooting and Repair manuals have an exploded parts diagram. The manuals also insinuate that the lift pumps are rebuildable, but AC or Carter won't sell the parts!



They have to eat too I guess.

 

[BrentL]

Andy, I have not done anything with the lift pump other than monitor the fuel pressure. I don't believe that the numerous times the dealer looked at it they did either. They did drop the tank and change the sending unit since my trouble occurred at half tank or less. They also checked the fuel pressure.

I understand there is a filter or screen that can be removed on the lift pump. I will take a look at this. Since this only occurs at less than half tank it makes me wonder why it would be anything in the lift pump, although I considered replacing it just to rule it out. I think I noted in a previous post, the fuel pressure goes from a variable range (30 to 35) when running okay, to a steady 38 lbs. when the problem occurs. So what do you think I should check or replace next?

 

[illflem]

Originally posted by BrentL

Bill, have you had any problems yet on the 2500 after replacing your by-pass valve?

Brent, I haven't had a problem since replacing the by-pass but according to my for sure right on mechanical FP gauge it made no difference in FP with the new valve, still 22-26 psi at all times. Probably the only reason it hasn't acted up is because I've always had a place to pull over since then, it's waiting to get me at the worst possible time like the time it did it in Salem OR at 5 PM rush hour, two lane interstate that should have been four, under construction with concrete barriers at the edge of each lane. It also likes snow covered mountain pass roadsides during blizzards.



Your overflow valve needs to be replaced though, 38 psi is way too high. My two screens, tank and main filter have always been clean. Lift pump is the original stock one but FP indicates it's good.

 

[drees1]

Some additional thoughts based on CAT experience.

Fix the high fuel pressure problem. I have seen blocked overflow cause the plungers to stick in the pump so the governor could not move the rack. On CAT, a 35 psi spec could go over 150 psi! But CAT uses an oil pressure hydraulic servo on the rack. Does ours have oil pressure assist, or is it just the governor weights and spring? If just weights and spring then it might not take too much over pressure to bind the plungers.



Is there any way to put the press gage on the pump body? Or does it matter?



If you are getting pressure in the pump body then solenoid or anything upstream is not the problem. With the location on the top of the filter head, anything downstream is suspect.



Even though the tank is below the engine in terms of elevation, there is a slightly greater suction to pull fuel from a low tank.



I think we are talking about stuck rack, air in fuel, or restriction downstream of your gage.



Keep in mind if air in fuel, a low tank does not allow the air comming in on the return line to settle out as well as a full tank. Could be a minor air problem agrevated by a low tank.



The fact that you are getting more than enough pressure at the filter head should rule out a blockage on the pickup tube.



At CAT we used sight glasses upstream and downstream of the injection pump to diagnose air. Since some air was always present (tiny foaming bubbles) it took some experience to tell what was the problem in some cases. In any event, gross, large air bubbles are a problem.



It would be nearly impossible for it to be the injectors, unless it is knocking and bucking like they are dropping out.



A Cummins shop would be much better at this problem than the Dodge Dealer.



Is there any white or blue smoke while this is happening? If you see white or blue it is almost surely air. But it may be impossible to tell when it is running at speed. Right after it dies, let it set a moment and restart with 1/2 throttle and check for a puff of white or blue. May need to stand right at the pipe exit.



Keep us posted.



Doug Rees

 

[BrentL]

I ordered a new overflow valve from Piers yesterday. Maybe it's the sticky plunger as a result of high pressure... . at least I hope!



If it were air getting into the system, would the engine start just moments after it dies and run to full throttle without a single miss? It has never had to be bled to restart when this happens. Just crank it for a few seconds and it's running normal again.



I have never noticed any excessive smoke when this occurs. I've

looked every time it happens during the daylight hours expecting

to see a cloud..... but nothing I can notice from the cab.



Has anyone experienced a sticky plunger on this pump, and what

were the symptoms?



Now that I think about it... ..... there's still something about that half tank or less that plays into this... ... ... ... ... ... ... .



Thanks for everyones help!



Brent

 

[illflem]

Brent, have you noticed it won't do it if you shut down even for just five minutes every couple hours, I have. Leads me back to the hot fuel theory.

 

[drees1]

illflem,



I hear what your saying, but how do you think the hot fuel is playing into the picture? In order for it to behave the way it is it must be: Rack unable to rotate plungers (for whatever reason), Air in fuel (reducing the actual amount of fuel injected) or restriction in fuel flow downstream of gage. I don't see where hot fuel, in and of itself would cause a power loss other than due to reduced density because of expansion, which is not too great. If I remember right, #2 cracks down around 460F. Up to that temp, it is pretty stable. I doubt if it is hot enough in the tank to cause a heat related problem with the pump or injectors. The injector tips surely don't run that hot.



I am looking at it from the fundementals that it is loss of fuel injected into the cylinder causing the problem. Are there any other things that can cause these symptoms?



A truck in good condition that is shut off and re-started will fire on the 1st or 2nd piston to go over on compression, especially with a small amount of accelerator input. If this truck actually cranks a second or two before starting, then the problem is still present, but the system is able to deliver the idle quantity of fuel to get it running and make it seem normal.



The fact that throttle position has no effect seems to indicate it is starving for fuel, or so much air entrained it can't pump much fuel.



What is EGT and Boost doing when this happens?



One other question. For those with fuel pressure gages. When you shutdown how slow or fast does the pressure bleed down when you turn off the key? How does that compare with the shutdown of the problem child?



Sorry, one more question, if anyone knows. What happens if the overflow is blocked all together on the P7100? On some pumps this creates problems with air in the pump. Fuel can cavitate some as it enters the barrels and in some pumps it is REQUIRED to flow fuel through to keep it clean of "air". That is the foaming we see when we use sight glasses.



Keep this thread going, I want to know what is really going on!!

 

[drees1]

Can't get this off my brain!!!



OK. Let's talk air in the fuel, but not due to a leak! Question: Can a bad overflow valve airate the fuel as it exits? Or can air in the fuel create a mixture that offers different resistance in the overflow valve causing it to increase pressure? Since the overflow relieves pressure, any air traveling accross it will expand greatly as it exits to lower pressure in the return line. The overflow is simply a spring biased plug, so if downstream pressure in the return line is raised, so will the pump housing pressure upstream of the over flow. A sticking overflow would cause fluxuations in fuel pressure as the throttle was moved. I think there is merit to my theroy that the air in the return line does not settle out in a tank without a lot of fuel as well as a full tank. In other words, maybe some air in the return line fuel is being picked up by the suction tube in the tank. What ever the real cause, the answer must validate ALL of the evidence, including high fuel pressure, low fuel level.



I'm sure it could be resolved on a chassis dyno with a fuel pressure gage, various fuel levels, and sight glasses. But, that would cost $300 - $500 unless you know someone.



If the new overflow does not solve it, what next??



Doug Rees

 

[KYOUNG]

how about the tank gets half empty, and the return line inside

the tank is split above the fuel level and is aerating the remaining fuel in the tank..... causing it to try to run on foamy fuel.

this has got to be an inside the tank problemOo.

 

[BrentL]

Bill, Never tried to shut it down as you suggested. When I have it loaded up and pulling, less than half a tank, and in the 2500 rpm range, I'll do good to make it much over an hour before the problem begins. I have had times when I was loaded and had to run on the two lane highway instead of interstate to keep the rpm's from running that steady 2500. I guess a stop light or the turning vehicles every now and then may serve the same purpose as you suggested.



I'll make some better notes on the boost and EGT's the next time

this occurs. If I recall last time the EGT's were 800 to 900 (Pre turbo) and boost still in the 20 range while pulling. I do know that what little acceleration I had left did impact both.



I'll keep an eye on the fuel pressure pre & post shut-down to

see for sure where it's at. I think I'm going to leave a notebook in the truck and start recording everything.



As far as the next step... ... if the new overflow valve is not the fix

... ... ... . I'll plan to pull the tank and dissect it!

 

[BrentL]

It has been almost four months and 4K miles since I replaced the overflow valve. As of today still no problems have been encountered. I'll wait until next Fall before I claim this problem

is fixed. It may need a few July days and long hauls to put

it through a real test.



Bill, Any problems so far on yours since the overflow valve replacement?

 

[illflem]

None Brent. I'm hoping that was the problem but still have my doubts...

 

[RJ2]

Anyone got a picture of the shutdown solenoid . In case i ever need to tie it up on the road. Thanks RJ

 

[illflem]

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[illflem]

The lever pin below is the part to lift upwards



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[RJ2]

YOUR THE MAN ! Thanks RJ