Some Diagnosis.

[Motu]

I've had a couple of cars in this week that I've had to diagnose electronic problems on,so thought I might take you through how I blunder my way to success.I haven't done much of this over the last couple of years,personal problems and now living 85km from work hasn't given me much time - and I normaly do this after hours,I could of knocked both these out over a glass of wine in 1/2hr each after work,but both were 2 day repairs.

We'll look at the 1992 Mitisubishi Lancer first,towed in as a no go and told by the AA that the fuel pump was faulty (yeah right) It starts and runs for a couple of seconds and stops,sounds like it's running out of fuel alright.The first thing I pick up for diagnosis is my Snap On Vantage,a Dual Channel Graphing Digital Multimeter (GDMM) with built in data base,it's very easy to use and uses a couple of D cells which last for months.I want to check the fuel pump first,so hook my Low Amp probe on and access the fuel pump wire,can't find the fuse to loop into,so rip out the rear seat and hook into the fuel pump wire with the clamp probe....the first image shows the amp draw on the fuel pump,each hump is a bar of the comutator.If I knew how many bars on the com I could calculate rpm,but don't see the need - the wave form looks clean,speed about right,and it runs all the way until the engine stops,so I reckon the pumps ok.If the amps went high and the pump slowed down I'd say it was siezing or the filter was blocked,if it speeded up with low amps I'd say it was running out of fuel...if it cut out as the engine stopped the pump would be faulty.

I also notice it's only running on 2 cyl,2 & 3 are out,the plugs are ok,leads ok,and both coils have the same resistance.Luckily we have a Mirage in with the same 4G91 engine for an alt repair,so we do the old swapparoo,change coils and ign module between cars - the Lancer coils and module work perfectly in the Mirage,the Lancer still has 2 cyls out with the Mirage parts.
That means the signal from the computer is missing for those cyls,so go off on another tangent to check the computer.Mitsi's have bad computers and it will pay to check before I go any further,we pluck the board out and see it has already had a couple of capacitors replaced,and repairs to the circuit board as leaking caps damage them,there is some signs of overheating and other signs of stress....we put it back in with that knowledge in the back of my mind.

Back on the case I have my scanner hooked up and clear the codes and check some inputs and outputs.Checking the injector pulse I find this is what's killing the engine - it runs up,then the injectors quit and it dies,confirmed on the scanner,it keeps bringing up cam angle sensor fault,so I check the cam and crank sensors.I check the cam/crank sensor and find the crank sensor good as in the second image,but just a 5 volt line for the can sensor - so that's it,fault found.

The cam/crank sensor is on the back of the cyl head where the distributor used to sit,so get a second hand unit and fit it - the motor fires up on 4 cyls and continues to run...fixed! The next image is the missing cam angle sensor wave form,both these are Hall Effect sensors and so show a nice square wave form,the crank sensor is even and tells the computer how fast it's going,the cam sensor tells where the motor is,and as it's a DIS 4 cyl with 2 coils each coil fires once a rev,so a wide and narrow wave form.

OK,so maybe I should of plugged the scanner in first,but it won't tell me if the fuel pump is faulty,so I felt I needed to eliminate the pump first,and I also needed to confirm a coil fault wasn't knocking out those 2 cyls.These images were captured on my Fluke 98,a DSO (Digital Storage Oscilloscope) it's much more powerful than the Vantage and I use it to narrow down on a fault.

[James Deuce]

Very nice work Mr Motu. I know where I'd be taking my car if I lived up your way.

[bugjuice]

yup, nice work alright..
my 'Check Engine' light keeps coming on, and then going out after a few seconds on my 98 impreza even tho nothing changes with the car. Can ya fix that?
or is the car just bored and making sure I'm paying attention?

[MSTRS]

yup, nice work alright..
my 'Check Engine' light keeps coming on, and then going out after a few seconds on my 98 impreza even tho nothing changes with the car. Can ya fix that?
or is the car just bored and making sure I'm paying attention?
Used to happen on my Subaru too. Got rid of the horrid piece of junk and voila, no more problem.;)

[2much]

Damn, I wish I had some flash toys like that!

[2much]

yup, nice work alright..
my 'Check Engine' light keeps coming on, and then going out after a few seconds on my 98 impreza even tho nothing changes with the car. Can ya fix that?
or is the car just bored and making sure I'm paying attention?

That's an easy one BJ, take the bulb out!:innocent:

[Lou Girardin]

:sherlock: :clap: :clap: :clap: :clap: :clap: :clap: :clap: :clap: :clap:
Excellent!

[SPORK]

:sherlock:

That is all.

[kro]

I love reading shit like this, always interesting for wannabe mechanics like myself, thanks Motu.

[Motu]

I was wondering if I could get those images out of that programe.Check Engine light setting and going out means it's got an intermitent fault,it may be nothing,or something ready to fail anytime soon.Subaru's have mega AC ripple from the alt,this can upset the old computer sometimes.

Next was a 1997 Mitsubishi Legnum with a 6A12 V6,actualy it was first,having come in on saturday afternoon,so look at it first thing monday.It runs,but dies under load,if you are gentle it'll rev,but any throttle kills it....air flow meter is my first thought.I hook the scanner in first on this one,I can get pretty good data out of these,but the codes I get are pretty well crap...like vehicle speed sensor has got nothing to do with it sitting on the floor.I scope the air flow meter and it looks good....I have a suspicion about the ign system so send my mechanic off onto a good tune up on it.You have to remove the inlet manifold on these to access the plugs and leads on the rear cyl head...the rear plugs are plats,the leads ok and we replace the front plugs which are just standard jobs.

I go off on a tangent with this one too - I get a bee in my bonnet about the idle air control valve...it tests fine,but out of the throttle body when the key is turned the pintle won't retract to the wide open position like it should,we do the swaparoo with the Lancer which has the same IAC valve.Same thing,hooked up to the Lancer both IACs retact the pintle,both don't work in the Legnum - only one thing controls the idle,the computer.OK,I'll file that.

We haven't fixed a thing,it still dies under load,so now I can hook the Fluke up and check the ignition - the first image shows what I saw,not a good look.The Fluke 98 is a powerful DSO set up for automotive use,and I find it good for ign diagnosis,and I can really crank the time base down to some silly figures - here I have focused on the ignition event,that's the plug firing - we are watching the spark as it's actualy going across the gap.The plug is firing,but burn time is almost non existant,the voltage just fades away in that sloping arc.I reckon that a load is just killing the spark,and so it dies.

But how to prove? We have to get that coil out and have a look at it,but it's part of the dist and burried deep - we have to pull a few things like half the cooling system apart to get it out,remove the Hall Effect cam angle sensor and get the coil out of the body.There is no physical damage,and resistance tests inconclusive - readings are all over the place,the primary readings keep changing and it takes me some time to settle on what I think they are.But they are out of spec,and I take the gamble to get another used dist for $395 retail.I test the replacement and find the figures good - fit the dist and the engine starts and runs fine - fixed!

The second image is the new dist and coil - it shows a good flat burn line of over 2 ms,with a burn voltage of 1.28kv,that's pretty good and the motor no longer dies under load.mission accomplished.

[Winston001]

Fascinating stuff. My respect for auto-electricians is vastly enhanced. Very enjoyable.

[riffer]

Hey Motu, have you ever considered a book, or maybe a column for a motoring mag?

I'd read it. :)

[Flyingpony]

Lovely stuff Motu!

[rfc85]

damn good,interesting reading,thank you

[F5 Dave]

A good friend of mine is a talented auto electrician (sadly defected to briz). His best advice ever is:

Listen to what people say, but don’t listen to what people say.(customers in his case)

ie: Someone tells you it is the fuel pump or whatever you will let it cloud your judgement. I’m surprised in some threads here that people don’t describe the symptoms very clearly at all & leave out what they have previously done, has it ever run properly or what the vehicle is.

[Motu]

Yeah,when the customer says ''don't worry about the ''*****'' that's been fully rebuilt'' - that's the first thing we look at,I'll bet my life on it!

I'm no auto electrician,far from it,I'm just a dumb mechanic.Like most mechanics we have ignored the electrical side of the game - we have mates in the trade who deal with that stuff.I have a problem with electronics and maths....maybe a left/right brain thing,as I'm left handed.I don't have an anylitical mind...I think I work in pictures and patterns.

As a little fulla in school we were learning subtraction - I had no idea what was going on,I hadn't understood a word the teacher said.We were given a line of sums to do and I just sat there looking at them...totaly clueless.I figured the next best thing to do was cheat,so checked out the girl next to me,and watched how she was doing it - ah,no worries,I got the idea pretty quick,I picked out the pattern straight away,something like 1,1,2,1,1,2,1,1,2,3 - so I raced through all the sums with that pattern,and got most wrong.More talking and more sums...so I applied the correct method,and got them all wrong! I checked the girl beside me again and picked up the new pattern - wrong again! In the 4th form maths was an optional subject,and I dropped it real quick! - phew!


By the early 90s cars were a whole new game,we bought $25,000 tune scopes,went on training courses and tried to force our fuddled brains to take on the new concepts...but it didn't work - the normal reaction from a mechanic to some electronic failure is to panic and try and pick the most complicated thing wrong...just throw parts at the car and hope you fix it.By the late 90s I was getting annoyed as I did as much on a car then sent if off to the experts,only to have them send it back with a list of ''possible'' faults I had already eliminated.Time to up my game.

With the new found internet as my university I applied myself to learning how these systems worked,making it make sense to my poorly educated brain.I got my Fluke 98,then later the Vantage,having dome my homework on what I needed - and they opened up a whole new world to me - electronics in pictures,and patterns.I don't have to know how a Hall Effect generator works or what it does,I just have to know it's place in the scheme of things,and know what sort of reading I should see on my scope.I just walk up to a car and plug into as many wires as I can get at,look at what I see and build up my mental library of waveforms,good and bad.I don't have to know the intracies of how the system works,just what each thing does and what it should look like - I keep my mind clear and just think about what effects what.

There are new systems out there now,I need to step up to the plate again - but I don't think I will,time for new challenges,not old ones revisited.

[Brian d marge]

Yup that was a good bit of mechanicing there Motu!
I was thinking about this thread last nite , and the funny thing is , Computer of no computer. 1901 clackhammer ..or 2007 F1 missile, It came down to spark/fuel/compression ..Same as its ever been . ( except you have that vantage , I am envious there !!!!)

just reading you last post , I found myself thinking nope I am opposite ...but for the same reasons. I also think in pictures, and in order to learn I need to see and do...Its no use untill I do both it just doesnt stick.

Maths ...Maths was black stocking and a young relief teacher ...I failed on both accounts ..It just didnt make sence.

But Electricity, for some reason its easy ...I just get a feeling and can see through the process ...... and because no one else knows about it they leave me alone ... I think it was when my tutor explained electrics as the same as a lazy student ..then I twigged

its a funny ole game, thanks for that bit of sharing , it was a good read and a good bit of Mechanicing

Did ya charge ...( bet you didnt !!!) ????


Stephen

[WINJA]

full credit , i love this sorta stuff

[2_SL0]

Christ I dont need to read this, its like a day at work. I do enjoy solving problems, especially when other people have looked and couldnt.

Nice write up Motu.
Fluke meter, one of my favs.

Went down a similar track, did all the courses etc, got all the software etc, but at the end of the day I spent a good number of hours, days working with the technology and understanding what did what and how it all intereacts. The laptop/pda is great. But they dont solve the problem I find I take the information they present and use it to track the real cause down. That might sound strange to someone who hasnt experienced Engine management programs, but those who have will understand. Often the software gives you a code of what is faulty, but you need to track down what has caused that item to become fautly or give the impression it is faulty.

[Motu]

So many mechanics are looking,hoping for the black box they plug into the computer and it tells them what's wrong and how to fix it - it doesn't exist,and is not needed,all that's necessary is an understanding of the systems and a basic scope or GDMM.I have a scanner,the Snap On brick is old and basic these days,and I just use it for a guide on what to look at.

Although I used it today to diagnose a stalling complaint on a Nissan Sunny,throttle body injection.It told me it had an air flow meter problem 2 key starts ago - I didn't even bother to check,I know it's right,because I knew it would say that....5 min diagnosis.

How to charge? that's always a hard one....I've wasted hours I never charged for not being able to find problems,I've spent hours training myself,paying for it...just the 3 meters I can hold altogether in one hand cost me $20,000...who pays for that????

Man,I get angry about people who bleat about how much mechanic's charge!!!

[F5 Dave]

. . .& the same people complain about what dentists charge as they sit in a 10 thousand dollar set & the drill set alone is $70,000 (my father was a dentist & to put these prices in context he retired 10 years ago & was probably 10 years before when he updated).

Just to run off on a tangent, he ran two surgeries so the patient could be set up by the nurse & ready to go when he’d finished the other, or if there was a process that needed to wait for a while. Of course it required twice as much gear + new gloves every time, but it was efficient & saved everybody chargeable time.

Problem was people only saw that they were in the seat what seemed like 5 min & “How much?” People never see the cost of the latest technology required or the price of consumables & specialise services.

[Motu]

Some more this week - on sunday I drove the son in laws '89 VN Commodore up to the workshop,running on 4 cyls and shaking like mad over 80kph.

First thing I did was put my low amp probe on the DSO and current ramp the coil pack.Checking voltages tells if a signal is being sent,but not if it's being acted upon - the current draw tells us what work is being done,it's called current ramping because of the shape of the waveform and is useful for checking ign coils,fuel pumps and fuel injectors.The Commodore VN is DIS (distributorless ignition system) and uses a 3 coil pack on top of the ign module,I just clamp the loom going to the module,and get the waveform in image one.The 3 double ended coils will get one signal each,we can see two higher ramps and one little bump...one coil isn't working,but suspect it's getting triggered to give the little bump.I clamp my cordless timing light on the wires and it's obvious the top coil isn't working - 5 minutes and 90% of the diagnostic work is done

I take the coil off and check resistances,and find everything in spec - so,it's not the coil pack.While the coil is off I check the three signals coming from the module and find I have 3,but one is weak - with the coil hooked up and a load on the signal disapears - one ign module required.I did one of these on Xmas Eve too.I also check the crank angle sensor and cam sensor,the next 2 images - the crank sensor is all even,but the cam angle sensor has 3 different sized gaps between signals to tell the computer where each cyl is.

Next image is the coil ramp again,all 3 coils working,but I'm not too happy with what I see,fluctuating current draw on the coils,changing between cyls.I check secondary ign on all cyls and find those on the right bank losing burn time occasionaly,not so much missing,more ''fluffing'',and the idle is a bit rough.The next tool I pull from my weapons cabinet is one I made myself - a vacuum probe.It uses a MAP sensor from a Commodore,4xAA battery pack and a couple of pots to adjust the range - it doesn't give a vacuum reading,but shows the actual vacuum pulses in the intake manifold as a wave form.I can't get a good reading from the Commodore,but thought I'd show you anyway - I can usualy get a good waveform,can trigger from no1 cyl and have found broken valve springs with it.

The latest theory,which I am sifting through my brain and testing...is that altering ign KV spikes are caused by sticking valves - the only thing that can alter pressures in the cyl are the valves,so altering kv demand and current are influenced by the valves.I'm thinking that's what we have here.Now the cooling fan isn't coming on and I'm having difficulty sorting such a simple thing like that out...my daughter is picking it up tonight.

Also in this week is a '97 BMW 316 with no power - it's been to the experts who have plugged in a scanner,replaced the knock sensor and fixed nothing...a typical mechanic with a magic box that tells him what to do...but he forgot to use his brain.It's gutless alright,no power at all - so check the fuel filter first,BMWs are prone to blocking them...but it's fine.I see the tailpipe is white...click,click - up on the hoist and I hear a rattle in the cat converter.It's a one piece system so cut the pipe and drop the converter - while the boys smash out the matrix I blast around the block with an open exhaust - yeeehaa!!! I weld it back together,refit and we have as much power as one can expect from a 316.Just basic mechanicing on this one,no need to be scared of the high tech Euro.The customer is an eastern European who first came to me as a new immigrant...I took the time to listen to his poor English and do the best I could on the old worn out cars he drove.Actualy in his home country he was a lawyer,and now has his NZ qualifications,practising law,I've seen him on TV even.He drives across the city to bring his flash cars to me,as someone who helped him in his early days in the country he holds me as someone he can trust.

Also in today was an '87 300E Merc...with no power,oh,easy you say...you just did that! Not so - first check was the fuel filter,collapsed,the element rattling inside.This is K Jetronic,the mechanical fuel injection system...and I don't go near them.We run over the ign system,do some housework on vacuum hoses,some are not connected,some collapsed,current ramp the pump (not a good look) It will only rev to 3500rpm,and if we add fuel into the throttle body (carb clean,engine start) it revs out.With more info from the customer I find they ran it out of fuel (new to them,and on it's first trip back from Levin it ran out at 3/4 on the gauge) With the faulty fuel filter and sucking the tank dry I reckon the distributor head is blocked,and I back out of this one...but we have improved it.The customer is an old friend - 25 yrs ago I used to see her in the Farmers monthly flyer...nudge nudge,wink,wink.

Win some,lose some...it's been a week from hell.