gratian

Hello my friends.I was in the army in last 4 months, so that is the reason that i was quaiet.But when i come back, i go directly in my garage and start my love, the 924S.All seems to be OK, but after 2 seconds car stops suddenly,and wont start again.So from 6 days I measure all components of L-jetronic System and all I found is that is very tiny sparks on the exit of ignition coil(which I measure it and put to another car and its working!).So, from DME pin no. 1 comes some signal but to weak.Could somebody give some advises?Maybe a motronic m.l.3.1 drawings?Thanks for anything.Gra

Tom Carson

you are saying the ignition coil is known to be good, but you think the signal (a 'ground' pulse) from the DME to the coil on the green wire might be weak, because the high voltage spark from the coil to the distributor is weak…

are you sure you have very good connections for the +12 volts to the coil?

the coil gets it’s +12v on the coil’s small black wire...it comes from #15 of the key switch (black) which goes through the key switch (#30 red) and back to the + battery terminal post (one of the small red wires)

what happens if you run a temporary wire directly from the +12 volt battery terminal post to the coil's small black? this would ‘by-pass’ the key switch completely

it is also good practice to take ALL the wires off the + battery terminal post and clean them real good...this supplies +12 to the DME computer too so the connection must be good

also there is reference sensor in the bell housing that might be the problem...this is an input to the DME and the signal from it might be weak

the reference sensor is the one of two sensors...it is the sensor closer to the front

follow the sensor’s wires…close to the oil filler tube there is a connector/plug that might need to be opened and cleaned…if this does not correct the problem you should change it with a sensor that is good

if you need to remove the sensor use a penetrating oil (WD-40 etc) and let it soak for a while...it is in a bracket but the bracket is carefully adjusted, so don't loosen this...only the sensor

(the second sensor behind it is used to turn the fuel pump on and off...and it does some other things too)

gratian

I MEASURE THE SENSOR AND I THINK AND ONLY THINK THAT THE SENSOR IS GOOD BECAUSE HE HAS THE SAME RESISTANCE THAT ANOTHER ONE.I MEASURE ALL WIRES FROM AND TO THE DME AND ALL ARE GOOD.I DON'T KNOW WHAT COULD BE WRONG.

gratian

I ALSO DISASSEMBLE THE DME, AND A FRIEND OF MINE TRY TO MEASURE THE TRANSISTORS IN THERE THAT PROVIDES GROUND SIGNAL, BUT WE HAVE NO VALUES

gratian

I already remove both sensors and cleaned them, but no change.Can i make a swap between those two sensors?

Tom Carson

yes, you can swap...they are the same

if you need to adjust the bracket to set the sensor/flywheel spacing go to:

<a href="http://www.clarks-garage.com/shop-manual/ign-02.htm" target="_blank">http://www.clarks-garage.com/shop-manual/ign-02.htm</a>

Martin

Your battery is down or flat, or you need a new DME relay, or you need to unplug one injector and see if it fires, if so change the fuel pressure regulator.

Tom Carson

so an extra load on the injectors could pull down the DME’s ignition output as well as the injector output signal...that's good to know

gratian

I measure all connectors that comes to each injector and there is ground and 12V impulses when i try to start,I bypass the DME relay with some wires and connectors so i can hear that gasoline pump is working,and the injectors are `clicking`.Is a little curious that,after many start atemps,the spark plugs are not very wet,just a little moistened.You are saying that if there are not a good injector signal there is no ground signal for ignition coil?But how can i measure injector signal,because it takes only 1.6 mseconds?

Chris_924s

sounds all to familiar.. make sure the grounds are clean and free from oxidation (Expecially the intake manifold ground) check the DME relay contacts- you can force the fuel pump into an "always on" situation by temporarily closing the contacts with paper (the wadded paper trick). you should hear the fuel pump as soon as the key is in. ( I used a helper while I listened behind the rear pass wheel).
I had spark, and fuel. Mine turned out to be coil. It WAS in spec- but not enough to properly fully fire the plugs. so coil and plugs were replaced. (2 tows later..)
My mech SWEARS by bosch coppers, I had plats in and he yelled at me..

Good luck!!

billybones

I am ignorant on a 924s, But did you check the cap and rotor? Make sure the rotor is attached, on a 944 this is a common failure.

Tom Carson

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Martin:
<strong>or you need to unplug one injector and see if it fires, if so change the fuel pressure regulator.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">did you try this?

starting and shutting down after 2 seconds is a symptom of a bad FPR

gratian

I clean all grounds and i bypass the DME relay with some wires,so the pump provide fuel.Tom, you say to fire one injector,i recognize that I don't fire them, only i measure the impulses that comes to the injectors plug and i can hear them making 'clac'clac'but, after all,if the injectors are not working,why i do not have sparks?.I measure today the signal that comes from DME to green wire to the coil with an digital tachometer and it shows about 120 rpm but when i measure on one spark plug wire, nothing, so the signal is very weak.Chris,when you have the problem with your coil,did you have or not sparks? I am trying now to find an oscilloscope to measure correctly the signal and after the new ignition coil will come from Germany,maybe somebody can measure his signal too to compare them?Thanks,GRA

Lorenfb

Check out this website, systemsc.com. It may
provide some help. You may have a DME problem.

Go to the Diagnostics page.

Good luck
Loren
Systemsc.com

Tom Carson

Martin is suggesting that you should disconnect one of the plug wires to one of the injectors leaving 3 instead of 4 injectors connected

this should reduce the injector’s electrical current 'load' on the DME allowing additional current to be supplied from the DME ignition output stage to the ignition coil...it is a simple testing method

if the engine runs (on 3 cylinders) it means the FPR (Fuel Pump Regulator) has failed in the ‘closed’ position and the fuel pressure is too high which might ‘load down’ both the fuel injector and ignition output stages of the DME