Big Diesel, MPG increase ideas?

[raubvogel]

I do not know if your truck would get annoyed but for the PCM thingie consider the glow plug relay off a 80s Mercedes diesel. Self-contained module (it might read signal from coolant sensor but I may be mistaken): apply power, wait, and then crank engine.

[ps2fixer]

Been a while since I gave an update. Rear and front drive shafts have all new U-joints, so the truck is drive-able now. Front axle U-joints are still trashed so can't use 4x4 at speed till fixed, if I need 4x4 on snowy roads, then I probably won't be going too fast anyway.

Took the truck up town for some shopping and filled it up, over 22 gals and the front tank was at 1/2 and the rear was below 1/4. Running the front (smaller) tank to try to get some reasonable numbers to get atleast something for a base line with my driving style and environment.

Generally the truck has been starting well in the cold temps (20-30f), but it did give me a fit the day I wanted to drive it home from my parent's place. I'm about to head out to do some diag work, but suspect the glow plug relay might have a bad spot, if not then high resistance at the glow plugs (aka they don't get as hot).

If the glow plug relay is going out, there's a much larger one rated for 200amp continuous and 600amp peak that's a common upgrade for these trucks, about $55-80 for it. I read the glow plugs should draw around 190-195 amps when new, so the relay based on specs should last a very long time as long as salt doesn't kill it first. I'm half expecting the relay and the glow plugs to be bad.

Hate to say it, but the "mechanic" that owned this truck was a terrible mechanic, so many things rigged up on it. Like there's a wire tapped into that goes to the wiper motor that runs over to the washer fluid pump... the wire is fusable link wire.. the whole way except about 12in where a different wire is spliced into the main harness. There's a 1/4in spade connector with no insulation on it at all. The ash try is broken, and the wires for the cig lighter were loose so they shorted out and blew the fuse, same fuse that runs the OBD port. The second cig lighter plug in the dash is free willy in the dash, nothing holding it in.

I still have a major boost leak, the passenger side exhaust manifold bolts to the pipe that runs to the turbo has broken bolts (rotted to nothing). The driver's side is the same way, just the bolt's aren't broken yet.

Even though it needed work, it was priced pretty well. I have yet to find another truck in similar condition (body wise) and anything near the lowish miles (190k) for under $10k in this area that also has the manual transmission. Tons of trucks with autos.

Ran out for some quick photos to show the stuff a bit better, nice layer of freezing rain on everything, might hold off a bit to climb on the truck to check things out.

I also work with wiring and such a lot for my business, so this kind of work is super annoying to me. Reminds me of the first Toyota pickup I had, the tail lights would go out sometimes, found the fuse with wire wrapped around the base, very lucky the truck didn't catch on fire because the wire at the back of the truck was bare for like 3-4 feet for the running lights.

Oh also bad news, Scan Gauge 2 does not talk with this truck. My laptop with FORscan can, so maybe I'll throw a cheap (small) laptop in the truck and have a remote display setup somewhere to try to get an instant MPG type of gauge. Haven't really thought about it too much.

On a good note, it sounds like the truck does really good at cutting the fuel off for in gear coasting. I normally coast in neutral, but for this truck I'm wondering if coasting in gear would be the better option to be more friendlier in traffic.

Also note that the red wire on the left side in the one pic isn't connected to anything, you can see the other cut end near the black wire. I'll have to undo the rig up and see what they were trying to do and do the repair correctly if it's a bad wire, or hook up the orig wire back up as it was intended from the factory.

I also unplugged the exhaust brake since it would come on while driving even when warmed up a fair amount. Since the truck appears to have been lacking maintenance for so long I'm planning an oil change, fuel filter (aka diesel tune up), trans fluid, axles, etc. In cold weather the trans is stiff to shift, says right on the trans to use only synthetic fluid. In one of my other trucks I had a similar issue and put in red line fluid for the trans and it shifted great even with -10f overnight temps, that truck called for gear lube, 80w90 if I recall correctly.

Anyway, hope you guys enjoy the pics, got a reasonable side shot view of the truck, and a direct front on shot. The side shot is to show the angle of the bumper doesn't match the body, guess it was done so it would be more likely to push than to slide off.

I know the fuel gauge is a horrible way to gauge mpg, but drove the truck around 30 miles and the needle on the tank moved about a needle width. Pretty sure the front tank is 16 gal, 1/4 is 4gal, so if it is linear and such it used about 1gal which is in the ball park of what I'd expect. I'd guess 2 gals I'd see it move more, but depends on how the float/resister design is (more points = more accurate).

Also neat little tid bit with Ford's design (based on reading atleast), the temp gauge is the same as a gas engine, however Ford put a resister inline with the sensor to make it read colder than the gas trucks. With the grill block I'm in the "O" area and what I read the gas trucks read right in the middle, like around the "R" to "M" spot in "Normal". If/when I get something setup for MPG display, I will be wanting digital temp readings too so I can see what the computer sees and make sure temp sensors are within spec and such.

[Piotrsko]

Find the resistor behind the panel for each of the gauges and short it. You will then have fully functioning gauges that displays correct values instead of averaged. Ford got a lot of complaints around then because the gauges were reporting out of tolerance conditions.

You are on your own for the fuel tanks, my 38 gallon single has weird characteristics: 160 miles before it comes off the full bump then drops like a rock to 3/4, then reacts irrationally to 1/2. Below 1/2, it is a reasonable relationship to fuel/mileage. Thank god for the odometer.

[ps2fixer]

Yea I might do the resistor short mod, it's not an average thing, it just lowers the reading, the actual temp sensor is a resistor as well that changes with temp.

Yea the fuel tank should be interesting, my uncle had a gas truck that was really wacky, If I remember right it went from full to empty in 1/2 tank, then empty back to full for when it was actually empty. Can't recall if his was dual tank or not, but it was a 97. If I remember right, some of his parts were 98 while other parts were 97 (and older), I guess it would be a 97.5 truck if I'm remembering things right.

Also fun to own a vehicle that doesn't have a trip odometer, haven't had to write down the last 3-4 numbers and calc how far I've gone since fill up in a long time. If I setup some sort of gauge/screen, I'll probably add a trip to that. I'm sure I should be able to see the VSS via OBD. It's a really odd system, I guess the ODB on my truck is like a ODB 1.5, it has some ODB2 characteristics like the same connector, pin out (atleast power), but communication standard isn't OBD2 until the 98 or 99 trucks. For cars the mandate was 96 if I remember right.

I've gotten used to the shift pattern on the truck pretty quick, start off in 2nd (first is like a creeper gear), 2nd into 3rd requires a bit more revs since it's a fairly big jump, then the rest of the gears can be short shifted and feel like pretty even jumps. Since I'm not getting boost till higher rpm, I've been shifting about 2000-2100 for 2nd into 3rd, and about 1900ish for the rest of the gears. I suspect I can drop 100-200 rpm once the boost leak is fixed without lugging the engine. Gas engines are pretty easy to tell when they are lugging, but for a diesel, I haven't really had the experience. It seems like it just runs a bit more ruff when I shift too early.

I didn't mention it before, but I'm also a programmer, so if I can't find software to do what I want for the MPG gauge stuff, I might make my own program if I can find any of the specs for the Ford ODB communication protocol. I did find an open source project years back for OBD2 standard vehicles. Back then I was thinking about data logging trips for different routes, loads, monitor hills (gps) etc then see what the "ideal" driving pattern would be for the given situations based on several trips on my exact vehicle. Never got that far though.

[ps2fixer]

Braved the ice ground, man is it slick out there today. Anyway, found some interesting things. First up, most of my glow plugs are junk, out of the 6 I could get to easily to read, only 2 passed. 3 read open circuit (no connection) and 1 read 0.00 ohms which I'm unsure if that's good or bad. This is after running the engine to get it closer to the tools. I read spec is under 1 ohm, new comes around 0.5-0.6 ohms. Also did a voltage drop test across the relay while under load (of whatever glow plugs are actually working) and I see 0.65v across the two big terminals. Most places I read says it should be under 0.5v so it's probably on it's way out. Battery voltage after running a short time was at 13v, with glow plugs on it dropped to just a tiny bit under 12v so the batteries seem healthy, but replacing the glow plugs will really tell the story. Since it's lacking maintenance so bad, I'm thinking I'll replace all 8 glow plugs, fair chance they are orig or only replaced once. I guess glow plugs, then retest the glow plug relay and the battery voltage drop while under load to see how things look at that point.

[Isaac Zachary]

Originally Posted by ps2fixer

Gas engines are pretty easy to tell when they are lugging, but for a diesel, I haven't really had the experience. It seems like it just runs a bit more ruff when I shift too early.

I could be wrong but my rule of thumb is just keep the RPM's over 1,000. If lower than that then it's not a good idea to put much foot into the accelerator: that is I keep it at no more than half load or less. But at 1,000 and up I feel flooring it is ok.

[Piotrsko]

When I was training for schoolbus the lugging rule was: if it is floored and RPM doesn't increase, it's lugging. Other than that AFAIK there is no other way since they rattle and knock at all speeds. Might be able to tell if you're running an EGT because it will be close to 1300 degrees but EGT on schoolbusses is scary.

[ps2fixer]

That seems to make a lot of sense, I figured a diesel under heavy load would vibrate and such a lot more, probably just the firing of the engine shacking everything enough for me to feel it more. Seems to be around 900-1000 rpm when I notice it lol. I basically never floor any vehicle of mine. In my gasser's, 1/4-1/2 throttle was plenty to get the LOD reading on the scan gauge to around 80. My Corolla was great for it's shift points and not down shifting till 3/4-full throttle or the speed dropped too much.

I wouldn't mind getting a EGT gauge setup. Empty it's probably little to no concern unless the truck has a hotter tune in it, but with a load there's a lot more wind resistance and weight.

Not sure how much I mentioned about my dad's truck, but we are thinking the torque converter went out on it. My idea is to throw in the torque converter from the parts truck into it to test (still a lot of work), and if it made it go, decide on buying a new one or run the 300k miles one that's probably just fine and drive it. The more we research things, it sounds like either get the stick with these trucks, or spend the $3600+ to upgrade the stock auto trans to handle the power. I haven't found what all is replaced, I know the torque converter alone is something like $800 or so, input and output shafts are like $1200, standard rebuild kit for the clutches, seals, etc seem to run $100-600. Not sure what the big upgrade parts are, unless it's just the torque converter and shafts.

I really need to get some way to measure MPG (or any kind of number to ABA test ideas on). First thing up is shift points, easyish throttle (like 1/4-1/2) and shift around 2k rpm and the truck gets up to speed fairly quick, or drop the shift point to say 1700, loose a lot of boost (my big leak probably is why) and the shift starts out around 1000 rpm and takes probably 50% longer for the rev up in the given gear with even more throttle. In my mind, the slower rev up route should be bad for MPG since i theory it's dumping more fuel, but it might just be the line where the turbo is building pressure vs doing almost nothing from the leak. Would be nice to get a boost gauge too so I can see what it's actually running at. I suspect the computer is tuned to dump more fuel in the range when the boost should be good. I haven't kept a good eye on the exhaust, but a couple times I checked while taking off somewhat hard and saw no black smoke (wasted fuel), so it seems I'm getting enough air to keep things somewhat happy.

Got more parts in the mail, block heater cord is burnt in half at the engine, new one is $20 shipped. Atleast 1/2 the glow plugs are bad so bought a set of 8 (motorcraft) for $88 shipped from autozone, and since I have a 0.65v drop across the glow plug relay, I bought the upgrade relay, shipped $70.

https://www.dieselorings.com/1994-19...lug-relay.html

Check out the size difference OEM vs the monster.



Have to love vehicles that have been lacking maintenance, the good is, you know everything needs replaced, the bad is replacing everything (or upgrading when possible).

It's beyond my scope right now, but from what I read the 6 speed ZF6 is a fair bit heavier built than the ZF5 5 speed. First is lower on the 6 speed, and 6th is higher than the 5 speed's 5th so in theory could take off easier with a load, and when empty have a higher final drive ratio. I haven't done the math, but it would be interesting to look into making the axles higher geared and swap the 6 speed in so the 1-5th is roughly the same as the 6 speed and the 6th gear is like a 2nd over drive. I have to drive the truck to get a feel if any of my planned larger loads would be any issue power wise for the truck though. Lot of time and money to invest for the sake of mpg, but in theory it would make the most reliable version of the truck possible that I'm aware of. I think one of the things people have been going after is I guess the owner's manual suggests to not run in 5th gear with the ZF5 while hauling a load, but the newer manuals says it's ok to run in 6th with the ZF6. I have the 95 manual, but haven't looked for that yet.

I also noticed the dinger or whatever you'd want to call it is missing or disabled on my truck. I'm used to driving Toyota and Lexus vehicles where the headlights automatically turn off once the vehicle is turned off and the driver's door opens, caught myself leaving the lights on twice already. Need to either setup a buzzer for key off, door open, lights on, or just key off lights on would work too. Of course another route is to wire up the headlights so they turn off with the ignition switch, ideally 2 relays so if there's a failure, in theory only one would fail instead of both. Another feature I'm missing a little is the door auto unlock again on the Toyota/Lexus vehicles, unlock the driver's door 2x and it unlocks all doors, unlock the passenger side once and all doors unlock. I don't think it would be too easy to add that feature in the truck, it just makes me a little lazy vs pressing the unlock button on the door. Btw, the Lexus with these features is a 1990 lol, Toyota started with the auto headlights and such around 96ish from what I can tell. By auto lights, I do not mean a big delay after the vehicle is off. To me that's just a battery killer, if they wanted to design lights like that, just use the marker lights.

I've thought about the idea of a transmission from a buss or larger truck for my dad's truck. It sounds like they run an adapter plate factory to go from the Ford IH bolt pattern to the Allison (SAE?) bolt pattern. It would get him the trans he would like (must have over drive), but it would be quite a job getting it to fit in the truck I'd think lol. He has an old 70's manual trans from a IH buss, 4 speed, no over drive though, it had a IH gas engine, not sure if there's any difference there, same engine that was put in the IH Scouts.

[Isaac Zachary]

Originally Posted by Piotrsko

When I was training for schoolbus the lugging rule was: if it is floored and RPM doesn't increase, it's lugging. Other than that AFAIK there is no other way since they rattle and knock at all speeds. Might be able to tell if you're running an EGT because it will be close to 1300 degrees but EGT on schoolbusses is scary.

Would EGT's indicate lugging? I thought lugging was bad for the bearing surfaces since there's not enough movement to get the engine parts to float over the oil.

I drove school bus too. I never heard that floored and no increase in RPM were indications of lugging. You'd have to be well below idle speed for that to happen on flat ground.

Not that I was easy on the school bus engines. One time I accidentally dumped the clutch at a stop and quickly stepped on the clutch again. The engine kept running, but as I tried to pull away the bus started backing up. I had changed the rotational direction of the engine and it was now running backwards!

[ps2fixer]

If the engine was running backwards, then the exhaust would have been blowing out the intake, not a good thing xD.

I drove the truck today for a package run and the rpm drops a bit more than I was thinking between gears, looks like around 1200rpm is what I've been targeting roughly for the start of each gear, below that and the engine isn't super happy (slow to increase speed).

For the sake of testing things, I got into 3rd or 4th and floored it and the "mild" take off and floored felt exactly the same to me, maybe the computer determines the max speed increase it is willing to do since it is a drive by wire type of system. For sure something I wasn't expecting. I rev'ed it out in the gear with it floored and watched for black smoke, nothing at all that I could see (smaller mirror).

Kind of funny, this truck (and my dad's) is the biggest vehicle I've driven, atleast ones that ran. I helped tow in a full sized school bus shortly after getting my license. Back roads and slow speeds, I'm sure it wasn't a fully legal thing to do but we got the job done.

The bearing wear for lugging is what I had in mind, but the exhaust gas temps makes sense too since that's the silent killer of diesels. Since my engine has the HEUI injection system, of how I understand it, the oil pump is a higher flow one than normal. Not sure if it builds up higher pressures or not though, the pressure should be what keeps the metal from contacting each other.

Diesels are a bit of a new world for me, I knew the basics of how they worked but have been learning a ton about them since I got this truck.

Oh last trip the fuel gauge needle dropped a fair bit, it did run idle for around 10 mins while I got packages situated so it would be ready to go. Bit longer than I normally would but I was pressing time and it's my only vehicle at my house atm (car at my parents yet). Before the temps drop I'll have to get the truck back to my parent's place to work on it. Hopefully the glow plugs all come out whole, I've read the tips can break off and likely requires the head to be pulled if that happens.

I'm not 100% sure if I got the front take full either, the front take needle went to the full mark, basically pumped till click off, then slow till click off again, same trick I use on my lexus to top it off. The rear tank I did the same thing and the needle for it goes slightly over full. I couldn't see diesel in the fill tube so it could have taken more. I try to leave a bit of room so it can vent correctly and such. First MPG numbers won't be too great probably from all of the issues I'm working with.