'pants

Past ten days or so, my truck has been losing power and dying while on the freeway, even when under load at 60MPH. I've been able to coast in N and get over out of the way with no PS and sketchy brakes, but this is no way to live.

After pulling over, it restarts. This may be immediately, but not a normal start; it acts as if it's got air in the system and takes a bit of cranking. Once it's restarted, it runs fine, until...it doesn't, which might mean another ten minutes on the freeway. (Thus far, this has only happened on the freeway.)

I long ago modified it by installing an in-tank electric pump, so any leak between pump and IP would show up as a fuel-leak, not an air leak.

That still leaves the suction-side of the pump to be verified as unblocked, but I think I've got that covered, too: I've got an unfancy mechanical fuel-pressure gauge that's currently poking out from under the hood near the wiper-blade, so I can monitor fuel-pressure by peering out at this gauge while driving. It's plumbed into the last fitting at the IP inlet. Thus, today when the engine started to feel fuel-starved and then died on the freeway, I was able to verify immediately that the fuel pressure was still normal (20-25psi while cruising). I've not seen it dip below 20psi at all, and it gets there almost instantaneously when the key is in the on position.

What else is there to look at?

Lary Ellis (Top)

Probably a silly question but when was the last time you changed the filter?

'pants

Doesn't really make diagnostic sense to change the fuel-filter, since the fuel-pressure is a consistent 20+psi AFTER the filter, right at the IP inlet, where it counts. When the filter is obstructed, it'll drop to ~5psi and stay there, at which pressure it will barely idle, maybe limp home at 800RPM if I'm lucky...

Lary Ellis (Top)

Only if you truly trust your "unfancy mechanical fuel-pressure gauge that's currently poking out from under the hood near the wiper-blade".....I always go with the simple things first......only time my 96 ever fell on it's face like that was when the filter was dirty.

torquefan

Next thing would do is, next time it dies, without touching the key, coast to the side of the road and have a look at the fuel shutdown solenoid and make sure it's still in the fully up position. It would be very unusual for it to drop while driving, but I would sure want to rule it out. After the incoming fuel pressure, and that solenoid, there's not too many other potential causes other than an internal injection pump problem.

patdaly

This is where I would be looking as well. Best guess is there is an intermittent in the solenoid wiring, and it isn't always feeding power to the pull circuit.

oliver foster

I agree if it is getting fuel and the FSS is working correctly, it should not stop running.
I would check both closely first.

'pants

Good thought about the FSS - I hadn't even thought about checking that...but for sure, my brain and fingers have forgotten where things are supposed to be when it's working right. I poked at it a little, only able to note that it 'sticks' magnetically all the way up, when pushed way up and key on (without running), but it wouldn't get there without my pushing it up. I'm vaguely recalling now that this happens with throttle-cable-assistance during the normal startup procedure, right?

But here's the thing: I took the same route out to a jobsite this morning as I did the other day when it died on me, and the loss of power happened within a few hundred feet of where it happened the other day...some 12 miles into my 'commute.' It was actually a little spooky to be in that very same spot again, pulled over. No amount of throttle-abuse would keep it running, as I fought to keep it alive over the 5-10 seconds it took to die while working my way over to the shoulder, though the FP continued purring along with no dips at about 22psi.

It restarted after I'd coasted to a stop and cranked it fairly hard (say three sessions of 15 seconds each, with no coughs or splutters until it restarted, much like an out-of-fuel session). I drove off my exit with it feeling normal...whereupon it died yet again, about a mile after the previous event. I couldn't help but block traffic briefly while restarting it, and (once on surface streets) it didn't give me trouble during low-speed maneuvers into Pearl Harbor, where my jobsite is, a few miles further.

On the way HOME on the freeway, with my speed a bit lower due to rush traffic, it seemed like it might not complain, but...again, at the 12-mile mark or so - and two miles off the freeway in my residential neighborhood, at ~25MPH - it died AGAIN. Until that happened, I was thinking it was a cruising-speed-related issue. Restart was as described above.

I can only think to eliminate the possible FSS weirdness. I'll almost certainly have more chances to find out whether the FSS is somehow letting loose...partially? As a heat-related thing? ****...

'pants

No problem enroute to jobsite this morning...but four episodes on the way home, the first of which was on the freeway. I'll never get "used to" that routine, since there's always traffic, and not always a shoulder, nor a convenient coasting zone.

Anyway, the FSS was fully retracted/up when I pulled over, and again when I checked it during the third event. (That's good, right?)

Last 3 times were on surface-streets. Fuel-pressure never showed any variations. I am out of ideas, other than for the possibility that somehow occasional slugs of air air are getting into the pump intake, but maybe the pressure-variations are small enough so as not to be obvious on the pressure-gauge. I had the module out after I got home and couldn't see anything amiss.

In the past, when I was tweaking the immersed-pump module setup, I found that if the return-fuel is routed outside of the module to the tank in general, the pump will fairly quickly cavitate, because the fuel can't quickly enough recharge through the relatively fine mesh that keeps crud out of the module, but the return hose was still in place, and there's an audible alert to the cavitation (you can hear the pumping speed fluctuating wildly) so I don't really think that's it either.

Anything?

'pants

More insanity-diagnostics: I put a coil of transparent fuel line in line with the IP inlet, and tied it up so it's peeking out from under the hood near the windshield, thinking maybe I'd see air whipping through the line at some point. Nope. Died four times on the way here, with no bubbles or loss of fuel pressure.

But it finally occurred to me to look at my air-filter. I neglect some aspects of maintenance badly, and this is one...it's UGLY-tarry on the intake side. It clearly needs changing badly, even if it's NOT the problem.

I'd know what to expect from a clogged AF in an internal-combustion engine (choking and enriching the mixture to the point of causing various problems), but what happens in the diesel-injection setting when the air-flow is obstructed? Does this 'dying after several miles, but restarting without too much trouble' sound like a symptom of terrible air-flow?

oliver foster

What boost #s have you been running with the dirty air filter?

Busboy

Try running some fuel system cleaner with an algaecide.

'pants

Algaecide - good thinking, but I'm all too intimately familiar with the innards of my tank. I've had the fuel module out a few times in the last ten days or so, and use a flashlight sometimes in that process to inspect stuff - there's no trace of algae in the fuel.

Update: I've found that with my tank above about 1/2, I never have the dying-on-the-freeway problem. Thus, it's impossible for me not to conclude that somehow, air is being sucked into my in-tank pump when the tank volume gets a little low. I can't crack that nut, though. I've not changed anything about that setup for quite some time.

Further update: I'd been resting comfortably with the above conclusion in mind, just keeping tank level up, and in the interest of general maintenance, replaced a segment of fuel-hose that (per my mods ten years ago) connects the 'from tank' tube to the banjo-inlet-fitting at the IP. The tubing had been rotting at the ends and had begun to drip from stresses during my recent testing. I test-ran the engine after that project; since I have an electric pump, there probably wasn't much air trapped after the pump had run for even 10 seconds, and it started up fine. I ran it and revved it a bit to be sure, then shut it off.

The next morning, it started HARD. I figured there must be some air trapped after all, and I drove 13 miles to work, and back home later, with no problem. Next morning: harder start. Repeat of the above, except that my long-observed "standard startup method" no longer worked, even later in the day. (Standard startup used to be this: crank for about 3 seconds, then stop. Next key-over would make it start immediately.)

I'm in Honolulu. Temp in the AM is 74, and on the way home, 88.

Morning starts are variable now, but generally hard. Twice in the last week, including this AM, I've given up and used a brief shot of ether. And this afternoon, it started hard after work.

Maybe I need to treat this as an entirely separate problem from the "coasting over to the shoulder on the freeway" engine deaths this thread started off with. There are too many symptoms and other variables for me to process.

So if I just said:
a) my engine starts hard, but runs fine once it's running,
b) fuel-pressure is never less than 20psi at the IP inlet
...what would I be looking at?

Not to be too gloomy, but in my very limited experience with diesel IPs, this new set of symptoms ended up with my having to rebuild my excavator's IP, to the tune of $2K...but not before probably wasting time and money on rebuilding injectors first.

--Dave

patdaly

Ok, before you try to start it when you believe it should start hard, prime the system with the lift pump primer until you hear the overflow valve singing loudly. If it starts easily, then you know that you have air intrusion. Lots of guys just go rubber all the way from the tank to the pump with diesel rated hose......

'pants

Hey Pat,

You're talking about just switching the key on and listening under the hood, then, in my case? I long ago retrofitted it with an electric in-tank pump...If it's quiet enough, I think I can hear the buzz you're talking about even from the cab, but I can't say I've looked for it lately. Will check this AM.

BTW, is that buzz the fluttering of that pressure-control spring check-valve I remember being near the IP outlet?

Thing is, my simple mech pressure-gauge is right there in front of me, poking out from under the hood, and it never fails to sweep up to 25-ish PSI, within a second of keying over. When I was first tweaking my homebrew in-tank pump setup, and it was taking in air (without the engine on), I'd definitely hear that buzz, with the pitch changing all over the place (higher when cavitating). During the weeks that I've been dealing with this collection of problems, I've not heard that - but can't swear it's not drowned out by road-noise, other cars, etc.

--Dave