Thread: Mech VS elec.....

Ok... lets be definative about this.

theres lots of different schools of getting fuel from your dieso tank into your combustion chamber. theres CAV pumps, VE pumps, Direct injection, indirect injection, common rail, unit injection, hydraulically actuated injection, electrically controlled injection, hydraulically actuated electronically controlled injection and now total electronic common rail injection along with some hybrid stuff like mechanically actuated electronically controlled injection. And I haven't even gotten round to thinking about filtration and fuel lift techniques.

But lets break it down and keep it simple at the end of the day theres 2 common ways of defining what type of diesel you have a mechanically injected engine or an electronically injected engine.

So whats the fuss? Theres an inherent miss trust of electronic stuff on stuff thats ment to be reliable and why? personally I blame bill gates and windows. If hed managed to actually get a computer stable in the first place people would probably be more receptive of them.

I know, I can hear you ranting Whats your point?

ITs actually easier to fix an electronic diesel engine than it is a mechanical one. you just need to be carrying the right gear.

Wait, no, stop dont even think about going the line of "But Dave, your recent trip to purgatory has left your brain addled we never had to carry specialist gear to fix the old engines." actually yes you did if you wanted to fix some of the problems you could have encountered.

dont believe me? ok lets break down a diesel injection system.

To start with generically whats the injection system do.

1. it raises the pressure of the fuel to allow atomization upon injection
2. it decides when to inject the fuel
3. it injects a predetermined quantity of fuel as required by the conditions of speed and load on the engine.

so if you want to do that mechanically you need a very fine tolerance pump, some form of mechanical timing device and a mechanical metering device which means lots of springs, levers, cams, balancing acts and high pressure fittings as well as the obligatory fine tolerance injectors. and if any of that went seriously west you'd need the right specialist gear to setup your pump again after you put it all back together. Spring scales, micrometers, Depth gauges, a pump calibration rack, spill timer tube, Pump aligning tool

and if you want to do that electronically you need about the same but you can do away with a heap of the fine tolerance parts, the balancing acts, cams and depending on which injection method you use you can off load the fine tolerance pump because it becomes part of the injector itself then you replace all of this with a couple of sensors and a computer, hereafter referred to as the ECU. and if it went west youd need a full suite of electronics repair gear to have a hope at repairing it cro, multimeter, logic probe, clean room, laptop yada yada yada.

ok you can say it now.... everyone all together.

"Dave your off your meatballs, what happens when the ECU spits itself"

Exactly the same thing if the primary drive gear for the injector pump spits itself on any of the standard injector pumps or if the primary plunger on a cav or VE pump cracks. The engine stops.

So how do you fix it? simple on the Electronic vehicle you replace the ECU with the spare you just happened to be carrying. which is exactly the same thing you do with the injector pump when your primary drive gear on your injector pump spits or you crack the plunger. Sounds easy right?

Well in the case of the ECU yes it is, undo a handful of bolts a couple of electrical connectors and then replace the unit put the plugs back on and do up the bolts. In the case of your mechanical injection pump the basic list is as follows.

Set the engine to the injection timing point, on the compression stroke
remove and seal the injector lines and injectors.
remove and seal the fuel lines, ditto for the lift pump depending on where it fits
remove the injector pump
do the coarse timing of the injector pump
fit the spare injector pump
unseal and re-install the the lift pump and fuel lines
bleed up the fuel system to the injector pump
spill time the injector pump
unseal and install the injector lines to the injectors
bleed and prime the injectors
start the engine.

simple huh....

and that doesnt even go to cover some of the other possabilities like, say the weight return spring on fly weights of the governor lets go (the engine wont start or run) or if the link from the governor to the fuel control rail lets go (runaway engine)

just for kicks, how much does a fully setup injector pump cost and weigh, compare that to the cost of a standby ECU.

some other arguments....

no-one carries the equipment to diagnose an ECU in the event of a sensor failure stopping the show. urm, how many people now a days go bush with a laptop, PDA and in some cases a really good phone? all of those things with the aid of the right connectors and software can talk to an ECU. Lets look at the other side of that...

how many people go bush with an inline injector crack pressure tester? how about a precision depth gauge to set plunger bump clearances no, none of that? how about a pump calibration rack? spill timing line? cmon really none of you driving old school diesels carry any of that? so how do you re-time the pump if you have to remove it?

At the end of the day it all comes down to trip preparation and knowledge. mechanically speaking its a hell of a lot easier to diagnose and repair an electronically controlled engine if you carry the right gear and spares which unlike a mechanical diesel engine every sensor and in some cases all the diagnostics gear fits neatly into a box about the size of a shoebox.

But a mechanical engine if you know and I mean REALLY know the principals of your engine you can field repair it providing you diagnose it in the first place and then can get yourself to somewhere that has all the gear to manufacture or repair your damaged part.

Summarising,

Any electronic part that can cause an electronically controlled engine to stop has a similar mechanical component (often more than one) doing the same job and if that part (or parts) fails then your in exactly the same boat as the bloke with the electronic engine but I'm tipping (and this excludes things like head gaskets and piston failure) that any failure of the same nature that stops both engines will be repaired quicker on the electronic engine.

There are basically none. (on this forum)

actually I have found 1 now..