Extra gauges for a turbodiesel
 

Hello all,

I'm planning to install cruise control and a MPGuino on my car and as those two requires a lot of work behind the dash, I've decided to think of other things I can do at the same time, to save time, and someone suggested getting some gauges.

My 1.7 turbodiesel already has tacho, speedo, fuel and water temp (only shows temp between 70 - 110 deg C though) gauges and that's it.

What other information would be useful to help me improve my FE? A boost gauge? I.e., the lower boost, the better? Would that work on a diesel? Any others? Am I correct in thinking a vacuum gauge is useless on a diesel considering diesels don't create vacuums?

A voltmeter and an oil pressure gauge would be nice but those won't contribte towards hypermiling.

My car doesn't have an OBD-II port so can't use gauges that needs the OBD-II port.

Thanks for your time in advance!

Measuring volts may be useful if you plan on installing an off switch for the alternator. Measuring amps would be better: it tells you how much electrical load is on alternator, and so on the engine.

Maybe so, but I wouldn't want to send my entire electrical system through the ammeter which would need hefty cables to and from the battery?

Would an air/fuel ratio work on a diesel and would it be useful at all?

I would think that the Air fuel ratio might come in handy, though I have never seen one for a diesel, I am sure that they sell them.
In a diesel I think the ratio of air to fuel is 100:1, whereas in a gasoline (petrol) engine it's 14.7:1. So any changes that are made to your engine will have to make major swings to get rich or lean in comparison.
As far as the Turbo is concerned, you want to have quite a bit of boost, so don't turn it down. If anything, turn it up. I am not sure what pressure diesel runs most efficiently, but the higher the compression ratio, the higher the efficiency. check what others are running and tune your engine accordingly.
"Diesel engine

In an auto-ignition diesel engine, (no electrical sparking plug--the hot air of compression lights the injected fuel) the CR will customarily exceed 14:1. Ratios over 22:1 are common. The appropriate compression ratio depends on the design of the cylinder head. The figure is usually between 14:1 and 16:1 for direct injection engines and between 18:1 and 20:1 for indirect injection engines."
Check out this Wikipedia article for more info, hope I helped.

I see what you mean, but reading the Haynes manual for my car (found here) and when explaining how the fuel injection system work, one section says:

"A turbocharger is fitted to increase engine efficiency by raising the pressure in the inlet manifold above atmospheric pressure. Instead of the air simply being sucked into the cylinders, it is forced in. Additional fuel is supplied by the injection pump in proportion to the increased air intake".

Note "Additional fuel". That's not quite what we want? BTW the Haynes manual mentions the compression ratio for this engine is 18.4:1 even though it is direct injection.

Thanks for your help, much appreciated!

It's very difficult to get an air/fuel ratio gauge for a diesel, so I'm leaving that out.

So it boils down to 4 gauges:

Turbo boost
Exhaust gas temperature
Voltmeter
Oil Pressure

I can only have 3 gauges. Keep in mind that the EGT gauge is very expensive, and I'm worried about the sensor breaking off and messing up the turbo.

Which gauge should I drop?

If it is possible to get a mpguino derivative working reasonably well on your vehicle (I don't know anything about astras, or a lot of other vehicles for that matter) that would be your %99 return.

EGT (exhaust gas temp) gauge will tell you the most about your motor. When Exhaust temps are high, it is usually because you have inefficient burn and some of the fuel is finishing combustion after the power stroke.

If you plan to tune the motor, one of the first 'tricks' is to turn the fuel up or down (up=more power, down=more economy... to a point!). If you do that, you'll need an EGT and pyrometer (the pyrometer is what reads the temp, the gauge displays the results, EGT is what is being read).

If you are really worried about the turbo being damaged by the pyro, then install it after the turbo. It won't be as accurate, and will certainly read much lower than before turbo, but it will still give you an idea as to the relative changes in fuel load.

It will also allow you to fiddle with your boost settings, which can yield a big increase in power or economy. Basically: as your motor gets more load, boost should go up to a given point. I don't know your motor so I won't suggest maximum boost settings as too much boost will pooch the motor for sure. For a large 6cyl Toyota diesel (4.2liter) "normal" boost is up to about 13psi. Some folks run 16 w/o issue. For a large cummins motor, I've heard of people running into the 30's without issue.

As boost goes up, EGT's are likely to spike (compressing air heats it). You want boost, you don't want high exhaust temps as you can easily reach temperatures in which you start to run the risk of damaging internal parts.

Short answer: I'd add EGT and Boost to any diesel. Period. Beyond that.... Oil pressure doesn't tell you much besides "time to rebuild". Several gauge companies make combined gauges for stuff that doesn't need high resolution- like oil px or voltmeter.

Should I get EGT and boost even though I'm not looking to tune the engine or fiddle with the boost settings?

Can I use a petrol turbo boost gauge and ignore the vacuum scale, or do I have to get a specific diesel boost gauge which I've not found any so far?

I would like a split oil pressure/voltmeter gauge but again, I've not found that sort of thing anywhere apart from an incredibly expensive digital gauge which I'm not going to get.