Low mpg IDI

[derjackistweg]

Hi,
Living in Germany we are panicked when mpgs are low

But actually my experience with my E350 Quickley is not too great in that regard:
Recently I calculated 19l/100 km. Which is roughly slight under 13mpg.
It has 4.11 gears, 315/75-16, and a high roof of roughly 10". N/A 1994, very late one!
IP had been relooked (rebuild advanced piston).
Injectors rebuild but remixed with (good) old ones by a mechanic who thought he is smarter

I drove it half with 75 mph, half 60mph but with 4 to total weight and 20 miles town.
Could have been worse but also better.

Reason why I think it could be better is: exhaust tip is black and it had been less carbon before. Which = to unbured fuel.

Timing is roughly standard, when I installed the IP.

It's a van so fuel screw is not an option, but maybe going a little advance?

 

[dgr]

You're at 12.4 mpg in American gallons.

Quigley is a 4x4 conversion right? My 4x4 without overdrive truck with the same rear axle gets 10-11 mpg, 22/100km

Does your exhaust put out black smoke when you press the pedal? That would indicate too much fuel.

Did the mechanic pop test the injectors to match the pressures? Timing depends on injector opening pressure.

If you are getting black smoke with normal driving, I would turn the fuel screw down a little. I've never heard this can't be done on a van injection pump.

 

[derjackistweg]

Right forgot to mention: no smoke on idle, no smoke visible in the mirror when driving and not even when accelerating.

All injectors have been professionally rebuild and tested - then came the mechanic overwhelmed by blue smoke (advance piston IP stuck) and tried harder on the injectors and mixed them with old ones by "testing the spray". As these have been perfect before I don't know how they react to each other now. But even the "ild ones" are under 80k miles.

What's your FINAL drive? 29/31/33/35" tires?
11 mpg is quite very poor, when unloaded on normal roads.

I would expect 18 under very good condition, unloaded.

 

[dgr]

I'm on stock tires. 235/85r16 tires. 31.7 inches. I don't have a locking torque converter or overdrive. I assume you have an E40D transmission. My pedal is on the floor to keep up with traffic on the freeway.

You have a lot of front area to push through the wind. Maybe some other van owners will chime in on their mileage. Not too many 4x4 vans running around. Mileage varies with each driver. I think 4.11 gears and 18 mpg do not belong in the same sentence

 

[derjackistweg]

35 + 4.10 = 3.55 + 235/75-15 stock tires.

 

[nelstomlinson]

My crew cab with e4od automatic gets around 12 to 14 MGP. My crew cab with ZF5 gets about 14 to 16 or maybe 17. Both with stock tires.

 

[oregon96psd]

My 97 will get 17-18 IF I keep it under 75 mph, really starts to drop after that. The 86 14-15 at the same speeds, both 4.10 ratios with zf5's and same size tires.

 

[dgr]

That's true on the gear ratios. But I've never seen a truck putting bigger, heavier, wider tires on getting better mileage.

 

[chillman88]

You may be able to tweak it to get a little better, but at the end of the day you have significant losses from height and added drag from the tires. Best way to get better MPG is lower it and get skinnier tires but I realize that's typically either unattainable or undesirable or both, just mentioning it though.

 

[Thewespaul]

With a 150cc pump, 33” tires, zf5 and 3.55s I average around 16 with mostly city driving.

 

[Christian9112]

I get 11-14mpg weighing at 12,000+ lbs. with my ambulance.
The only main advantage with our engine, I think, is running multi-fuel. It's cheap to repair if anything goes wrong from running the fuel. It's not good in power and its not good in fuel economy, but she aint too picky in fuel.

 

[derjackistweg]

You may be able to tweak it to get a little better, but at the end of the day you have significant losses from height and added drag from the tires. Best way to get better MPG is lower it and get skinnier tires but I realize that's typically either unattainable or undesirable or both, just mentioning it though.

It is not that simple.
Vans are higher but their aerodynamic shape is pretty good and I do not have stupid roof racks or so on. cw x qm.
Drag from tires to not come from width in but mostly from tire pressure and profile. It makes a huge difference if you are running mine e.g. with 2 bar, as they are supposed to be for 2 to or 3 bar, as I am running for a max of 2,8 to/ axle!

Of course aerodynamic gets worse the higher the truck is, but at the same time my RPM goes down: I am now on the same final drive, as a standard Econoline IDI Van with seats: 3,55:1 + 245/75-16. Mine is 4,10:1 + 315/75-16.

For 60mph you do not need more that 50 HP (on flat roads, of course), probably less, you can calculate that. Ergo you can run the engine with lower RPM, like I do.



PS: Before I was running 265/75-16 on the same truck, with NO difference in mileage. Not quite comparable driving, I had always a lover mileage with that configuration, for sure not a better one.

 

[Clb]

Ive not read the whole thread.
My .02...
You need a wrench with a meter and idi knowledge (no reason to mix injectors) I was stationed in Manheim that's a lotta bonn to burn right there in a Quigley!

 

[franklin2]

It is not that simple.
Vans are higher but their aerodynamic shape is pretty good and I do not have stupid roof racks or so on. cw x qm.
Drag from tires to not come from width in but mostly from tire pressure and profile. It makes a huge difference if you are running mine e.g. with 2 bar, as they are supposed to be for 2 to or 3 bar, as I am running for a max of 2,8 to/ axle!

Of course aerodynamic gets worse the higher the truck is, but at the same time my RPM goes down: I am now on the same final drive, as a standard Econoline IDI Van with seats: 3,55:1 + 245/75-16. Mine is 4,10:1 + 315/75-16.

For 60mph you do not need more that 50 HP (on flat roads, of course), probably less, you can calculate that. Ergo you can run the engine with lower RPM, like I do.



PS: Before I was running 265/75-16 on the same truck, with NO difference in mileage. Not quite comparable driving, I had always a lover mileage with that configuration, for sure not a better one.

Larger tires never give better fuel mileage. While the engine is turning slower, the amount of weight you are having to move is increased quite a bit. Large tires are heavy and hard to get going, hard to stop.

 

[03wr250f]

After reading everything it honestly sounds like you are on the right track. I would assume timing would help. I would not mess with fuel delivery it sounds perfect. It is ok for a little bit of black to show on the xhaust tip. espeicalliy since you say you dont see any smoke ever.
couple things may help gaining mpg. 1. drive like you have 50 miles to go and the low fuel light is on (i know there is no actual light but still)
2 how are all the fluids in the drive train? trans, tcase, front and rear diffs? if they are needing to be replaced i would recommend synthetics.
3 timing the pump will help 4 clean air filter, and fuel filter. 5 make sure you are getting decent pressure (at idle running should be about 4 psi) at the fuel filter shrader valve, 6 a free flowing exhaust will help as well. 7 make sure no injector return lines are wet, and that the injection pump is not leaking anywhere. those should get ya closer