1989 MX5: Crank no spark, but ignition test gives spark.

[atlex]

TL/DR: Not enough dwell to produce good sparks at the cranking voltage, Needed a second battery to run the timing gun as the voltage draw was too much to both spark and strobe.

Hi Folks,

Car: 1989 Eunos Roadster (Early JDM MX5). Turbocharged.

Old ECU: ME221 (that was working fine, but yuck!)

Installed the G4X and I've been going through the setup steps.

I've calibrated TPS/IAT/ECT/MAP - the ISC and Boost Solenoid also work when tested. AEM-X Lambda looks OK too.

I'm at the stage of timing the engine without any injection.

This car runs a Hall Effect CAS on the back of the intake cam. Both trigger1 and trigger2 go to the same CAS.

I've got a timing gun and when I run the ignition test mode the timing gun flashes as one would expect off the first plug wire.

When I use the key to crank the motor, the ECU tells me the ignition 1 / ignition 2 (it's wasted spark) are being activated.

But there's no flashes out the timing gun when I do this - as below, with the lead and plug out and laying on the cam cover there is no spark.

When I turn the key back to the 'on' position I get one flash out the gun, and I get one spark out the plug.

With the fuel pump on or off it makes no difference, with injection or not it makes no difference.

[ I've verified a friend's working map for the same model car has the same trigger configuration. So I'm a bit stumped. ]

Cranking log and trigger scope logs and screenshots attached as well as the current map.

 

Thank you

Alex

Blue No Spark on Crank - PC Datalog - 2022-10-15 6;42;05 pm.llgx Blue No Spark on Crank - TriggerScopeLog.llgx 1989 Eunos Turbo First Map.pclx

Edited October 17, 2022 by atlex
TL/DR for posterity

[atlex]

I found Vaughn's helpful post showing a valid MX5 trigger scope pattern and it looks like mine is the same so 'good'.

But that 'Trig1 Signal No' ?

[Adamw]

There is correct, stable cranking RPM and dwell showing in the log, so the ecu is commanding a spark.  The rest of the setup looks ok to me.  Some timing lights wont reliably pick up a spark during cranking if for example the timing is way off.

Can you actually pull a plug out so you can see the spark gap and watch it while cranking.  

[atlex]

10 hours ago, Adamw said:

There is correct, stable cranking RPM and dwell showing in the log, so the ecu is commanding a spark.  The rest of the setup looks ok to me.  Some timing lights wont reliably pick up a spark during cranking if for example the timing is way off.

Can you actually pull a plug out so you can see the spark gap and watch it while cranking.  

Plug/lead out and left laying on the head and there's definitely no spark when cranking/starting.

It gives just one spark when I stop the process, confirming what I saw in the timing gun.

Plenty of spark when I do the ignition test, confirmed with the plug/lead out.

[Adamw]

23 minutes ago, atlex said:

I did this and there's definitely no spark when cranking/starting.

I really cant see any reason for this.  Has anything changed since running with the other ECU?  Relocated battery or anything?  Does it still run with the other ecu?  Can you check the coils still have 12V when cranking.  

[atlex]

58 minutes ago, Adamw said:

I really cant see any reason for this.  Has anything changed since running with the other ECU?  Relocated battery or anything?  Does it still run with the other ecu?  Can you check the coils still have 12V when cranking.  

I've tried the Old ECU again and it starts up just fine, idles as old.

I've even tried a spare new-in-box G4X I have laying about (to go in another Eunos Roadster, an ITB car) wired it up as the other,  unlocked it, loaded the map, no spark on crank.

I will go see how 12v is on the coil pack when cranking.

[atlex]

3 hours ago, atlex said:

I will go see how 12v is on the coil pack when cranking.

OK. Seeing 12V in the on position and it drops a bit while cranking (but stays above 10v).

This is off the 'blue' wire per attached diagram.

With the fluke hooked up to these wires during an 'ignition test' it stays at 12v with the key in the on position.

[atlex]

There's only one significant difference between the G4X setup and the old ecu's. That's the TPS wiring. I tried to pick up the voltage off the pins 'stock' pins for the TPS but none of the wires could see the voltage. I've left the old wiring in place but done G4X TPS connection via the extension port AN Volt 5 for Signal and Ground/+5v off that same extension loom. I used that loom for the knock sensor wiring also so it was just laying there.

I tried connecting the TPS to the old connector and it made no difference to the crank no spark condition.

[atlex]

I hooked up the multimeter to the red and white wires that are for the coil pack - there are 3, red/white ("ignition") and blue (12v) - this system earths through the sparks themselves. Without the coil pack actually connected.. just using the inputs to it, results are:

0.06 volts when doing the ignition test.

0.1 volts when cranking and them a peak of 0.13 volts when I turn the key back

which is the point we'd see resulting in a solitary spark (safely discharging the coils ?) if the pack was connected.

[atlex]

I hooked up the FP control (AFM wires grounded). The fuel pump is running nicely now.

I've had a go now at night and I can now see spark while cranking, but the timing gun isn't picking it up. The timing gun only picks it up if it is the ignition test.

The difference being, when cranking the starter and FP are eating all the electrical pies.

Looks like I might need to boost the power supply to do the timing without injection.

[Adamw]

Your batt voltage measured at the ecu when cranking drops to about 10.2V, looking at the dwell table it is possibly a bit conservative around that voltage.  You could try increasing that to 7ms or so, it may give a bit more ign energy.  The other thing I would try is just turn on the injection to see if it runs.  A trigger offset of 0 should be close enough to run one of these I think.  Then check timing once running.  

[atlex]

It's idling. Timing was a mere 2.5 deg off. The timing gun needed more voltage than there was available off the battery to actually pick up the firing and run the bulb. I pulled a jumper battery and ran the gun off that.

Within 10 minutes it's was idling at stoich.

Great job Link! and thank you especially @Adamw