Engine/Transmission (1994 - 1998) Fuel contamination or lift pump?

[Jfam]

Well I have read a fair amount on the forum re: occasional stalling and sputtering…. symptoms I am having on my 94 with 225k. Two things I noticed that I did not see mentioned.

1. When changing the fuel filter I poured out the contents and noticed some small black flaky material, not a lot. I also noticed the same material in the heater screen. Cleaned and replaced both and she ran OK for a couple of weeks.

2. Today when symptoms reappeared I decided to drain a little fuel from the filter (Fleet Guard) and noticed that it came out VERY slowly. . dripping as opposed to a “normal” flow. I also saw one of the black flakes. They disintegrate rapidly upon touch.



The engine sputtered and would stall if I backed off the throttle, but it cleared up in about 3 miles. I heard a ticking sound when it was at its worst, something like the hydraulic tappets did on my ’56 Olds back in the dark ages.



I am leaning toward contamination and guess that the “ticking” was a clogged injector, though of course that could be completely off.



I will cut the filter tomorrow and check for contamination.



The return fuel line was replaced about 50k ago with steel braided racing line.



Any suggestions would be appreciated.

 

[nfox]

ticking

The ticking sound you described is your lift pump is getting bad. They will sound like a bad lift when they are getting weak.

 

[illflem]

Your overflow valve will also tick when it's going bad. The black particles you see are a normal component of all diesel fuel called asphaltene, don't worry about it unless it's excessive.



Fuel filters and what clogs them http://www.baldwinfilter.com/engineer/94_14.html

 

[Jfam]

I ordered a new lift pump today. An inspection of the dissected fuel filter revealed that it was clean.



Would a defective overflow valve create the same symptoms as I described?



Thanks...

 

[illflem]

The problem you describe is definitely fuel related but may not be the lift pump or even the overflow valve. Before you install the pump it would be a good idea to check the fuel pressure so as not to waste your money needlessly. It almost sounds like you're sucking air somewhere but that will usually result in hard starting also. Don't think a clogged injector is your problem. It very well could be the '94 & '95 ''mystery problem"

Read this and see if it describes your problem-- https://www.turbodieselregister.com/forums/showthread.php?s=&threadid=33480 .

 

[Jfam]

Well, I know what the problem isn’t! I replaced the lift pump and the supply line hose (the return line was replaced about 50k ago). But the problem persists. Not worried about the expense as the engine has 225 k and I suppose the replacement is not a bad idea.



Got a pressure gauge ordered .



I have noted that it is ONLY –as far as I can tell—when the truck has been running for about 30 minutes, and then stopped for less time than a complete cool down, and especially if it is parked on a slope. Then hard starting, and occassionally bad "missing" and sputtering.



My next fix would be the overflow valve, which LOOKS like a simple operation. Unscrew the old one and in with the new, right? Would the above clues be consistent with a defective overflow valve?



Any information appreciated…

 

[illflem]

Could very well be the overflow valve, hard to tell without a gauge. Many times as the overflow valve weakens heated fuel will cause the spring to lose tension resulting in lower fuel pressure and poor performance.

 

[wcjp]

Have you replaced the fuel preheater to lift pump hose?

 

[Joe G.]

I want to reinforce illflem's remarks. Buy, borrow, rent, or steal a fuel pressure gauge before buying ANY more parts. It may be something real simple, but unless you know what your pressure is when it's running ok and when it's failing you will be just guessing and spending money you don't need to spend.

 

[Jfam]

I ordered and installed a fuel pressure gauge (range 0-30, electrical sender) from Geno’s Garage for $91. Real nice.



The sender is installed in one of the diagnostic ports of the Prime-Loc Remote Fuel Filter mount. Pressure floats around depending on rpm, but stays in the 22-30 range. 50 mph results in fairly constant 28-30 lbs. Occasionally, there is a very sharp spike from (e. g. ) 30 to 26 and back in a split second. Not at all like a spring-loaded valve opening and closing.



The symptoms persist: Only when fully warmed up, if shut down and restarted while still hot, slightly to moderately hard to start, with very rare sputtering, “missing,” and stalling if rmp drops too low. Symptoms clear up within a couple of miles. I have not seen the rare symptoms since I installed the gauge.



Recap on current fixes:

Lift pump replaced, supply and return fuel line hoses replaced.

Fuel filter dissected (very clean) and replaced.

High-pressure leak test (cardboard test) = negative.



Remaining guesses are:

Overflow Valve

Clogged fuel tank vent.

Fuel heater hose

Leak in the water detection module of the fuel filter.



Any other thoughts greatly appreciated.



PS Anyone know which wire on the engine firewall is the dimmer switch wire so I can have light for my pressure gauge?

 

[illflem]

Be interesting to see what your fuel pressure reads the next time your problem appears.

On my '95s the dimmer circuit wires are tan. Easiest place to tap into one is in the bundle that goes from the steering column area over to the stereo.

 

[Jfam]

Final clues??!!!



Problem appeared again today. As usual, after engine hot and sat for 20 minutes. Fuel pressure dropped dramatically (28 to 15, then stall. ) Additional notes: Ticking noted. Also, and this really worries me, foot pressure on accelator noticably increased. That is, a resistance to the pressure applied by my foot to the accelatorator pedal. I have noticed this before.



I shut the engine down and restarted about a minute later and all well.



Overflow valve, or (God forbid!) injector pump?



Thanks for all your help so far. WHAT'S NEXT???

 

[illflem]

Sounds like the overflow valve is acting up when it gets hot, replace it.

 

[johnjackson]

I don't think they go bad very often but when fuel shutoff solenoid starts going do they act like this?



John

 

[illflem]

I've never experienced the solenoid act up when hot but Piers once suggested it to me. I think I'd still replace the overflow valve first since most will eventually fail at some point anyways.

 

[Jfam]

Went to the dealer to pick up the overflow valve and had a great talk with the technician. He seemed very knowledgeable. He said that he had a similar case that was caused by a bad starter relay. It also would tick when acting up. What he said was happening was that the relay would not activate the shut-off solenoid continuously, but that it would fluctuate rapidly, thus causing the ticking. After setting for a few minutes, it would be OK! Well, I might try that next if overflow valve is not the problem.



Is it a simple matter of unscrewing the old and screwing in the new, or does the injector pump (or anything else) have to be removed? It appears that that there MAY be clearance for the removal of the valve, but would greatly appreciate hearing from someone who has already done it…



Thanks again…



Joe Fam

 

[illflem]

Some OF valve clear, others don't. You can grind or file off a little of the part that the valve hits on to make it easier. Stuff a rag in-between the injection pump and the block so the sealing washers on the OF valve don't fall too far.

 

[PHaller]

Try loosening the fuel cap and check to see if the infamous early 12 valve RED CAP is in place.

The red cap is located on the top of tank module covering the 1/8 inch tank vent.

The fuel system is sealed and will build vacuum. Many early trucks were shipped with the cap in place and caused vacuum inside the tank with enough inches mercury to deform the tank. IMHO, that may very well be the "mystery problem" .

Just crawl under and look at the top of the tank module. An inspection mirror helps. If the cap is there remove it or run with the fuel cap loose.

-Paul R. Haller-Oo. Oo.

 

[Jfam]

I replaced the overflow valve and the fuel pressure rose in the entire range about 4 lbs. That is, the range before the change was 20-30; after the change it is 26 to buried on the 30-point gauge. When the engine is hot and has been stopped for at least several minutes, it still takes about 2 seconds to turn over, as opposed to immediate turnover when cold, and the pressure at 500 rpm idle is 24. Once I did hear the “growling” symptom (like when you rapidly, but lightly tap the accelerator pedal). So I am still not 100% sure of the fix, though it appears that the valve was certainly failing. And I suppose the slightly harder start when it is hot could be just due to age (226k).



I had to file part of the (I guess it’s the intake manifold housing) away in order to install the overflow valve. Looks like that was an oversight in the original design plans for the engine because a section seems to have been cut away with a torch. The unclean cut left a little nipple, which I had to file.



For those who have a similar problem: hard starting after sitting when hot, BUT NOT sever missing once started, I would recommend based on my experiences:



1. Replace the fuel return hose line.

2. As all have said, get a good fuel pressure gauge. I think the one from Geno’s is excellent, though I wish there was such a thing as a 0-40 range. The hardest part of the whole installation was finding the dimmer switch wire. Once I discovered that the dash trim is snap-on, with the exception of having to remove the cup holders and ashtray, it was easy to access the switch itself and tap into the proper wire.

3. If hard starting and missing are the problems, followed by clear up after a mile or two, in my case at least, it seems SO FAR to have been the overflow valve. I do not know how you would diagnose the difference between a failing overflow valve and the lift pump, but someone on the site would. . probably illflem.



Thanks to all for the help, especially illflem. The next really hot day should tell the tale!



Joe Fam

 

[PHaller]

I think you can check if it's the lift pump or overflow valve by pinching the rubber portion of the fuel return line and checking for pressure rise on a pressure gauge. If its your lift pump, the pressure will rise slowly on the gauge or not at all after pinching the return line. If it's your overflow, the fuel pressure will rise immediately to about 60 PSI.

-Paul R. Haller-