Whilst this video is a shameless plug for DDTSB showing how useful it can be - providing they have come across the problem before, if not, they offer ongoing support.

His general videos show a very detailed "Test Not Guess" fault finding process)
The video shows me the following:

• The need for dedicated code readers (in our case Forscan) that can show manufacturer specific codes if there are any, if not then live data comes to the fore to find some evidence.
• The danger of changing expensive components based on "We've seen this before and it was fixed by changing (in this case) the EGR" (Ouch!)... with no real evidence.
• The main dealer changing a full set of injectors (Ouch!) on the basis of "Experience"... with no real evidence.
• The need for detailed diagnostic knowledge AND experience before finding and changing the correct part basked on looking at live data for obvious inconsistencies (fuel temp of 100 degrees when car was cold!)
• The danger of changing expensive parts at customer expense with no comeback/refund if it doesn't work - based on guesswork.

Anyway worth a look IMHO:
https://www.youtube.com/watch?v=V5WY6Mo8xho

 

While that sounds great on paper, it just doesn't work in the real world, at least not in the current UK society.

Testing everything is very time consuming, bad for both the garage and the customer, and all the other customers who have to wait longer and longer for bookings.

And proper diag tools are too expensive for most garages and DIY'ers.  Injector test-rigs & oscilloscopes for example.

There will always be some 'losers' in this system, who do end up with wrong diagnosis and needing additional parts, but for the majority of customers it is cheaper and quicker to use experience and a bit of a trial & error.

If it's a cheap part that's easy to fit then that may be worth a guess but IMHO  for a part costing £100s and multiple labour hours to change whilst STILL  being a guess, it has to be worth doing a realistic amount of testing?
I agree there's eventually got to be a trade off.
Cheap oscilloscopes and, for example injector leak off kits are available and sending components for testing by specialists before simply replacing is another option
If owner can work as far as possible on the basics and give the full history that may reduce the overall time but expensive guessing at customer's expense just doesn't sit right so I hope it doesn't happen to me!

Ford dealership labour rates are around £130 per hour. Independent garage are around £80 per hour.

If it takes two hours to diagnosis a fault then you will have spent £260 (£160 indy) just to find and confirm the fault.

If the part that needs replaced is £400 plus an hour to fit £130 (£80 indy) then final bill is going to be £790 Ford dealer or £640 for the independent garage.

Taking an educated guess at replacing the £400 without spending two hours doing the diagnostics means the bill is £530 (£480 indy)

If you give the customer the choice of paying for diagnostics and being 90% sure, or just taking a chance and being only 70% sure, I would expect that most would go for the cheaper option every time.🤔

12 hours ago, Shearers said:

Cheap oscilloscopes and, for example injector leak off kits are available and sending components for testing by specialists before simply replacing is another option

Leak-off tests aren't that accurate and only measure one thing.  Sending injectors away to be put on a proper test rig is the way to go.  But who pays for the garage lift that the car is stuck on while waiting for the injectors to come back?  Does the garage lose 2-3 days worth of work?  Or does the customer pay for all of those hours?  It's just not practical.  Chuck another injector in and get the car out again.

I agree that if the owner can do their own work, isn't considering their time as a valuable commodity, and has access to a fully equipped workshop, then by all means do all the testing they like.  But it's not going to happen at a UK garage.

I hope we can generally agree that it's best if you have a reliable car that is well maintained (to try to avoid avoidable breakdowns)
Beyond that, if you can't find the fault yourself (as said, I can spend the time at "no cost") you want a trusted tech who knows your vehicle and its faults in detail or can get to the root of the problem quickly using whatever diagnostic equipment is needed (or that they have)
Beyond that, it's a potentially bottomless pit of expense that you just have to smile and pay or get rid of it.

I'm not even sure about that any more.  All of my breakdowns were unavoidable.  Oil and filters changes wouldn't have prevented any of them.  I started following my own maintenance routine instead.  Based on experience rather than manufacturers recommendations.

Perhaps I would have had 'avoidable' breakdowns if I'd just ignored all maintenance though.  Can't prove that either way now, of course.

I don't know a single trusted tech in my area, and I've been here over a decade now.  Don't know anyone I'd trust to do a dry cambelt let alone anything requiring diagnostics.

I was in the camp of cutting losses and getting rid when a car became financially unviable and I could no longer fix it myself cheaply.  But post-2020 the car world is completely different.  Everything costs more.  Don't think you can pick up cheap, reliable used cars easily now so probably stuck with what you've got unless you get into debt taking out bank loan.

All a bit of a moot point for me really.  It's coming up to half a decade since I was last able to drive, and longer since I could properly fix cars.  I really don't know what my strategy would be if I started driving again.  I try to answer posts on here as best option for the poster, rather than what I would do for my own car and area, but that doesn't always work out unfortunately.