Engine/Transmission (1994 - 1998) once truck warms, it misses and then stalls

[DCatanzaro]

Some info:



1994 12V 5. 9 200,000 miles, biodiesel gas for past year or more



Starts great, no smoke, no problems, runs great...



after a variable period of time, (motor warms up) the motor will then obviously begin to "miss" and then stall once you slow down and come off the gas pedal.



Coast to side of road, starts right back up... no problems, then it happens again,



You travel less distance each time before it stalls out.



changed fuel filter - no better



in fact, problem is getting worse. . l



HELP!!!

 

[hsmith]

My bet is the pre screen filter is restricted from the bio fuel. I had one recently so stopped up I don't see how it make it to the shop. He had been running a lot of cooking oil, etc.

 

[DCatanzaro]

Thanks for the quik response. My poor truck has not been right for months and i miss driving it. I will check this out.



Question: If the pre-filter is clogged/restricted, why do you think it would run really good till warmup?

 

[mwilson]

Fuel shutoff might be failing and dropping the lever after it warms up, that will cause some strange symptoms.



Shutoff linkage could be dried out, also.



Just a thought...



Mike.

 

[DCatanzaro]

Thanks ever so much... what has me most confused is that if I trigger the "missing" in the driveway, the motor will continue to run somewhat rough and the injector pump makes a clicking sound.



in other words, the motor does not always cut off completely every time.



does this still indicate a fuel solenoid problem?



again, thanks for all the ideas. I am a new member and this is my first post so bear with me if you can.

 

[hsmith]

Well, that could be a sticking plunger on the solenoid also. Take it off and inspect. The boot is probably deterioated.

 

[Nyoest]

Probably the p pump going out. One of the plungers is sticking in the bore and the cam is slapping it. I've seen the same exact failure on two other pumps.

Get it running, get it to miss/clicking and feel each individual cylinder of the p pump. If its one of the barrels you'l feel it.

 

[BIGNASTY]

Quote One of the plungers is sticking in the bore and the cam is slapping it



RUN SOME ADDITIVE LIKE AMALGAMATED SEE IF IT UN STICKS. I KNOW FOR A FACT THAT IT CLEANS THINGS JMO

 

[mwilson]

Probably the p pump going out. One of the plungers is sticking in the bore and the cam is slapping it. I've seen the same exact failure on two other pumps.



Get it running, get it to miss/clicking and feel each individual cylinder of the p pump. If its one of the barrels you'l feel it.

I hadn't ever heard that one before.



If that Bio is kinda' dry and has scored the bore I can see why that could take place.



The warmer it gets, the harder the plunger would stick... .



Wow... . learn something every day on here.



Mike.

 

[BIGNASTY]

Bio is a VERY good cleaner didn't see that he ran it.

 

[DCatanzaro]

Update:

spent a lovely saturday with my beloved but ailing cummins...

1) checked prf-filter, not too dirty, took a pic, will try to figure out how to post it, seemed very loose upon removal, put back tight



2) solenoid seems OK, did not take off since boot was intact and passed t he tests in manual for proper operation



after this, the truck was much harder to get to stumble - would not miss in driveway, had to take out on road to act up, able to limp back and keep motor running if I kept a little gas going while I braked.



OUCH!!! THE PUMP HAS ENTERED THE DISCUSSION>>> I need more advice on how to determine pump status. It seems like the motor stumbles and then the clicking shows up, occurs about every five seconds or so...



with reference to BIGNASTY, i have run biodisel quite a bit and i cannot find out where the amalgamaed additive is available.



Thanks to everybody...

 

[fest3er]

My bet is rotted fuel line letting air in. The stumble may be that air working through the p-pump.

 

[DCatanzaro]

I guess one of the previous mechanics ahd the same idea you did. The return fuel line hose has been replaced.



I MADE A PRESSURE GAUGE from the information here at TDR, got the connector, installed the connector and observed the folowing:



1. pressure at idle is 14; specs in manual say 25 minimum

2. when I installed the new banjo bolt, i had to prime the pump. each time I pressed the lift pump plumger I heard a hiss-type sound by the injector pump.



The directions to install the connector indicated that you should pump the plunger till you get 20 psi and hear a hiss from the overflow valve, then start motor.



Should I hear a hiss each time I press the lift pump plunger? Also, I was never able to build up pressure to 20 psi. The truck started fine.



What is going on?

 

[MLee]

Old overflow valve? If it is, you can do one of two things, replace it, Or, if it has the screw on top take this off and remove the spring, don't lose the check valve,(bearing looking thing inside bottom under the spring). stretch the spring till its 1/2" + . 050 or 550" (thousandth) total, or just a hair over 1/2". this should bring you up to 20# psi @ idle, 30# @ 2000. Just be careful that you don't break the spring so easy does it. Just something else to consider for low fuel pressure @ the pump.

 

[DCatanzaro]

I guess it is time to visit the overflow valve which does appear to be quite old/untouched in a long time.



HOLY COW, BATMAN!!! Figure this out... when I do the classic check for the overflow valve by pinching off the return hose the pressure goes DOWN!!!!!!! The opposite of what one would expect.



This would seem to me to bve a very significant diagnostic key except I have no idea what it means other than creating a vacuum from the tank.



I will check the overflow valve. Can anybody help explain the drop in pressure (to zero wichin 10 seconds and immediately recovers after letting go) when the return fuel hose is pinched???



thanks for the advise, MLee

 

[hsmith]

You may be pinching the supply, not the return.

 

[DCatanzaro]

With the pressure drop to zero upon pinching off the return fuel line, could the previous mechanic have accidentally reversed the lines At the fuel sender? If so, would the motor still run and explain the low pressure?



Does anyone know which is the supply and which is the return connectio on the fuel sender? One is toward the motor and the other toward the tailgate.



Stay with me, this is getting interesting...

 

[MLee]

The lines are a different size, and the original connectors are different unless they have been changed and hose clamps are now in place.

And maybe they were switched by the fire wall. There again different size, but could be forced on if clamps were used and not changed one at a time. follow the return line from the OV back above the intake, that one should be the 5/16 line. The other would go to the fuel pump area.

 

[hsmith]

I'm thinking if the lines could possibly be reversed, wouldn't it cause a no run at all issue?