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Car died and will not start, Coil problem?

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  • Car died and will not start, Coil problem?

    Car died on me coming out of a junction yesterday morning, I was getting low on fuel (in the red) but had no warning light. I thought it was that I had just run out of fuel but after sticking 15 litres in I now have 1/4 tank on the gauge but it still won't fire.

    Checked for a spark and I don't seem to be getting one, I have 12V on the coil. The coil is not open circuit but the ratio from one side to the other seems very low to me, is there anyone who has a spare coil they could measure for me? or maybe measure the one on their car? (You need to disconnect the terminals to measure the resistance otherwise you won't get a true reading)

    I got 0.5 ohms on one side and 50 ohms on the other which is only a 1:100 ratio this would give 1200V and I was expecting in the order of 10000V, does this sound reasonable?
    Last edited by Andy; 11-12-2004, 12:05 AM.

  • #2
    You'll have to acess the fuel pump relay behind the offside plastic panel behind the coolant overflow tank.
    Remove the fuel pump relay and jump T30 to T87 on the relay connector and listen for fuel pump activity.
    You have most likely drained the battery with attempts to restart the car. this would tend to make your ign tests in valid.
    Roller type fuel pumps as used in your car tend to overheat , swell and fail with repeated attempts to start on a dry tank. They use fuel for cooling and lubrication.
    m
    Last edited by Mmark; 11-12-2004, 01:56 AM.

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    • #3
      Battery is definitely not dead, (Car is cranking over) and I charged it overnight just to make sure anyway.

      I also tried to start it using Easy Start (Ether based) and it did not even try to fire up, therefore it should be ignition based not fuel related, I could just about get my motorbike to run on Easy start as long as you kept spraying it into the inlet when I had fuel problems in the past.

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      • #4
        Did anything in a search help you? What did you physically try?

        http://www.s14.net/forums/search.php...der=descending

        http://www.s14.net/forums/search.php...der=descending


        Disclaimer: Remember, I know absolutely nothing, but it doesn't prevent me from having an opinion or suggestion. :

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        • #5
          Cheers Magnus,
          I did a search earlier for 'coil' but I only got about 4 results, none of which helped. I'm not sure what I did different but I'll look through those links you posted.

          So far this is what happened,

          Car was running fine, but fuel was in the red, no warning light though. I pulled out of a junction and it stalled, then it would'nt restart. I went and stuck 5l of fuel in still would'nt start. I pushed it the 1/2 mile home and got it towed up my road, put the battery on charge overnight. This morning I reconnected the battery and tried to start it while spraying an ether based starter spray into the plenum, still nothing at all. Car cranks over but does not fire. Since the car should at least try and fire on the ether even if it's getting no fuel I figured it's ignition related. Checked for a spark on the plugs, nothing (They were really sooty too) Checked for 12V at the coil, that's there. Then we shorted the coil to get it to fire independant of the ignition, using the coil lead to ground you get a very weak spark swapping the coil lead for a plug lead (To bypass the distributor) the plug gives no spark at all.

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          • #6
            Sounds like your coil is goosed. You should have around 5k to 8k ohms secondary resistance. Your primary resistance sounds right at 0.5 ohm.
            Steve
            Scottish Cecotto

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            • #7
              before you had this problem did you ever notice fluctuating lights. I have noticed in the past, that a crude way to detect a bad coil, is the light in the glove box. Leave the glove box open while you drive, and pay attention to the light when you stop. It should stay stary pretty consistant, this doesn't work if you have a fluctuating idle in the first place. Of course this is not fool proof, but the theory has been tried and tested.

              On a side note, Im not sure if everyone knows, or doesn't know, but to check your alternator you disconnect the Negative lead on your battery while its running. If it shuts off your alternator is weak, if it stays on, well you get it.

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              • #8
                Cheers Guys

                I proved the coil was okay in the end by using a switch to get it to fire on the bench. The resistance on the secondary coil was actually 5.7k the autorange had me fooled for a bit!

                Following the troubleshooting guide that I think was posted by HANDBLT (Thanks by the way!) on one of the threads that came up on the search Magnus did for me I've found that there is no ground signal from the ECU the resistance measured between ground and pin #1 is about 42 Meg ohms and stays the same as you try and crank the car over.

                I also put a timing light on the coil to see if the EMF in the coil was being generated. It worked fine on the bench but not on the car.

                Now I have the ECU apart it looks visually okay no burnt transistors or anything.

                I could really do with a known to be working ECU just to prove that is the problem. If any UK guys have a spare on I could borrow to try I would be very grateful.

                Thanks Andy

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                • #9
                  One other thing I was going to ask

                  Has anyone ever replaced the main power transistor in the ECU?
                  It's the big three legged one attached to the heatsink, mine had 1012 7/0353 printed on the side.

                  I was wondering if anyone knew what an equivalent part number for it might be?

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                  • #10
                    Whilst you're waiting for a fellow-briton to lend you his ECU, take the time to check the circuit board under bright lighting and a magnifying glas and look for cracked solderings.
                    Another way to find out whether it's a bad soldering is to let your motronic dangle off the wiring loom and tap/shake/hit (in that order ;-)) the motronic during cranking. If it fires up ypu definately know its bad soldering, you only need to find out where. In my case it was the transistor you mentioned.

                    Do a search with solder* and you'll find many other locations.

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                    • #11
                      Andy,

                      Uwe had a similar fault not so long ago and I`m sure he posted pic`s of the faulty component in his ECU both on this forum and the GB car club forum.

                      If Uwe picks up on your post I`m sure he will advise, if not I`ve sent you a PM as I have spare ecu`s.
                      E30 M3 for the Road
                      & one for the Track &
                      a S14 2002 for fun

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                      • #12
                        Originally posted by hardtailer
                        Whilst you're waiting for a fellow-briton to lend you his ECU, take the time to check the circuit board under bright lighting and a magnifying glas and look for cracked solderings.
                        Another way to find out whether it's a bad soldering is to let your motronic dangle off the wiring loom and tap/shake/hit (in that order ;-)) the motronic during cranking. If it fires up ypu definately know its bad soldering, you only need to find out where. In my case it was the transistor you mentioned.

                        Do a search with solder* and you'll find many other locations.
                        Thanks for the advice..
                        Do you know what part number you used for the replacement transistor?

                        Looks like I might have an ECU in the pipeline too!

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                        • #13


                          Finally got it running again, learnt lots into the bargain too!

                          Turned out to be one of the main 12V supply cables (the smaller of the two) from the battery to the engine bay had broken somewhere internally.

                          This meant that although my main relay was clicking on and off there was no supply for it to switch, I've not pulled the old cable out to find where it broke but have run a temporary replacement in (with inline fuse!!) which started the car fine first time.

                          This was after I thought I had a bad coil / ECU so I'm pretty happy that it's a cheap fix !

                          Thanks for you 're help guys
                          Andy

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                          • #14
                            Just a quick update,

                            After I replaced the 50amp fuse in the trunk, the car seemed to be running fine, I took it out for a few short trips without incident. But when I attempted to take it on a longer run it stalled for no reason and I instantly knew that the fuse had blown again, checked the trunk and sure enough it had gone. :sosad:

                            But this time whenever I put a temporary fuse in it's place it just blew straight away. I got the car towed back home and got the multimeter out to have a look around. The circuit that the main relay switches was down to earth, I managed to track it to the injectors but could not find anything. I moved the wiring about and lost the earth but I couldn't get it back. It turned out that the main supply to the injectors loops underneath the throttle bodies and comes up the front of the engine near the throttle position sensor, there is a 'U' shaped arm that is part of the throttle body casting to hold these wires. Well the main 12v supply one (Thick Red and White) had worn through and was arc'ing to earth, this caused the 50A trunk fuse to blow.

                            Hopefully that's it fixed now!

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