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[Entwood]

Cheers Entwood.... that's pretty easy then and definitely a score for GM. And makes sense why you advised me last time to research the exact system you're looking at before going straight to a wiring diagram.

If however, like in the Saab example above that there's no easy diagnosis with the test plug and all you have is the wiring diagram.... would my way be best?

 

Personally I'd attack things a tad more logically.

If you use your diagram .. the speaker is an independent "branch" so I would check the speaker first, is there a speaker output voltage from the ECU ... if there IS then the system is working you just can't hear anything .. suspect speaker ..

If there is no speaker voltage then the problem is somewhere  along the "main line" ... so start at the fuse, then the wiring to the ECU, is power reaching the ECU (input voltage) ? If it isn't .. reverse selector? wiring ??  If it is .. is power LEAVING the ECU .. check for output voltages ?  If in but not out .. suspect ECU.  If output OK is the power reaching the sensors ... and so on ...

Basically, start at one end and work along in a continuous manner .. your way you are jumping about all over the place ....  but that's just the way I was taught to fault trace ..

[Webby the Bear]

that's exactly what I was looking for  the reason I am jumping around in my approach is just i'm trying to go on easiest access first 

I've never actually seen an ECU other than it being a square box in the engine bay with a HUGE wiring harness/connector going in. can you take the lid off and find the connectors to search for the voltage coming from there? 

[Entwood]

that's exactly what I was looking for  the reason I am jumping around in my approach is just i'm trying to go on easiest access first 

I've never actually seen an ECU other than it being a square box in the engine bay with a HUGE wiring harness/connector going in. can you take the lid off and find the connectors to search for the voltage coming from there? 

ECU will have a loom going in .. your tester can be used with needle point feelers to check for voltages through the wires, you just need to be sure which ones you are checking !! So colour codes off a wiring diagram or good research and wire following - the latter being very time consuming !!

[Marks DTM Calib]

Just a note regarding the starter and alternator tests, the on car tests are actualy more valid as the bench tests have no significant loads (be it engine compression for a starter or electrical loads for the alternator) and its under such conditions that the faults will be visable.

As an overview of an alternator and how it works, consider the following.

A basic alternator (e.g. not a modern ECU controlled unit) consists of a stationary part (stator) and a rotating part (rotor), rectifier, regulator and as the name suggests, it produces an alternating current (AC) and not a direct current (DC).

This current is produced by exiting a coil on the rotor to produce a magnetic field, as this magnetic field rotates, it induces a current in a set of windings in the stator.

The stator will have at least three windings (usualy many more!) and produces three phase AC.

To turn this AC into DC to charge a battery it is fed into a rectifier (often refered to as a bridge rectifier or bridge), this is made up of 6 diodes which rectify the AC into DC.

So, thats the basics, there are a few more bits to consider.

Voltage regulation, if not controlled the output voltage will increase to high levels as the rotor speed goes up and/or the electrical load reduces, to combat this, a regulator is fitted.

This device controls the amount of current that is fed to the rotor winding via the slip rings and brushes and hence it is possible to vary the magnetic field in the rotor. This consequently varies the stator currrent and therefore the output voltage. The regulator measures the output voltage and automaticaly limits it to a preset value (this can be upto 14.6V for a calcium battery based system and can be seen with little electrical load and a charged battery).

The dash lamp does have a main use to. The basic alternator regulators do NOT take the power for the field from the battery (or they the rotor filed would be permanently energised with the igniton off and drain the battery), they get it from the dash lamp and an additional small rectifier.

So when you start the car, the ignition provides battery positive to one side of the lamp, the other side is connected to the regulator, this gives the regulator a feed to initilaise the field winding on the rotor (this explains why the bulbs used for the charge indicator are normaly quite a few watts). As the rotor starts to spin, the stator windings produce an output current, this is rectified by the additional small rectifier which feeds the resulting volts to the regulator on the lamp side. The bulb now goes out as it has positive volts on both sides and the regulator now has an alterntive power source from the alternator

So possible issues.

Regulator failure - These normaly fail short circuit and hence the output volts go way beyond the max volts as there is no control present, note the dash lamp will extinguish in this case. If they go open circuit then dash lamp will remain on.

Rectifier failure - Normaly spotted by reports of poor charging and a slightly flickering dash lamp. This is because only one of the diodes generaly fails at a time so the alternator still outputs current but it is reduced.

Dash bulb failure - will stop the alternator working altogether.

Bearing failure - Results in noise

Brush wear - Very rare these days although the awful old top mounted brush system as used by lucas in the 70's/80's does suffer this. Symptoms would be no charging and dashlight iluminated.


As an aside, those who have ever stripped an alternator may have noticed that the iron sections of the rotor are triangular in shape, this is by design and is done so that the AC output is not a true sinusoid and is more 'flat topped' with steeper edges. This gives the result of an electricaly quieter alternator with less 'ripple' on the output.

Dont be afraid of alternators, they are simple and pretty easy to repair.

[aaronjb]

Where does the torsion bar come in to this? obviously all the ones ive highlighted have springs and dampers. are these ever utuilised in addition to springs? I assume not. is the torsion bar an old system?

Torsion beam (since I brought it up, I suppose I ought to answer this ) is - on the rear - usually a semi trailing arm suspension where you have to imagine that the spring is attached to the pivot point of the trailing arm..

Harder to describe than it really is if you look at one

A good example (well, easy to see!) is on the 2CV where both front and rear is torsion beam; on the front it's a 'leading arm' and on the rear a 'trailing arm' but you get the idea:



The round tube going across the chassis is the torsion beam element while the black curved arm(s) toward the bottom of the picture are the trailing arm(s) with the wheel attached. On other cars the damper (shock absorber) would go between the wheel end of the trailing arm and the chassis, but the 2CV uses a bell crank (i.e. a protrusion on the trailing arm that, in this case, would be pointing toward the ground) with the damper connected between that and the chassis in a horizontal plane - you can see it in the photo, just.


Here's a double wishbone torsion bar setup where the red part is the torsion bar, twisted as the lower wishbone assembly rotates, to provide the 'spring' effect:




All in all they're largely rare on modern cars so not worth losing too much sleep over as long as you know the basics and when to spot one (usually there's no 'spring' visible which is a bit of a giveaway!).. All round torsion cars would be things like the 2CV and original Beetle with most French small cars of the 1980s and 1990s having rear torsion beam only with front Mac struts.

[omega3000]

All round torsion cars would be things like the 2CV 

Great for off roading ...

[Kevin Wood]

.. and then you get exotica like my old morris ital that featured torsion bars and lever arm shock absorbers on the front and leaf springs on the back to truly give you the worst of both worlds when it comes to comfort and handling. <shudder>

[aaronjb]

Actually thinking more about it, is the 2CV actually torsion beam? I always thought it was, but those big central canisters also contain springs.. so is it just crank arm remote springs and shocks?

The Beetle is definitely torsion beam front & rear though, isn't it..

[Shackeng]

Actually thinking more about it, is the 2CV actually torsion beam? I always thought it was, but those big central canisters also contain springs.. so is it just crank arm remote springs and shocks?

The Beetle is definitely torsion beam front & rear though, isn't it..

The early ones had torsion bar front, and independent rear, suspension, later models had Macpherson struts on the front. I had Beetles as second cars for about 20 years, and drove in RAC controlled rallies in a '59 Beetle, (semaphore arm indicators) even winning a special stage once! Although the 6V electrics did not make for good headlight beams. 

[Kevin Wood]

Actually thinking more about it, is the 2CV actually torsion beam? I always thought it was, but those big central canisters also contain springs.. so is it just crank arm remote springs and shocks?

Yes, I was wondering about that.

Never got close enough to a beetle to know what they have, but did get tempted to build one of these once:

http://www.madabout-kitcars.com/kitcar/kitcar_details.php?7

Looks fun, in a minimalist, "drive it at 10 tenths all the time" kind of way.

[aaronjb]

Thanks Shackeng - I wonder what car I was thinking of that's all torsion beam.. either that or I've just been very misled about the 2CV for years


Kev, you've started something now.. Amy has a thing for 2CVs and I just mistakenly suggested we could turn one into one of those (although now I check they no longer make that kit, but they do make a bike or VW-powered 'Zero') to which her response was "Oh yes!".

Looks like I may have picked up another project

[Shackeng]

Thanks Shackeng - I wonder what car I was thinking of that's all torsion beam.. either that or I've just been very misled about the 2CV for years

Kev, you've started something now.. Amy has a thing for 2CVs and I just mistakenly suggested we could turn one into one of those (although now I check they no longer make that kit, but they do make a bike or VW-powered 'Zero') to which her response was "Oh yes!".

Looks like I may have picked up another project

I had a Renault 16TL which also had torsion bar rear suspension. I found it very good on it and the Beetle, giving no problems whatsoever and good road holding, (OK, the Beetle could turn over if pushed ). I was surprised when VW went with the Mac struts, perhaps to give more space between the wheels for the tank, or luggage. No doubt someone on here will know.

[Marks DTM Calib]

Be careful as the torsion beam/tube/bar setup is still very widely used.

The setup where the spring function is part of the beam/tube/bar is pretty much extinct as it has a major number of compromises with repsect to road holding, noise and handling characteristics. It also used to see weld failures and placed megs stresses on certain parts (e.g. the Renaults used to eat the rubber bushes at the end of the torsion bars)

Plenty of setups still about with beam/tube/bar setup and seperate coil springs.

[Shackeng]

Be careful as the torsion beam/tube/bar setup is still very widely used.

The setup where the spring function is part of the beam/tube/bar is pretty much extinct as it has a major number of compromises with repsect to road holding, noise and handling characteristics. It also used to see weld failures and placed megs stresses on certain parts (e.g. the Renaults used to eat the rubber bushes at the end of the torsion bars)

Plenty of setups still about with beam/tube/bar setup and seperate coil springs.

I had my R16 for 10 years, and 85k with no issues, but I am not a hard driver. The body rusted off the 'chassis' before mechanicals failed, so no surprise that you never see one now, but I loved that car, it was the only one I've owned that approached the Omega for comfort, (inc XJ6).

[Shackeng]

Actually thinking more about it, is the 2CV actually torsion beam? I always thought it was, but those big central canisters also contain springs.. so is it just crank arm remote springs and shocks?

Yes, I was wondering about that.

Never got close enough to a beetle to know what they have, but did get tempted to build one of these once:

http://www.madabout-kitcars.com/kitcar/kitcar_details.php?7

Looks fun, in a minimalist, "drive it at 10 tenths all the time" kind of way.

With apologies to Webby for being off topic, I certainly drove my first beetle with the 'heel to the steel', the engine was unburstable, if low on power, but great fun to drive, and an ideal car for first owners, as the engine could be dropped out in comfortably less than 1 hour. My son started out with one and loved it also