No spark 350i tasmin
Discussion
I am restoring an 1985 TVR Tasmin 350i and not its assembled I can't start the engine. I have installed a new high torque starter, tried a new distributor and coil but have reverted back to the original as a bench test shows a good spark with the original coil and distributor.
I have a good earth on the engine but when I install the distributor in the engine and turn it over on the starter I don't get a spark.
I have tried turning it over faster by removing all the spark plugs and I get a very weak spark. When it's on the bench I get a very big spark by spinning the distributor quickly.
I have tried a separate battery feed to the coil but that doesn't help. I have measured the voltage at the coil and it doesn't drop significantly when the starter motor is operated.
I am at a loss now as I've tried most things and had the distributor on the bench a few time to double check the spark amplifier is working.
Is there something I am missing?
I have a good earth on the engine but when I install the distributor in the engine and turn it over on the starter I don't get a spark.
I have tried turning it over faster by removing all the spark plugs and I get a very weak spark. When it's on the bench I get a very big spark by spinning the distributor quickly.
I have tried a separate battery feed to the coil but that doesn't help. I have measured the voltage at the coil and it doesn't drop significantly when the starter motor is operated.
I am at a loss now as I've tried most things and had the distributor on the bench a few time to double check the spark amplifier is working.
Is there something I am missing?
John, that sounds like a good one 
By any chance when you refit the distributor, are you reconnecting the trigger wire that goes to the injection ECU from the ignition amp?
If so I would try disconnecting it (usually the infamous bullet connector over by the AFM) and see if the sparks improve - obviously it won't start but if the sparks get better it might imply a short in the injection loom that's pulling the trigger signal down and reducing the coil efficiency.
Otherwise, try tying the distributor body directly to the battery negative, in case there's a high-resistance earth return through the engine.
Assuming your ignition amp is the type mounted on the distributor (35DLM8), it is earthed to the dissy by its mounting screws through two brass bosses in the body of the amp. It all needs to be sparkling clean, and ideally you should polish the back of the amp and the mating face of the mounting plate and use a smear of heat transfer compound between the two when fitting - they need the coupling to conduct heat away from the amp.
There were other cars that used the 2-pin amp variant and their amps will work just as well despite having different part numbers and are usually cheaper - Austin Metro springs to mind!
By any chance when you refit the distributor, are you reconnecting the trigger wire that goes to the injection ECU from the ignition amp?
If so I would try disconnecting it (usually the infamous bullet connector over by the AFM) and see if the sparks improve - obviously it won't start but if the sparks get better it might imply a short in the injection loom that's pulling the trigger signal down and reducing the coil efficiency.
Otherwise, try tying the distributor body directly to the battery negative, in case there's a high-resistance earth return through the engine.
Assuming your ignition amp is the type mounted on the distributor (35DLM8), it is earthed to the dissy by its mounting screws through two brass bosses in the body of the amp. It all needs to be sparkling clean, and ideally you should polish the back of the amp and the mating face of the mounting plate and use a smear of heat transfer compound between the two when fitting - they need the coupling to conduct heat away from the amp.
There were other cars that used the 2-pin amp variant and their amps will work just as well despite having different part numbers and are usually cheaper - Austin Metro springs to mind!
Thank you, the bullet connector is not connected just the pos and neg to the coil from the amplifier. The amplifier is making a good spark when I manually spin the distributor. I have tried an earth direct to the battery from the side of the distributor, still no spark. Where does the bullet connector attach to on the distributor? It looks like it's never been attached.
Assuming it's the white/black wire, it should go to whichever terminal on the ignition amp triggers the negative side of the coil.
It's the only thing that tells the injection system that the engine wants fuel... but if it's not connected it wouldn't explain the lack of sparks, although it wouldn't start even if they were present.
As you do have some sparks on occasion, it suggests the amp is correctly connected to the coil... although we are assuming the wiring is the right way around. I'm not sure what the effect might be if you reversed them... but I'm not about to try it on my car to find out for you
It's the only thing that tells the injection system that the engine wants fuel... but if it's not connected it wouldn't explain the lack of sparks, although it wouldn't start even if they were present.
As you do have some sparks on occasion, it suggests the amp is correctly connected to the coil... although we are assuming the wiring is the right way around. I'm not sure what the effect might be if you reversed them... but I'm not about to try it on my car to find out for you
Interesting I've heard about ths dizzy coil pickup starting to fail.
This would "gel" with your observation that spinning it fast gets a good spark. Because the faster you spin, the higher the voltage induced in teh coil.
As Keith says yes the ign amps can fail (will fail!) too.
If you take the ign amp off and measure the resistance of the two amplifier connections on the dizzy, what do you get? It should probably be maybe 100ohms to 600 ohms depending? If it's infinite then there's a problem.
This would "gel" with your observation that spinning it fast gets a good spark. Because the faster you spin, the higher the voltage induced in teh coil.
As Keith says yes the ign amps can fail (will fail!) too.
If you take the ign amp off and measure the resistance of the two amplifier connections on the dizzy, what do you get? It should probably be maybe 100ohms to 600 ohms depending? If it's infinite then there's a problem.
adam quantrill said:
Interesting I've heard about ths dizzy coil pickup starting to fail.
This would "gel" with your observation that spinning it fast gets a good spark. Because the faster you spin, the higher the voltage induced in teh coil.
As Keith says yes the ign amps can fail (will fail!) too.
If you take the ign amp off and measure the resistance of the two amplifier connections on the dizzy, what do you get? It should probably be maybe 100ohms to 600 ohms depending? If it's infinite then there's a problem.
Off the top of my head the pickup coil resistance is about what you say, maybe a bit higher. I can check my notes later when I get home.This would "gel" with your observation that spinning it fast gets a good spark. Because the faster you spin, the higher the voltage induced in teh coil.
As Keith says yes the ign amps can fail (will fail!) too.
If you take the ign amp off and measure the resistance of the two amplifier connections on the dizzy, what do you get? It should probably be maybe 100ohms to 600 ohms depending? If it's infinite then there's a problem.
When mine was starting to fail it acted as a rev limiter as it seemed to be breaking down at higher revs. Eventually it failed open-circuit and the car wouldn't start.
Aha! Ramon (R.I.P) to the rescue
http://www.vintagemodelairplane.com/pages/Download...
So 500-1500 ohms roughly. Plus also see the rest of that page for other things to test.
http://www.vintagemodelairplane.com/pages/Download...
So 500-1500 ohms roughly. Plus also see the rest of that page for other things to test.
adam quantrill said:
Also worth checking that it's infinite between a connector and dizzy body? Because the coil should be "floating" electrically.
Definitely!A quick way to test the ignition amp (and the pickup coil) is to disconnect the wire between it and the coil negative and connect to one side of a 21W bulb. Add 12v to the other side, take off the distributor cap and twist the rotor arm back and forward against the vac advance - the bulb should flash on and off, varying in brightness depending on how quickly you flick the rotor.
Edited by Wedg1e on Friday 1st November 23:44
Gassing Station | Wedges | Top of Page | What's New | My Stuff