Forde E350 short school bus 7.3L IDI - surging at idle

[Max Mini]

Hey everyone!

Like the headline says, my little bus is doing a weird thing at idle, but not all the time. Most of the time it starts up great if it the block heater's been plugged in, but if starting completely cold it will sort of chug (which is what I think people describe as surging) and / or throw out white smoke. It stalled twice, but I'm unclear if both times were the same issue or if that was an isolated thing. I'm in New England so cold actually means cold. It's a 91, I don't seem to be able to edit the headline to add that.

The day it stalled - and this doesn't seem like it could be related, but I'm putting it out there because it happened - I clipped the edge of a fairly large snowbank. It was only snow, nothing got damaged, but almost immediately it began to run rough and then stalled. I got it started right up again, then parked and did some business. When I came out, it started ok, but a few miles later stalled at a stop light. I was able to get it started again fairly quickly and I have to say the behavior seemed like something very familiar, that is, how it behaves with water in the fuel (something I saw a lot when I was having fuel pump problems). No more issues came up in a 45 minute drive, and then all was well for several days.

The next incident was that the engine sound changed - again, I guess you would call it surging - at a traffic light. Once I was moving again it seemed ok, though slightly noisier than normal, maybe - thought that could have been paranoia because it's always pretty damn loud.

That night, after it was parked for a few hours in serious cold, it started up ok but then started surging for maybe 30 seconds. The behavior eventually stopped and I had no issues driving home.

The other thing I have been observing is a loss of fuel economy, to the tune of about a mile per gallon, over the past month or so, and I often have to press the pedal to the floor to get 55 mph out of it. I initially attributed this to the fact that my throttle cable has never been the same since it was replaced, but even though it has required more pressure since then, that change (initially at least) IMPROVED my fuel economy - probably because I wasn't able to drive as fast I guess.

I don't know anything about anything but from what I have been googling, I'm thinking an injector issue? Does that sound likely? What else does it sound like? Do you typically replace ALL the injectors at once or if one is bad, do you just do that one?

I am not comfortable messing around with this myself, and the only mechanic I can find who can work on it where I won't have a three week wait (I live in this bus, which is converted to an RV, so being without it is problematic) is telling me he can't find anything wrong, that it hasn't misbehaved for him. He says he doesn't have any computer for a vehicle this old so he can only diagnose it if it happens while in his care. That doesn't sound right to me - isn't there some way to test injectors directly? This guy has done good work for me before but he generally needs to be pointed toward something and is not exactly a great detective for finding the problem. No one near me is experienced with these old vehicles (no one trustworthy, anyway - plenty of people who see a woman with a diesel truck coming and jack the price up or even charge for work they don't actually do). Well, there are a few places, but they're booking very far out and can pick and choose what they work on. I don't think a 1991 short bus is anyone's first choice.

What I am looking for is something to point the mechanic toward. I know it seems dumb to have to do that, but it's what I have.

There's no chance this could just be some kind of simple cold weather behavior, is there?

Sorry for writing a novel about this! I just want to give you everything I know. The big problem is I am scheduled to embark on a 3000 mile drive next week; I have to be in Arizona by the 18th (I am presenting a seminar) and want to leave as soon as possible so as to minimize the amount of miles I have to drive per day. But at the same time I don't want a breakdown halfway across the country. And yes, I have to drive, because the seminar pertains to my conversion.

I know someone is probably going to point out that driving a 30 year old truck cross country isn't that smart but again, it's what I have.

 

[Cubey]

know someone is probably going to point out that driving a 30 year old truck cross country isn't that smart but again, it's what I have.

Not a thing wrong with driving an old vehicle across country. Most of that idea comes from car dealers wanting you to buy a new car.

Carry roadside assistance and either have savings or a credit card for emergency expenses. Also have as many basic hand tools as you can, extra fluids, etc.

The one time I needed a tow was for my F250 when the starter literally broke and it wouldn't even activate/turn. It was at a Lowes in a city and was just a few miles to a repair shop.

In 2009, I drove a 1991 Corolla from AR to DC and back. A friend was concerned about me driving it that far. The only problem it had was a bad negative battery connection one time. I fueled up, tried to start and it wouldn't, acted like it lost power. I checked the battery terminals first thing and yeah, just a loose/bad connection. Wiggled it down on the terminal better and went on my way, no more issue with that ever again in the car while I had it.

Later in 2009, I rode a 1987 Honda Helix scooter (with a trike kit. I miss that scooter!!) about 1,000 miles round trip from home to a scooter rally in KC. Due to an alignment issue with the trike kit (more like training wheels due to it not replacing the rear drive wheel) it ate up the rear drive tire. Somebody at the scooter rally gave me a used spare and mounted it for me. I got me back almost home. The tire was almost gonna wear through when I got to a small town in rural Arkansas where I knew a scooter shop was. So I stopped there and bought a new tire and had it installed. I fixed the alignent later and eventually sold it around 2012. (Much regret...)

Around 2015, I drove a 1993 Geo Metro 3cyl about 4500 miles from WA to AR and back with a blown head gasket, having to refill the oil and coolant every 100-150 miles from it burning (but not mixing). It had a bad inner wheel bearing on the rear on one side when I got back too. Still got 30-35mpg hwy too.

I have driven aforementioned 1987 F250 IDI across country including into the mountains of Colorado, 10k feet up. It was air starving and running poorly at that altitude, but once I got to roughly 9-9.5k it was fine again. It did have problems like the vacuum pump going out in TX (bought a Napa tool kit for pulley changing and changed it in their parking lot), alternator went out in WA (changed it in the O'Reilly parking lot), and on the return trip from WA, the driveshaft carrier bearing went bad. I should have probably had a tow for that but eh, I limped it to a motel until the next day, since a shop couldn't start on it at like 4pm I had to wait until the next morning. That next morning I still drove it to the shop that way. It cost about $300-350 and they had it fixed within a few hours. Plus about $50 for one night at a Motel 6.

Now I'm driving an 85 E350 IDI RV full time that I got almost a year ago. It keeps needing stuff due to being all original, but I fix stuff as it goes/as I can afford it. The only emergency thing that has happened in the past 3k miles (not counting the brakes when I first bought it, that's a whole messy story) was I lost the alternator belt about a month ago. It was my fault for not doing routine belt inspections, it was loose and I didn't notice/attend to it. I took a pic a few day before and didn't notice it loose on the pulley, as the picture captured. I had a spare and put it on at a truck stop the next morning when the engine was cold. Bought a batch of new belts to install plus spares, so it shouldn't be as much of a problem as it was before when I was lacking many spare belts.

It's not for the faint of heart though. You should have some at least basic mechanical skill to help you survive long trips in old vehicles. (I'd say I'm moderate level). Even on the scooter trip, I was carrying some basic hand tools. I had to stop and fix fuel system/carb issues a couple times on the trip. Honestly, that Helix gave me the most problems of anything I've ever owned, including other Honda and Yamaha scooters. But I also drove it more miles due to it being just barely interstate capable at WOT (You can run it WOT all day and it doesn't hurt it).

 

[Cubey]

Now to try to answer your actual post's main contents...

Have you checked the basics like air filter and tire pressure? Could be a clogged up fuel filter, if you haven't changed it in a long time.

Any diesel smell around the engine, indicating fuel leaks/air intrusion? Any fuel hose leaks along the frame underneath? Is there a fuel tank selector valve in fuel that could be causing problems? Might be a failing fuel pump (mechanical still, I'm guessing?) that's weak at idle. Just taking stabs in the dark at things that come to mind.

You might try this stuff before you start tearing things apart. It's even on sale right now, $2 off:
https://www.tractorsupply.com/tsc/product/hot-shots-secret-diesel-extreme-32-oz

Or you might try this, if you can't find a store with Hot Shots. It's easier to find Clear-Diesel at Walmart, O'Reilly, etc.
https://powerservice.com/psp_product/clear-diesel-fuel-tank-cleaner/

My IP/injectors got fouled and my RV's MPG dropped noticeably (about 1mpg hwy I'd say). In a single digit mpg vehicle, that's massive! That stuff seemed to clean it up in one 8oz dose for an 18gal tank, putting my MPG back to how it was this summer before it got fouled.

Some people just remove the fuel filter, dump out the diesel (I put it back in the tank with a funnel) and fill the filter with the cheapest quart of transmission fluid you can get. Then start the engine and run it for about 30 seconds, then shut it off and let it sit overnight. I tried this before Hot Shots, but I don't think I let it idle long enough before shutting it off, and I didn't let it sit overnight. I'm impatient like that sometimes.

With Hot Shots, you can dump in the 8oz right before you fill your tank and it'll clean everything while you drive. You could also dump in a quart of transmission fluid in your tank before you fill up and you might get similar results, but I haven't done that myself.

It won't help if you actually need injectors or other physical parts replaced, but it's a cheap way to rule out a dirty fuel system before you spend $1000+ replacing parts.

 

[Fixnstuff]

Hey everyone!


The day it stalled - and this doesn't seem like it could be related, but I'm putting it out there because it happened - I clipped the edge of a fairly large snowbank. It was only snow, nothing got damaged, but almost immediately it began to run rough and then stalled. I got it started right up again, then parked and did some business. When I came out, it started ok, but a few miles later stalled at a stop light. I was able to get it started again fairly quickly and I have to say the behavior seemed like something very familiar, that is, how it behaves with water in the fuel (something I saw a lot when I was having fuel pump problems). No more issues came up in a 45 minute drive, and then all was well for several days.

The next incident was that the engine sound changed - again, I guess you would call it surging - at a traffic light. Once I was moving again it seemed ok, though ...

That night, after it was parked for a few hours in serious cold, it started up ok but then started surging for maybe 30 seconds. The behavior eventually stopped and I had no issues driving home.

What I am looking for is something to point the mechanic toward. I know it seems dumb to have to do that, but it's what I have.

The big problem is I am scheduled to embark on a 3000 mile drive next week; I have to be in Arizona by the 18th (I am presenting a seminar) and want to leave as soon as possible so as to minimize the amount of miles I have to drive per day. But at the same time I don't want a breakdown halfway across the country. And yes, I have to drive, because the seminar pertains to my conversion....

My first thought: Probably when you hit/clipped the snow bank, the snow impacted against the main fuel line that goes to the fuel supply pump (aka: Lift Pump) on the lower front passenger side of the engine block, images and text from the 87-91 shop manual below. You'll see a rubber fuel line hose that has a loop in it between the lift pump and the frame, the loop is just extra hose and I think it's there to allow for movement between the engine and the frame without putting any tension or stress on the fuel line.

Rubber fuel lines can appear to be good but underneath the hose clamps they will, after time, get hard, brittle and crack easily. (same with vacuum and water hoses). If the snow impacted against that hose, there is a good possibility that the hose cracked under or adjacent to one or both of the hose clamps and is now sucking some air into the supply pump, and up to the filter and to your injection pump.
If/when replacing that section of rubber fuel line remember to put the loop in it.

It's also possible that impacting the snow bank could have cause a similar stress and caused a small leak at any connection in the fuel lines, probably closer to the front of the bus if that's where the impact was. ALSO it could have put enough stress on the lift pump to cause it to come loose or start sucking air. It's all explained below.

These images are from the first edition of the 87-91 8th generation Ford Truck, Van & Bronco shop manuals which were originally printed in July 1986. It's showing the 87 6.9L configuration but what we are looking for here, fuel line leaks or a lift pump issue, is almost identical and these should be good enough.
The rubber fuel line with the loop I mentioned is labelled "Supply Tube."

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[Fixnstuff]

BY the way, if a line is cracked and sucking air it's also likely to be leaking fuel, maybe a very small amount. Look for wet spots cause by7 diesel fule at connections and along the lines. (also return fuel lines) I found that in dark spaces a bright flash light (LED) helps to find a fuel leak because the light will reflect off of wet spots. I think the manual suggested doing this while the truck is running(??)

THE SECOND possibility (that I can think of) that could cause the surging is a fuel line obstruction. First I would look for a crimped fuel line.
Another possibility could be water in the fuel, but that would show up in your fuel/water separator which on yours, assuming it's a 7.3L is on the bottom of the filter.

Condensation forming in the tanks during cold winter months will settle as water in the tank and in diesel tanks ALGAE can grow in that water. It's black slimy stuff. In very wet or cold climates I would add an algaecide with fuel condition every year BUT NOT TOO MUCH it only takes a little bit.

NEXT: If the collision with the snow bank jolted or jarred the engine enough you might have fuel return line air/fuel leaks at one or more of the return line caps on top of the injectors. Old rubber return lines can also look good until you remove the clamps that clamp them to the caps and find brittle rubber that may be cracked under the clamp and sucking air.

When was the last time the fuel return lines and caps were replaced? If they have not been replaced since you acquired the bus and you don't know if the previous owner changed them out within a reasonable time before you got it I would look at buying a return fuel line kit and replacing them.
If one connection at a fuel injector cap is found to be leaking then others will likely follow SO REPLACE ALL OF THEM at the same time so you don't have to hunt and peck to find thee next old one that begins leaking.
I don't know how long a new fuel return line kit lasts, depends upon variables like usage and climate but mone are just fine after 6 years and I expect they'll reach 10 years but I do not drive many miles each year.

A few fuel supply connections on the top side of the engine, I didn't mention but those are obvious. At the fuel filter and going to the Injection Pump.

I hope you find the problem in the line down by the supply pump (lift pump).

NOTE: If the supply pump needs to be replaced, they are inexpensive AND NOTE: The new pumps have a nearly straight lever arm that goes UNDER the cam lobe, (with cam lobe facing up is easiest), just like the dog-leg shaped lever arm in the original and older style replacement pump does.
BOTH styles work equally well.

That's all from me, GOOD LUCK AND ENJOY ARIZONA!

 

[Max Mini]

Thanks so much! My instinct was the hit to the snowbank did something but it seemed so far-fetched. I will check all of this out, and report back here when I figure it out!

 

[Max Mini]

Forgot to say thanks also for telling me about -

You might try this stuff before you start tearing things apart. It's even on sale right now, $2 off:
https://www.tractorsupply.com/tsc/product/hot-shots-secret-diesel-extreme-32-oz

Or you might try this, if you can't find a store with Hot Shots. It's easier to find Clear-Diesel at Walmart, O'Reilly, etc.
https://powerservice.com/psp_product/clear-diesel-fuel-tank-cleaner/

I didn't know a product this product!

 

[Cubey]

Ah yes, the short hose at the lift pump. My RV's was leaky, causing hard starts sometimes. I replaced it, but then one of the clamps was bad and wasn't clamping, so I had to go back and replace the clamp shortly after.

 

[Leroy]

It sounds like a failing fuel pump, fuel restriction, sucking air, or a failing injection pump.

In order of hopefulness of what the problem is.

I would recommend replacing the lift pump first, add a fuel pressure gauge and check for pressure, and flow out of the fuel filter base schrader valve.

install a length of clear hose before the IP and look for air bubbles.

Remove and inspect the hard line between the fuel filter base and center inlet of the IP, should have good seal and olive gaskets and make sure they're not leaking here.

If you have good fuel pump, pressure and flow, not much air in the lines then your IP is toast, it sounds more to me like a bad lift pump and possible fuel restriction or an injection pump on it's way out.

I would deffininetely diagnose and repair this problem before heading on a road trip, it's one of those things that if it's another of the problems it can be fixed before damaging the injection pump.

if it's not, and the pump is failing it will probably not be easy to find an affordable good replacement stranded in the middle of nowhere.

Many things seem to work their course, but not fueling or IP problems, they get worse until it's fixed or breaks down.

 

[Max Mini]

It sounds like a failing fuel pump, fuel restriction, sucking air, or a failing injection pump.

OK, I'll check all this out, thanks.

 

[Stu Bailey]

I bought my 86 6.9 of Craigslist sight unseen and then drove it from Alaska to San Diego and then to New York without any problems! Now I’m starting to see a few minor problems but still nothing bad at all. Glad to see another guy out there buying a classic truck and rambling across the country!

 

[Max Mini]

I bought my 86 6.9 of Craigslist sight unseen and then drove it from Alaska to San Diego and then to New York without any problems! Now I’m starting to see a few minor problems but still nothing bad at all. Glad to see another guy out there buying a classic truck and rambling across the country!

Thanks, except this guy is a girl!

Happy New Year!

 

[Stu Bailey]

So I’ve installed the manual glow plug switch and the glow plugs aren’t getting power... The engine is cranking and exhaust is coming out. I attached a picture of the relay, maybe that is bad now? So the yellow circle is the positive connection from the battery where I have 12VDC. The red circle is, was, where the purple wire connected to the relay post. I clipped it and used it to hold down the new ring terminal that goes back to my momentary push button. That terminal has 0VDC for some reason... even when I turn the keys to on. Shouldn’t it have 12VDC as well? Also, a 10amp fuse should be sufficient for the push button right?

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[Stu Bailey]

God damnt I posted this on the wrong thread! Hahah

 

[Cubey]

(disregard)