View Full Version : diesel tune up

05-10-2010, 06:36 AM
Hi, I am about to visit a mechanic to have my clutch repaired.

While I'm there I wanted to ask him about a tuneup, and seeing if I can boost the driveability of my 80 scout ii, especially in lower gears.

Engine wise, are these the things I should have him look into?

compression leak down test
air intake (on this note, had anyone had results adding air intake, I saw this link where he drilled out holes to get more air intake https://mail.google.com/mail/?shva=1#label/scout/12874634f59ab08e

is that a good idea?

Overall, just any information on how to get the most out of the diesel scout is appreciated, thanks! I'm also going to have him look at the axle ratio for me as I;m told that can be part of the reason starts are very slow.

05-10-2010, 09:40 AM
I'd definitely have all the injectors rebuilt if I were you. Their shelf life is around 25,000 miles before they start spraying abnormally. Abnormal spray=uneven fuel burn in cylinders=cracked pistons. Luckily, they're really cheap and easy to get done though. Any local diesel mechanic shop should be able to do them for you, and the price should be around 15.00-20.00 per injector.


That's a great set up for getting a little more performance on the top end and better fuel economy out of our Diesels. Basically what he did was put a non-turbo intake on because it has bigger intake ports and fabricated his own cold air intake. I did something very similar with mine but with a few more "power" upgrades; feel free to ask anything you can think of and I'll let you know what all I've done.

You're really not going to get off-the-line power from these things; they were designed for fuel mileage on the highway, so they've got pretty low gears in the axles. Your two choices are to get different gears and sacrifice your mileage on the top end to get better response on the low end, or stay with what you've got and keep your economy on the top end with slow response in town.

One last thing... I'd also invest in a good Pyrometer to keep track of your engine. If you do ANY upgrades to it for more power, then you're going to want one to keep an eye on the internals and make sure you don't cook them.

05-10-2010, 10:13 AM
thanks for this info.

I think the thing I understand the least is the gear ratio or axle ratio?

This is is something I can swap out?

Overall, I don't plan to use this as a highway vehicle much, mostly around town, so a swing towards a little less fuel economy on the high end would be ok. Is there a way to gauge though how much? Are we walking going from 21 to 10? Or 21 to 18 etc?

If you can enlighten me on the axle or gear ratio swapping please do, thanks again fro your reply.

05-10-2010, 10:17 AM
also, on your note about the pyrometer, I think I'm going to avoid and mods because I'm too ignorant mechanically

in other words, this car has lasted a long time, has good mileage, and I don't want to screw it up

so I am thinking instead that my line of improvements would only be examining if the axle ratio can be lower or higher and drive a little better for my taste (lower or higher I get confused)

and the other thing of course is I just want to do any maintenance that will make it drive at the specs it was built for: good mileage for example. to that end I will definitely look into the injectors, please let me know if theres anything else you can think of I should mention to the mechanic. I plan to ask him to look up the axle ratio as its worn off the glovebox sticker

05-10-2010, 10:47 AM
Basically the higher the number for your ratio, the more response you get on the lower end from your torque. The first number is the number of times the driveshaft rotates and the second number is the number of times the tires rotate. So say you had a 3.73:1, your driveshaft will rotate 3.73 times for every 1 rotation of the tires. Then, say you have that 3.73:1 ratio and went to a 4.11:1, then you'd get a little more response on the low end. Your fuel economy would drop a little, but since you're driving more in town anyway, you probably wouldn't notice anything more than 1 or 2 mpg less, and that's being pretty liberal with it.

I think I might have said it backwards before... but low gears are highway gears and high gears are towing gears. Diesel Scouts came with low gears for the extra economy.

It is something you can have changed by doing a full axle swap or by doing a gear swap by tearing into the pumpkin and replacing your gears with a new set. Just make sure that whatever you have done to the rear axle, do the same to the front. If you don't, then you'll be blowing up your axle gears and messing up your transfer case.

05-10-2010, 10:57 AM
when you say go from 3.73:1 ratio and to a 4.11:1

how do you do that? are the gears adjusted are is it a different part?

I'm not doing this myself, just trying to know what I'm talking about with my mechanic :)

05-10-2010, 10:58 AM
I keep on editing this... might as well start a new reply.

The mods really aren't that hard to accomplish. More of a thing of dedication and money than anything.

While it's true that the more air you get into your engine the better the response will be, but more air would require more fuel. The extra fuel and extra air would give you better throttle response, but also give you a higher EGT. That's the reason for wanting the pyrometer to monitor the temperatures.

So on mine, I have an electric fuel pump, slightly bigger injectors than stock (because they were rebuilt that way), a MUCH bigger turbo than stock, and a Cold Air Intake with an intercooler to lower the intake and therefore exhaust temperatures, and a non-turbo intake manifold to help get more air into the engine. All these were fairly simple to do, and I just keep a close eye on the pyrometer to make sure I'm not cooking the internals on my engine, and the easiest way to keep from doing that is to NOT put the gas pedal to the floor every chance I get. Less fuel and air in the engine=lower EGT temperatures. Simple as that.

05-10-2010, 11:00 AM
when you say go from 3.73:1 ratio and to a 4.11:1

how do you do that? are the gears adjusted are is it a different part?

I'm not doing this myself, just trying to know what I'm talking about with my mechanic :)

It would be putting in a completely different set of gears. You can't modify anything on the ones that are in there because that's not how they work. They're a set-in-stone ratio and to change them means changing out the whole assembly.