1992 Eunos Roadster, MSLabs Mini MS3, Toyota COPs, EV14s, TD04 turbo.

I've got a really annoying issue that makes the car a pig to drive. I think its always been there since I went turbo. Coming off idle, or pressing the accelerator at lower engine speeds, the engine stumbles and the revs drop. It's not the AE. I've been all over the mapping and also had the guys as Basset Down Balancing work on the mapping, and it seems all the fuelling side is right and doing what it should. We've tried all different settings of AE and event turned it off completely, the problem seems to be that the spark is inconsistent / not happening initially on acceleration. I'm getting sooty fuel coming out the tailpipe if I sit on the drive blipping the throttle to make this happen. After half a second of stumbling the engine then sorts itself out and will then pull really well all the way up to the redline, and is making 220hp (measured at the wheels) in its current state of tune.

WTF could be causing this? I've tried replacing all the COP wiring with brand new, thick (14 AWG) wires and decent crimped connectors. No difference. Also tried replacing the ground wires to all the analogue sensors (TPS, IAT, CLT, CAS) and running these to the sensor ground pin on the ECU (and nowhere else). No difference. I've tried adjusting the spark dwell time between 2.5ms and 4.5ms. Still does it.

If I still had hair I'd be tearing it out over this. I'm tempted to scrap the Toyota coils and replace with Audi/VW (I'm in the UK and these aren't too expensive over here) but I'm getting sick of spending money on parts only with no improvement.

Attached is a log of the car sitting on the driveway and me blipping the throttle. Also my current MSQ.

Anyone got any ideas?

 

The TPS in your log runs from a min of -37.7 to a max of -25.6. I never used the TPS on my original 1.6 because I did the FM BMW TPS conversion with the MS, so I don't know what it is supposed have for a range. Supposedly its just an on off switch, but still seems like it needs to be calibrated. It runs lean when you open the throttle which seems as if it's an AE issue. Although a misfire will show a lean AFR.

 

I've also got the BMW TPS. It needed recalibrating in that log (now done - not the problem). Quite suspicious of those Toyota COPs, think I'll try changing them for Audi ones

 

I am working on a throttle issue currently and don't have a solution but I can provide some next steps to try.

1) Make sure the TPS is properly grounded
2) make sure the TPS is pinned out correctly. I had to swap the two outside connection on my 01-05 tps.

Just some thoughts

 

Re-calibrate and see if it works correctly with a 0-100% range. If not, then the wiring is wrong. If I remember correctly the outside wires have to be switched. Since you have a vtps I would change your AE to 100% accel based with no MAP. Make sure your spark plug gap is set correctly. I run .032" (.75-.8mm) with no issues with the OE ignition.

 

May or may not be related to your problem, but I had similar issues with Toyota COPs.

Engine would sputter while gaining revs under load for a while.. (Running 18 psi on a progressive twin turbo setup)
Then it started shutting off under high load. I would have to cycle the key to start the engine. It would not fire otherwise.
After a while, it would just die with anything over 35-40% throttle input.

I spoke with Dimitris (Revenant) and he said he has seen this issue with Toyota coils...
He advised me to switch over to R8 coils. They are far more capable than the Toyota coils apparently.

One important issue to keep in mind is the R8 coils' current demands... They require 16-18 Amps per coil, and if you are running a wasted spark setup, demand per ignition cycle will easily exceed what the Miata wiring is designed for. I mean, the ignition circuit has a 15 Amp fuse, and the wiring is fairly light.
So I am running a 40 Amp relay to feed the said coils now. I am just using the ignition power circuit to trigger that relay. Peace of mind.

 

Thanks for that. I'm deeply suspicious of those Toyota COPs now and have ordered some pukka NGK R8 coils to replace them. I'll also wire in a relay and power them directly from the battery as you've suggested.

To secure the R8 COPs and to stop the plug holes from collecting water / grime I'm thinking I could try slicing the rubber gromit section below the coil heads and sliding it down a bit? Or maybe try wrapping some spongey tape around the coils to achieve a snug fit in the plug holes.

I'll report back on whether this sorts the problem and how I secured them, just to increase the knowledge recorded on this forum

 

I made a fairly simple adapter/holder for the coils.
Will post a pic when I go to the garage this evening.

 

You really should consider some way to solid mount the coils. The R8 coils don't seem to have a traditional COP bolt hole like the Toyota/Honda coils.




I think this mounting method from Monster Tune would work on the Miata if you used a plate with some standoffs from McMaster-Carr Racing.


Basically what I did, but then you need some kind of fork shaped plate to hold the coil.