How hard do I try to diagnose a departing truck?

I have a '91 F250, 7.3L diesel.

We bought it to run on biodiesel, but switched back to normal after having a shop replace the lift pump and describe the failure as one they see as common with biodiesel (I really don't want to get into whether bio is good, bad, not quite ready for prime time, or what; the truck's leaving, so it's not my concern right now).

What is my concern is that the truck's ongoing issue was the nasty sludge the the bio seemed to have loosened up, which had been otherwise happily sleeping on the bottoms of the tanks. In reality, this is probably more likely the culprit than the biodiesel itself. But it's nasty stuff, and there's a lot of it (the rear tank's floor was about 1/8" deep with it; it's got a consistency somewhere between toothpaste and tar, with the stickiness of syrup).

For months after they emptied the tanks of bio, I ended up changing a ($20!) fuel filter every couple of hundred miles. We only drive the truck to fetch home improvement supplies, so it wasn't bad enough to take drastic actions.

Finally just being unable to cope with the stupidity of that situation, I ordered a new rear tank. In the meantime, we'd been using the truck only on the front tank, and the sludge getting to the filter seemed to be subsiding.

Anyhow, when I arbitrarily picked the rear tank to replace, I picked wrong. It's just a big pain because the way it fits between frame rails and crossmembers, there's no access to the hoses 'til you drop the tank, and you can barely move the tank 'til you undo the hoses. I wanted to throttle the guy who did the Viton fuel line update we had a shop do.

Much cursing later, the rear tank was in. I ran down and put a half tank in it, and proceeded to observe my failure.

I believe the problem with the rear tank is that the rubber pickup "bell" (bell/funnel-shaped pickup and screen holder) that went on the tube softened up a lot from all the carb cleaner I used to get the gel/paste/sediment off of it, and it's sucking air around the joint between the bell and pickup tube.

In the meantime, it's become recalcitrant to start, even on the front tank with a fresh fuel filter. Put it on a block heater for a few hours and one day it starts great, two days later with the same maneuver, I run the battery down twice with no start.

As the title suggests, I'm about ready to be done with this truck, and I'm more or less ready to sell it in its current state and just walk away. But of course it's easier to sell a truck when it starts every time, and you probably get more money for it, too

So, here are the likely candidates, and what they apply to.

• lift pump again (it has had to pump a bunch of crap); this would affect both tanks.
• front pickup finally completely clogged with crud; hence the now-not-wanting-to-run-on-front-tank
• rear pickup sucking air to to carb cleaner degradation; this would explain why since replacing the rear tank, a truck which would run okay on the sludgy front tank won't run on the new rear tank but briefly.
• the injection pump, which IIRC was probably a year or two too old to be Viton and thus biodiesel compatible for the long haul, finally expired? Seems unlikely, as it has recently run quite well.
• further unspecified problems finally coming home to roost

Here are things I'm contemplating doing, with varying amounts of disgust:

• Walk away, selling cheap and not looking back.
• Gamble $80 to put enough diesel in the rear tank to submerge the joint between pickup tube and bell. If this works, it still has to be fixed, but at least I know what the issue is for sure.
• Drop the rear tank again to put a hose clamp on the pickup bell, and hope really hard that I'm not doing this nasty job for nothing.

What would GRM do? What would GRM have me do? Same thing, or different?

Chualk it up as a life lesson about buying Ford products? Hey at least the driveshaft didn't explode.

nicksta43 wrote: Chualk it up as a life lesson about buying Ford products? Hey at least the driveshaft didn't explode.

I've owned plenty of Fords and only blown up one driveshaft.

Fill rear tank and see what happens. you can always drain it if it doesn't work. Sell with full tank.

Fuel lines probably need to be purged. Your gloppy goo is probably clothing like an artery. She's having a heart attack. The block heater probably works, but only when the clot is near the injector.

Are you sure that this is a fuel problem again? Did anybody check the condition of the glow plugs?

Fix, if so inclined or full disclosure when sold. Only legit options. Sounds like you are done with it. Get it started for new buyer, explain issues, discount price a bit, and let it go.

Thanks for the input.

It's a ratty old truck, so its value running isn't going to be as far above its value not running. We paid about $2500 for it several years ago, and it's got some value as the hulk of a fullsize diesel 4x4.

I think I'm going to gamble the diesel on the rear tank. Maybe it'll start today, and I can drive it down to the station on the front tank. Making four or five trips with the jerry can sounds tedious...

In reply to Boxhead Tim: I haven't explicitly checked them, but its modus operandi is to fire quite well when it does, and not do a lot of "five cylinders, now six and a half... eight!", and until quite recently, it didn't even require the block heater. It was just a matter of "if it doesn't start, change out the fuel filter and everything's good again". Of course it's possible one or more glow plugs have gone in the interim, but increasing pluggage of the forward tank's pickup seems more likely.

The fill-the-rear-tank option is nice because it answers two things: If it runs correctly after that, my theory about the rear pickup is correct, and we know the the front-tank issue is almost certainly a clogged pickup. If it doesn't fix it, things are still foggy. But as gearheadotaku points out, it's still 19 gallons of viable diesel, it just needs to be pumped into the other tank to access it and to make the rear tank light enough to drop it back out...

Whatever the state of it when it goes, any potential buyer will get the full scoop.

FYI: Biodiesel acts like a heavy duty detergent. Good news is that it cleans as you use it, bad news is that it removes what is probably 300k miles of crap in the fuel system while it does that.

In reply to Timeormoney:

I will go ahead and regard that biodiesel fact as a generally nifty thing, even if it is the root of a giant PITA for me... When you say 300k, it makes me cringe. This poor truck's only got 135k on it (if you listen to the odo and carfax, which I'm not entirely sure I would). I don't know what was on the floor of the tank, but it's an 1/8" of the thickest, stickiest paste I've ever encountered in a vehicle.

I went and put the full 19 gallons in the rear tank (one balky, unvented 5-gal can at a time), so the pickup is now submerged for sure, and the seal to the pickup tube is irrelevant...

It's tried to start twice but cut right out. I'm giving it a break 'til tomorrow, but am still crossing my fingers that it just needs to run to purge a bit. Figure I'll throw the block heater on it while I'm working, and give it its best chance of firing up... Even if it doesn't need the heat for combustion, it'll help with the cranking.

Wish I knew more about the mechanically injected fords. I had the 6.0 and ran a couple tanks of high biofuel mix in it, checked my filters and never ran it again. I wish you the best of luck, my guess is that the truck sat for a long time that sludge is the remnants of a once full tank of diesel. That motor is rumored to be highly bullet proof and is often sought after, the 1995 being the "one" to have.

I would find out if you need to prime anything for that mechanical injection.

1995 Fords were not mechanically injected. Those were all Power Strokes using the HEUI injection system which loves bio. If I had to pick one truck to run on bio, it would be a 7.3 Powerstroke.

I stand corrected. My diesel mechanic buddy always told me to be on the lookout for the 95 as the year to get because of the injection. Learn something new everyday.

I have little to add except; recalcitrant. Nice.

This just looks like a standard fuel system cleaning to me. Pull both tanks, put a gallon of acetone and a handful of 2B gravel in each one. Put them in the bed of a truck, the trailer of a tractor, strap them to the roof of your Miata, whatever. Get 'em sloshin'. Pull the fuel line off at the filter housing and clean out the lines with solvent.

If you still have issues after that, sludge has made it past the filter to the injector pump and/or injectors. You can try running a few tanks with some diesel injector cleaner and see if it works its way out, but chances are (if you have injector issues) its because either air or debris has damaged/clogged the pintles and seats in the injectors.

The injector pumps are pretty robust. I would expect the injectors to become damaged long before the pump.

But, then you are back to the same question.... will your investment of time and money to diagnose/repair be offset by the additional money you would get from the sale? I can tell you this... diesels scare a lot of buyers. A poorly running diesel is scrap in the eyes of most buyers. Lack of education means that you will be basically limiting your buyers to diesel techs or mechanics who think they are diesel techs.

In reply to curtis73:

Thanks! It is a good word, isn't it?

I love that not only is Miata The Answer, it's assumed that everyone will have one one in their toolbox for tank cleaning and so forth. I'm actually between Miatas right now, unfortunately... In better news, I have a Shiny New rear tank, so at least that saves me one cleaning. Given that it took me two cans of carb cleaner, a toothbrush, and about 45 minutes just to clean the pickup and sending unit, I'm not enthusiastic about attempting to resurrect the original tanks.

You could well be right about the injectors. I'm still crossing my fingers because it ran fine when I actually got it to start last week. I'll try the injector cleaner if I can get it to start. Bummer that even testing things like fuel volume and pressure on a diesel involve getting it running first

I fall into that category of people scared of diesels, either despite or because of owning this one. Perhaps if I had a nice scaffolding... There's plenty of room around a lot of stuff, but that big engine bay so far off the ground I actually find to be really difficult to work in. And a lot of stuff seems to be visible, but just really awkward to get a wrench on.

If it doesn't fire up off the full rear tank, I guess that means that either it's developed a new problem, or finally succumbed to the abuse it was getting from all that crap at a relatively coincidental time. Could easily happen. With the loose-ish pickup submerged, the only other things I could have fouled up on the rear tank are perhaps not getting a fitting slid back on all the way (seems fairly unlikely), or kinking a line. I don't think I did so, but stranger things have happened, and I have caused some of them.

I'll post again tomorrow after work when I try to start it after eight hours on a block heater...

Oh, here's what the rear tank's pickup looked like before I cleaned it. I believe it was only using the emergency restriction bypass flapper on the side, which itself was 75% clogged...

The pile of dirt in the background is the old tank... The blue tarp in the background covers building supplies for the garage expansion

That really looks like glycerin. How good was the bio you put in it?

In reply to curtis73:

Hrm. It was from a seemingly popular and centrally located SeQuential Biofuels dealer here in diesel-adoring Portland.

Not that any of the above guarantees a darn thing.

is that a co-op or commercial? co-ops have a chance of occasional bad batches, but its pretty rare. Commercial suppliers have to conform with ASTM which I think requires less than 1/2% glycerol. Still a possibility, but highly unlikely. I was basically asking if you got it from a pump or if you made it yourself.

Maybe its just some yicky junk

In reply to curtis73:

I believe they are commercial, and claim to meet ASTM standards: http://www.sqbiofuels.com/production

It's definitely yicky...