Urgent help my car wont start

Posted: Fri Sep 05, 2003 4:11 pm

Help

My car wont start I have checked the spark plugs and there is no spark.
Anybody have any ideas? Its a 1992 Audi 80 V6 2.8

I started it this morning for 2 mins while I move the car about a foot. The switched it off to go to work on my bike. Now the stupid thing wont start.

ANy body have any idea what to check etc..........

Thanks
Tony

Posted: Fri Sep 05, 2003 4:37 pm

Be carefull when checking for a spark on that engien as it produces a very high voltage, and current.

Have you checked to see if there is a spark coming out of the coil ?

And checked to see if there is a voltage at the coil ?

DOes that card have an imobilser, as this could be part of the problem.

Posted: Fri Sep 05, 2003 4:47 pm

HI

Its no prob I am used to working with high voltages. I have checked two sprk plugs and there isnt a spark at either of them. I cannot see a way to get onto the low voltage side of the coil to check if there is a signal there?

Could the ECU need resetting? if so how do I do this?

HElp I'm getting desperate

Thanks

Tony

Posted: Fri Sep 05, 2003 5:24 pm

you need to check if there is a spark out of the king lead (which runs to the coil and to the centre of the dis cap). if theres no spark there you need to check for power at the coil. on the other side of the coil you will have the wires that run to the ign module. at the coil you should have a switching signal (you need a dwell meter to check this). you also need to find out if the fuel pump is being switched on as it could be a pick up problem.
are you sure you don't have a spark cos by the way you have moved the car only a few feet you may have flooded the engine. (very common when a car is started from cold and then switched off again) if all else fails and the car still wont go get the aa or rac out, they should at least get the car started for ya.

mark.

Posted: Fri Sep 05, 2003 5:54 pm

Ok just checked the low voktage side of the coil and it is sitting high at 25V AC whne measured on my meter

Is this normal???
Still getting no spark at the plug???

I am stumped anybody any ideas on a 2.8V6 Car doesnt have an imobiliser apart from the VAG fitted alarm which is switched of by the key.

Cheers

Tony

Posted: Fri Sep 05, 2003 6:01 pm

er you should only have battery voltage at the coil, 12 volts.
don't why your getting a reading of 25????

Posted: Fri Sep 05, 2003 6:29 pm

Sounds like the hall sender sensor has gone bad Mad

- That's the cam shaft position sensor which is located on the rear of the right cylinder head looking at the engine from the front. Look for the plug that goes to a black round plastic sensor next to the exit of the vent tube.

If the sensor goes bad or is disconnected the ECU will not send a voltage to the coil packs to ingnite the cylinders, that is why you do not get a spark! I bet money on it Razz

Oh, the V6 ebgine is distributerless and timing is goverened by the crank position sensor and the cam position sensor (hall sender).

Posted: Fri Sep 05, 2003 6:39 pm

ah coil packs Confused

didn't think it had them. might be a crank postion sensor, are the injectors switching?

Posted: Fri Sep 05, 2003 10:36 pm

AAAAAHH thanks fast28 I have seen the sensor you mean but didnt know what it was.

Will give Audi a ring in the morning to see if I can get a replacement.
Any idea as to what they might cost?

Thanks guys will keep you posted. Need to get it going soon otherwise I'm stranded.

Cheers

Tony

Posted: Sat Sep 06, 2003 3:06 pm

I've heard quite a few 2.8 v6's have this sensor fail and it might prove to be an expensive item, you can try the various Audi breakers in the country but obviously a new sensor will give piece of mind in the long term. Cool

Hall Sender pt no. : 078 905 161 C (get the dealer to cross reference it to your year and model)

Posted: Mon Sep 08, 2003 8:52 am

Right folks

My car is still dead. Not having much luck with this car so far!

A new hall sender is £189 so I cant afford to buy one to try it if it isnt the problem, so my question is how do I extract the fault codes from the ECU on the 2.8 V6 engine in my 1992 Audi 80?

Managed to find a few sites where the codes are listed but not procedure to extract the codes. Help!!!!!!!!!!!!!!!!!!!!!!!!!!!

Posted: Mon Sep 08, 2003 10:31 pm

Suggest you re-check coil L.T. voltage - should be 12V D.C. not A.C. Did you have your meter on the correct reading scale ? Alternatively, check coil terminals are clean, check for spark directly from the end of the king lead, check dizzy cap is in good condition:- dry, no cracks or earth track marks & the carbon centre contact has plenty left on it & moves in & out easily on the spring. Also, check the rotor arm is in good condition, clean & not loose on the pinion. Dizzy cap is cheaper than a sensor !

Posted: Tue Sep 09, 2003 8:13 am

Hi Dougal

The switching signal from the ignition module would be an AC signal wouldnt it? As it switches the spark plugs on/off
otherwise the coil wouldnt work as it is basically a transformer which is basically a short circuit to a DC source.

So the low voltage at the Low tension side of the coil should be an AC voltage.

Unfortunately on the V6 there is no dizzy as it runs off a cam angle sensor to an ignition module to the coil. I strongly suspect the cam angle sensor (hall sensor) but at nearly £200 I am a bit reluctant to buy one without knowing for sure.

Does anybody know a way to extract the fault codes from the ECU?

I have found a few procedures involving two connectors in the passenger side foot well and a test lamp.

Does anybody know if this might be correct?

Cheers

Tony

Posted: Tue Sep 09, 2003 10:33 am

I suggest you take Dougals advice (and others) the voltage at the coil will be 12v DC, it the the current which passes through the coil which induces the high voltage, this is done by completing the coil circuit, nothing to do with AC voltage.

If you do not understand this i suggest you take to a mechanic before you break something or waste you money.

Posted: Tue Sep 09, 2003 11:57 am

I dont think I will break something. I am en electrical design engineer!!!!!

How on earth can a DC voltage induce a current in a coil???????????????
It is a short circuit!!!!!!

The DC is switched which means the signal at the low tension side of the coil is AC.

Ie has a frequency!!! DC is as it states direct current! no frequency!!

Posted: Tue Sep 09, 2003 12:35 pm

http://auto.howstuffworks.com/ignition-system3.htm

http://www.familycar.com/Classroom/ignition.htm

http://www.musclecarclub.com/library/tech/ignition.shtml

http://www.mycarwizard.com/autoshop/ignition.html

Posted: Tue Sep 09, 2003 1:50 pm

These sites all prove my point!!!!!!!!!!!!!!!

The DC is switched by either the points in the low voltage sde of the dizzy converting the DC to AC or in my case by the ecu firing AC pulses to the ignition module to the low voltage side of the coil.

As it says a coil is a transformer which only works on AC Elcetricity. The DC is switched by the points for example gives an AC signal ie 0-12V-0 etc........ or in some cases -12V-0V-+12V which would give a peak to peak value of 24V.

So I think what I was reading was correct????

My car is a V6 so it has no distributor it is run from a hall sensor (cam angle sensor) which sends timing signals to the ECU which then pulses the ignition module which amplifies the signal to the low volatge side of the coil which then through the coil is converted to a high voltage pulse to the spark plugs.

Razz

Posted: Tue Sep 09, 2003 2:27 pm

How do you get -12v ??

What does DC and AC stand for ??

Posted: Tue Sep 09, 2003 2:48 pm

-12V is achieved by running an isolated circuit from the battery with the wires crossed over, quite common on posotive ground systems or where a higher secondary volatge is required, such as a spark plug.

AC = Alternating current ie 0-12V-0V or -12V-0V-+12v

DC is direct current is +12v continously with no return to 0V in any time period until the power is switched off.

DC is the stuff you cant let go of should you get electrocuted, not a problem until above 50V though

Cheers

Tony

Posted: Tue Sep 09, 2003 3:24 pm

Audi are negative earth cars are they not ?

switching the low tension circuit from 0 -> 12 -> 0 etc only means that you are switching the voltage from 0 to 12v and back the current direction is not changing.

I see what you are saying that you could switch the wires over to, but according to those links you switch the 12 low tension circuit on and off.

Whilst the coil is a type of transformer ina car ignition circuit is is not used in exactly the same manner.

The test was just supposed to be to check the voltage at the coil, engine not running as you said it would not start. Thus getting a bit more info about why you were not getting a spark. Are you getting 25 volts when cranking the engine ? If so why not say this in your post.

Posted: Tue Sep 09, 2003 10:31 pm

Now then chaps!.
Just to put my 2p worth in....
I think you are both right. There is a clue in the word 'Alternator'. The engine turns the alternator, which produces the AC. This is fed into a Bridge Rectifier, which converts the AC to DC. Everything after the Bridge Rectifier is DC.
Alternating Current is constantly reverisng polarity (60Hz).
Direct Current is just what it says it is. It just goes in a single direction (Negative -> Positive).
In an ignition circuit it is rapidly pulsed, but polarity does not change.

None of this is really helping to fix your car though! Sad

I would say go for the sender or take it to a garage you trust, for some advice.

Cheers Si. Cool

Posted: Tue Sep 09, 2003 10:51 pm

Sorry Tony, but this is not right.
My dad got electrocuted by a drill pluged into AC. He couldn't let go. I know. I pulled the plug out!. AC or DC will put your muscles into seious contractions at surprisingly low currents.

Please be careful when working on the ignition side of your car. Hazardous voltages exist.

Si.
(My dad was ok Very Happy

)

Posted: Wed Sep 10, 2003 7:10 am

Spirited discussion from all comers! Facts for older points and distributer ignition fired engines combined with facts for ECU controlled ignition types such as your V6. The problem however is the car will not start. This may be the ECU or the Crank/Cam position sensor, or more unlikely the coil packs. I checked my 94 2.6V6 and can see no easy way to measure the coil pack low voltage side for you, as the wires disappear into the loom at the rear of the motor. With the high cost of parts involved, try and read those fault codes, or haul the car to a dealer, it will be well worth it. Most serious workshops have a universal analyser with adapter connectors to fit a range of vehicles and makes, but I say go to an Audi dealer.
My view of the theory is that there are 3 x coil packs that each transform a DC low voltage pulse to a high voltage pulse under the control of the ECU. (Probably uses SCR's in the ECU) Only 3 coil packs are needed as each fires 2 cylinders together, one spark is wasted in a cylinder on its exhaust stroke, the other fires a cylinder on its compression stroke. Therefore only 3 coil packs are needed for 6 cylinders. As for the voltage you are reading it may well be greater than the anticipated 12 Volts if there is some form of capacitor discharge arrangement to deliver a higher voltage, so that a smaller coil (transformer) can be used and a higher voltage spark generated at the plugs. Do be careful, use only a well insulated hi impedance DVM to avoid danger to you and the ECU. You will agree I think that a single DC pulse into the coil pack acts like one half of an AC sinewave, rising from 0V to 12V or whatever voltage the ECU is producing.
My money is on the Hall Effect sensor, but plse post the method for reading the trouble codes if you ever find out how, and good luck.

Posted: Wed Sep 10, 2003 8:08 am

very interesting reading guys, but as ninenails said "its not fixing your car".
a quick check to see if its a crank sensor problem is to see if the fuel pump is working. when you turn on the igntion you should hear the pump prime, upon cranking the fuel pump will be switched on by the same sensor as the igntion, if the pump is working then the problem lies in the igntion, but if the pump does not work then its a crank/hall sensor problem.

Posted: Wed Sep 10, 2003 9:50 am

Blimey chaps

Thanks for the posts!!

It is easy to get carried away!! sorry!!
Your right its not fixing my car!!!. I am still in the dark as to reading the fault codes so have had to bite the bullet and get the local garage involved (maind Audi dealer is 20miles away so dont want the towing costs!)
I think or I am almost sure its the hall sensor but really dont wat to take th chance myself as it aint cheap!!

Nine nails
yes it can happen you can get stuck to mains volatges, I know I have had mains shocks and 400VDC shocks from huge capacitor banks!!!

The theory is as mains AC passes through 0V you have chance to let go as the votage is a 0V for a milli second but with DC it never reaches 0V so your muscles are frozen so you cant. I think it might be person dependent also as some people react differently to others.

I think the main thing is not to get a shock in the first place if you can help it!!!

Posted: Wed Sep 10, 2003 9:54 am

ooh one more post

Stormy

Thanks, yes I can hear the fuel pump wirring as I switch the ignition on. So yes it must be an ignition problem

Cheers

tony

Posted: Wed Sep 10, 2003 10:54 am

Please do let us know what the prob was when you get is sorted.

I think to read the fault codes there are two connectors in the fusebox very similar to the info on www.20v.org

there was a 12v site www.12v.org but is seems to be down.

Posted: Wed Sep 10, 2003 11:02 am

Thanks

I will certainly let you know what the problem was. I'll see if I can get on that site at somepoint cheers.

Cars..........................who needs em
well i do but would prefer it if the thing worked !!!!

Cheers

tony

Posted: Wed Sep 10, 2003 9:34 pm

Just a quick two-pennyworth on the A.C/D.C. farago:- car electrics are powered by a low-tension (12V) circuit from a battery. If a battery supplies the voltage directly (which it does) it HAS to be D.C.
Meter readings to the low tension supply are therefore tested on, say the 0-20 D.C. volts scale. Testing otherwise risks your meter. Test from L.T. supply to ground (any good earth). I agree you probably have a 'false' A.C. reading of 24V (2x12V.), although how this is achieved in a static system (i.e. engine not turning over) is beyond me. Even with coil packs the system is still the same, with the L.T. side inducing an H.T. voltage in that side. This still has to be distibuted to the sparkplugs, so the check procedures are the same for any ignition system. One other thought- is your battery in good condition & fully charged ? Have you checked the aternator (particularly the leads).

Posted: Thu Sep 11, 2003 7:36 am

Dougal

This was read with the engine cranking over, so the coil was being pulsed so a DC reading would be false.

Its no problem it wont damage my meter, reading voltage with the meter set to read current causes some nice sparks!!! Very Happy

Cheers
Tony