david@st ives

You may remember a few weeks ago i posted my car would not start and there is no spark at the spark plugs.

I was reccommended to get a scope and test the flywheel sensor, anyhow i bought a scope and it came with no probes, to cut a long story short even if it did i am a bit baffled by it all and i have decided to go down the just replace and see route,to get my car to porsche and just get a diagnosis would cost me at least £500 before they replaced anything.

I am going to attempt to change the flywheel sensor (as all clues lead there) and it is cheap enough to buy.

question is 1/ Is it easy to replace
2/ Is it easy to get to

Thanks

Dave
p.s anyone want to buy a scope

Smokin

Try a few of these searches I pulled up.https://rennlist.com/forums/showthre...lywheel+sensor

https://rennlist.com/forums/search.php?searchid=1186400

Hope this helps... There's a lot of reading... I'm sure others will chime in...

colo964

Easy (enough) to get to. Need to pull everything off the left side bottom (catpipe, wheel, shields etc) and left side top (fan etc) to replug it (UK the same layout as US???).

A quick check on the sensor: unplug the 55 pin plug under the driverseat. Put a voltmeter (or scope) in pins 47 and 48. Set voltmeter to ~5V AC. Then crank the starter. It should read 3V or so. The only benefit of the scope is to see if the gap reads (this tells the DME when the flywheel has made 360 degrees). If it does, it means your flywheel ring is still connected - but you can diagnose that by loud chatter + voltmeter = 0V.

I had the same problem - But it wasn't the flywheel sensor. I had one bad coil - silly me I put new ones in 2-3 yrs ago so never bothered to look there. Save yourself $$$$$$, get some new coils before anything else. Much easier to replace than the sensor.

Indycam

"Scope trace of signal from flywheel sensor." KirkF 09-24-2006
https://rennlist.com/forums/attachme...=142228&stc=1b

You are so close to being able to scope things ...........

Lorenfb

Check here for a picture (speed & ref - combined) of the pickup sensor:

www.systemsc.com/waveforms.htm

david@st ives

I have just tested pins 47 & 48

ignition off ohms reading was 524

voltage reading with engine being cranked 4.2 volts

I am thinking these are normal readings and it is the coils which are faulty ?

Is there another test i can do before replacing

Thanks

Dave

Lorenfb

"Is there another test i can do before replacing"

Check for a signal at the coils using a test light.

Also check for troubleshooting:

www.systemsc.com/diagnostic.htm

Red rooster

Dave ,
Just a small point. With your meter on AC volts you should not get a steady reading from a DC battery ! Make sure you are on AC volts.
I know it is stating the obvious but a motor in good mechanical shape needs fuel and a spark to run .
Crank it over . Pull a spark plug out. Can you smell gas ? If yes , push the plug back into its wire and rest the plug body on a good metal part of the motor.
Get someone to crank while you watch for a spark at the plug.
That will take 20 minutes for the first time and you will then have a clue to what is missing , spark/gas or both .
If you go down the path of guessing what the problem may be ,you will soon have a very desirable and expensive collection of parts !

Lets us know what happens.

Good luck

Geoff

david@st ives

Just to let you know i have absolutely no spark from the coil leads at all.

I can smell raw unburnt fuel when i crank it over ,

I did test on acv the voltage did go up and down slightly on cranking no lower than 4.0

Sorry for not stating this , i did on another post but could not find it so i had to post again ,

i have just found the original post, https://rennlist.com/forums/showthre...lywheel+sensor

Loren

where do you test for the signal at the coils , i assume there is a live going to them and an earth to ground ,

I take it you test with an electrical screw driver on the positive terminal ?

Is this correct

Thanks

Dave

ps i am reading the trouble shooting

Lorenfb

1. Check for power on the coils.
2. Check for a flashing test light on one of the two coil posts.
a. if yes, then if no spark on the coil wire (high voltage) then the coil/coils is/are bad
b. if no, then;
3. Check for power on the ignition modules & for a signal from the DME
a. if no, check for an injector pulse by removing an injector connector & using a small injector light
b. if yes, then then DME ignition output is bad
c. if no, then check form power on pins 18 & 37
d. if no, then DME relay is bad
e. if yes, then the DME is bad since the pickup sensor has been tested.

Not the best troubleshooting "tree", but should help.

JasonAndreas

The ballast resistor is for the rear heater blower motor and won't have anything to do with your starting problem.


The hole in the back of the fan casing might cause some amount of hot air to recirculate in the engine compartment instead getting blown out but other than that no problems.

JasonAndreas

The connector for the rear heater blower motor clips into there.

JasonAndreas

Look on the back of the connector that is attached to the rear blower motor that you plug into the cars wiring harness.

JasonAndreas

The rear blower motor (located in the engine compartment) is the black thing with a hole in it that you posted a photo of.

Lorenfb

"cant wait for my coils to arrive now."

VERY unlikely that both coils failed. Should've just gone to a basic auto parts store and bought
a standard coil for testing, i.e. much cheaper that the stock Bosch ones, e.g. an old 12 volt VW
Bug one.