Diagnostics - a real example

oooo youve diagnosed a lambda sensor, good for you, bit tired now? id go have a lay down!
you can just read the actual value. no need to produce graphs it should be obvious if the actual value isnt switching.

a good way i learned a while back with suspect lamdas is to introduce a small air leak in the inlet manifold (but not enough to upset the idle) like pulling the vac pipe off to the fuel pressure reg and see if the lambda sensor picks up on it. trying to compensate. also see if the co/hcs go down with a forced leaner mixture.

not meaning to put you down, I'm only joking!!!! very interesting this tho how other people go about fault finding like this, which mk4 engine is this btw?

we had a newish 3 cyl polo in a while back with a misfire (had another the same last week) both around 35k on the clock. the first one had been to another garage who fitted a new ecu!
anyway after a bit of investigative work, the switching signal to the injector disapeers as it registers a misfire fault on that cylinder. clear the fault code it comes back but still misfires slightly til the ecu works out which cyl it is then cuts it again after 10 mins of driving.
on checking the compressions/cylinder leakage that cylinder is about 40% down. on stripping it found no obvious problems till you look at the exhaust valve seat..... its gone oval....

what would be fun on here if we could post up interesting diagnostic jobs on here that we come across at work.....
weve got a 58 plate audi a8 with a crappy electric handbrake I'm currently trying to fix, if your interested? its been to the dealer but the faults down to water ingress to the ecu so its not covered under warrenty. the ecu is fubar so weve fitted a new one coded it in etc but its still showing fauts to both calipers and the handbrake switch. all wires check out to the calipers supplies to the ecu canbus etc etc....

a couple from this week.

a volvo s60 with an owner thinking it needed a service cus the display said "engine service required"
nope it was a kind of management light but the actual management light wasnt on.
on checking fault codes, it had a dodgy clutch switch. 5v supply to it but signal wire is supposed to read around 1v clutch down and around 3.2v clutch up....
was reading 0.15v all the time clutch up or down..... new switch time!

an a6 2.5 tdi v down on power...... with a dodgy crank sensor managing to read crank position to run but not rpm (sensor does two jobs) and then needing a new airmass sensor. (guy actually rang up after picking it saying how fast it wasm asking if we had chipped it or something cus the difference was night and day!)

a '99 1.9 tdi a4 down on power on the motorway giving under boost faults. another garage said it needed a turbo cus of the variable vane not working properly. nope it need the vacuum control solenoid to the vv actuator as the vac was leaking back inside.....

a 2.0 fsi a4 avant that with the engine loom melted into the egr pipe....

a 2.0 tdi 170 with the common injector failure one call to the dealer and they picked it up and fitted new injecters foc then brought it back to us the next day for the customer to collect from us!!.....

i could bore you to death with this sh1t!

8v 2.0.

I take your point about the lambda, but although you can just read the value (and I suspected it right from the MoT) I wanted to have a play around and make sure, particularly with the misfire code going on too. I'm trying to learn as much as possible about how it all works. I have the time, and don't have a workshop manager breathing down my neck. Also, I like graphs It's about proving my theory before picking up the phone and ordering a new sensor.

The audi handbrake thing sounds interesting!

God, is that all I'm staying self employed!

yeah, that's the one. It's a 5 door too.

The whole point of scope diagnostics is it shows you what's actually going on in the engine rather than what an ecu sees or a scan tool tells you. With a scope I can diagnose pretty much any fault on any make of car. Show me a scan tool for less then a grand that can do that. In fact show me one for less than twenty grand that can.

Come down here and ill get you on 15 pound an hour minimum. That's if your as good as you say you are.

ive changed numerous engines on tts, s3s 1400 golfs took heads off allsorts. did a broken cambelt on a renault 1800 16v senic last week, head gasket on a k series lotus elise 3 weeks ago. 3 years ago i changed the engine on a 5 litre v8 auto merc sl cus of the engine being drown by flood water.
not so long ago i did two cambelts on an v6 twin turbo s4 and a 2.5 tdi a6 in a day. you get quick at these things known the cars, having the right special tools and knowing what your doing.

you could strip a 1.8t engine completly down while i was blind folded throw all the nuts and bolts in the air. unblind fold me and id know where they all went.

I'm after a pay rise atm. i keep dropping hints and ive been for other jobs and been offered them but part of me thinks its better the devil you know..... maybe i should take a 2 week holiday next year if i don't get a pay rise? might make them realise they'd be a liitle fooked without me.

one thing that does wind me up is when they give a dianostic job to one of the other guys while I'm busy (oliver) they go read the fault codes, they come to ask me what they should check and look at..... i answer..... then oliver goes to the boss and regurgitates what ive told him looking all intelegent.... pisses me off!

did I mention ive been a tester since just before computerisation too?

id jump at £15 per hour. if you can keep me busy?

Believe me, it wouldnt.

I like autologic, we have that at the place where i do my day job. I can tell you the package we have for VW BMW and porsche costs over 20 grand alone. We also have a kts there but tbh i would rather use my snap on solus, its twice as fast and can read more codes than the bosch.
I'm in a posistion where I've worked on mercedes sprinters and vitos for almost ten years now and i agree that 90 or 95 percent of the time you can diagnose them without even looking, but every now and then you get something that will throw you a bit and thats when you realise how important it is to be versatile and think outside the box.
A good example is this from last week. A fiat scudo with a missfire from cold. No fault codes, nothing out of the ordinary in live data, relative compression good and glow plugs working fine. I scoped out the fuel pressure and injector signals and got this.



The blue trace is injector current and the red is frp sensor.
Zoom in a bit and the problem starts to show up.



See the pattern of two flats followed by two big dips in pressure, that No 3 and No4 injectors letting in two much fuel. Two injectors and the problem is solved. Whats more we were actually able to look the guy in the face and say 'this is your problem', not 'we think if we change this it might get better'.
Main dealers wanted to charge him over two grand for a pump and four injectors.
The point i'm trying to make here is that fault wouldnt have shown up on any scan tool. Even a running leak off test wasnt conclusive. It showed no3 leaking off slightly more than the others but not enough that i would be confident in changing it.